CH+25+Reduce+the+Rejection+Rate+of+Fibre+Coating+Diameter

Journal of Membrane Science209(2002)321–335Purification of oligosaccharides by nanofiltration Athanasios K.Goulas,Petros G.Kapasakalidis,Haydn R.Sinclair,Robert A.Rastall,Alistair S.Grandison∗School of Food Biosciences,The University of Reading,P.O.Box226,Whiteknights,Reading RG66AP,UKReceived16April2002;received in revised form3June2002;accepted25July2002AbstractNanofiltration(NF)of a model sugar solution and a commercial galacto-oligosaccharide mixture has been studied with a cross-flowfiltration unit in an attempt to investigate the significance of the operating parameters and evaluate a possible purification process.The pressure,feed concentration andfiltration temperature effects were studied in experiments carried out in full recycle mode of operation.The rejection factors of the sugar components present in the solutions increased with increasing pressure due to increased solventflux and also compaction of the membranes(e.g.rejection factor increased from 0.10to0.42for fructose),with this effect being greater for the low molecular weight sugars in the solutions.Increasing the total sugar concentration of the feed caused a decrease to the rejections of the sugars(e.g.from0.58to0.43for glucose). Increasing thefiltration temperature caused a decrease to the observed rejections of the low molecular weight sugars of the solutions(e.g.from0.72to0.48for fructose).Continuous diafiltration(CD)purification using NF-CA-50membranes(at 25◦C)and DS-5-DL membranes(at60◦C),gave yield values of14–18%for the monosaccharide,59–89%for the disaccharide and81–98%for the trisaccharide(oligosaccharide),respectively.The study clearly demonstrates the potential of cross-flow nanofiltration in the purification of oligosaccharide from mixtures containing contaminant monosaccharides.©2002Elsevier Science B.V.All rights reserved.Keywords:Nanofiltration;Oligosaccharides;Monosaccharides;Diafiltration;Sugar fractionation1.IntroductionCertain oligosaccharides are considered to be functional food ingredients,combining prebiotic properties,beneficial to the human health,and physic-ochemical properties beneficial in food processing [1].Prebiotic oligosaccharides,generally consist-ing of2–10linked sugar monomers,are defined as non-digestible food ingredients that beneficially af-fect the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria ∗Corresponding author.Tel.:+44-118-931-6724;fax:+44-118-931-0080.E-mail address:a.s.grandison@(A.S.Grandison).in the colon(i.e.Bifidobacterium sp.and Lacto-bacillus sp.)[1].They are produced by enzymatic trans-glycosylation or controlled degradation reac-tions,in complex synthesis mixtures[2].Microfiltration and ultrafiltration,are well estab-lished separation processes in the biotechnology and fermentation industry,used as a means of purifying oligosaccharides from high molecular weight en-zymes and polysaccharides[2–5].However,these commercial products often contain low molecular weight sugars that do not contribute to the beneficial properties of the higher molecular weight oligosac-charides.Nanofiltration(NF)appears to be a potential industrial scale method for purification and concen-tration of oligosaccharide mixtures.The potential of0376-7388/02/$–see front matter©2002Elsevier Science B.V.All rights reserved. PII:S0376-7388(02)00362-9322 A.K.Goulas et al./Journal of Membrane Science209(2002)321–335NomenclatureA effective membrane area(m2)C solute concentration in the feedsolution(g ml−1)C i solute concentration in the initialfeed solution(g ml−1)C f solute concentration in thefinalfeed solution(g ml−1)C P solute concentration in thepermeate(g ml−1)CD continuous diafiltrationJ V volumetric permeateflux throughthe NF membrane(l m−2h−1)MWCO molecular weight cut-off(Da)NF nanofiltrationR observed fractional rejection of solute t time(h)V c cumulative permeate volumeduring the CD(ml)V s feed solution volume duringthe CD(ml)V P permeate volume(l)Y percentage yield of a soluteduring the CDNF to fractionate oligosaccharide mixtures has not yet been critically evaluated.Whilst there has been some patent activity,very few reports have appeared in peer-reviewed literature.According to Playne and Crittenden[2],short-chain fructo-oligosaccharides have been produced in Japan using loose reverse os-mosis membranes,although chromatography is still the principal method.Lopez Leiva and Guzman[6], reported that concentration and some purification of oligosaccharide mixtures is possible using NF membranes as an alternative to more expensive chro-matographic techniques.In addition,Matsubara et al.[7]reported partial concentration of oligosaccharides from steamed soybean wastewater using NF mem-branes.Sarney et al.[8]used NF for the fractionation of human milk oligosaccharides and produced bio-logically active oligosaccharide mixtures with very little contaminating lactose.The molecular weight cut-off(MWCO)of NF mem-branes lies in the range200–1000Da[9],combining ultrafiltration and reverse osmosis separation prop-erties.However,these boundaries are not precisely defined and there are literature reports where mem-branes with MWCO values out of this range are re-ferred to as NF membranes.Due to the heterogeneity of the NF membrane structure and composition,the mass transport and segregation characteristics of this membrane process result from several mechanisms [10].Mass transport is based on two mechanisms: sieving and charge effects[9].Charge effects can play a very important role in electrolyte separations, because of the electrostatic forces generated between the membranes and the ions.Some sugars,like pec-tate oligosaccharides(which are acidic in aqueous solutions),carry an electric charge,which affects their separation properties by NF membranes[11].How-ever,most sugars are neutral molecules in aqueous solution,whose mass transport through NF mem-branes is controlled by convection and diffusion[9]. Pontalier et al.[10],reported that diffusive transport of sugars depends on the concentration gradient and remains pressure independent,whereas convective transport increases with pressure.Although literature reports(e.g.Aydogan et al.[12])have stated that NF separations of sugars,with differences in their molecular size in the range of a few glucosyl units,are not feasible due to poor selectivity, the present study is an attempt to evaluate cross-flow NF as a possible fractionation and purification pro-cess for oligosaccharide mixtures.Pressure depen-dence experiments werefirst carried out with a model solution containing a mono-,di-,and trisaccharide, at concentrations resembling those of commercial oligosaccharide synthesis mixtures(not in all cases). The significance of the feed concentration and tem-perature were then studied to optimise the separation. Finally,taking account of previous experiments,con-tinuous diafiltration purification of a model solution, and of a commercial oligosaccharide,was performed.2.TheoryThe volumetricflux of permeate was expressed in (l m−2h−1):J V=V PAt(1) where V P is the permeate volume,A the membrane effective area,t the time necessary for the V P litres of permeate to be collected.A.K.Goulas et al./Journal of Membrane Science 209(2002)321–335323The observed rejection for a given solute,based on the concentration determined from the sample analy-sis,was calculated from the equation:R =1−C P C(2)where C P and C are the concentration of the solute in the permeate and the feed,respectively.The yield values for each individual component throughout the continuous diafiltration,were calcu-lated as the fraction of the original solute concentra-tion remaining in the feed:Y =C fC i×100%(3)where C f and C i are the concentrations in the final and initial feed,respectively.Continuous diafiltration (CD)is a membrane pro-cess where water,at the appropriate pH and tempera-ture,is added to the feed tank at the same rate as the permeate flux,thus keeping the feed volume constant during processing [3].Mathematical models found in the literature (e.g.Pontalier et al.[15]),describe mass transfer in nanofiltration separation processes by taking into account the membrane characteristics (e.g.pore size,charge),the feed solute and solvent characteristics (e.g.solution viscosity,solute radius),and also the type of solute flux through the membrane (e.g.diffusive,convective).The purpose of this study was to estimate the extent of the CD purification pos-sible,therefore a simple mathematical analysis of the CD process,as described by Grandison and Lewis [4],was used:when R =0for a given solute;and C P =C(1−R)the concentration of that solute in the feed can be calculated using the following equation:ln C i C f =(1−R)V c V s (4)where V s and V c are the feed volume and the cumu-lative permeate volume removed during the course of the process.In the same way,the variation in con-centration of a specific solute in the permeate can be monitored from the equation:ln C i (1−R)C P =(1−R)V c V s (5)Both Eqs.(4)and (5)are applicable when the rejec-tion rate of a solute remains constant throughout theCD process,which in the case of this study requires the total sugar concentration to remain fairly constant throughout processing.3.Experimental 3.1.ChemicalsAnalytical grade purity d (−)-fructose and sucrose were supplied by BDH Laboratory Chemicals (Poole,Dorset,UK),and d (+)-raffinose pentahydrate was supplied by Sigma Chemicals (Poole,Dorset,UK).These were used for the preparation of the model sugar solutions and as standards for HPLC analysis.The commercial oligosaccharide mixture used was a galacto-oligosaccharide syrup (Vivinal ®GOS),a gift from Friesland Coberco Dairy Foods (Deventer,The Netherlands),with typical specifications:73wt.%dry matter of which,57wt.%were galacto-oligosaccha-rides,23wt.%lactose,19wt.%glucose and 0.9wt.%galactose (values provided by the manufacturer).All solutions were prepared in demineralised water.3.2.MembranesTwo flat sheet asymmetric cellulose acetate mem-branes were used,NF-CA-50and UF-CA-1,sup-plied by Intersep Ltd.(Wokingham,UK).According to the specifications supplied by the manufacturer,NF-CA-50had a nominal 50%rejection of NaCl and UF-CA-1had a molecular weight cut-off (MWCO)of 1000Da.Both membranes had a maximum oper-ating pressure of 35bar and a maximum operating temperature of 30◦C.Three thin film composite membranes,DS-5-DL (Class NF),DS-51-HL (Class NF)and DS-GE (Class UF)were supplied by Osmonics Desal (Le Mee sur Seine,France).According to the manufacturer,DS-5-DL and DS-51-HL completely rejected su-crose and glucose,and gave 96and 95%rejection of MgSO 4,respectively.The DS-GE had a MWCO of 1000Da.Further information about the properties and application range of these membranes are summarised in Table 1.Membranes were cut to size and soaked overnight in demineralised water in order to remove any preser-vative material such as glycerol or azide.To facilitate324 A.K.Goulas et al./Journal of Membrane Science209(2002)321–335 Table1Properties of the NF/UF membranesType NMWCO(Da)Rejection NaClor MgSO4pH range Maximumpressure(bar)Maximumtemperature(◦C)NF-CA-50–50%NaCl–3530 UF-CA-11000––3530 DS-5-DL On sucrose and glucose96%MgSO41–112790 DS-51-HL On sucrose and glucose95%MgSO43–92050 DS-GE1000–2–112790fitting of the membranes,a25vol.%ethanol solution in demineralised water was used to wet the effective filtration surface of the cells where the membranes were placed.Membranes were conditioned by compressing them to a steady state of compaction(determined by the flux of permeate),with demineralised water as feed, at an intermediate pressure according to their pressure limits(at25◦C).However,compaction offlat sheet membranes is not permanent,and the membranes ex-hibit considerable reversibility[13],thus compaction effects were not completely excluded from the results. Membranes were stored in10vol.%ethanol solu-tions at4◦C after each experimental run with sugar solutions.3.3.High pressure cell test unitThe high pressure cell test unit(Fig.1)was sup-plied by Osmonics Desal(Le Mee sur Seine,France) and consisted of a tri-piston pump,a feed tank and two stainless steel high pressure cross-flow cells connected in parallel to the pump outlet.Before the separation of the feed stream from the pump to the two inlets of the NF cells,a pressure gauge wasfitted to allow read-ings of the system pressure.The unit had a maximum operating pressure of70bar,a maximum operating temperature of90◦C,a pH operating range of1–13, and the pump had a feedflow rate of220.8l h−1. The feed tank(2–5l capacity)had a vertically po-sitioned baffle to prevent aeration and turbulence.A cooling/heating coil connected to a temperature con-trolled water bath,wasfitted to allow temperature control of the feed.Each high pressurefiltration cell consisted of a square stainless steel base,in which a stainless steel porous support disc was centrally positioned.The sup-port disc had an effective membrane area of81cm2 and0.16cm thickness.The base underneath the sup-port was designed to prevent back-pressure generation in the permeate side;and thus the trans-membrane pressure was assumed to be the pressure measured in the feed inlet of the cells.In order to maximise tur-bulence in the feed and thus minimise concentration polarisation,the feed solution inlet on the stainless steel cover was positioned towards the perimeter of the cylindrical space above the membrane,and the concentrate outlet was positioned centrally.An O-ring was alsofitted on the perimeter of the top plate in order to ensure adequate sealing of the cell,and a back-pressure regulator on the concentrate outlet was used to control the pressure.Due to the parallel configuration of the two cells,a flow meter was used to ensure that the same pressure was applied to both cells.Theflow meter was con-nected to the concentrate outlets in parallel with the concentrate outlets leading to the feed tank(see Fig.1). Thus,by adjusting the feedflow rate of the two cells to the same level,the same trans-membrane pressure was applied to both cells.This was carried out by redi-recting theflow of the concentrate from one cell to the flow meter,while maintaining theflow of concentrate from the other to the feed tank,and vice versa.In addition to the temperature control coil in the feed tank,the twofiltration cells were maintained in a water bath,to ensure adequate control of thefiltration temperature.The equilibrium between the water supplied(with a peristaltic pump)and the permeate removed in the CD experiments was achieved:(a)by adjusting the pump flow rate to theflow rate of the permeates measured at set time intervals;(b)by continuously controlling the amount of total cumulative permeate and water added; and(c)by controlling the feed volume in the feed tank.A.K.Goulas et al./Journal of Membrane Science209(2002)321–335325Fig.1.Cross-flow membrane unit:(1–3)temperature controlled water bath,Pump,and cooling or heating coil for temperature control of the feed;(4)feed tank,(5and6)volumetric cylinder and pump for water addition,used only during the CD experiments;(7)tri-piston pump;(8)by-pass valve kept closed during the experimental runs;(9)pressure gauge;(10)nanofiltration cells;(11)back-pressure regulator valves;(12)valves used for redirecting the retentateflow of each cell towards theflow meter(one at the time)in order to equalise the pressure applied to the two cells;(13)flow meter.In thefigure the permeate streams are recycled to the feed(total recycle mode),but when CD was used,the permeates from the two cells were removed.3.4.Experimental3.4.1.Experimental procedureAfter conditioning of the membranes the waterflux was measured at various pressures within the pres-sure range for each membrane,at25±1◦C.These initial waterflux measurements were compared with measurements carried out under the same conditions after each experiment,to indicate any irreversible fouling or membrane damage.With the sugar solu-tions used,however,irreversible fouling was never observed.In experiments where the dependence of the sepa-ration on a varying condition(e.g.pressure,concen-tration,temperature)was studied,total recycle mode was used(both concentrates and permeates were re-cycled to the feed tank)in order to avoid changes in the feed concentration.Purification of oligosaccharide mixtures was performed with CD.Sugar solutions(always2l),were added to the filtration system(after drainage of the existing dem-ineralised water)and circulated for10min,before the initial feed concentrations were measured.All per-meate concentration andflux values presented in this study are the average value of bothfiltration cells of the unit.For the total recycle experiments,unless otherwise stated,measurements for a set offiltration conditions were taken as follows:the pressure and temperature were adjusted to the desired levels,and the system was allowed to stabilise for45min.Flux measurements were taken,and the feed and permeates were sam-pled.In experiments where the sugar concentrations or the temperatures were varied,the pressure was326 A.K.Goulas et al./Journal of Membrane Science209(2002)321–335kept constant,and the system was allowed to stabilise for45min(or1h for the temperature experiment) under the set conditions before any measurements or samples were taken.In the CD experiments,the desired pressure and temperature were set,and the system was allowed to stabilise for1h in total recycle mode.Permeate flux measurements and samples(zero cumulative per-meate)were then taken and CD started.During the process at time intervals of30or60min,samples of the feed and permeate were taken,and the permeate flux and total cumulative permeate collected during this period,were measured.This was carried out by stopping the CD(returning to total recycle mode), in order to perform the measurements and sampling, assuming that the system was at steady state for the conditions measured.3.4.2.Pressure and temperature dependence experimentsIn order to investigate the effect of pressure on the separation of sugars,four experiments were carried out using a model solution of approximately0.07–0.08g ml−1total sugars,at25±1◦C.The model solu-tion,composed of approximately equal concentrations of fructose,sucrose,and raffinose pentahydrate,was tested at four pressures,varying for each membrane according to their pressure range.Taking in account the information provided in the literature[9],the thinfilm composite DS-5-DL mem-brane,which in preliminary experiments had given high rejections of monosaccharides,was used to per-form a temperature dependence study.This membrane had a maximum operating temperature of90◦C and a high porosity,which was reflected in the high permeate fluxes obtained even at low temperatures.The exper-iments were carried out using a model solution(total sugar0.055g ml−1),at13.8bar pressure,and temper-atures25,35,45,60±1◦C.Additionally,and based on the results from the temperature dependence exper-iments,the pressure effect on the separation charac-teristics of this membrane was tested at25and60◦C.3.4.3.Concentration dependence experimentsThe effect of feed concentration on the separation characteristics of the sugar components in an oligosac-charide mixture was studied with varying concen-trations of the commercial oligosaccharide mixture Vivinal®GOS.The sugar composition of this oligosac-charide mixture allowed comparisons with the model sugar solution experiments,because it contained glucose and lactose,which have similar molecular weights to fructose and sucrose,respectively,and higher oligosaccharides with molecular sizes in the same range as raffinose.An approximately0.07–0.08g ml−1initial feed solution of the syrup was prepared in demineralised water,placed into the feed tank,and then an inter-mediate pressure according to the pressure limits of each membrane was applied(at25±0.5◦C).After each measurement appropriate dilutions of the feed solution with water were carried out in order to obtain a series of lower concentration measurements.All experiments were carried out total recycle mode of operation,in order to ensure constant feed concentra-tion.3.4.4.Continuous diafiltrationThe NF-CA-50and DS-5-DL(at60◦C)mem-branes gave the best separation characteristics of monosaccharides from oligosaccharides with respect to the retention of the oligosaccharides,which were the target components in this study.For that reason, CD purification of a model solution and a commer-cial oligosaccharide mixture,was carried out using these membranes at13.8bar pressure,with tempera-ture regulated at25±0.5◦C for the NF-CA-50,and at60±0.5◦C for the DS-5-DL.The total cumulative permeate which had to be removed in order to achieve afive-fold purification of these mixtures relative to the monosaccharide was calculated to be in the range of6.0–6.5l using Eq.(4),assuming that the rejection of this sugar(taken from the data of the pressure de-pendence experiments)remained constant throughout the CD process.Further information about the solu-tion concentrations and the total cumulative permeate removed is shown in Table4.3.4.5.Sample analysisSugar solution samples were analysed using an Aminex HPX-87C Ca2+resin-based column (300mm×7.7mm)supplied by Bio-Rad Laborato-ries Ltd.(Hertfordshire,UK)and an HPLC analyser coupled to a refractive index detector.The column was maintained at85◦C and HPLC grade water was used as mobile phase at aflow rate0.6ml min−1.A.K.Goulas et al./Journal of Membrane Science 209(2002)321–335327Calibration curves were prepared for each sugar separately,and for the galacto-oligosaccharide mix-ture,calibration curves were prepared from the ac-tual mixture and also from glucose and lactose.The oligosaccharide mixture appeared as three separate peaks,the third and the second corresponding to the retention times of glucose and lactose,respectively.Thus,in the discussion and presentation of the re-sults,the term glucose is used to refer to all the monosaccharides present in the mixture (since it is the predominant one),the term lactose stands for all the disaccharides (since it is the predominant one),and the term “oligos”for all the sugars which had a higher molecular weight than a disaccharide.Each sample was analysed twice and the average was used.4.Results and discussion4.1.Effect of pressure and temperatureAll membranes tested with sugar solutions showed a linear relationship between the permeate flux and the applied pressure (Fig.2).No irreversible fouling occurred during the experiments since there were no differences in the demineralised water flux mea-surements before and after each filtration run.With cellulose acetate membranes at the higher pressures,the effect on permeate flux increased to a limiting flux value,presumably due to the resistance in the boundary layer of the membrane [12].Table 2summarises the rejection values for the sugars of the model solution.The observeddiffer-Fig.2.Permeate flux vs.pressure for the model sugar solution at 25◦C during cross-flow NF.ences between the rejection values of the sugars present in the solution indicate the potential of some NF membranes for purifying oligosaccharides from monosaccharides.The rejection values for the three sugars were directly dependent on the total sugar concentration of the feed solution,and increased with pressure due to membrane compaction and also due to increased solvent flpaction reduces the membrane thickness,and that normally would lead to an increased permeate flux.However,pore size reduc-tion,caused also by compaction,is the predominant characteristic upon which the rejection of neutral so-lutes is dependent (sieving effect),hence causing an overall increase in the rejections observed.Increased pressure also caused the differences between the re-jections of the three sugars to decrease,indicating a less effective separation.That is because the effect of pressure on rejection is less marked as the molecular weight of the sugar increases,with respect to the pore size of the membranes used.As pore size decreases,increasing pressure causes the convective flux of so-lutes to decrease to a much greater extent than the diffusive flux [10].Thus,with NF membranes,and neutral solutes,the significance of convective solute flux becomes greater as the molecular size of the sugar decreases leading to greater changes in rejection.The increase in the rejection rate at higher pressures caused by the higher solvent flux was observed because the diffusive transport of solutes through the membranes remained the same at higher pressures,thus reducing the solute concentration in the permeate stream.The significance of convective and diffusive solute flux,with respect to the MWCO of the membranes,328 A.K.Goulas et al./Journal of Membrane Science209(2002)321–335Table2Rejection values for raffinose,sucrose and fructose at a range of applied pressures during cross-flow NF of a model solution of the three sugarsNF-CA-50a/0.0761g ml−1b UF-CA-1/0.0754g ml−16.9c13.8c20.7c27.6c 6.9c13.8c20.7c27.6cRaffinose0.800.900.930.950.710.800.840.87Sucrose0.560.730.790.830.450.600.660.72 Fructose0.100.260.350.420.110.220.290.35 DS-GE/0.0775g ml−1DS-51-HL/0.0702g ml−16.9c13.8c20.7c24.1c 6.9c10.3c13.8c17.2cRaffinose0.700.790.800.800.840.920.950.96Sucrose0.410.560.610.620.770.870.920.93 Fructose0.080.180.240.250.510.670.760.78 DS-5-DL(25◦C)/0.0496g ml−1DS-5-DL(60◦C)/0.0496g ml−16.9c13.8c20.7c 6.9c13.8c20.7cRaffinose 1.00 1.00 1.000.99 1.00 1.00Sucrose0.990.990.990.940.970.97Fructose0.540.720.770.280.480.53a Membrane type.b Feed concentrations varied due to dilution of the hold-up volume of the system.In the DS-5-DL experiment lower concentration was used due to lack of raffinose.c Pressure in bar.becomes more evident by looking to the soluteflux values presented in Fig.3a–e.Soluteflux is directly dependent on the pressure when permeation of the so-lutes is convective controlled,while it becomes inde-pendent of the pressure when permeation is diffusive controlled.The linear increase of the fructoseflux with pressure,seen with the UF-CA-1,DS-GE,NF-CA-50 (at25◦C),and DS-5-DL(at temperatures higher than 25◦C)membranes,shows that fructose permeation through these membranes is mainly convective con-trolled,with compaction leading to a limiting solute flux for the two cellulose acetate membranes.At the same time,diffusion becomes increasingly important for sugar permeation through these membranes as the molecular size of the sugars increases and the MWCO of the membranes decreases.For the lower MWCO membranes DS-51-HL and DS-5-DL(at25◦C),it ap-pears that diffusion is the main phenomenon control-ling solute permeation.Results from the DS-5-DL membrane with varying temperature(Fig.4a)show that theflux increased with increasing temperature,as expected,and the effect of pressure was the same at low and high tem-peratures.There are several potential explanations for this behaviour according to Tsuru et al.[9].(A)The increased thermal energy of the solvent molecules at higher temperatures allows them to overcome the energy barrier generated in the micropores due to the pore wall frictional forces.(B)The effective pore diameter increases with temperature,because the ad-sorbed water layer on the hydrophilic pore surface becomes thinner.(C)Reduced viscosity at higher temperatures leads to higherfluxes.Increased temperature caused the sugar rejections to decrease(Fig.4b),but the effect was quite dif-ferent for the three sugars in the model solution. The monosaccharide(fructose)showed the greatest change in rejection values,followed by the disac-charide(sucrose),which showed a similar,but less marked,change in rejection than fructose(about10 times smaller).The rejection of raffinose,which was totally rejected at25◦C,remained constant at elevated temperatures.These results are in agreement with the results reported from Tsuru et al.[9],for the effect of temperature on the transport performance of inor-ganic NF membranes.Since diffusion of molecules。

Lattice vibrations and dielectric functions of ferroelectric SrBi 2Àx Nd x Nb 2O 9bismuth layer-structured ceramics determined by infrared reflectance spectraM.Zhu a ,L.Sun b ,W.W.Li b ,W.L.Yu b ,Y.W.Li b ,Z.G.Hu b ,*,J.H.Chu ba Department of Physics,Shanghai Jiao Tong University,Shanghai 200240,People’s Republic of ChinabKey Laboratory of Polar Materials and Devices,Ministry of Education,Department of Electronic Engineering,East China Normal University,Shanghai 200241,People’s Republic of China1.IntroductionRecently,perovskite ferroelectric (FE)materials have received much attention in view of their wide applications in nonvolatile random access memories,electro-optic switches,pyroelectric detectors,optical modulators,and mixers.Among them,bismuth layer-structured ferroelectrics (BLSFs)with Aurivillius phase have the general formula of (Bi 2O 2)2+(A n À1B n O 3n +1)2À,where A and B sites of the crystals could take a variety of cations and n is the number of corner sharing octahedra forming the perovskite-type layers [1–6].Note that A-site cations can be Ca 2+,Sr 2+,Ba 2+,Pb 2+,Bi 3+,K +,Na +,rare earth ions,or mixture of these,however,B site invariably contains small highly charged cations like Nb 5+,Ta 5+,Ti 4+,Mo 6+,W 6+,or V 5+,and n =1–6[1].Especially,SrBi 2Nb 2O 9(SBN)with n =2has been regarded as a promising FE material owing to low dielectric constants and excellent electro-optic properties [7–9].The increasing interest is also due to fatigue-free behavior and low leakage currents of these compounds [10,11].Moreover,it was found that for the SBN,the transition from a normal ferroelectric to a relaxorlike ferroelectric is reduced by the substitution of rare earth ions such as Pr 3+and La 3+for Bi 3+in the Bi 2O 2layers [7].Relaxor ferroelectrics have been attracting great attention for both their practical applications,such as a high capacitance capacitor in electronic industry and the fundamental understanding about distorted systems [6,12].Most of the relaxormaterials studied for the immense potential applications in microelectronic devices are lead based compositions,however,ecofriendly materials are more advantageous [13].Attempts have been made towards identification of suitable dopant in bismuth layered structures for making relaxors.This could promote some further applications in microelectronics and optoelectronics of doped SBN relaxor FE materials.As we know,FE materials show nonlinear optical and electro-optic properties because of the interaction between spontaneous electronic polarization and incident polarized light [14].Many research groups have focused on the fabrications and dielectric properties of SBN and doped-SBN films and ceramics [6,7].Although there are some studies on the influences from the replacement of A and B sites on the structural and FE properties [8,15],the effects on infrared (IR)dielectric function,which is one of the crucial issues for BLSFs-based optoelectronic devices,are still scarce and need further investigations [11].This is because the optical function is a prerequisite for IR detector designs and optimizations.The total light absorption of detectors based on doped-SBN materials can be evaluated using the obtained dielectric functions.Therefore,a detailed IR spectroscopic study is necessary to exploit the potential applications of SBN ceramics in the optoelectronic field.On the other hand,the crystalline disorder such as chemical composition fluctuation and grain boundary conditions is strongly related to the FE transition,which occurs as a result of a delicate balance between long-range Coulomb inter-actions and short-range forces [16].In particular,the splitting between the frequencies of the longitudinal-optical (LO)and transverse-optical (TO)phonon modes,which is proportional toMaterials Research Bulletin 45(2010)1654–1658A R T I C L E I N F O Article history:Received 3March 2010Received in revised form 8June 2010Accepted 16July 2010Available online 29July 2010Keywords:A.CeramicsC.Infrared spectroscopyD.Optical propertiesA B S T R A C TInfrared optical properties of SrBi 2Àx Nd x Nb 2O 9(SBNN)ceramics with different Nd compositions (from 0to 0.2)have been investigated by near-normal incident reflectance technique.The experimental spectra in the wavenumbers range of 350–1500cm À1were analyzed using the Lorentz oscillator model for five infrared-active phonon mode observed.It is found that the frequencies of the NbO 6tilting and symmetric stretching modes linearly decrease with the Nd composition due to the octahedra distortion.The high-frequency dielectric constant varies in the range from 4.55Æ0.04to 4.80Æ0.04.Owing to the contribution from the stronger electronic transitions,the real part of dielectric function Re(e )is estimated to about 4.0in the high-frequency transparent region.ß2010Elsevier Ltd.All rights reserved.*Corresponding author.Tel.:+862154345150;fax:+862154345119.E-mail address:zghu@ (Z.G.Hu).Contents lists available at ScienceDirectMaterials Research Bulletinj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /m a t re s b u0025-5408/$–see front matter ß2010Elsevier Ltd.All rights reserved.doi:10.1016/j.materresbull.2010.07.007dynamical polarization of lattice vibration,is one of the direct effects from the Coulomb interaction.Up to date,few reports on the phonon modes of SBN and doped-SBN materials have been presented with the aid of Raman scattering experiments.Recently, the effects from the A and B site dopants on lattice vibrations of BLSFs nanocrystalline powders andfilms have been given,but not for optical functions[17].Note that the dielectric functions of SrBi2Ta2O9(SBT)ceramics and single crystal have been reported by reflectance spectra[18].For SBN with the orthorhombic A21am symmetry at room temperature(RT),there are16IR-active phonon modes[3].IR reflectance spectroscopy is a nondestructive probe technique,which is an attractive and powerful tool for optical characterizations of SBN ceramics.As compared with Raman scattering[17],it not only determines phonon mode character-istics,but also provides dielectric functions of the materials studied[18,19].In this article,the effects from the Bi site replacement on phonon modes and dielectric functions for SrBi2Àx Nd x Nb2O9 (SBNN)ceramics have been studied by IR reflectance spectra in detail.The lattice absorption peaks are assigned and their physical origins have been presented.2.Experimental detailsThe SBNN(x=0,0.05,0.1,and0.2)ceramics were prepared by a conventional solid-state reaction sintering[7].The starting raw materials with an analytical purity were SrCO3,Bi2O3,Nb2O5,and Nd2O3.To compensate the evaporation of Bi2O3at high tempera-tures,excess Bi2O3of1wt%of the stoichiometric composition was added into the starting powders.The powders of starting chemicals were admixed by ball milling for24h and then were presintered at 8508C for2h.The presintered powders were ground and ball milled into thefine powders for24h.The obtained powders were admixed with polyvinyl alcohol as a binder and pressed uniaxially into pellets.All ceramic wafers were double-side polished for the spectral measurements.The crystalline structure of the SBNN ceramics was analyzed by X-ray diffraction(XRD)using Cu K a radiation(D/MAX-2550V,Rigaku Co.).The XRD patterns of the ceramics at different Nd compositions were shown in Fig.1.As we can see,the results indicate that all ceramic samples are of pure single phase without other impurity structures,such as the second phases from the raw materials of SrCO3,Bi2O3,Nb2O5,and Nd2O3. Compared with undoped SBN ceramic,it can be observed that the peaks of the SBNN samples slightly shift towards a higher angle direction,as seen in the inset of Fig.1.This could be attributed to the fact that the ionic radius of Nd3+is smaller than that of Bi3+.It further confirms that the Nd atoms are located in the Bi sites,which are partly replaced.The grain size r can be calculated from the (115)diffraction peak according to the well-known Scherrer equation:r=K l/b cos u,here K%1is the shape factor,l=1.540A˚is the average wavelength of Cu K a radiation,b is the full width at half-maximum(FWHM),and u is the diffraction angle.The average grain size is estimated to about52,54,30and33nm for the SBNN ceramics,respectively.Note that the grain size is smallest for the ceramics with x=0.1.IR reflectance spectra were recorded over the wavenumbers range of350–1500cmÀ1using a Bruker VERTEX80V Fourier transform infrared(FTIR)spectrometer.The reflectance experi-ments were carried out at near-normal incident configuration(the angle of incidence is about118by spectral reflectance accessory A510Q/T).For the high frequency region of450–1500cmÀ1,a liquid nitrogen cooled MCT detector and optimized KBr beams-plitter were used with a spectral resolution of4cmÀ1.A TGS/POLY detector and6m m thick mylar beamsplitter were employed for the measurements in the low frequency region of350–700cmÀ1with a spectral resolution of2cmÀ1.As we know,the MCT detector is sensitive only for the mid-infrared photon energy beyond 420cmÀ1,however,the TGS/POLY detector is sensitive for the light frequency below700cmÀ1[20].Aluminum(Al)and Gold(Au) mirrors,whose absolute reflectances were directly measured,were used as references for the reflectance spectra in the low and high frequency regions,respectively.This is because the Al and Au mirrors have relatively high reflectance in the two different photon energy regions,respectively.Note that the samples were at RT for all measurements and no mathematical smoothing has been performed on the experimental data.3.Results and discussionA semi-infinite medium approach is applied to reproduce the reflectance spectra R of the SBNN ceramics with about0.5mm thickness[19,20].The dielectric function of SBNN ceramics could be obtained using the well-known equation:R¼ffiffiffie pÀ1=ffiffiffie pþ12. For FE polar materials,IR dielectric response can be described by the harmonic Lorentz oscillator model,in which the dielectric function is defined as a response function having many pairs of simple poles.Although the orthorhombic structure is generally optical anisotropic,the present SBNN ceramics are polycrystalline formation,which results in an average effect from various crystalline directions and shows the isotropic property.Based on the spectral peaks from the experimental reflectance and the reported results in Ref.[18],five Lorentz oscillators are necessary to be considered for IR optical response of the SBNN ceramics in the present measured region.Therefore,the dielectric function can be written as:e¼e1þX5j¼1S j v2TO;jðv TO;jÀv2Ài vg jÞ:(1)Here,e1,v TO,j,S j,g j,and v represent,in order,the high-frequency dielectric constants,the TO phonon frequencies,the oscillator strengths,the damping of the TO phonons,and incident light frequency.Note that the formula S j¼e1½ðv2LO;j=v2TO;jÞÀ1 is applied in Eq.(1),where v LO,j is the LO phonon frequencies.It should be emphasized that the present dielectric function model used is the most simple one(i.e.,sum of independent Lorentz oscillators),which really works well on isotropic single crystals or when using a polarized light in the reflection experiments,the electric vector is oriented along one of the principle axis.However, it does not work entirely well on polycrystalline samples, particularly when the crystallites are anisotropic[21].Generally, a complicated dielectric function model containing both the effective medium approximation(EMA)and average refractiveFig.1.The XRD patterns of the SrBi2Àx Nd x Nb2O9ceramics at room temperature.Theinset shows an enlarged angle region of27–348.For clarity,some strong diffractionpeaks are labeled.M.Zhu et al./Materials Research Bulletin45(2010)1654–16581655index theory is requisite for reproducing the experimental reflectance data well [22–24].Owing to the intrinsic complexity,however,the above model are applied to calculate reflectance spectra only when the dielectric tensor is already known from the experiments on single crystals [24].Although the presented dielectric function model is approximate due to the incomplete theory used,the derived reflectance and dielectric function of the SBNN ceramics can be well accepted because of the reasonable fitting quality and errors.Finally,the best-fit parameter values in Eq.(1)can be found by applying a Levenberg–Marquardt algorithm,which is an efficient nonlinear calculation method for many parameter fitting [25].The fitting is based on minimizingthe following error function:x ¼1N P n i ¼1j R i ;exp ÀR i ;cal j 2,where N is the number of experimental data points,and R i ,exp and R i ,cal are the experimental and calculation values,respectively.The experimental reflectance spectra of the SBNN ceramics with the composition x from 0to 0.2are plotted in Fig.2with the dotted lines.It should be emphasized that the IR reflectance spectra are similar to those of the SBT ceramics at RT [18].As we know,the factor group analysis in the A 21am space group predicts 16IR-active phonon modes at RT [3].However,the reflectance of the SBT single crystal only revealed 14modes at 10K [18].The increase in damping with the temperature causes the broadening of the bands and decrease of their vibration intensity.Although there are many phonons below 350cm À1,not all phonons can be observed because of possible mode overlapping and/or their small intensity,as seen in Ref.[18].Moreover,the phonon damping obviously increases with the temperature,suggesting that the low-frequency phonons are not easily assigned and modeled with the Lorentz oscillator model.When the phonon broadening increases,the vibration intensity further decreases and the strong over-lapping among the phonons appears,especially for some weak phonon modes.The phenomena could increase the fitting uncertainty of the Lorentz oscillator parameters and strong correlation coefficients,which make the convergence slower in the fitting calculation.Therefore,some stronger lattice vibrations are mainly studied to give an insight on the electronic band structure of the SBNN ceramics in the present work.The spectra can be roughly divided into two separated parts:transparent and lattice absorption regions.Below the wavenumbers of about900cm À1,the lattice vibration characteristics are dominant in the spectral lineshape due to the phonon response.Although some phonon modes are overlapped by each other,five reflectance extremum are still observed,which can be unambiguously assigned to the IR-active vibration modes.The fitted parameter values are summarized in Table 1,and the simulated reflectance data are also presented in Fig.2by the solid lines.A good agreement is obtained between the experimental and calculated spectra in the entirely measured frequency range.The e 1generally increases with the Nd composition except for the sample of x =0.1.Based on the effective mass approximation theory [26],the shift value of the electronic band from the bulk single crystal is inversely proportional to the square of the grain size.Thus,the derivation could be due to a smaller grain size because the parameter e 1accounts for the socalled high-frequency limit,which can be derived from the high energy electronic transition contributions.Correspondingly,it also indicates that the high-energy electronic transition contributions become more remarkable with increasing Nd composition.Nevertheless,these values are slightly less than that (5.75)from relaxor ferroelectric Pb(Mg 1/3Nb 2/3)O 3(PMN)single crystal [19].It could be ascribed to the differences from the crystalline structure and formation because the polycrystallinity can partly make the long-range order and symmetry deteriorated [16].On the other hand,the oscillator strength S 1is much larger than those for other TO phonon modes.It indicates that the LO–TO splitting of about 350cm À1mode is the most prominent among these IR-active phonons observed.Although the fitted v TO,1of the SBNN ceramics with x =0.1and 0.05are lower than the experimental frequency limitation of 350cm À1,the values are beyond the limitation for two higher Nd compositions from Table 1.It should be emphasized that the lower phonon frequency is necessary for reproducing the strong vibration peak near 350cm À1well (see Fig.2).The phenomena can be ascribed to the lower phonon mode,which is located in the frequency range of 346–357cm À1from the fitting calculations.As shown in Fig.3,the obtained phonon frequency was linearly varied with increasing Nd composition.The changing trend can be attributed to the local variation of the lattice constants induced by the Nd incorporation.It was confirmed by the XRD patterns,as previously discussed.Moreover,the Nd replacementsFig.2.Experimental (dotted lines)and best-fit (solid lines)infrared reflectance spectra of the SrBi 2Àx Nd x Nb 2O 9ceramics.Note that each spectrum is successively shifted by 0.7in the vertical direction.The horizontal coordinate is the logarithmic unit to enlarge the phonon response region.The dashed lines are applied to approximately distinguish two different frequency regions.Table 1The parameter values of the Lorentz oscillator model for the SrBi 2Àx Nd x Nb 2O 9ceramics are determined from the simulation of the reflectance spectra in Fig.2.The 90%reliability of the fitting parameters is given with (Æ).Note that j is the oscillator number.x e 1j S jv TO,j (cm À1)g j (cm À1)4.63Æ0.041 5.77Æ0.24346.3Æ2.661.3Æ1.820.71Æ0.06553.6Æ1.550.3Æ4.030.62Æ0.05599.2Æ0.838.3Æ2.540.39Æ0.03678.6Æ2.1109.8Æ5.750.02Æ0.01820.2Æ4.936.3Æ14.40.05 4.79Æ0.041 6.04Æ0.22348.1Æ2.356.0Æ1.620.78Æ0.07556.2Æ1.752.2Æ4.130.66Æ0.06598.1Æ0.834.7Æ2.240.37Æ0.03681.0Æ1.8108.0Æ5.650.03Æ0.01817.7Æ4.942.1Æ15.00.1 4.55Æ0.041 5.20Æ0.17356.8Æ1.955.6Æ1.620.64Æ0.11564.1Æ3.554.2Æ6.230.70Æ0.09598.2Æ1.032.8Æ2.540.33Æ0.03691.0Æ1.7106.5Æ6.850.03Æ0.01813.0Æ5.045.9Æ14.10.2 4.80Æ0.041 5.92Æ0.20351.3Æ2.052.9Æ1.520.81Æ0.08559.5Æ2.254.9Æ4.630.68Æ0.07597.4Æ0.832.3Æ2.240.35Æ0.02685.4Æ1.6106.0Æ5.850.03Æ0.01814.8Æ4.946.6Æ15.3M.Zhu et al./Materials Research Bulletin 45(2010)1654–16581656to the Bi sites reduce the bonding forces owing to the ionic radius discrepancy.This can further destroy the translational symmetry of the crystal lattice,resulting in the shift of the phonon frequency [6,16,27].Compared with the results from Raman scattering,the phonon modes in the high frequency region by IR reflectance spectra are slightly deviated.The phonon frequencies of about599cmÀ1and 820cmÀ1can be uniquely assigned to the tilting and symmetric stretching of the NbO6octahedra,respectively.Note that theses values are575cmÀ1and838cmÀ1from Raman measurement [6,7].It is noted that the two mode frequencies related to the octahedra decrease with the Nd composition.It is well known that the NbO6octahedra is linked to the Bi site for the layered perovskite FE materials.Due to the Nd replacement with a smaller ionic radius,the formation of the octahedra could be slightly shrinked,which induces the force variation of the tilting and symmetric stretching.The incorporation of Nd in the Bi site for the SBNN ceramics decreases the compressive stress and the tilting degree of NbO6group is reduced[6,28].Therefore,the dopant effects will directly appear on the phonon mode shift.The other vibrations,which could be related to the bending modes of the NbO6octahedra and lattice modes,linearly increase with the Nd composition[30].It is important to note that the phonon mode cannot be related to the Sr site vibration because all mode frequencies observed present the shift trend with the composition. On the other hand,the damping of thefive phonon modes is varied from32.3Æ2.2cmÀ1to109.8Æ5.7cmÀ1.From the reflec-tance spectra,the phonon mode of about685cmÀ1does not show an obvious peak pattern due to a larger damping coefficient.Moreover, these data agree well with the phonon damping from the PMN single crystal,which indicating that the crystalline quality of the SBNN ceramics are well-defined and does not significantly change with the Nd compositions studied so far[19].This is consistence with the slight variation trend of the phonon modes discussed earlier.The IR dielectric functions are the basic parameters for optoelectronic device designs,e.g.,spectral responsivity,spectral bandwidth,and threshold frequency of pyroelectric detectors.It can provide an insight on the electronic structure and optical dispersion behavior of materials studied.The evaluated dielectric functions of the SBNN ceramics,which can be uniquely determined byfitting the model function to the experimental data,as seen in Fig.4.Generally, the real part Re(e)increases with the photon energy beyond the wavenumbers of900cmÀ1,however,the imaginary part Im(e) approaches zero.It indicates that the SBNN ceramics are transparent in the experimental frequency region of900–1500cmÀ1because FE materials usually have a wide band gap[14,29].In the range,the dielectric response is mainly affected by the hardest mode(about 820cmÀ1)and a stronger electronic transition in the absorption region.At the frequency of1500cmÀ1,the Re(e)(=n2Àk2)value was approximately varied from3.9to4.1or the ceramics with the Nd composition.This suggests that the refractive index n correspond-ingly increases from 1.98to 2.02due to a smaller extinction coefficient k(about10À3).These values are closer to those from other perovskite FE materials,such as SBT and BaCo x Ti1Àx O3(BCT)[18,29]. At lower photon energy region,the e rapidly increases with decreasing light frequency,which agree well with the dielectric response of the SBN single crystal in the terahertz(THz)spectral range[11].Nevertheless,variable-temperature IR spectral experi-ment is necessary to further clarify the above physical properties. The energy loss function Im(À1/e)provides the maximum at the corresponding LO phonon frequency,as plotted in the inset of Fig.4. Owing to small S j values,the v LO,j are closer to v TO,j except for the phonon mode of about350cmÀ1based on the known Lyddane–Sachs–Teller relation:ðv2LO;j=v2TO;jÞ¼ðS j=e1þ1Þ.The phenomena were similar to those from other FE crystals[23,30].Therefore,the Nd incorporation influences on the LO phonon cannot be prominent, as compared with the TO mode in the present SBNN ceramics. 4.ConclusionsIn conclusion,the composition dependence of the phonon modes and dielectric functions in the SBNN ceramics have been determined by the IR reflectance technique.Thefive IR-active phonon frequencies are observed and present a linear variation trend with increasing Nd composition.It is found that the frequencies of the NbO6tilting and symmetric stretching modes linearly decrease with the Nd composition due to the octahedra distortion.In the transparent region,the real part of dielectric function Re(e)value was approximately varied from3.9to4.1for the ceramics with the Nd composition.The present results may be crucial for the realization of SBNN based infrared optoelectronic devices.AcknowledgmentsThis work wasfinancially supported by Natural Science Foundation of China(grant no.60906046),Major State Basic Research Development Program of China(grant no. 2007CB924901),Program of New Century Excellent Talents, MOE(grant no.NCET-08-0192),Shanghai Municipal CommissionFig.3.The lattice vibration frequencies of the SrBi2Àx Nd x Nb2O9ceramics are variedwith different Nd compositions.The solid lines are the linearfitting results to guidethe eyes.Fig.4.The infrared dielectric functions of the SrBi2Àx Nd x Nb2O9ceramics are variedwith different Nd compositions.For clarity,the real and imaginary parts are shown.Each curve is successively shifted by5in the vertical direction.Note that the inset isan enlargement of the energy loss function Im(À1/e).M.Zhu et al./Materials Research Bulletin45(2010)1654–16581657of Science and Technology Project(grant nos.10DJ1400201, 08JC1409000,0852*******,and09ZZ42),and the Fundamental Research Funds for the Central Universities.References[1]B.Aurivillius,P.H.Fang,Phys.Rev.126(3)(1962)893–896.[2]C.A.de Araujo,J.D.Cuchlaro,L.D.Mcmillan,M.C.Scott,J.F.Scott,Nature(London)374(6523)(1995)627–629.[3]P.R.Graves,G.Hua,S.Myhra,J.G.Thompson,J.Solid State Chem.114(1)(1995)112–122.[4]H.N.Lee,D.Hesse,N.Zakharov,U.Go¨sele,Science296(5575)(2002)2006–2009.[5]L.Sun,J.H.Chu,C.D.Feng,L.D.Chen,Appl.Phys.Lett.91(24)(2007)242902-1-3.[6]M.Verma,K.Sreenivas,V.Gupta,J.Appl.Phys.105(2)(2009)024511-1-6.[7]L.Sun,C.D.Feng,L.D.Chen,S.M.Huang,J.Appl.Phys.101(8)(2007)084102-1-5.[8]Y.Wu,M.J.Forbess,S.Seraji,S.J.Limmer,T.P.Chou,C.Nguyen,G.Cao,J.Appl.Phys.90(10)(2001)5296–5302.[9]D.P.Volanti,L.S.Cavalcante,E.C.Paris,A.Z.Simo˜es,D.Keyson,V.M.Longo,A.T.deFigueiredo,E.Longo,J.A.Varela,F.S.De Vicente,A.C.Hernandes,Appl.Phys.Lett.90(26)(2007)261913-1-3.[10]Y.Shimakawa,H.Imai,H.Kimura,S.Kimura,Y.Kubo,E.Nishibori,M.Takata,M.Sakata,K.Kato,Z.Hiroi,Phys.Rev.B66(14)(2002)144110-1-5.[11]D.Nuzhnyy,S.Kamba,P.Kuzˇel,S.Veljko,V.Bovtun,M.Savinov,J.Petzelt,H.Amorı´n,M.E.V.Costa,A.L.Kholkin,Ph.Boullay,Phys.Rev.B74(13)(2006) 134105-1-7.[12]S.M.Huang,L.Sun,C.D.Feng,L.D.Chen,J.Appl.Phys.99(07)(2006)076104-1-3.[13]Z.Kighelman,D.Damjanovic,N.Setter,J.Appl.Phys.90(09)(2001)4682–4689.[14]Z.G.Hu,Y.W.Li,F.Y.Yue,Z.Q.Zhu,J.H.Chu,Appl.Phys.Lett.91(22)(2007)221903-1-3.[15]B.H.Venkataraman,K.B.R.Varma,Ferroelectrics315(1)(2005)45–60.[16]W.Zhong,R.D.King-Smith,D.Vanderbilt,Phys.Rev.Lett.72(22)(1994)3618–3621.[17]P.S.Dobal,R.S.Katiyar,J.Raman Spectrosc.33(6)(2002)405–423.[18]S.Kamba,J.Pokorny´,V.Porokhonskyy,J.Petzelt,M.P.Moret,A.Garg,Z.H.Barber,R.Zallen,Appl.Phys.Lett.81(6)(2002)1056–1058.[19]J.Hlinka,T.Ostapchuk,D.Noujni,S.Kamba,J.Petzelt,Phys.Rev.Lett.96(2)(2006)027601-1-4.[20]Z.G.Hu,A.B.Weerasekara,N.Dietz,A.G.U.Perera,M.Strassburg,M.H.Kane,A.Asghar,I.T.Ferguson,Phys.Rev.B75(20)(2007)205320-1-8.[21]C.Pechroma´n,J.E.Iglesias,J.Phys.:Condens.Matter6(35)(1994)7125–7141.[22]T.G.Mayerho¨fer,H.H.Dunken,R.Keding,C.Ru¨ssel,Phys.Chem.Glasses42(6)(2001)353–357.[23]T.G.Mayerho¨fer,H.H.Dunken,R.Keding,C.Ru¨ssel,J.Non-Cryst.Solids333(2)(2004)172–181.[24]T.G.Mayerho¨fer,Z.Shen,R.Keding,J.L.Musfeldt,Phys.Rev.B71(18)(2005)184116-1-5.[25]W.H.Press,S.A.Teukolsky,W.T.Vetterling,B.P.Flannery,Numerical Recipes in C:The Art of Scientific Computing,Cambridge University Press,Cambridge,MA, 1992,pp.688–692.[26]Z.G.Hu,Y.W.Li,M.Zhu,Z.Q.Zhu,J.H.Chu,Phys.Lett.A372(24)(2008)4521–4526.[27]E.Buixaderas,I.Gregora,S.Kamba,J.Petzelt,M.Kosec,J.Phys.:Condens.Matter20(34)(2008),345229-1-10.[28]S.M.Huang,C.D.Feng,L.D.Chen,X.W.Wen,Solid State Commun.133(6)(2005)375–379.[29]Z.G.Hu,Y.W.Li,M.Zhu,Z.Q.Zhu,J.H.Chu,Appl.Phys.Lett.92(8)(2008)081904-1-3.[30]M.Maczka,W.Paraguassu,A.G.Souza Filho,P.T.C.Freire,A.Majchrowski,J.Mendes Filho,J.Hanuza,Phys.Rev.B78(6)(2008),064116-1-11.M.Zhu et al./Materials Research Bulletin45(2010)1654–1658 1658。

VOL
Low Level Output Voltage (R L = 10kΩ) o Tamb = +25 C Tmin. ≤ Tamb ≤ Tmax. Slew Rate VCC = 15V, VI = 0.5 to 3V, RL = 2kΩ, C L = 100pF, unity gain) Gain Bandwidth Product VCC = 30V, f = 100kHz, Vin = 10mV RL = 2kΩ, CL = 100pF Total Harmonic Distortion f = 1kHz, AV = 20dB, RL = 2kΩ, VO = 2Vpp CL = 100pF, VCC = 30V Equivalent Input Noise Voltage f = 1kHz, Rs = 100Ω, VCC = 30V Input Offset Voltage Drift Input Offset Current Drift Channel Separation (note 5) 1kHz ≤ f ≤ 20kHz
LOW INPUT OFFSET CURRENT : 2nA WIDE POWER SUPPLY RANGE : SINGLE SUPPLY : +3V TO +30V DUAL SUPPLIES : ±1.5V TO ±15V
P TSSOP14 (Thin Shrink Small Outline Package)
DESCRIPTION These circuits consist of four independent, high gain, internally frequency compensated operational amplifiers . They operate from a single power supply over a wide range of voltages. Operation from split power supplies is also possible and the low power supply current drain is independent of the magnitude of the power supply voltage. PIN CONNECTIONS (top view)

作者简介：刘景宜，本科，主管药师。

研究方向：药品检验。

E-mail ：***************硝苯地平缓释片Ⅰ释放度影响因素研究刘景宜洛阳市食品药品检验所，河南 洛阳 471023［摘要］目的：研究硝苯地平缓释片Ⅰ释放度的影响因素。

方法：参照国家食品药品监督管理局国家药品标准WS1-（X-056）-2004Z ，采用紫外可见分光光度法在237 nm 测定吸光度，计算硝苯地平缓释片Ⅰ释放度。

结果：对照品性质稳定，多次测量RSD 为0.65%；滤膜对2 h 释放度结果影响误差为5.1%~9.4%；温度在相差1 ℃时，吸光度的平均差值为2.3%。

结论：对照品在正常检验时不用考虑；温度仅在检验结果为边缘时需要考虑；滤膜是影响释放度结果的主要因素，在检验时必须考虑滤膜的影响。

［关键词］硝苯地平缓释片Ⅰ；药物释放；滤膜；温度；溶出仪；紫外可见分光光度法DOI: 10.19939/ki.1672-2809.2021.08.07Study on the Influence Factors of Nifedipine Sustained Release Tablet I Release DegreeLIU JingyiLuoyang Food and Drug Inspection Institute, Luoyang Henan 471023, China.[Abstract] Objective: To study the influence factors of Nifedipine sustained release tablet I release degree. Methods: By reference to the National Drug Standard WS1-(X-056)-2004Z of the State Food and Drug Administration, the absorbance was measured at 237 nm using ultraviolet visible method to calculate the degree of release. Results: The standard substance was stable with RSD of 0.65%; the influence error of membrane on 2 h release rate was 5.1%~9.4%; when the temperature difference is 1 ℃, the average difference of absorbance is 2.3%. Conclusion: The standard substance should not be considered in normal test; temperature only needs to be considered when the inspection result is edge; filter membrane is the main factor affecting the results of release, so the influence of filter membrane must be considered in the test.[Key Words] Nifedipine sustained release tablet I; Drug liberation; Filter membrane; Temperature; Dissolution apparatus; Ultraviolet visible spectrodiometer确保检验方法的准确性［12］。