Uniaxial pressure dependencies of the phase transitions in GdMnO$_3$

Temperature and acidity effects on WO 3nanostructures and gas-sensing properties of WO 3nanoplatesHuili Zhang a ,Zhifang Liu b ,Jiaqin Yang b ,Wei Guo b ,Lianjie Zhu a ,*,Wenjun Zheng b ,**aSchool of Chemistry and Chemical Engineering,Tianjin Key Laboratory of Organic Solar Cells and Photochemical Conversion,Tianjin University of Technology,Tianjin 300384,PR China bDepartment of Materials Chemistry,Key Laboratory of Advanced Energy Materials Chemistry (MOE),TKL of Metal and Molecule-based Material Chemistry,Synergetic Innovation Centre of Chemical Science and Engineering (Tianjin),College of Chemistry,Nankai University,Tianjin 300071,PR ChinaA R T I C L E I N F OArticle history:Received 4January 2014Received in revised form 28May 2014Accepted 11June 2014Available online 12June 2014Keywords:Nanostructures SolvothermalElectron microscopy X-ray diffractionA B S T R A C TWO 3nanostructures were successfully synthesized by a facile hydrothermal method using Na 2WO 4Á2H 2O and HNO 3as raw materials.They are characterized by X-ray diffraction (XRD),scanning electron microscope (SEM)and transmission electron microscope (TEM).The speci fic surface area was obtained from N 2adsorption –desorption isotherm.The effects of the amount of HNO 3,hydrothermal temperature and reaction time on the crystal phases and morphologies of the WO 3nanostructures were investigated in detail,and the reaction mechanism was rge amount of acid is found for the first time to be helpful to the oriented growth of tungsten oxides,forming nanoplate-like products,while hydrothermal temperature has more in fluence on the crystal phase of the product.Gas-sensing properties of the series of as-prepared WO 3nanoplates were tested by means of acetone,ethanol,formaldehyde and ammonia.One of the WO 3nanoplates with high speci fic surface area and high crystallinity displays high sensitivity,fast response and distinct sensing selectivity to acetone gas.ã2014Elsevier Ltd.All rights reserved.1.IntroductionAs an n -type indirect band gap semiconductor,WO 3has attracted much attention and been studied extensively in recent years.So far,many methods have been reported for synthesis of WO 3nanomaterials with various morphologies,such as nano-plates [1–5],nanorods [6–8],nanowires [9–11],nanoparticles [12]and nano fibres [13]etc .Recently,Zou et al.have prepared a new WO 3nanoplate via a simple thermal treatment process from a W-containing inorganic –organic nanohybrid precursor [14].Leaf-like WO 3nanoplatelets were fabricated via aging treatment of the precursor solutions obtained by pulsed laser ablating pure tungsten target immersed in deionized water [15].Ma et al.have prepared triclinic WO 3nanoplates by a simple hydrothermal method at various temperatures using Na 2WO 4Á2H 2O and HBF 4as precursors [1].Nimittrakoolchai and Supothina have synthesized WO 3ÁH 2O and H 2WO 4ÁH 2O platelet particles by a precipitation method using (NH 4)10W 12O 41Á5H 2O and HNO 3as precursors,and investigated the effect of nitric concentration on the yield [16].However,so far,no reference has been found concerning the effectsof both hydrothermal temperature and the amount of acid on crystal phases and morphologies of WO 3nanostructures.WO 3nanostructures could be extensively applied in electro-chromic and photochromic devices [6,17–20],lithium ion batteries [21–22],photoelectrodes [23],photocatalysts [24–26],solar energy devices [27–28],field electron emission [29–30]and gas sensors [1,10,13,14,16,31–42]etc.Being one of the important gas-sensor materials,more and more WO 3nanomaterials with new structures or morphologies have been synthesized because the gas-sensing properties could be tuned by the structures and morphologies of the materials.For instance,WO 3nanowires [10],nano fibers [13],hollow microspheres [31],nanocrystals [32,33],thin films [34]and WO 3nanorods/graphene nanocomposites [35]have been used as the sensing materials for detection of nitrogen oxides,NH 3and ethylene.More gaseous species,such as H 2[14,34,36],ethanol [1,14,37,38],CO [14,37],H 2S [39],and ozone [37,40]could also be detected by WO 3-based nanocrystals and films.However,so far there are few reports on acetone [14,41]and formaldehyde [14]sensing properties of WO 3nanoplates although acetone and formaldehyde are harmful to health,as common reagents widely used in industries and labs.Besides,a nanoplate-like material normally has a high sensitivityand rapid response [42]due to the effective and rapid diffusion of the analyte gas onto the entire sensing surface through the two-dimensional (2D)nanostructures.Therefore,it is worthwhile studying the gas sensing properties of the 2D WO 3nanoplates.*Corresponding author.Tel.:+862260214259;fax:+862260214252.**Corresponding author.Tel.:+862223507951;fax:+862223502458.E-mail addresses:zhulj@ (L.Zhu),zhwj@ (W.Zheng)./10.1016/j.materresbull.2014.06.0130025-5408/ã2014Elsevier Ltd.All rights reserved.Materials Research Bulletin 57(2014)260–267Contents 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 r e s buHerein,a facile hydrothermal route was adopted for syntheses of series of WO3nanostructures.The effects of the amount of HNO3,hydrothermal temperature and reaction time on crystal phases and morphologies of WO3products were investigated and discussed.The formation mechanism of the WO3nanoplates was studied on the basis of control experiments.The gas-sensing properties of the as-prepared WO3on acetone,ethanol,formalde-hyde and ammonia were evaluated,and a nanoplate-like WO3 shows a high sensitivity,rapid response and distinct selectivity to acetone gas.2.Experimental2.1.Synthesis of WO3nanostructuresIn a typical procedure,0.3299g of Na2WO4Á2H2O(1mmol)was added into certain volume of distilled water and dissolved thoroughly under stirring.Then,certain amount of HNO3(w, 65%)was dropped into the solution and kept stirring for10min. The total volume of the solution was always kept to be25.0mL.The above mixture was transferred into a33.0mL of Teflon-lined stainless steel autoclave,sealed and kept in an electric oven at certain temperature for12h.The autoclave was then taken out and allowed to cool naturally to room temperature.The obtained precipitate was separated by centrifugation,washed by distilled water and absolute ethanol for three times,respectively,and dried at50 C.2.2.CharacterizationsThe XRD measurements were performed on a Rigaku D/max-2500diffractometer with Cu K a radiation(l=0.154056nm)at 40kV and100mA.The SEM images were taken with a JEOL JSM-6700F scanning electron microscope.The TEM and high resolution TEM(HRTEM)images of the WO3nanoplates were obtained on a JEOL JEM-2100F microscope operating at200kV.The N2adsorp-tion–desorption isotherm measurements were operated on a V-Sorb2800P surface area and pore size analyzer.2.3.Fabrication and test of WO3gas sensorsThe schematic illustration of the gas-sensing measurement and working principle of HW-30A system can be found in the references[1,43].The WO3nanoplates were slightly grinded with several drops of terpineol in an agate mortar.The formed slurry was coated onto an alumina tube with a diameter of1mm and length of4mm,positioned with a pair of Au electrodes and four Pt wires on both ends of the tube.After calcination at400 C for1h, the alumina tube was jointed with the measuring electric circuit.In order to improve the stability and repeatability,the gas-sensing element was aged at340 C for two weeks before the measure-ment.Acetone,ethanol,formaldehyde and ammonia with various concentrations were chosen to evaluate the gas-sensing properties of the as-prepared WO3.The sensor response is defined as S=R a/R g, where R a and R g are the electrical resistance of the sensor in air and in test gas,respectively.The response and recovery time is defined as the time for the sensor to reach90%of its maximum response and fall to10%of its maximum response,respectively.3.Results and discussion3.1.Effects of hydrothermal temperature and the amount of HNO3on the crystal phases and morphologies of the productsFig.1shows the crystal phase evolution of the products obtained at120 C using various amount of HNO3.When0.5mL of HNO3is used,the main product is orthorhombic WO3ÁH2O(JCPDS 43-0679)with a little impurity(Fig.1a).Increasing the amount of HNO3to1.5mL leads to the formation of a pure orthorhombic WO3ÁH2O(Fig.1b).The monoclinic phase of unhydrous WO3 (JCPDS43-1035)appears when2.5mL of HNO3is used and the relative peak intensity of this phase increases gradually by increasing the volume of HNO3until12.0mL(Fig.1c–f).When the amount of HNO3is further increased,however,no pure phase of monoclinic WO3is produced(Fig.1g and h).On the contrary,the relative intensity of the diffraction peaks of the monoclinic WO3 becomes lower,but that of the WO3ÁH2O phase becomes higher again.When the volume of HNO3reaches20.0mL,the diffraction peaks of the monoclinic WO3phase become even faint.The morphology evolution of the products prepared at120 C using various amount of HNO3is demonstrated in Fig.2.It was observed that the product’s morphology changes greatly in the low volume region of HNO3.A nanoparticle and nanorod mixture was collected when0.5mL of HNO3was used in the reaction system. Slightly increasing the volume of HNO3to1.5mL would lead to the formation of a bigflower-like hierarchical structure which is composed of many crossed and lapped quasi-round nanoplates with rough surfaces.The accumulated quasi-round nanoplates start dispersal and the surfaces become smooth when the volume of HNO3is increased to2.5mL.Most of the nanoplates are about 600nm in diameter and25nm in thickness.If5.0mL of HNO3is used,square-like nanoplates with a side length of around200nm and thickness of30–40nm are obtained.The surfaces of these nanoplates are rather smooth.When the volume of HNO3is in the range of 5.0–12.0mL,the products’morphologies are similar, unless the size of the nanoplate gradually becomes smaller with increasing the acid quantity.Some square-like nanoplates become a bit irregular and their surface roughness also increases if the amount of HNO3reaches15.0mL.Further increasing the amount of HNO3to20.0mL,irregularly shaped nanoplates with rather rough surfaces were obtained.This morphology is similar to that of the product in Fig.2c,unless the size is much smaller.One may notice that the phase composition of these two products(Fig.1c and h)is also similar.The other series of products were obtained at180 C,a higher hydrothermal temperature.The corresponding XRD patterns are shown in Fig.3.Orthorhombic WO3ÁH2O(JCPDS43–0679)was produced using0.5mL of HNO3.Increasing the amount of HNO3to 1.5mL leads to the formation of a mixture with most orthorhombic WO3ÁH2O and a little monoclinic WO3(JCPDS43–1035).The phase compositions of the products change dramatically withslightlyFig. 1.XRD patterns of the products prepared by hydrothermal method at120 C using various amount of HNO3:(a)0.5mL,(b)1.5mL,(c)2.5mL,(d)5.0mL,(e) 10.0mL,(f)12.0mL,(g)15.0mL and(h)20.0mL.H.Zhang et al./Materials Research Bulletin57(2014)260–267261increasing the volume of HNO 3from 1.5mL to 2.0mL.Pure monoclinic WO 3is obtained in the presence of 2.0mL of HNO 3.With further increasing the amount of HNO 3,the crystal phases of the products do not change any more.But the intensity of the diffraction peaks increases firstly and then declines slightly.The peak intensity reaches maximum using 10mL of HNO 3,which indicates the highest crystallinity of the WO 3product obtained at this condition.Thus,10mL of HNO 3is a suitable amount to obtain a pure monoclinic WO 3with a high crystallinity.The morphology evolution of the products prepared at 180 C using various amount of HNO 3is demonstrated in Fig.4.When 0.5mL of HNO 3is used,a nanoparticle –nanorod mixture (Fig.4a)is obtained,similar to the morphology of the product prepared at 120 C (Fig.2a).However,in the case of 1.5mL HNO 3,the two products prepared at these two hydrothermal temperatures have completely different morphologies.As shown in Fig.4b,the product comprises many non-uniform big rectangular blocks andplates.Slightly increasing the HNO 3–2.0mL leads to formation of WO 3nanoplates with different size,and some nanoplates accumulate with their large surfaces.When 10.0mL or 15.0mL of HNO 3is used,the product is well-dispersed nanoplates with the large surfaces exposed (Fig.4d and e).The side length and thickness of an individual nanoplate are approximately 100nm and 40nm,respectively.Changing the amount of HNO 3in the range of 10–15mL does not in fluence the morphology of the products.But in case of 20.0mL HNO 3,the uniformity of the product decreases and the size of the nanoplate increases to certain extent,although its crystal phase is kept unchanged.Because both the uniformity and crystallinity of the sample prepared at 180 C using 10.0mL of HNO 3are high,its TEM and HRTEM images were taken.As shown in Fig.5a,the side length and thickness of the most WO 3nanoplates are around 100nm and 30–40nm,respectively,which is consistent with the SEM result.The clear 2D crystal lattice (Fig.5b)shows that theinterplanarFig. 2.SEM images of the products prepared by hydrothermal method at 120 C using various amount of HNO 3:(a)0.5mL,(b)1.5mL,(c)2.5mL,(d)5.0mL,(e)10.0mL,(f)12.0mL,(g)15.0mL and (h)20.0mL.262H.Zhang et al./Materials Research Bulletin 57(2014)260–267distances are 0.37and 0.38nm,corresponding to (020)and (002)crystal planes,respectively.The fast Fourier transform pattern (the inset)indicates its single crystalline nature.On the basis of above results we conclude that both hydrothermal temperature and the amount of HNO 3in fluence the crystal phase and morphology of the product.Fig.6shows a summary of these two effects.Similar to the result in our previous work [1],low temperature favours the formation of WO 3ÁH 2O andhigh temperature is propitious to production of anhydrous WO 3.Increasing temperature results in dehydration of WO 3ÁH 2O,forming pure WO 3phase,even using a small volume of HNO 3(for example,2.0mL HNO 3).However,at the low hydrothermal temperature,120 C,no pure phase of WO 3was obtained even if a large volume of HNO 3was used.In the region of small volume of HNO 3,the crystal phases and morphologies of the products are found more sensitive to the change in acid quantity and reaction temperature.For instance,when 1.5mL of HNO 3was used,a hierarchical flower-like hydrous WO 3was formed at 120 C,but a non-uniform rectangular block and plate-like hydrous and anhydrous WO 3mixture is the main product at 180 C.This may be attributed to different nucleation rate,diffusion rate of nanoparticles and dehydration rate at different temperatures.At high temperature,the formation rate of tungsten oxide nucleus is fast and the hydrous WO 3loses water quickly once beyond its decomposition temperature,which partially counteracts the in fluence of larger amount of water on the crystal phase of the product when small volume of HNO 3is used.Moreover,the diffusion rate of nanoparticles is low at low temperature,which contributes to the formation of a big architecture.But a high diffusion rate at high temperature helps to epitaxy along certain crystal face [44].Therefore,different morphological products were produced at two hydrothermal temperatures using 1.5mL of HNO 3.When large amount of HNO 3(for instance,10mL HNO 3)is used,however,it is different from the above case.The similar morphology of the two products obtained at the twotemperaturesFig. 3.XRD patterns of the products prepared by hydrothermal method at 180 C using various amount of HNO 3:(a)0.5mL,(b)1.5mL,(c)2.0mL,(d)10.0mL,(e)15.0mL and (f)20.0mL.Fig.4.SEM images of the products prepared by hydrothermal method at 180 C using various amount of HNO 3:(a)0.5mL,(b)1.5mL,(c)2.0mL,(d)10.0mL,(e)15.0mL and (f)20.0mL.H.Zhang et al./Materials Research Bulletin 57(2014)260–267263clearly shows that large amount of acid is bene ficial to the oriented growth of the tungsten oxides,forming nanoplates.This,on the one hand,may be related to the high degree of supersaturation of the solution,which will increase the nucleation rate and dehydration rate of H 2WO 4,and ultimately increase the reaction rate.On the other hand,the acidity of a reaction system in fluences surface energies of certain crystal facets [45],which may signi ficantly in fluence the oriented growth of a crystal,and consequently in fluence the morphology of the product.Thus,suitable amount of acid is a dominant factor to the formation of nanoplate-like morphology.However,the acidity effect on the crystal phase of the product is found weaker than that of temperature.The low nucleation rate at 120 C results in the larger size of the nanoplates (compared to the product prepared at 180 C),which accords with the crystallization principle.The low dehydration rate at the lower temperature leads to incomplete dehydration of the product,forming a mixed phase of product.Thus,a larger size of mixed phase of nanoplate was obtained at 120 C using 10mL of HNO 3.3.2.Formation mechanismBecause the product prepared at 180 C using 15.0mL of HNO 3shows the better gas-sensing property,its time-dependent crystal phase and morphology evolutions were investigated.It represents the effect of hydrothermal time on the crystal phase and morphology of a WO 3nanostructure.As shown in Fig.S1and S2in the supporting information (ESI),pure uniform orthorhombic WO 3ÁH 2O (JCPDS 43–0679)nanoplates were obtained at 1h,which were quickly transformed to WO 3nanoplates.A mixture of WO 3ÁH 2O and WO 3was collected at 1.5h and pure monoclinic WO 3(JCPDS 43-1035)nanoplates were produced at 2h.These results con firm that a hydrous WO 3was formed at the early stage of the reaction and prolonging hydrothermal time results in a quick dehydration of WO 3ÁH 2O.The corresponding chemical reactions contain:WO 2À4þ2H þ!WO 3ÁH 2O(1)WO 3ÁH 2O !WO 3þH 2O(2)This reaction process is similar to the work by Lee et al.[46,46],where the high concentrations of HNO 3(0.29–11.5mol L À1)were replaced by low concentrations of HCl (pH 2–6)and NaCl was used as a capping agent.However,WO 3nanorods were obtained in their work although a similar procedure was applied.Lee et al.believed that NaCl selectively adsorbed onto the crystal planes parallel to the c -axes of WO 3crystal nucleus to accelerate the preferential growth,resulting in the formation of 1D structure.In our case,no capping agent or directing agent was used.Besides,as shown in Fig.6,a large amount of acid is bene ficial to the oriented growth of nanoplate-like tungsten oxides.Except the external factors,the intrinsic crystal structure is also an essential factor for morphology control of the product.The orthorhombic H 2WO 4consists of layers of [WO 6]octahedra,which share their four equatorial oxygen atoms.Water molecules and oxygen atoms in the axial positions of the [WO 6]octahedra form hydrogen bonds with the neighboring layers [3],as shown in Fig.S3a in the ESI.The monoclinic WO 3possesses a distorted ReO 3structure,see Fig.S3b.The layers of [WO 6]octahedra in the orthorhombic H 2WO 4and the monoclinic WO 3are similar.The shared four equatorial oxygen atoms extend forming a 2D plane structure.At high temperature,the hydrogen bonds in the layers of [WO 5(OH 2)]octahedra of the H 2WO 4were replaced by W ÀÀO ÀÀW bonds forming a three-dimensional W ÀÀO ÀÀW lattice-work and losing the crystal waters.The similarity of the WO 6octahedral sheets in H 2WO 4and WO 3results in the formation of the nanoplate-like WO 3.3.3.Gas-sensing properties and mechanismAll gas-sensing measurements were operated at 300 C.Therefore,the samples were calcined at 450 C for 2h before the gas-sensing measurements to ensure their thermal stability.The XRD patterns of the calcined WO 3samples are shown in Fig.S4in the ESI.All diffraction peaks for all the samples can be indexedtoFig. 5.(a)TEM and (b)HRTEM images of the sample prepared at 180 C using 10.0mL of HNO 3(the inset is the fast Fourier transformpattern).Fig.6.Schematic representation of the formation of the WO 3nanostructures with various morphologies and crystal phases:(a)orthorhombic WO 3ÁH 2O,(b)a mixture of orthorhombic WO 3ÁH 2O and monoclinic WO 3and (c)monoclinic WO 3,prepared at two hydrothermal temperatures using various amount of HNO 3.264H.Zhang et al./Materials Research Bulletin 57(2014)260–267monoclinic WO3(JCPDS43-1035),which indicates that pureanhydrous WO3products were obtained after the heat treatment.The SEM images of the calcined WO3samples,Fig.S5in the ESI,demonstrate that the product morphologies before and after theheat treatment are similar,which verifies again that thecondensation from WO3ÁH2O to WO3is a topotactic conversion process.The synthetic conditions of the precursors,the morphol-ogies and Brunauer–Emmett–Teller(BET)surface areas of thecalcined WO3products are summarized in Table1.The gas-sensing properties of the series of WO3nanomaterialsarefirst evaluated by means of200ppm acetone gas(Fig.7a).Theresults show that the sensor based on the S3sample is moresensitive than the others.The response of the S2sensor is slightlylower than that of the S3sensor.The third sensitive sensor is basedon the P3sample.The high responses of the S2,S3and P3sensorsmay be attributed to their high BET surface areas,highcrystallinities and plate-like morphologies[38].The most sensitive three sensors based on the samples S2,S3and P3were then chosen to investigate the sensitivities in thepresence of various concentrations of acetone gases,from10ppmto400ppm.As shown in Fig.7b,the S3sensor always has thehigher response than the other two sensors to any concentration ofacetone gas.The responses for all the three sensors increasesignificantly with increasing the concentration of acetone gas.Forinstance,the response for the S3sensor increases from4.1to15.8with increasing the concentration of acetone from10ppm to400ppm.Fig.8a represents the dynamic responses of the S2,S3and P3sensors to acetone gases with various concentrations from10ppmto400ppm.Sharp rises and drops in voltage values were observedfor all concentrations of acetone gases when they were injectedand discharged,respectively.This indicates that the WO3nano-plate sensors have a wide range of acetone-detecting abilities andare of fast response and recovery speeds to acetone gases.Forexample,the response and recovery time of the S3sensor are7sand23s,respectively,for100ppm acetone gas(Fig.8b).The resultsalso show that the response increases with increasing theconcentration of acetone gas at the same operating conditions.The sensing selectivity of the S3sensor was explored bycomparing the responses of the S3sensor to acetone,ethanol,formaldehyde and ammonia gases with various concentrations.Asshown in Fig.9,the responses of the S3sensor to all the four gasesincrease gradually with increasing the concentrations of the gases.However,the order of magnitude of the responses to differentgases is quite different.It is less sensitive to ethanol and almostinsensitive to formaldehyde and ammonia,compared to acetone.Thus,the as-prepared WO3nanoplate(S3)displays a distinctsensing selectivity to acetone gas,which could be explained byconsidering its sensing mechanism.As an n-type semiconductor,the sensing mechanism of theWO3nanoplate could be explained using the classical electrondepletion theory[41,47,48].Oxygen molecules in airfirst physically adsorb on the surface of WO3semiconductor.The O2(ads)capturesan electron from WO3forming OÀ2(ads).At an elevated tempera-ture,the chemically adsorbed O2(ads)molecules can obtainenough energy to capture two electrons or OÀ2(ads)to capture one more electron forming OÀ(ads).Because the oxygen ionosorption depletes electrons in the conduction band,conductance of the WO3 sensor is decreased.When the WO3nanoplate sensor is exposed to the reducing gases,acetone,ethanol,formaldehyde and ammonia, the gases react with the OÀ(ads)on the surface of WO3.Referring to the references[49,50],the reactions could be expressed by the following Eqs.(3)–(6).CH2Oþ2OÀðadsÞ!CO2þH2Oþ2eÀ(3) C2H5OHþ6OÀðadsÞ!2CO2þ3H2Oþ6eÀ(4) CH3COCH3þ8OÀðadsÞ!3CO2þ3H2Oþ8eÀ(5) NH3þ5=2OÀðadsÞ!NOþ3=2H2Oþ5=2eÀ(6) The gas removes chemisorbed oxygen anions and releases electrons to the conduction band.This will decrease the amount of the surface OÀ(ads)and increase the concentration of electrons in the conduction band,which eventually increases the conductance of the WO3sensor.According to the Eqs.(3)–(5),more electrons are released with increasing carbon chain.Consequently,the response increases because of the increased conductance of the sensor. Therefore,the gas response of acetone is higher than those of ethanol and formaldehyde gases at the equivalent concentration.As it is known that WO3is an acid oxide and generally it shows relatively high response to ammonia[13,41,51,52],but this is not always the case.For instance,Yu et al.reported that the gas responses of the WO3nanorods are7.6,18and27.5for1mL of ammonia,ethanol and acetone,respectively[35].A similar result was also found by Li and his co-workers[53],where the gas responses of the WO3hollow-spheres are2.89,6.14and13.50for 500ppm of ammonia,ethanol and acetone gases,respectively. These works show that the responses of the WO3nanostructures to ammonia gases are low and much lower than those of ethanol and acetone gases at the equivalent condition,which is similar to our result.Wefind that the response of the as-prepared WO3nanoplate to the alkaline gas,NH3,is lower than those of ethanol and acetone gases although it is slightly higher than that of formaldehyde.One may notice that the four gas responses(Fig.9)of the WO3 nanoplate increase with increasing the quantity of the released electrons(Eqs.3–6).This further confirms the proposed sensing mechanism above.From this point of view,it is reasonable that the as-prepared WO3nanoplate shows a distinct sensing selectivity to acetone gas.The sensing performance of a material can be strongly affected by a few factors.The higher the BET surface area is,the higher the oxygen-adsorption quantity is,and the higher sensitivity the WO3 sensor has[54].High crystallinity is also beneficial to highTable1The synthetic conditions of the precursors and properties of the WO3products after calcination at450 C for2h.Samples T( C)HNO3(mL)[H+](mol LÀ1)Morphologies Surface areas(m2gÀ1)P1120 5.0 2.9Nanoplate17.6P212010.0 5.8Nanoplate24.2P312012.0 6.9Nanoplate28.7P412015.08.6Nanoplate25.3S1180 2.0 1.2Big block and plate12.2S218010.0 5.8Nanoplate23.9S318015.08.6Nanoplate40.1S418020.011.5Nanoplate19.4H.Zhang et al./Materials Research Bulletin57(2014)260–267265sensitivity of a WO 3sensor [38].Therefore,the S3sensor has the highest value of acetone response due to the largest BET surface area exposed to gas and good crystallinity.Besides,the plate-like morphology of the WO 3allows for rapid diffusion of acetone molecules,which results in a fast gas-sensing response.In a word,the WO 3nanoplate (S3)is very promising for fabrication of an acetone gas sensor because of its high sensitivity,distinct selectivity and fast response to acetone gas.4.ConclusionsSeries of tungsten oxide nanostructures with different crystal phases and morphologies have been synthesized at two temper-atures by a facile hydrothermal method using various amount of HNO 3,and the formation mechanism of the WO 3nanoplate was explored based on series of time-dependant control experiments.The results show that the tungstate first reacts with hydrion forming hydrous WO 3,followed by a dehydration rge amount of acid,high temperature and long reaction time are found generally bene ficial to the formation of anhydrous WO 3nano-plates.It is worth mentioning that large amount of acid is found helpful to the oriented growth of the tungsten oxides,forming a nanoplate-like product.But the effect of acid quantity on the crystal phase of a product is weaker than that of temperature.The low dehydration rate at the low temperature (120 C)leads to incompletely dehydration of the product,forming a WO 3ÁH 2O and WO 3mixed phase of nanoplate,even if a large amount of acid (10mL)is used.At the high hydrothermal temperature (180 C)the nucleation rate,diffusion rate of nanoparticles and dehydration rate are increased signi ficantly,resulting in the formation of pure monoclinic WO 3nanoplates,even if a small amount of acid (2mL)is used.The gas-sensing measurements show that the sensitivities of the sensors based on the S3,S2and P3samples are the top three in the presence of 200ppm acetone gas.The S3sensor shows a distinct selectivity and fast response to acetone gas,which implies that the WO 3nanoplate (S3)is a promising material for fabrication of an acetone gassensor.Fig.7.Response comparison of the sensors based on the samples (a)P1-P4and S1-S4in the presence of 200ppm acetone gas and (b)P3,S2and S3in the presence of various concentrations of acetonegases.Fig.8.(a)Dynamic response –recovery curves of the P3,S2and S3sensors for acetone gas detection and (b)response transients of the S3sensor to 100ppm acetone gas.R e s p o n s eConce ntration /pp mFig.9.Sensing selectivity of the S3sensor to four gases with variousconcentrations.266H.Zhang et al./Materials Research Bulletin 57(2014)260–267。

第36卷 第4期 无 机 材 料 学 报Vol. 36No. 42021年4月Journal of Inorganic Materials Apr., 2021收稿日期: 2020-07-02; 收到修改稿日期: 2020-09-27; 网络出版日期: 2020-10-19基金项目: 国家自然科学基金(51972027) National Natural Science Foundation of China (51972027) 作者简介: 王皓轩(1994–), 男, 博士研究生.E-mail:*********************WANGHaoxuan(1994–),male,PhDcandidate.E-mail:*********************通信作者: 王一光, 教授.E-mail:*******************.cn文章编号: 1000-324X(2021)04-0355-10 DOI: 10.15541/jim20200366高熵过渡金属碳化物陶瓷的研究进展王皓轩1, 刘巧沐2, 王一光3(1. 西北工业大学 超高温结构复合材料重点实验室, 西安710072; 2. 中国燃气涡轮研究院, 成都 610500; 3. 北京理工大学 先进技术结构研究院, 北京 100081)摘 要: 高熵陶瓷作为新型材料, 较大的构型熵赋予其独特的性能, 其中高熵过渡金属碳化物有望成为高超声速飞行器热防护系统的备选材料。

相比于单组元碳化物陶瓷, 高熵化的单相陶瓷在综合性能上有较大地提高。

目前, 高熵过渡金属碳化物陶瓷的研究还处于初始阶段, 关于高熵过渡金属碳化物的成分设计和理论分析还缺少足够的研究支撑。

另外, 如何制备高纯度高熵过渡金属碳化物还需要进一步探索。

在高熵过渡金属碳化物陶瓷的性能方面, 还缺少深入的研究。

本文针对高熵陶瓷的理论设计和制备方法展开综述, 详细介绍了高熵过渡金属碳化物的力学、热导及抗氧化性能的研究进展, 并指出了高熵过渡金属碳化物陶瓷在超高温陶瓷领域存在的科学问题, 展望了高熵过渡金属碳化物陶瓷未来的发展方向。

SCI写作句型汇总S C I论文写作中一些常用的句型总结(一)很多文献已经讨论过了一、在Introduction里面经常会使用到的一个句子：很多文献已经讨论过了。

它的可能的说法有很多很多，这里列举几种我很久以前搜集的：A.??Solar energy conversion by photoelectrochemical cells?has been intensively investigated.?(Nature 1991, 353, 737 - 740?)B.?This was demonstrated in a number of studies that?showed that composite plasmonic-metal/semiconductor photocatalysts achieved significantly higher rates in various photocatalytic reactions compared with their pure semiconductor counterparts.C.?Several excellent reviews describing?these applications are available, and we do not discuss these topicsD.?Much work so far has focused on?wide band gap semiconductors for water splitting for the sake of chemical stability.（DOI:10.1038/NMAT3151）E.?Recent developments of?Lewis acids and water-soluble organometalliccatalysts?have attracted much attention.（Chem. Rev. 2002, 102, 3641?3666）F.?An interesting approach?in the use of zeolite as a water-tolerant solid acid?was described by?Ogawa et al（Chem.Rev. 2002, 102, 3641?3666）G.?Considerable research efforts have been devoted to?the direct transition metal-catalyzed conversion of aryl halides toaryl nitriles. (J. Org. Chem. 2000, 65, 7984-7989) H.?There are manyexcellent reviews in the literature dealing with the basic concepts of?the photocatalytic processand the reader is referred in particular to those by Hoffmann and coworkers,Mills and coworkers, and Kamat.(Metal oxide catalysis,19,P755)I. Nishimiya and Tsutsumi?have reported on（proposed）the influence of the Si/Al ratio of various zeolites on the acid strength, which were estimated by calorimetry using ammonia. (Chem.Rev. 2002, 102, 3641?3666)二、在results and discussion中经常会用到的：如图所示A. GIXRD patterns in?Figure 1A show?the bulk structural information on as-deposited films.?B.?As shown in Figure 7B,?the steady-state current density decreases after cycling between 0.35 and 0.7 V, which is probably due to the dissolution of FeOx.?C.?As can be seen from?parts a and b of Figure 7, the reaction cycles start with the thermodynamically most favorable VOx structures（J. Phys. Chem. C 2014, 118, 24950?24958）这与XX能够相互印证：A.?This is supported by?the appearance in the Ni-doped compounds of an ultraviolet–visible absorption band at 420–520nm (see Fig. 3 inset), corresponding to an energy range of about 2.9 to 2.3 eV.B. ?This?is consistent with the observation from?SEM–EDS. (Z.Zou et al. / Chemical Physics Letters 332 (2000) 271–277)C.?This indicates a good agreement between?the observed and calculated intensities in monoclinic with space groupP2/c when the O atoms are included in the model.D. The results?are in good consistent with?the observed photocatalytic activity...E. Identical conclusions were obtained in studies?where the SPR intensity and wavelength were modulated by manipulating the composition, shape,or size of plasmonic nanostructures.?F.??It was also found that areas of persistent divergent surfaceflow?coincide?with?regions where convection appears to be consistently suppressed even when SSTs are above 27.5°C.(二)1. 值得注意的是...A.?It must also be mentioned that?the recycling of aqueous organic solvent is less desirable than that of pure organic liquid.B.?Another interesting finding is that?zeolites with 10-membered ring pores showed high selectivities (>99%) to cyclohexanol, whereas those with 12-membered ring pores, such as mordenite, produced large amounts of dicyclohexyl ether. (Chem. Rev. 2002, 102,3641?3666)C.?It should be pointed out that?the nanometer-scale distribution of electrocatalyst centers on the electrode surface is also a predominant factor for high ORR electrocatalytic activity.D.?Notably,?the Ru II and Rh I complexes possessing the same BINAP chirality form antipodal amino acids as the predominant products.?(Angew. Chem. Int. Ed., 2002, 41: 2008–2022)E. Given the multitude of various transformations published,?it is noteworthy that?only very few distinct?activation?methods have been identified.?(Chem. Soc. Rev., 2009,?38, 2178-2189)F.?It is important to highlight that?these two directing effects will lead to different enantiomers of the products even if both the“H-bond-catalyst” and the?cata lyst?acting by steric shielding have the same absolute stereochemistry. (Chem. Soc. Rev.,?2009,?38, 2178-2189)G.?It is worthwhile mentioning that?these PPNDs can be very stable for several months without the observations of any floating or precipitated dots, which is attributed to the electrostatic repulsions between the positively charge PPNDs resulting in electrosteric stabilization.(Adv. Mater., 2012, 24: 2037–2041)2.?...仍然是个挑战A.?There is thereby an urgent need but it is still a significant challenge to?rationally design and delicately tail or the electroactive MTMOs for advanced LIBs, ECs, MOBs, and FCs.?（Angew. Chem. Int. Ed.2 014, 53, 1488 – 1504）B.?However, systems that are?sufficiently stable and efficient for practical use?have not yet been realized.C.??It?remains?challenging?to?develop highly active HER catalysts based on materials that are more abundant at lower costs. (J. Am. Chem.Soc.,?2011,?133, ?7296–7299)D.?One of the?great?challenges?in the twenty-first century?is?unquestionably energy storage. (Nature Materials?2005, 4, 366 - 377?)众所周知A.?It is well established (accepted) / It is known to all / It is commonlyknown?that?many characteristics of functional materials, such as composition, crystalline phase, structural and morphological features, and the sur-/interface properties between the electrode and electrolyte, would greatly influencethe performance of these unique MTMOs in electrochemical energy storage/conversion applications.（Angew. Chem. Int. Ed.2014,53, 1488 – 1504）B.?It is generally accepted (believed) that?for a-Fe2O3-based sensors the change in resistance is mainly caused by the adsorption and desorption of gases on the surface of the sensor structure. (Adv. Mater. 2005, 17, 582)C.?As we all know,?soybean abounds with carbon,?nitrogen?and oxygen elements owing to the existence of sugar,?proteins?and?lipids. (Chem. Commun., 2012,?48, 9367-9369)D.?There is no denying that?their presence may mediate spin moments to align parallel without acting alone to show d0-FM. (Nanoscale, 2013,?5, 3918-3930)(三)1. 正如下文将提到的...A.?As will be described below（也可以是As we shall see below）,?as the Si/Al ratio increases, the surface of the zeolite becomes more hydrophobic and possesses stronger affinity for ethyl acetate and the number of acid sites decreases.（Chem. Rev. 2002, 102, 3641?3666）B. This behavior is to be expected and?will?be?further?discussed?below. (J. Am. Chem. Soc.,?1955,?77, 3701–3707)C.?There are also some small deviations with respect to the flow direction,?whichwe?will?discuss?below.（Science, 2001, 291, 630-633）D.?Below,?we?will?see?what this implies.E.?Complete details of this case?will?be provided at a?later?time.E.?很多论文中，也经常直接用see below来表示，比如：The observation of nanocluster spheres at the ends of the nanowires is suggestive of a VLS growth process (see?below). (Science, 1998, ?279, 208-211)2. 这与XX能够相互印证...A.?This is supported by?the appearance in the Ni-doped compounds of an ultraviolet–visible absorption band at 420–520 nm (see Fig. 3 inset), corresponding to an energy range of about2.9 to 2.3 eVB.This is consistent with the observation from?SEM–EDS. (Chem. Phys. Lett. 2000, 332, 271–277)C.?Identical conclusions were obtained?in studies where the SPR intensity and wavelength were modulated by manipulating the composition, shape, or size of plasmonic nanostructures.?（Nat. Mater. 2011, DOI: 10.1038/NMAT3151）D. In addition, the shape of the titration curve versus the PPi/1 ratio,?coinciding withthat?obtained by fluorescent titration studies, suggested that both 2:1 and 1:1 host-to-guest complexes are formed. (J. Am. Chem. Soc. 1999, 121, 9463-9464)E.?This unusual luminescence behavior is?in accord with?a recent theoretical prediction; MoS2, an indirect bandgap material in its bulk form, becomes a direct bandgapsemiconductor when thinned to a monolayer.?(Nano Lett.,?2010,?10, 1271–1275)3.?我们的研究可能在哪些方面得到应用A.?Our ?ndings suggest that?the use of solar energy for photocatalytic watersplitting?might provide a viable source for?‘clean’ hydrogen fuel, once the catalyticef?ciency of the semiconductor system has been improved by increasing its surface area and suitable modi?cations of the surface sites.B. Along with this green and cost-effective protocol of synthesis,?we expect that?these novel carbon nanodots?have potential applications in?bioimaging andelectrocatalysis.(Chem. Commun., 2012,?48, 9367-9369)C.?This system could potentially be applied as?the gain medium of solid-state organic-based lasers or as a component of high value photovoltaic (PV) materials, where destructive high energy UV radiation would be converted to useful low energy NIR radiation. (Chem. Soc. Rev., 2013,?42, 29-43)D.?Since the use of?graphene?may enhance the photocatalytic properties of TiO2?under UV and visible-light irradiation,?graphene–TiO2?composites?may potentially be used to?enhance the bactericidal activity.?(Chem. Soc. Rev., 2012,?41, 782-796)E.??It is the first report that CQDs are both amino-functionalized and highly fluorescent,?which suggests their promising applications in?chemical sensing.(Carbon, 2012,?50,?2810–2815)(四)1. 什么东西还尚未发现/系统研究A. However,systems that are sufficiently stable and efficient for practical use?have not yet been realized.B. Nevertheless,for conventional nanostructured MTMOs as mentioned above,?some problematic disadvantages cannot be overlooked.（Angew. Chem. Int. Ed.2014,53, 1488 – 1504）C.?There are relatively few studies devoted to?determination of cmc values for block copolymer micelles. (Macromolecules1991, 24, 1033-1040)D. This might be the reason why, despite of the great influence of the preparation on the catalytic activity of gold catalysts,?no systematic study concerning?the synthesis conditions?has been published yet.?(Applied Catalysis A: General 2002, 226, ?1–13)E.?These possibilities remain to be?explored.F.??Further effort is required to?understand and better control the parameters dominating the particle surface passivation and resulting properties for carbon dots of brighter photoluminescence. (J. Am. Chem. Soc.,?2006,?128?, 7756–7757)2.?由于/因为...A.?Liquid ammonia?is particularly attractive as?an alternative to water?due to?its stability in the presence of strong reducing agents such as alkali metals that are used to access lower oxidation states.B.?The unique nature of?the cyanide ligand?results from?its ability to act both as a σdonor and a π acceptor combined with its negativecharge and ambidentate nature.C.?Qdots are also excellent probes for two-photon confocalmicroscopy?because?they are characterized by a very large absorption cross section?(Science ?2005,?307, 538-544).D.?As a result of?the reductive strategy we used and of the strong bonding between the surface and the aryl groups, low residual currents (similar to those observed at a bare electrode) were obtained over a large window of potentials, the same as for the unmodified parent GC electrode. (J. Am. Chem. Soc. 1992, 114, 5883-5884)E.?The small Tafel slope of the defect-rich MoS2 ultrathin nanosheets is advantageous for practical?applications,?since?itwill lead to a faster increment of HER rate with increasing overpotential.(Adv. Mater., 2013, 25: 5807–5813)F. Fluorescent carbon-based materials have drawn increasing attention in recent years?owing to?exceptional advantages such as high optical absorptivity, chemical stability, biocompatibility, and low toxicity.(Angew. Chem. Int. Ed., 2013, 52: 3953–3957)G.??On the basis of?measurements of the heat of immersion of water on zeolites, Tsutsumi etal. claimed that the surface consists of siloxane bondings and is hydrophobicin the region of low Al content. (Chem. Rev. 2002, 102, 3641?3666)H.?Nanoparticle spatial distributions might have a large significance for catalyst stability,?given that?metal particle growth is a relevant deactivation mechanism for commercial catalysts.?3. ...很重要A.?The inhibition of additional nucleation during growth, in other words, the complete separation?of nucleation and growth,?is?critical(essential, important)?for?the successful synthesis of monodisperse nanocrystals. (Nature Materials?3, 891 - 895 (2004))B.??In the current study,?Cys,?homocysteine?(Hcy) and?glutathione?(GSH) were chosen as model?thiol?compounds since they?play important (significant, vital, critical) roles?in many biological processes and monitoring of these?thiol?compounds?is of great importance for?diagnosis of diseases.(Chem. Commun., 2012,?48, 1147-1149)C.?This is because according to nucleation theory,?what really matters?in addition to the change in temperature ΔT?(or supersaturation) is the cooling rate.(Chem. Soc. Rev., 2014,?43, 2013-2026)(五)1. 相反/不同于A.?On the contrary,?mononuclear complexes, called single-ion magnets (SIM), have shown hysteresis loops of butterfly/phonon bottleneck type, with negligiblecoercivity, and therefore with much shorter relaxation times of magnetization. (Angew. Chem. Int. Ed., 2014, 53: 4413–4417)B.?In contrast,?the Dy compound has significantly larger value of the transversal magnetic moment already in the ground state (ca. 10?1?μB), therefore allowing a fast Q TM. （Angew. Chem. Int. Ed., 2014, 53: 4413–4417）C.?In contrast to?the structural similarity of these complexes, their magnetic behavior exhibits strong divergence.?(Angew. Chem. Int. Ed., 2014, 53: 4413–4417)D.?Contrary to?other conducting polymer semiconductors, carbon nitride ischemically and thermally stable and does not rely on complicated device manufacturing. (Nature materials, 2009, 8(1): 76-80.)E.?Unlike?the spherical particles they are derived from that Rayleigh light-scatter in the blue, these nanoprisms exhibit scattering in the red, which could be useful in developing multicolor diagnostic labels on the basis not only of nanoparticle composition and size but also of shape. (Science 2001,? 294, 1901-1903)2. 发现，阐明，报道，证实可供选择的词包括：verify, confirm, elucidate, identify, define, characterize, clarify, establish, ascertain, explain, observe, illuminate, illustrate，demonstrate, show, indicate, exhibit, presented, reveal, display, manifest，suggest, propose, estimate, prove, imply, disclose，report, describe，facilitate theidentification of?举例：A. These stacks appear as nanorods in the two-dimensional TEM images, but tilting experiments?confirm that they are nanoprisms.?(Science 2001,? 294, 1901-1903)B. Note that TEM?shows?that about 20% of the nanoprisms are truncated.?(Science 2001,? 294, 1901-1903)C. Therefore, these calculations not only allow us to?identify?the important features in the spectrum of the nanoprisms but also the subtle relation between particle shape and the frequency of the bands that make up their spectra.?(Science 2001,? 294, 1901-1903)D. We?observed?a decrease in intensity of the characteristic surface plasmon band in the ultraviolet-visible (UV-Vis) spectroscopy for the spherical particles at λmax?= 400 nm with a concomitant grow th of three new bands of λmax?= 335 (weak), 470 (medium), and 670 nm (strong), respectively. (Science 2001,? 294, 1901-1903)E. In this article, we present data?demonstrating?that opiate and nonopiate analgesia systems can be selectively activated by different environmental manipulationsand?describe?the neural circuitry involved. (Science 1982, 216, 1185-1192)F. This?suggests?that the cobalt in CoP has a partial positive charge (δ+), while the phosphorus has a partial negative charge (δ?),?implying?a tran sfer of electron density from Co to P.?(Angew. Chem., 2014, 126: 6828–6832)3. 如何指出当前研究的不足A. Although these inorganic substructures can exhibit a high density of functional groups, such as bridging OH groups, andthe substructures contribute significantly to the adsorption properties of the material,surprisingly little attention has been devoted to?the post-synthetic functionalization of the inorganic units within MOFs. (Chem. Eur. J., 2013, 19: 5533–5536.)B.?Little is known,?however, about the microstructure of this material. (Nature Materials 2013,12, 554–561)C.?So far, very little information is available, and only in?the absorber film, not in the whole operational devices. （Nano Lett.,?2014,?14?(2), pp 888–893）D.?In fact it should be noted that very little optimisation work has been carried out on?these devices. (Chem. Commun., 2013,?49, 7893-7895)E. By far the most architectures have been prepared using a solution processed perovskite material,?yet a few examples have been reported that?have used an evaporated perovskite layer. (Adv. Mater., 2014, 27: 1837–1841.)F. Water balance issues have been effectively addressed in PEMFC technology through a large body of work encompassing imaging, detailed water content and water balance measurements, materials optimization and modeling,?but very few of these activities have been undertaken for?anion exchange membrane fuel cells,? primarily due to limited materials availability and device lifetime. (J. Polym. Sci. Part B: Polym. Phys., 2013, 51: 1727–1735)G. However,?none of these studies?tested for Th17 memory, a recently identified T cell that specializes in controlling extracellular bacterial infections at mucosal surfaces. (PNAS, 2013,?111, 787–792)H. However,?uncertainty still remains as to?the mechanism by which Li salt addition results in an extension of the cathodicreduction limit. (Energy Environ. Sci., 2014,?7, 232-250)I.?There have been a number of high profile cases where failure to?identify the most stable crystal form of a drug has led to severe formulation problems in manufacture. (Chem. Soc. Rev., 2014,?43, 2080-2088)J. However,?these measurements systematically underestimate?the amount of ordered material. ( Nature Materials 2013, 12, 1038–1044)(六)1.?取决于a.?This is an important distinction, as the overall activity of a catalyst will?depend on?the material properties, synthesis method, and other possible species that can be formed during activation.?(Nat. Mater.?2017,16,225–229)b.?This quantitative partitioning?was determined by?growing crystals of the 1:1 host–guest complex between?ExBox4+?and corannulene. (Nat. Chem.?2014,?6177–178)c.?They suggested that the Au particle size may?be the decisive factor for?achieving highly active Au catalysts.(Acc. Chem. Res.,?2014,?47, 740–749)d.?Low-valent late transition-metal catalysis has?become indispensable to?chemical synthesis, but homogeneous high-valent transition-metal catalysis is underdeveloped, mainly owing to the reactivity of high-valent transition-metal complexes and the challenges associated with synthesizing them.?(Nature2015,?517,449–454)e.?The polar effect?is a remarkable property that enables?considerably endergonic C–H abstractions?that would not be possible otherwise.?(Nature?2015, 525, 87–90)f.?Advances in heterogeneous catalysis?must rely on?the rational design of new catalysts. (Nat. Nanotechnol.?2017, 12, 100–101)g.?Likely, the origin of the chemoselectivity may?be also closely related to?the H?bonding with the N or O?atom of the nitroso moiety, a similar H-bonding effect is known in enamine-based nitroso chemistry. (Angew. Chem. Int. Ed.?2014, 53: 4149–4153)2.?有很大潜力a.?The quest for new methodologies to assemble complex organic molecules?continues to be a great impetus to?research efforts to discover or to optimize new catalytic transformations. (Nat. Chem.?2015,?7, 477–482)b.?Nanosized faujasite (FAU) crystals?have great potential as?catalysts or adsorbents to more efficiently process present and forthcoming synthetic and renewablefeedstocks in oil refining, petrochemistry and fine chemistry. (Nat. Mater.?2015, 14, 447–451)c.?For this purpose, vibrational spectroscopy?has proved promising?and very useful.?(Acc Chem Res. 2015, 48, 407–413.)d.?While a detailed mechanism remains to be elucidated and?there is room for improvement?in the yields and selectivities, it should be remarked that chirality transfer upon trifluoromethylation of enantioenriched allylsilanes was shown. (Top Catal.?2014,?57: 967.?)e.?The future looks bright for?the use of PGMs as catalysts, both on laboratory and industrial scales, because the preparation of most kinds of single-atom metal catalyst is likely to be straightforward, and because characterization of such catalysts has become easier with the advent of techniques that readilydiscriminate single atoms from small clusters and nanoparticles. (Nature?2015, 525, 325–326)f.?The unique mesostructure of the 3D-dendritic MSNSs with mesopore channels of short length and large diameter?is supposed to be the key role in?immobilization of active and robust heterogeneous catalysts, and?it would have more hopeful prospects in?catalytic applications. (ACS Appl. Mater. Interfaces,?2015,?7, 17450–17459)g.?Visible-light photoredox catalysis?offers exciting opportunities to?achieve challenging carbon–carbon bond formations under mild and ecologically benign conditions. (Acc. Chem. Res.,?2016, 49, 1990–1996)3. 因此同义词：Therefore, thus, consequently, hence, accordingly, so, as a result这一条比较简单，这里主要讲一下这些词的副词词性和灵活运用。

第58卷第2期2021年2月徵鈉电子技术Micronanoelectronic TechnologyVol. 58 No. 2F eb ru ary2021D O I：10. 13250/j. cnki. wndz. 2021. 02. 003令材料与结构$六方氮化硼在二维晶体微电子器件中的应用与进展高渤翔U2，方茹3，吴天如1(1.中国科学院上海微系统与信息技术研究所信息功能材料国家重点实验室，上海200050;2.中国科学院大学，北京100049; 3•中国电子科技集团公司第三十二研究所，上海201808)摘要：六方氮化硼U-B N)因其优异的性能和潜在的应用前景而受到广泛关注。

着眼于/i-BN 在微电子器件领域中的发展与应用，总结了近年来国内外通过化学气相沉积（C V D)方法实现A-B N的高质量、大规模可控制备及图形化的代表性工作。

围绕A-B N的高介电常数、原子级平滑表面、高导热性和高稳定性，重点介绍了/i-B N在二维晶体介电衬底、半导体器件热管理平台以及集成电路封装材料中应用的研究进展，并简述了将A-B N应用于隧穿器件和存储阵列的研究成果。

最后，对A-B N在新型微电子器件大规模应用的已有成果进行总结，并展望了该领域未来的研究与发展方向。

关键词：二维（2D)材料；六方氮化硼（A-B N);微电子器件；介电衬底；隧穿器件；存储阵列；封装材料中图分类号：0612.3;TN305 文献标识码：A 文章编号：1671-4776(2021) 02-0107-07Application and Progress of Hexagonal Boron Nitride in Two-Dimensional Crystal Microelectronic DevicesGao Boxiang1’2, Fang Ru3，Wu T ia n ru1(1. State K ey Laboratory o f Functional Materials fo r Informatics ^Shanghai Institute o f Microsystem andInform ation Technology^ Chinese A cadem y o f Sciences^ Shanghai200050» C h in a；2. University o f Chinese A ca d e m y o f Sciences ^Beijing100049, China \3. The32n d Research Institute^China Electronics Technology Group Corporation ^Shanghai201808, China)A bstract：Due to excellent properties and potential application prospects, H exagonal boron ni­tride (/i-B N) has received extensive attention. Based on the developm ent and application of /i-BN in microelectronic devices, the recent representative studies of high-quality, large-scale controlla­ble preparation and pattern in g of /i-BN achieved by chemical vapor deposition (C V D) m ethod at home and abroad are summarized. T he research progresses of /z-BN for tw o-dim ensional crystal dielectric s u b s tra te s, the therm al m anagem ent platform of sem iconductor devices and integrated circuit packaging m aterials are reviewed em phatically from the aspects of the high dielectric con­sta n t, atom ic level sm o o th surface, high therm al conductivity and high stability of /i-BN. T h e research results of the application of /i-BN in tunneling devices and m em ory arrays are briefly收稿日期：2020-08-17基金项目：中国科学院战略性先导科技专项（XDB3000()000)通信作者：吴天如，E-mail: *************微鈉电子技术presented. Finally, the obtained achievem ents of large-scale applications of /i-BN in new m icro­electronic devices are sum m arized, and the future research and trends of the field are prospected. Key w o rd s：two-dim ensional (2D) m a te ria l；hexagonal boron nitride (/i-B N)；microelectronic device；dielectric s u b s tr a te；tunneling device；memory a r r a y；packaging materialE E A C C：0500；2550()引百六方氮化硼U-BN)具有与石墨烯相似的二维蜂窝结构但完全不同的物理特性。