Embedded atom method study of the interaction between point
defects in iron aluminides:Triple defects
Renata N.Nogueira,Cla′udio G.Scho¨n*
Computational Materials Science Laboratory,Department of Metallurgical and Materials Engineering,Escola Polite′cnica da
Universidade de Sa?o Paulo,Av.Prof.Mello Moraes,2463—CEP05508-900,Sa?o Paulo-SP,Brazil
Received30August2004;received in revised form23March2005;accepted11April2005
Available online20June2005
Abstract
In the present work(part2of2),a follow-up of the investigation of the interaction between point defects(both vacancies and antisite atoms)in Fe–Al compounds with A2(Fe)and B2(FeAl)structures is performed using Embedded Atom Method(EAM)molecular statics atomistic simulations.This method is particularly useful in obtaining the self-energies of crystal defects characterized by strong local relaxation strains,which generate long-range elastic?elds.The methodology developed in the?rst part of this paper is applied here to the case of triple defect clusters,which are essential to understand diffusion in iron aluminides,with emphasis to B2alloys.Particular care was taken to assure that all simulations for a given compound refer to the same ensemble.
q2005Elsevier Ltd.All rights reserved.
Keywords:A.Iron aluminides(based on FeAl);B.Bonding;D.Defects:point defects;E.Simulations atomistic;E.Defects,theory
1.Introduction
In the?rst part of the present investigation,a systematic study of the interactions between pairs of point defects (both antisite defects and vacancies)was performed[1].In those cases,long-range anisotropic interactions were obtained,with variable strength and character(either attractive or repulsive)depending of the particular kind of pair.As general trends,divacancy complexes of nearest and next-nearest vacancy pairs are characterized by attractive bonds of the order of magnitude of K0.1eV,1 while Al antisite atom pairs(i.e.two aluminium atoms in iron lattice positions)present strong repulsive interactions (of the order of magnitude of C0.2eV)in the nearest neighbourhood.Another relevant?nding of the?rst part investigation was a sort of‘universality’in the dependence of the interactions of a vacancy pair with distance.For antisite-vacancy pairs,we found that their interactions are mainly governed by the con?guration of the?rst coordination shell around the vacancy.This poses the question whether a similar interaction can be found or not in more extended defect complexes,consisting of three point defects(i.e.triple defects).The present work handles this problem using the same approach employed in the ?rst part.
Triple defects are postulated to exist in iron aluminides, especially in the case of B2near stoichiometric alloys.This postulation is based on experimental observations that,due to their formation self-energies,the dominant kind of defect is different for under-and overstoichiometric alloys(antisite Fe Al atoms in the former and V Fe vacancies in the later2):in order to accommodate the two types of defects keeping the stoichiometric ratio constant at equiatomic compositions, two vacancies must be created for each antisite atom to be formed[2].It is interesting to observe that this rule is based only on mass balance considerations and that it can be ful?lled even if the three defects are not correlated(e.g.the three defects may be formed at different and quite
distant *Corresponding author.Tel.:C551130915726;fax:C55113091
5243.
E-mail addresses:rnogueir@usp.br(R.N.Nogueira),schoen@usp.br
(C.G.Scho¨n).
1With reference to the energy of a crystal containing the isolated defects.
2This notation has been introduced in the?rst part of the investigation.
X Y represents a defect of kind X(Fe,Al or V Z vacancy),located in
sublattice Y.
parts of the system and cannot be considered proper triple
defects,in the sense discussed in the present work).3A different situation,however,is found in the case of diffusion atomistics.Here the defects must interact (in other words,exchange positions)to produce mass transport,this leads necessarily to con?gurations with defects located on a nearest or next-nearest vicinity.All the three diffusion mechanisms postulated to explain diffusion in near stoichiometric B2alloys [2],involve some kind of triple defect in an intermediate stage in the diffusion path.This can be easily demonstrated by considering two of these mechanisms:
?The Antistructure Bridge (ASB)mechanisms and ?The ‘Triple Defect’(TRD)mechanism.
In the ASB mechanism (schematically represented in Fig.1),a V Al vacancy exchange position with an iron atom in the iron sublattice (i.e.Fe Fe )in the presence of an antisite Fe Al defect (Fig.1(a)),forming the triple defect complex Fe Al –V Fe –Fe Al (Fig.1(b)).In this particular ?gure,the three defects are located along a [111]direction.After a next jump,the vacancy exchange positions with the previous antisite atom (Fig.1(c)),leading to a net transfer of the iron
along lattice vector 12121
2??.
The TRD mechanism (Fig.2),on the other hand,involves the conversion of a divacancy, e.g.V Fe –V Al (Fig.2(a))into a triple defect like V Fe –Fe Al –V Fe ,by reaction with an Fe Fe atom (Fig.2(b)),resulting in the net transport of iron along lattice vector [100].The TRD mechanism leads to the coupling of the diffusion ?uxes for both species [2].
The third mechanism quoted by Mehrer [2],the six-jump cycle (6JC)mechanism,also includes the formation of triple defect complexes in intermediate steps in the diffusion path (for example,in steps 3and 5of the path shown in Fig.1of ref.[3]).The 6JC is supposed to play an essential role in the diffusion of highly ordered,near stoichiometric B2intermetallics [3–5],but,as Mehrer points out [2],its relevance should decrease as antisite defects are produced either by large deviations from the ideal stoichiometry or by the decrease of the order parameter at high temperatures.Experimental evidences for the activity of triple defects either by direct measurement (e.g.by Positron annihilation)or in diffusion and recovery process investigations in B2ordered compounds are found in CoGa [6],NiAl [7–9],PdIn [10],(Ni,Fe)Al [11]and FeAl [12,13].Theoretical considerations also provide evidences for the existence of triple defects in B2NiAl [14,15]and B2CoGa [16].
The role of triple defects in the diffusion mechanisms of B2FeAl is more controversial.Recent thermodynamic calcu-lations suggest that all four kinds of point defects are present in those alloys (i.e.V Al ,V Fe ,Fe Al and Al Fe )[17],and that there would be,therefore,no need to invoke the TRD mechanism to explain diffusion in iron aluminides.This view agrees with the experimental results of Refs.([18,19])
and is compatible with Mo
¨ssbauer spectroscopy results [20].From the above exposition it is clear that considerable doubt still remains on the importance of triple defects in B2alloys,in particular in the case of diffusion in FeAl.The aim of the present work is to investigate,using the procedure developed in the ?rst part [1],the stable con?gurations corresponding to triple defects in B2FeAl and A2Fe compounds,differing from stoichiometry only by the existence of the point defects.As in the previous case,all simulations for each compound are performed
containing
Fig.1.Schematic representation of the Antistructure Bridge Mechanism (ASB)of diffusion in iron aluminides:(a)initial con?guration,(b)intermediate con?guration (containing a triple defect Fe Al –V Fe –Fe Al ),(c)?nal con?guration with a net transfer of iron along lattice vector 12121
2h i
.
3
It is usual in the diffusion literature to reserve the term ‘triple defect’to describe the V Fe —Fe Al –V Fe defect here discussed.In the sense of the present work,however,all combinations of three point defects are referred to as triple defects.In all cases,where the term ‘triple defect’is used in the present work with the usual meaning,this distinction will be made by writing the term inside single quotes.
R.N.Nogueira,C.G.Scho
¨n /Intermetallics 13(2005)1245–12541246
the same number and kinds of point defects,so that all simulations for a given compound are performed with a constant number of atoms in the crystal block,i.e.the simulations are performed in the canonical ensemble.
2.Methodology 2.1.General
The procedure adopted in this work is the same we described in Part 1[1]:a set of point defects (both vacancies and antisite atoms)is placed in a ‘computer crystal’such that their distances are large enough to avoid any interaction between them.The EAM functional (Eq.(1)of Part 1[1])is
minimized with respect to the atom positions and the
minimum energy is labelled E 0.This corresponds to the reference state of the calculation.
In the simulation of a given triple defect,three isolated point defects (let us say x ,z and j )4are selected from those present in the computer crystal and placed near the centre of the atom block,such that they are now interacting.This procedure guarantees that the reference block and all triple defects contain the same number and kinds of atoms for a given compound,which means that the simulations are done in the canonical ensemble.The minimum energy corre-sponding to this con?guration is referred to as E xzj and the interaction energy of the defect complex is calculated as:D E xzj Z E xzj K E 0
(1a)
The triple defect,however,is built of three defect pairs,for which the interaction energies have been determined in Part 1[1],therefore,Eq.(1a)may be rewritten as D E xzj Z 3xzj C D E xz C D E xj C D E jz
(1b)
where D E xz ,D E xj and D E jz are the interaction energies of the corresponding defect pairs and 3xzj corresponds to an excess term of the interaction energy due to the formation of the triple defect.Both quantities,the interaction energy,D E xzj ,and the excess interaction energy,3xzj ,will be used in the discussion of the triple defect con?gurations investigated in the present work.2.2.Con?gurations
The multiplicity of possible triple defect con?gurations is too large and it does not allow an exhaustive study as performed for the pair con?gurations in Part 1[1].Therefore,it was necessary to restrain the presentation of the results using some criteria,in the hope that this choice would allow to draw conclusions about the general properties of the triple defects in the alloy.The following criteria have been adopted:
1.con?gurations which are experimentally observed in Fe–Al alloys will be discussed,
2.only con?gurations in the B2FeAl compound and in the A2Fe disordered host will be shown,
3.all discussed defects are formed by two equidistant pairs,which are used as reference to identify the given defect,and
4.the upper bound of the length of the equidistant pairs corresponds to the third neighbourhood.These restrictions have been tested by single calculations and will be discussed later on,when necessary,in the present
work.
Fig.2.Schematic representation of the Triple Defect (TRD)diffusion mechanism in iron aluminides:(a)initial con?guration,(b)intermediate con?guration (containing the triple defect V Fe –Fe Al –V Fe ),and (c)?nal con?guration (with the net transfer of Fe along lattice vector [100]).
4
As in Part 1[1],lattice positions are labelled using greek letters,while the species (or,in the present case,the defect)occupying the lattice site using roman letters.
R.N.Nogueira,C.G.Scho ¨n /Intermetallics 13(2005)1245–12541247
The nomenclature of the defects also plays an important
role here.In Part 1[1],each pair was identi?ed by the kind of point defects involved and by its size (i.e.the distance between the point defects in terms of neighbourhood).For triple defects,a third characteristic must be taken into account:the defect geometry.
Fig.3shows six [110]projections of the bcc lattice,each of them containing a different triple defect geometry investigated in this work.It is clearly seen that the con?gurations may be divided into two major groups:those that are arranged in the projection in the form of a triangle (Fig.1(a)–(c)),and those that are arranged in the form of a line (Fig.1(d)–(f)).A second characteristic is the size of the defect:it may be characterized by the distance between the point defects in the equidistant pairs:nearest neighbours (Fig.1(a)and (d)),next-nearest
neighbours
Fig.3.[110]Projection of a bcc lattice showing the schematic representation of spatial con?gurations of triple defects considered in this work:(a)1T,(b)2T,(c)3T,(d)1L,(e)2L and (f)3L.
R.N.Nogueira,C.G.Scho
¨n /Intermetallics 13(2005)1245–12541248
(Fig.1(b)and(e))and third neighbours(Fig.1(c)and(f)). The defect geometry will be identi?ed primarily by these two characteristics.For example,a2L con?guration
corresponds to a triple defect formed by two equidistant pairs of next-nearest neighbour point defects which are in line in the[110]projection(Fig.1(e));1T,on the other hand corresponds to a triangular arrangement of nearest neighbour pairs(Fig.1(a)).The geometries of the triple defects considered in this study are identi?ed in the legend of Fig.3.The individual defects are labelled a,b and g, being a the defect that is common to the equidistant pairs (i.e.the equidistant pairs correspond to ab and ag).Table1 shows the corresponding distance of the third pair(bg)for the six triple defects shown in Fig.3.
The types of point defects composing the triple defects are identi?ed as antisite atoms,5a,or vacancies;v,A triple defect will be,thus,identi?ed by its geometry(as described above)and by the types of point defects in positions a,b, and g;aaa,three antisite atoms;aav,antisite atoms at a and b and a vacancy at g,and so on.
For B2superlattices,one must notice that the considered geometries lead to two classes of defects,depending on the original occupancy of the a site.A?rst group corresponds to a site in the Fe sublattice and the second,to a site placed in the Al sublattice.Table2relates the occupancies of the sublattices corresponding to each point defect for the six cases shown in Fig.1in the B2lattice,depending on the original occupancy of the a sublattice.
3.Results and discussion
The results will be presented and discussed in two parts: Section3.1presents the results of defects in the disordered A2Fe lattice and Section 3.2,those for the B2FeAl compound.
3.1.Defects in A2Fe
Table3shows the results for the six classes of triple defects investigated in the present work.The analysis of the table shows that the excess interaction energy term, 3xzj,is very small in modulus,and the magnitude of the largest value is smaller than0.05eV.In most con?gur-ations,it corresponds to about10%of the interaction energy for the individual pairs,which form that defect[1]. In other words,the interactions responsible for the formation of pairs of defects are much more relevant that the ones responsible for the formation of triple defects in the disordered compound.
Since the excess interaction energy is very small,one may,as a?rst approximation,perform the analysis considering the individual pairs that form the triple defect. As discussed in Part1[1],interactions between aluminium atoms in the iron host are repulsive for nearest and next-nearest pairs,but become attractive for distances above the third neighbourhood.The interaction between vacancies follows the inverse trend,with attractive interactions in the nearest and next-nearest neighbourhood.On the other hand,antisite atom–vacancy pairs tend to show attractive interactions,but the magnitudes of these interactions are lower than those observed for the other pairs[1].This is re?ected in the interaction energies of the corresponding triple defects.For instance,in the aav–1T con?guration, one of the three pairs is a nearest neighbour Al Fe–Al Fe pair,which has a strong repulsive character(D E xz Z C 0.25eV[1])and the addition of a vacancy at position g creates two Al Fe–V Fe pairs,which have moderate attractive interaction.As a result,the repulsive character of the interaction for the triple defect is reduced to C0.11eV,less than half the value of the isolated pair. The other cases that also show similar behaviour are aaa–2T,aav–1T,avv–2T and avv–2L.
The negligible excess interaction for all investigated con?gurations shows that the formation of bound states corresponding to the triple defects is unlikely in the disordered alloy.Triple defects of statistical nature may be formed in the alloy,and it is possible that entropic contributions(either vibrational or con?gurational)could stabilize triple defect con?gurations,especially in concen-trated alloys at high temperatures.In other words,the possibility of formation of entropically stabilized triple defects in A2Fe–Al with increasing temperature should not be discarded.
Table1
Distance(in terms of neighbourhood)between the point defects in the bg pair of the six cases of triple defects shown in Fig.1(ab and ag are the equidistant pairs)
Triple
defect
1T2T3T1L2L3L
bg2363625Table2
Occupancy of the sublattices corresponding to sites b and g depending on the occupancy of the a sublattice(X),with X Z Fe0Y Z Al and X Z Al0 Y Z Fe
Triple defect b g
1T Y Y
1L Y Y
2T X X
2L X X
3T X X
3L X X
5As discussed in Part1[1],strictly speaking,one cannot refer to an
antisite atom in the case of the disordered A2lattice since no preferred
occupation of sublattices exists.In this case this defect corresponds to a
solute aluminium atom in the iron host.For the sake of simplicity,however,
the defect will be referred to as an antisite atom to compare with the
behaviour of the triple defects in the B2lattice.
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3.2.Defects in B2FeAl
For sake of clarity,the results concerning the triple defects in the B2FeAl compound will be discussed in two parts:Table 4contains the results for the defects for which the a position is in the Fe sublattice and Table 5contains the results for the defects for which the a position is in the Al sublattice.
Comparing Tables 3and 4,we observe that some con?gurations in the later are characterized by very large excess interaction energies,of the order of 1eV:avv –1T,aav –1L and avv –1L.These cases will be discussed separately in section 3.4.The case aav –1T is also troublesome:the minimization algorithm could not converge to an equilibrium solution,since the distance between some atoms during the simulation became too small.The remaining con?gurations show only small excess interaction energies (3abg %0.1eV),and vanish for con?gurations 2T,2L,3T and 3L.The range of the excess interaction energy for triple defects in the ordered B2lattice,thus,is considerably smaller than the one characteristic of defect pairs (which can extend up to the 5th neighbourhood [1]).This was veri?ed by single simulations,where one of the defects is placed progressively closer to a pair of defects.The isolated defect is unable to ‘sense’the pair unless it is in a close neighbourhood.This justi?es the limitation to the investigation of triple defects consisting of two equidistant pairs in the present work.
Contrary to the case of defects in the disordered lattice,some con?gurations,namely aaa –1T,vva –1T and vva –1L show potential to form stable bound states at low temperatures.These will be discussed in detail below.The aaa –1T con?guration corresponds to a Fe Al –Al Fe –Fe Al triple defect (the a position is the central one).As discussed in Part 1[1],such defect pairs show a large,negative,binding energy due to the restoration of a Al–Fe
Table 3
Interaction energies and excess interaction energies (in eV)of the triple defects listed in Fig.1for the case of the A2Fe compound Defect 1T 1L 2T 2L 3T 3L aaa D E abg C 0.51C 0.45C 0.06C 0.16K 0.14K 0.143abg K 0.05C 0.02C 0.01C 0.0300aav D E abg C 0.11C 0.14C 0.02C 0.04K 0.06K 0.073abg 0K 0.030C 0.0200avv D E abg K 0.36K 0.08K 0.05K 0.07C 0.0203abg C 0.02C 0.040000vva
D E abg K 0.29K 0.24K 0.26K 0.26C 0.05C 0.043abg
C 0.01
0.01
Table 4
Interaction energies and excess interaction energies (in eV)for the six triple defects listed in Fig.1for the B2FeAl compound in which the a position is in the Fe sublattice Defect 1T 1L 2T 2L 3T 3L aaa D E abg K 0.34K 0.41K 0.09K 0.07K 0.06K 0.053abg K 0.09C 0.02K 0.01000aav D E abg n.c.K 0.58K 0.09K 0.04K 0.07K 0.083abg n.c.C 1.86C 0.010.0200avv D E abg K 1.41K 0.67K 0.02K 0.03K 0.06K 0.093abg C 2.99C 3.77K 0.01K 0.0100vva
D E abg C 0.07K 0.18K 0.02K 0.16K 0.02K 0.013abg
K 0.05
K 0.10
C 0.01
Obs.:n.c.Z non-converged.
Table 5
Interaction energies and excess interaction energies (in eV)for the six triple defects listed in Fig.1for the B2FeAl compound in which the a position is in the Al sublattice Defect 1T 1L 2T 2L 3T 3L aaa D E abg K 0.36K 0.41C 0.18C 0.25K 0.08K 0.113abg K 0.04C 0.01K 0.01K 0.0200aav D E abg n.c.K 0.02C 0.20C 0.25K 0.11K 0.123abg n.c.C 0.080K 0.0100avv D E abg C 0.07C 0.15C 0.24C 0.29K 0.12K 0.123abg K 0.07K 0.16C 0.01C 0.0100vva
D E abg K 2.33n.c.C 0.07C 0.13K 0.10K 0.103abg
C 0.04
n.c.
K 0.01
Obs.:n.c.Z non-converged.
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¨n /Intermetallics 13(2005)1245–12541250
bond in relation to the con?gurations corresponding to the two isolated antisite defects.Con?guration aaa –1L,on the other hand,presents a small positive excess interaction energy,despite the fact that the Fe Al –Fe Al bg pair in the third neighbourhood (con?guration 1L)is energetically more stable than the Fe Al –Fe Al bg pair in the next-nearest neighbourhood [1],this last one being characteristic of the 1T defect.In this sense,aaa –1L is the anomalous con?guration.Fig.4shows schematically both https://www.doczj.com/doc/8718823472.html,paring both,one observes that the aaa –1T (Fig.4(a))is characterized by a large displacement of the Al Fe antisite defect towards the Fe Al –Fe Al pair,resulting thus in the negative excess interaction energy.Such large displace-ments,however,are not possible for con?guration aaa –1L (Fig.4(b)),since the Al Fe antisite defect lies in a mirror symmetry plane relative to the Fe Al –Fe Al pair.This shows that the anisotropy of the interactions,detected for the case of pair of defects [1],is also important for the case of the triple defects.This could be overlooked due to the small excess interaction energy characteristic of these defects.Con?gurations vva –1T and vva –1L correspond both to defect V Al –V Fe –Fe Al .Essentially this is a nearest neighbour divacancy with an antisite defect ‘attached’to it.Nearest neighbour divacancies have inherent attractive interactions [1]and this tendency is ampli?ed by the presence of the antisite defect in the neighbourhood,with the largest energy gain associated with the 1L con?guration.These obser-vations are quite relevant since experimental techniques like positron annihilation and differential dilatometry are based on the detection of the free volume associated with vacancies [21].Such triple defects would be,therefore,observed as single divacancies and not as triple defects in these experiments,leading to an effective concentration dependence in the formation energy of divacancies as the aluminium concentration is varied (and the amount of con?gurational antisite defects changes).
Table 5shows the results obtained for the triple defects in the B2compound which a position is in the Al sublattice.The analysis of this table shows that most excess interaction
energies are small in modulus (3abg %0.16eV)as in the previous cases (a position corresponding to the Fe sublattice).The main features are also comparable:the excess interactions are signi?cant only for the triple defects of the kind 1L and 1T (i.e.the interactions are short-range)and some cases (namely aav –1T and vva –1L)presented convergence problems in the simulation.
Comparing with Table 4,we observe that the magnitude of the excess interaction corresponding to defect Al Fe –Fe Al –Al Fe (aaa –1T and aaa –1L)is decreased in relation with the Fe Al –Al Fe –Fe Al (cases aaa –1T and aaa –1L of Table 4).B2alloys are usually characterized by large amounts of Fe antisite defects,due to the deviation of the ideal stoichiometry (most investigated alloys have less than 50at.%Al),so triple defects containing two Fe antisite atoms would be expected to prevail over the counterpart (triple defects containing three Al antisite defects),the excess interactions being weaker to the former indicate that such kind of defect complexes (i.e.consisting of three antisite defects)is unlikely to be observed in real alloys.
From the remaining con?gurations aav –1T and aav –1L are worth mentioning,corresponding both to a V Fe –Fe Al –V Fe triple defect and characterized by positive interaction energies,but with negative excess interaction energies of similar magnitude.This shows that both con?gurations are metastable with respect to the dissociation as individual pairs in the compound.This is the ‘triple defect’,referred to in the diffusion literature (see footnote 3),supposedly responsible for keeping the stoichiometry ratio constant in near stoichiometric alloys as the temperature increases.This result suggests that bound states corresponding to these defects are possible,but that the energy gain is not suf?cient to stabilize the ‘triple defect’in the compound.A picture corresponding to this af?rmation is the following:suppose that the alloy is dominated by a large number of pair of defects (mostly divacancies and antisite defect-vacancy pairs).As they diffuse through the alloy they eventually merge with isolated point defects,forming a ‘triple defect’(the activation barrier is quite small,and large populations of such defects may be formed).As the excess interaction energy is negative,this new defect presents some stability,but they are eventually destroyed by thermal ?uctuations.In other words,these triple defects would present a ?nite lifetime in the compound.As a matter of fact,this situation is favourable to the action of such defect in diffusion mechanisms (both ASB and TRD)since the ‘triple defect’must be formed and destroyed during the diffusion of the species:if the defects were too stable,the energy penalty necessary to destroy the defect would probably play against the realization of this diffusion path.
A remark about these discussions on diffusion in intermetallics is necessary at this point.Both the AS
B and the TRD cases discussed here assume that V Al vacancies are available in the alloy as a precondition for the diffusion to take place.Ab initio results,in the framework of the density functional theory (DFT),usually indicate that the
formation
Fig.4.Schematic representation of the displacements in the aaa –1T (a)and
aaa –1L (b)triple defect con?gurations.The ?gure corresponds to the projection of the bcc lattice along the [010]direction,the central atom (a position)is located;therefore,half lattice parameter below the plane of the remaining atoms.Dashed circles represent the atomic size of the aluminium atoms,the replacement of the large aluminium atoms by smaller iron atoms justify the observed defect core relaxations.
R.N.Nogueira,C.G.Scho ¨n /Intermetallics 13(2005)1245–12541251
energy of such defect is too high(see[22]and references therein)and that,therefore,its equilibrium concentration should be negligible in the alloy.Two points should be discussed in this context:?rst of all,the applicability of the DFT to Fe–Al alloys is still a controversial issue[23–28] and particularly the in?uence of nearest neighbour aluminium atoms on suppressing the magnetic moment of iron seems to be underestimated by the actual implemen-tations of the DFT[29,30].This in?uence is likely to play a signi?cant role in the formation energy of V Al vacancies. Second,it is not the aim of the present work to discuss whether V Al vacancies exist or not in Fe–Al alloys;we are here discussing the formation of triple defect complexes provided the individual defects are already available.
3.3.Anomalous con?gurations
Comparing Tables3–5,we observe that some con?gur-ations in the later two are characterized by very large interaction energies,of the order of1eV:avv–1T,aav–1L and avv–1L in Table4and vva–1T in Table5.All four cases involve Al Fe–V Al nearest neighbour pairs.As shown in Part1[1],in this kind of pair the defects spontaneously react and exchange place during the simulation,generating a vacancy in the iron sublattice and annihilating the antisite defect.Similar observations in a EAM/ab-initio modelling of diffusion mechanisms in B2NiAl have been published recently by Mishin et al[31].
From the anomalous cases investigated in the present work,two groups must be discussed separately.
In the cases of aav–1L(Table4)and vva–1T(Table5) con?gurations,the exchange takes place between pair ag and a contribution of the annihilation energy of the single antisite defect(Al Fe)is computed in the interaction energy obtained in the simulation).So,in the?nal con?gurations, the number and type of isolated defects are not the same as in the initial state,violating one of the main conditions imposed to the simulations.Therefore,the calculated ‘excess interaction energies’contain an additional contri-bution due to the annihilation of the defect and cannot be compared with the normal cases.
In cases avv–1T and avv–1L,on the other hand,the exchange may take place both for pairs ab and ag.Due to the symmetry of the simulation,however,the reaction is prevented and the calculation leads to a condition in which the antisite defect converges to an intermediate frustrated state.The signi?cance of these frustrated states must be questioned,since in the actual compound other excitations (like phonons,for example)would eventually contribute to the convergence to an equilibrium state,where the
antisite Fig.5.Metastable equilibrium con?guration corresponding to defect aav–1T,with an Al Fe antisite defect at position a.Iron and aluminium atoms are denoted, respectively,by light and dark grey spheres.Dots mark the position of the centre of the vacancies and a circle marks the original position of the antisite defect.
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1252
defect is annihilated by exchanging positions with one of the two vacancies.Attempts to destabilize these frustrated states in the simulation either by submitting the crystal block to a stress state or by destroying the local symmetry introducing a fourth defect in the neighbourhood of the complex were unsuccessful.
Fig.5presents the metastable equilibrium con?guration for the aav–1T defect,with an Al Fe antisite defect at a position.The antisite atom moved away from the equilibrium position,towards what seems to be an interstitial site of the bcc structure.Self-interstitials usually are characterized by very large formation energies,which lead to very low equilibrium populations for these defects. This is due,of course,to the absence of free space in the crystal structure,which lead to very large relaxation strains associated with the self-interstitials.The presence of the divacancy in the neighbourhood,however,generates enough free space in the structure to support the formation of the interstitial defect.The formation of such defect as a stable bound state,therefore,is possible and should be experimentally investigated.
4.Conclusions
Triple defect complexes composed of antisite defects and vacancies in both A2Fe and B2FeAl compounds have been modelled using the Embedded Atom Method(EAM). Contrary to the case of pair of defects(investigated by the present authors in Part1[1]),the characteristic interactions corresponding to these complexes are of low magnitude and are of short-range.In common with the case of pairs of defects,the triple defect complexes show anisotropic interactions.
For the case of the disordered A2structure,none of the investigated con?gurations showed potential to form bound states,with the excess interaction energies being either of low magnitude or positive.For the case of the ordered B2 compound,on the contrary,some con?gurations show potential for forming bound states at low temperatures, namely Fe Al–Al Fe–Fe Al(1T),V Al–V Fe–Fe Al(1L)and Al Fe–Fe Al–Al Fe(1T).
It is noteworthy that con?gurations corresponding to the ‘triple defect’V Fe–Fe Al–V Fe,usually postulated to play a signi?cant role in iron aluminide diffusion mechanisms,are predicted to be metastable,but with a low activation barrier for formation.This result agrees with those obtained with other theoretical methods[10,14],but shows that the formation of this triple defect is possible in non-equilibrium conditions.This situation is favourable to the action of such defects in diffusion mechanisms,since the defect must be formed and sequentially destroyed during the diffusion steps.
As in the case of the pair of defects,triple defect con?gurations containing a single nearest neighbour V Al–Al Fe pair are mechanically unstable and these defects exchange place,resulting in the annihilation of the antisite defect.For triple defect con?gurations containing two nearest neighbour V Al–Al Fe pairs,the annihilation is not possible due to symmetry constraints of the lattice.At least in one case,the?nal converged con?guration is character-ized by large displacements of the antisite defect,of the order of the lattice parameter.The relative stability of this con?guration could not be determined in the present simulations,but some indirect evidences suggest that it is, at least,metastable.
Acknowledgements
The authors thank to the Sa?o Paulo State Research Funding Agency(FAPESP)for?nancial support under grants No.99/07570-8and00/07299-1.The authors would like to thank Prof.Dr Diana Farkas(Virginia Technological Institute and State University,Blacksburg-VA,USA),Prof. Dr Gerhard Inden(Max-Planck-Institut fu¨r Eisenforschung, Du¨sseldorf,Germany)and Prof.Dr He′lio Goldenstein (Dept.of Metallurgical and Materials Engineering,Escola Polite′cnica da Universidade de Sa?o Paulo,Sa?o Paulo, Brazil)for helpful discussions.
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如何写先进个人事迹 篇一：如何写先进事迹材料 如何写先进事迹材料 一般有两种情况：一是先进个人，如先进工作者、优秀党员、劳动模范等；一是先进集体或先进单位，如先进党支部、先进车间或科室，抗洪抢险先进集体等。无论是先进个人还是先进集体，他们的先进事迹，内容各不相同，因此要整理材料，不可能固定一个模式。一般来说，可大体从以下方面进行整理。 (1)要拟定恰当的标题。先进事迹材料的标题，有两部分内容必不可少，一是要写明先进个人姓名和先进集体的名称，使人一眼便看出是哪个人或哪个集体、哪个单位的先进事迹。二是要概括标明先进事迹的主要内容或材料的用途。例如《王鬃同志端正党风的先进事迹》、《关于评选张鬃同志为全国新长征突击手的材料》、《关于评选鬃处党支部为省直机关先进党支部的材料》等。 (2)正文。正文的开头，要写明先进个人的简要情况，包括：姓名、性别、年龄、工作单位、职务、是否党团员等。此外，还要写明有关单位准备授予他(她)什么荣誉称号，或给予哪种形式的奖励。对先进集体、先进单位，要根据其先进事迹的主要内容，寥寥数语即应写明，不须用更多的文字。 然后，要写先进人物或先进集体的主要事迹。这部分内容是全篇材料
的主体，要下功夫写好，关键是要写得既具体，又不繁琐；既概括，又不抽象；既生动形象，又很实在。总之，就是要写得很有说服力，让人一看便可得出够得上先进的结论。比如，写一位端正党风先进人物的事迹材料，就应当着重写这位同志在发扬党的优良传统和作风方面都有哪些突出的先进事迹，在同不正之风作斗争中有哪些突出的表现。又如，写一位搞改革的先进人物的事迹材料，就应当着力写这位同志是从哪些方面进行改革的，已经取得了哪些突出的成果，特别是改革前后的．经济效益或社会效益都有了哪些明显的变化。在写这些先进事迹时，无论是先进个人还是先进集体的，都应选取那些具有代表性的具体事实来说明。必要时还可运用一些数字，以增强先进事迹材料的说服力。 为了使先进事迹的内容眉目清晰、更加条理化，在文字表述上还可分成若干自然段来写，特别是对那些涉及较多方面的先进事迹材料，采取这种写法尤为必要。如果将各方面内容材料都混在一起，是不易写明的。在分段写时，最好在每段之前根据内容标出小标题，或以明确的观点加以概括，使标题或观点与内容浑然一体。 最后，是先进事迹材料的署名。一般说，整理先进个人和先进集体的材料，都是以本级组织或上级组织的名义；是代表组织意见的。因此，材料整理完后，应经有关领导同志审定，以相应一级组织正式署名上报。这类材料不宜以个人名义署名。 写作典型经验材料-般包括以下几部分： (1)标题。有多种写法，通常是把典型经验高度集中地概括出来，一
介绍北京的英语作文(2) AsBeijinghasbeenconfirmedhomecityofOlympics2008,the spiritofgreenOlympics,scientificOlympicsandhumanizedOlymp icwillsurelybringmoreandmorechangestoBeijing,promotethed evelopmentofsportsandOlympicsinChinaaswellasintheworld,a ndstrengthenthefriendlycommunicationsbetweenChineseandf oreignpeople. 篇六：Beijing BeijingisthecapitalofPeoplesRepublicofChinaandthenation scentreforpolitics,economyandculture.Itenjoysalongandrichhis tory.Therearenumerousheritagesitesandwonderfulexamplesof ancientarchitecture,suchastheworld-famousGreatWall,theTem pleofHeavenandtheForbiddenCity. Besidessightseeingplaces,therearemanydeliciousfoodsuch asPekingducksandBeijingsnacks.Beijingisreallyagoodplacetotr avel. 篇七：Beijing AsthecaptainofChina，Beijinghasbeenthemostpopularcityofchina。SomoreandmorepeoplewanttovisitBeijing.
小学生个人读书事迹简介怎么写800字 书,是人类进步的阶梯,苏联作家高尔基的一句话道出了书的重要。书可谓是众多名人的“宠儿”。历来,名人说出关于书的名言数不胜数。今天小编在这给大家整理了小学生个人读书事迹,接下来随着小编一起来看看吧! 小学生个人读书事迹1 “万般皆下品,惟有读书高”、“书中自有颜如玉,书中自有黄金屋”,古往今来,读书的好处为人们所重视,有人“学而优则仕”,有人“满腹经纶”走上“传道授业解惑也”的道路……但是,从长远的角度看,笔者认为读书的好处在于增加了我们做事的成功率,改善了生活的质量。 三国时期的大将吕蒙,行伍出身,不重视文化的学习,行文时,常常要他人捉刀。经过主君孙权的劝导,吕蒙懂得了读书的重要性,从此手不释卷,成为了一代儒将,连东吴的智囊鲁肃都对他“刮目相待”。后来的事实证明,荆州之战的胜利,擒获“武圣”关羽,离不开吕蒙的“运筹帷幄,决胜千里”,而他的韬略离不开平时的读书。由此可见,一个人行事的成功率高低,与他的对读书,对知识的重视程度是密切相关的。 的物理学家牛顿曾近说过,“如果我比别人看得更远,那是因为我站在巨人的肩上”,鲜花和掌声面前,一代伟人没有迷失方向,自始至终对读书保持着热枕。牛顿的话语告诉我们,渊博的知识能让我们站在更高、更理性的角度来看问题,从而少犯错误,少走弯路。
读书的好处是显而易见的,但是,在社会发展日新月异的今天,依然不乏对读书,对知识缺乏认知的人,《今日说法》中我们反复看到农民工没有和用人单位签订劳动合同,最终讨薪无果;屠户不知道往牛肉里掺“巴西疯牛肉”是犯法的;某父母坚持“棍棒底下出孝子”,结果伤害了孩子的身心,也将自己送进了班房……对书本,对知识的零解读让他们付出了惨痛的代价,当他们奔波在讨薪的路上,当他们面对高墙电网时,幸福,从何谈起?高质量的生活,从何谈起? 读书,让我们体会到“锄禾日当午,汗滴禾下土”的艰辛;读书,让我们感知到“四海无闲田,农夫犹饿死”的无奈;读书,让我们感悟到“为报倾城随太守,西北望射天狼”的豪情壮志。 读书的好处在于提高了生活的质量,它填补了我们人生中的空白,让我们不至于在大好的年华里无所事事,从书本中,我们学会提炼出有用的信息,汲取成长所需的营养。所以,我们要认真读书,充分认识到读书对改善生活的重要意义,只有这样,才是一种负责任的生活态度。 小学生个人读书事迹2 所谓读一本好书就是交一个良师益友,但我认为读一本好书就是一次大冒险,大探究。一次体会书的过程,真的很有意思,咯咯的笑声,总是从书香里散发;沉思的目光也总是从书本里透露。是书给了我启示,是书填补了我无聊的夜空,也是书带我遨游整个古今中外。所以人活着就不能没有书,只要爱书你就是一个爱生活的人,只要爱书你就是一个大写的人,只要爱书你就是一个懂得珍惜与否的人。可真所谓
介绍北京的英语作文1篇 篇一MyFamily Ilovemyfamily,becauseIhaveahappyfamily. MyfatherisanEnglishteacher.HisnameisJacky.Heisthirty-eight.Helikesplay ingbasketball.What’smymotherjop?Issheateacher?Yes,you’reright!Mymotherisverykindandnice,sheisthirty-seven.Mymotherisalways laboriouswork.Ilovemyparents! OnStaurdayandSunday,Ioftengotothelibraryandplaythepiano,Myfathergot oplaybasketball.Sometimes,wewatchTVandlistentomusicathome. Ilovemyfamily.BecauseI’mveryhappytolivewithmyparentstogether! 篇二MyFamily MyFamily Everyonehasafamily.Weliveinitandfeelverywarm.Therearethreepersonsin myfamily,mymother,fatherandI.Welivetogetherveryhappilyandtherearema nyinterestingstoriesaboutmyfamily. Myfatherisahard-workingman.Heworksasadoctor.Healwaystrieshisbesttoh elpevery,patientandmakepatientscomfortable.Butsonetimesheworkssohard thathecan”trememberthedate.
个人先进事迹简介 01 在思想政治方面,xxxx同学积极向上,热爱祖国、热爱中国共产党,拥护中国共产党的领导.利用课余时间和党课机会认真学习政治理论,积极向党组织靠拢. 在学习上,xxxx同学认为只有把学习成绩确实提高才能为将来的实践打下扎实的基础,成为社会有用人才.学习努力、成绩优良. 在生活中,善于与人沟通,乐观向上,乐于助人.有健全的人格意识和良好的心理素质和从容、坦诚、乐观、快乐的生活态度,乐于帮助身边的同学,受到师生的好评. 02 xxx同学认真学习政治理论,积极上进,在校期间获得原院级三好生,和校级三好生,优秀团员称号,并获得三等奖学金. 在学习上遇到不理解的地方也常常向老师请教,还勇于向老师提出质疑.在完成自己学业的同时,能主动帮助其他同学解决学习上的难题,和其他同学共同探讨,共同进步. 在社会实践方面,xxxx同学参与了中国儿童文学精品“悦”读书系,插画绘制工作,xxxx同学在班中担任宣传委员,工作积极主动,认真负责,有较强的组织能力.能够在老师、班主任的指导下独立完成学院、班级布置的各项工作. 03 xxx同学在政治思想方面积极进取,严格要求自己.在学习方面刻苦努力,不断钻研,学习成绩优异,连续两年荣获国家励志奖学金；作
为一名学生干部,她总是充满激情的迎接并完成各项工作,荣获优秀团干部称号.在社会实践和志愿者活动中起到模范带头作用. 04 xxxx同学在思想方面,积极要求进步,为人诚实,尊敬师长.严格 要求自己.在大一期间就积极参加了党课初、高级班的学习,拥护中国共产党的领导,并积极向党组织靠拢. 在工作上,作为班中的学习委员,对待工作兢兢业业、尽职尽责 的完成班集体的各项工作任务.并在班级和系里能够起骨干带头作用.热心为同学服务,工作责任心强. 在学习上,学习目的明确、态度端正、刻苦努力,连续两学年在 班级的综合测评排名中获得第1.并荣获院级二等奖学金、三好生、优秀班干部、优秀团员等奖项. 在社会实践方面,积极参加学校和班级组织的各项政治活动,并 在志愿者活动中起到模范带头作用.积极锻炼身体.能够处理好学习与工作的关系,乐于助人,团结班中每一位同学,谦虚好学,受到师生的好评. 05 在思想方面,xxxx同学积极向上,热爱祖国、热爱中国共产党,拥护中国共产党的领导.作为一名共产党员时刻起到积极的带头作用,利用课余时间和党课机会认真学习政治理论. 在工作上,作为班中的团支部书记,xxxx同学积极策划组织各类 团活动,具有良好的组织能力. 在学习上,xxxx同学学习努力、成绩优良、并热心帮助在学习上有困难的同学,连续两年获得二等奖学金. 在生活中,善于与人沟通,乐观向上,乐于助人.有健全的人格意 识和良好的心理素质.
小学一年级介绍北京的英语作文 Beijing is an ancient city with a long history. Back in 3000 years ago in Zhou dynasty, Beijing, which was called Ji at the moment, had been named capital of Yan. Thereafter, Liao, Jin, Yuan, Ming and Qing dynasty all made Beijing their capital. Therefore, Beijing was famous for "Capital of a thousand years". The long history leaves Beijing precious cultural treasure. Winding for several kilometers in Beijing area, the Great Wall is the only man-made structure that could been seen in the space. The Summer Palace is a classic composition of ancient royal gardens, and the Forbidden City is the largest royal palaces in the world. Tiantan is where the emperor used to fete their ancestors, and also the soul of Chinese ancient constructions. The four sites above has been confirmed world cultural heritage by UNESCO. However, the best representatives for Beijing are the vanishing Hutongs and square courtyards. Through hundreds of years, they have become symbol of Beijing's life. Tian'anmen square being still brilliant today with cloverleaf junctions and skyscrapers everywhere, the old-timey scene and modern culture are combined to present a brand new visage of Beijing. As Beijing has been confirmed home city of Olympics 2008, the spirit of "green Olympics, scientific Olympics and humanized Olympic" will surely bring more and more changes to Beijing, promote the development of sports and Olympics in China as well as in the world, and strengthen the friendly communications between Chinese and foreign people. 北京是一个有着悠久历史的古城。 早在 3000 年前的周朝,北京,这叫霁,被命 名为首都燕。此后,辽、金、元、明、清都是北京首都。因此,北京著名的一千年 的“资本”。 悠久的历史使北京宝贵的文化瑰宝。绕组在北京地区几公里,长城是唯一的 人造结构,可以在空间。 颐和园是古代皇家园林的经典组合,和故宫是世界上最大 的皇家宫殿。 天坛是皇帝用来祭祀他们的祖先的地方,也是中国古代建筑的灵魂。 上面的四个网站已经确认被联合国教科文组织世界文化遗产。然而,北京最好的 代表是消失的胡同和广场庭院。数百年来,他们已经成为北京的生活的象征。天 安门广场到处都在今天依然灿烂的蝶式路口和摩天大楼的,古色古香的场景和现 代文化相结合,提出一个全新的北京的面貌。 随着北京 2008 年奥运会已被证实的家乡,精神的“绿色奥运、科技奥
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优秀党务工作者事迹简介范文 优秀党务工作者事迹简介范文 ***，男，198*年**月出生，200*年加入党组织，现为***支部书记。从事党务工作以来，兢兢业业、恪尽职守、辛勤工作，出色地完成了各项任务，在思想上、政治上同党中央保持高度一致，在业务上不断进取，团结同事，在工作岗位上取得了一定成绩。 一、严于律己，勤于学习 作为一名党务工作者，平时十分注重知识的更新，不断加强党的理论知识的学习，坚持把学习摆在重要位置，学习领会和及时掌握党和国家的路线、方针、政策，特别是党的十九大精神，注重政治理论水平的提高，具有坚定的理论信念;坚持党的基本路线，坚决执行党的各项方针政策，自觉履行党员义务，正确行使党员权利。平时注重加强业务和管理知识的学习，并运用到工作中去，不断提升自身工作能力，具有开拓创新精神，在思想上、政治上和行动上时刻同党中央保持高度一致。 二、求真务实，开拓进取 在工作中任劳任怨，踏实肯干，坚持原则，认真做好学院的党务工作，按照党章的要求，严格发展党员的每一个步骤，认真细致的对待每一份材料。配合党总支书记做好学院的党建工作，完善党总支建设方面的文件、材料和工作制度、管理制度等。
三、生活朴素，乐于助人 平时重视与同事间的关系，主动与同事打成一片，善于发现他人的难处，及时妥善地给予帮助。在其它同志遇到困难时，积极主动伸出援助之手，尽自己最大努力帮助有需要的人。养成了批评与自我批评的优良作风，时常反省自己的工作，学习和生活。不但能够真诚的指出同事的缺点，也能够正确的对待他人的批评和意见。面对误解，总是一笑而过，不会因为误解和批评而耿耿于怀，而是诚恳的接受，从而不断的提高自己。在生活上勤俭节朴，不铺张浪费。 身为一名老党员，我感到责任重大，应该做出表率，挤出更多的时间来投入到**党总支的工作中，不找借口，不讲条件，不畏困难，将总支建设摆在更重要的位置，解开工作中的思想疙瘩，为攻坚克难铺平道路，以支部为纽带，像战友一样团结，像家庭一样维系，像亲人一样关怀，践行入党誓言。把握机遇，迎接挑战，不负初心。
暑假去北京的英语作文 北京是我国的首都，有许多历史文化建筑，那么关于暑假去北京的英语作文怎么写呢?以下是为大家整理的暑假去北京游玩的英语作文，欢迎大家阅读。 暑假去北京游玩的英语作文篇一This summer holiday I visited to Beijing with my aunt. We visited to many famous places such as Tian'ann Men Square the Imperial Palace the Summer Palace the Great Wall and so on. Before that I just saw them on TV but this summer holiday they were all in front of my eyes. I was so exciting. Among them I like theSummerPalacethe most because it's so amazing and the scenery is very beautiful. BesidesBeijingis a modern city. There are many tall buildings. I like this city very much and I hope I can visit there again. 翻译： 这个暑假，我和叔叔到北京旅游。我们参观了很多地方，比如天安门广场，故宫，颐和园和长城等等。 在那之前我只是在电视上看见过它们，但是这个暑假我亲眼看到它们就在我的前面，我很兴奋。
主要事迹简介怎么写 概括?简要地反映?个单位(集体)或个?事迹的材料。简要事迹不?定很短，如果情况 多的话，也有?千字的。简要事迹虽然“简要”，但切忌语?空洞，写得像?学?期末鉴定。 ?应当以事实来说话。简要事迹是对某单位或个?情况概括?简要地反映情况，?如有三个??很突出，就写三个??，只是写某???时，要把主要事迹突出出来。 简要事迹?般来说，?少要包括两个??的内容。?是基本情况。简要事迹开头，往往要??段?字来表述?些基本情况。如写?个单位的简要事迹，应包括这个单位的?员、 承担的任务以及?段时间以来取得的主要成绩。如写个?的简要事迹，应包括该同志的性 别、出?年?、参加?作时间、籍贯、民族、?化程度以及何时起任现职和主要成绩。这 样上级组织在看了材料的开头，就会对这个单位或个?有?个基本印象。?是主要特点。 这是简要事迹的主体部分，最突出的事例有?个??就写成?块，并按照?定的逻辑关系进 ?排列，把同类的事例排在?起，?个??通常由?个?然段或?个?然段组成。 写作时，特别要注意以下四点： 1.?第三?称。就是把所要写的对象，是集体的?“他们”来表述，是个?的称之为“他(她)”。 (她)”，单位可直接写名称，个?可写其姓名。 为了避免连续出现?个“他们”或“他 2.掌握好时限。?论是单位或个?的简要事迹，都有?个时间跨度，既不要扯得太远，也不 要故意混淆时间概念，把过去的事当成现在的事写。这个时间跨度多长，要根据实际情况 ?定。如上级要某个同志担任乡长以来的情况就写他任乡长以来的事迹;上级要该同志两年 来的情况，就写两年来的事迹。当然，有时为了需要，也可适当地写?点超过这个时间的 背景情况。 3.?点他?的语?。就是在写简要事迹时，可?些群众的语?或有关?员的语?，这样会给??种?动、真切的感觉，衬托出写作对象?较?的思想境界。在?他?语?时，可适当加?，但不能造假。 4.?事实说话。简要事迹的每?个??可分为多个层次，?个层次先??句话作为观点，再???两个突出的事例来说明。?事实说话时，要尽量把?个事例说完整，以给?留下深 刻印象。
描述北京的英语作文 北京是我国的首都，也是个历史悠久、经济繁荣及科技发达的城市，但是北京也有人口拥堵雾霾严重等种种问题，你对北京是怎么看的呢?下面是橙子为大家整理的描述北京的英语作文，希望对大家有帮助。 北京 I’d like to go to asdfs beasdfsutiful plasdfsce. I think it would be Beijing. Beijing is not only our casdfspitasdfsl city, but asdfslso asdfs fasdfsmous city with long history asdfsnd wonderful culture. Beijing is asdfslso Chinasdfs’s politicasdfsl asdfsnd culturasdfsl center. There’re masdfsny old plasdfsces of greasdfst interest, such asdfss the Greasdfst Wasdfsll, the Summer Pasdfslasdfsce, the Forbidden City, the Temple of Heasdfsven, asdfsnd Tiasdfsnasdfsnmen Squasdfsre. Once you see Tiasdfsnasdfsnmen Squasdfsre, you will think of Beijing. It hasdfss been the symbol of Beijing since 1949. 我想去一个美丽的地方。我觉得那应该是北京。北京不仅仅是我们的首都，也是有着悠久的历史和精彩地文化的城市。北京也是中国的政治和文化中心。有很多古迹，比如，长城，颐和园，紫禁城，天坛，天安门广场。只要你看到天安门广场，你就会想起北京。自从1949年起它就是北京的象征了。 北京
树立榜样的个人事迹简介怎么写800字 榜样是阳光,温暖着我们的心;榜样如马鞭,鞭策着我们努力奋斗;榜样似路灯,照亮着我们前进的方向。今天小编在这给大家整理了树立榜样传递正能量事迹作文,接下来随着小编一起来看看吧! 树立榜样传递正能量事迹1 “一心向着党”,是他向着社会主义的坚定政治立场;“人的生命是有限的,可是,为人民服务是无限的,我要把有限的生命投入到无限的为人民服务中去”,是他的至理名言;“甘学革命的“螺丝钉”,是他干一行爱一行、钻一行的爱岗敬业态度。他——雷锋,是我们每一个人的“偶像”…… 雷锋的事迹传遍大江南北,他,曾被人们称为可敬的“傻子”。一九六零年八月,驻地抚顺发洪水,运输连接到了抗洪抢险命令。他强忍着刚刚参加救火工作被烧伤的手的疼痛,又和战友们在上寺水库大坝连续奋战了七天七夜,被记了一次二等功。望花区召开了大生产号召动员大会,声势很大,他上街办事,正好看到这个场面,他取出存折上在工厂和部队攒的200元钱,那时,他的存折上只剩下了203元,就跑到望花区党委办公室要为之捐献出来,为建设祖国做点贡献,接侍他的同志实在无法拒绝他的这份情谊,只好收下一半。另100元在辽阳遭受百年不遇洪水的时候,他捐献给了正处于水深火热之中的辽阳人民。在我国受到严重的自然灾害的情况下,他为国家建设,为灾区捐献出自已的全部积蓄,却舍不得喝一瓶汽水。就这样,他毫不犹豫的捐出了自己的所有积蓄,不求功名,不求名利,只求自己心安理得,只求为
革命献出自己的微薄之力,甘愿做革命的“螺丝钉”——在一次施工任务中,他整天驾驶汽车东奔西跑,很难抽出时间学习,他就把书装在挎包里,随身带在身边,只要车一停,没有其他工作时,就坐在驾驶室里看书。他曾经在自己的日记中写下这样一段话：”有些人说工作忙,没时间学习,我认为问题不在工作忙,而在于你愿不愿意学习,会不会挤时间来学习。要学习的时间是总是有的,问题是我们善不善于挤,愿不愿意钻。一块好好的木板,上面一个眼也没有,但钉子为什么能钉进去呢?这就是靠压力硬挤进去的。由此看来,钉子有两个长处：一个是挤劲,一个是钻劲。我们在学习上也要提倡这种”钉子“精神,善于挤和钻。”这就是他,用自己的实际行动来证明自己,用自己的亲生经历来感化世人,用自己的所作所为来传颂古今……人们都拼命地学习他的精神,他的精神被不同肤色的人所敬仰。现在,一切都在变,但是,那些决定人类向前发展的基本要素没有变,那些美好的事物没有变,那些所谓的“螺丝钉”精神没有变——而这正是他的功劳,是他开启了无私奉献精神的大门,为后人树立了做人的榜样…… 这就是他,一位中国家喻户晓的全心全意为人民服务的楷模,一位共产主义战士!他作为一名普通的中国人民解放军战士,在他短暂的一生中却助人无数。而且,伟大领袖毛泽东主席于1963年3月5日亲笔为他题词：“向雷锋同志学习”。 正是因为如此,全国刮起了学习雷锋的热潮。雷锋已经离开我们很长时间了。但是雷锋的精神却深深地在所有中国人心中扎下了根,现在它已经长成一株小树。正以其顽强的生命力,茁壮成长。我坚信,
关于去北京的英语作文 北京是中国的首都，是经济、政治、文化的中心，也是一座历史悠久的现代化城市。下面小编为大家搜集整理有关北京的英语作文，仅供阅读! 北京Beijing Id like to go to a beautiful place. I think it would be Beijing. Beijing is not only our capital city, but also a famous city with long history and wonderful culture. Beijing is also Chinas political and cultural center. Therere many old places of great interest, such as the Great Wall, the Summer Palace, the Forbidden City, the Temple of Heaven, and Tiananmen Square. Once you see Tiananmen Square, you will think of Beijing. It has been the symbol of Beijing since 1949. 我想去一个美丽的地方。我觉得那应该是北京。北京不仅仅是我们的首都，也是有着悠久的历史和精彩地文化的著名城市。北京也是中国的政治和文化中心。有很多古迹，比如，长城，颐和园，紫禁城，天坛，天安门广场。只要你看到天安门广场，你就会想起北京。自从1949年起它就是北京的象征了。 北京之旅Journey to Beijing This summer holiday, I visited toBeijingwith my aunt. We visited to many famous places, such as TiananMen Square, theImperialPalace,
大学生先进事迹简介怎么写 苑xx，男，汉族，1990年07月22日出生，中国共青团团员，入党积极分子，现任xx学院电气优创0902班班长，担任xx学院09级总负责人、xx学院团委学生会科创部干事、xx学院文艺团主持部部长。 步入大学生活一年以来，他思想积极，表现优秀，努力向党组织靠拢，学习刻苦，品学兼优，工作认真负责，脚踏实地，生活勤俭节约，乐于助人。一直坚持多方面发展，全面锻炼自我，注重综合能力、素质拓展能力的培养。再不懈的努力下获得了多项荣誉： ●获得09-10学年xx大学“百佳千优”(文化体育)一等奖学金和“百佳千优”(班级建设)二等奖学金; ●获得09-10学年xx大学“优秀学生干部”荣誉称号; ●2010年xx大学普通话知识竞赛中获得一等奖; ●2010年xx大学主持人大赛中获得一等奖，被评为金话筒; ●xx学院首届“大学生文明修身”活动周——再生比赛中获得一等奖; ●xx学院首届“大学生文明修身”活动周——演讲比赛中获得一等奖。 一、刻苦钻研树学风 作为班长，他在学习方面，将班级同学分成各个学习小组，布置每日学习任务，分组竞争，通过开展各项趣味学习活动，全面调动班级同学的积极性，如：排演英语戏剧、文学常识竞答、数学辅导小组等。他带领全班同学努力学习、勤奋刻苦，全班同学奖学金获得率达91%，四级通过率达66%。 二、勤劳负责建班风
在日常班级工作中，他尽心尽力，通过网络组织建立班级博客，把班级的日常情况，班级比赛，特色主题班会等活动，及时上传到 班级博客，以方便更多同学了解自己的班级，也把班级的魅力、特色，更全面、更具体的展现出来。 在班级建设中，他带领全班同学参加学院组织的各项文体活动中也收获颇多： ●在xx学院首届“大学生文明修身”活动周中荣获第二名， ●xx学院首届乒乓球比赛中荣获第一名、精神文明奖， ●在xx学院“迎新杯”男子篮球赛中荣获第四名、最佳组织奖。 除了参加学院组织的各项活动外，为了进一步丰富班级同学们的课余生活，他在班级内积极开展各式各样的课余活动： ●普通话知识趣味比赛，感受中华语言的魅力，复习语文文学常识，为南方同学打牢普通话基础，推广普通话知识。 ●“我的团队我的班”主题班会活动中，创办特色活动“情暖你我心”天使行动，亲切问候、照顾其他同学的生活、学习方面细节 小事，即使在寒冷的冬天，也要让外省的同学感受到家一样的温暖。 ●“预览科技知识”科技宫之行，作为现代大学生，不能只顾书本知识，也要跟上时代，了解时代前沿最新科技。 ●感恩节“感谢我们身边的人”主题班会活动，在这个特殊的节日里，他带领同学们通过寄贺卡、送礼物等方式，来感谢老师辛勤 的付出;每人写一封家书，寄给父母，感谢父母劳苦的抚育，把他们 的感激之情，转化为实际行动来感化周围的人;印发感恩宣传单，发 给行人，唤醒人们的感恩的心。 三、热情关怀暖人心 生活中，他更能发挥榜样力量，团结同学，增强班级凝聚力。时刻观察每一位同学的情绪状态，在心理上帮助同学。他待人热情诚恳，积极帮助生活中有困难的同学：得知班级同学生病高烧，病情 严重，马上放下午饭，赶到同学寝室，背起重病同学到校医院进行
初中英语作文：关于北京(About Beijing) 2017-12-02虽然言语很简单，却在字里行间透露出自己的情感，不错的初中英语作文。 (天添资源网收集整理)初中英语作文：关于北京(aboutbeijing)(收集:https://www.doczj.com/doc/8718823472.html,)beijinghasahistoryofover3,000yearswithapopula tionofnearly13millionandalotofplacesofinterestaroundit.inrecentyears,thec ityofbeijinghasbeenadvancingveryquickly.youcanseemoremuseums,parksa nshoppingcentershereandthere.moreandmorehighwaysandoverheadwalk wayshavebeenbuiltup.what'smore,alotmorebuseswhichburncleanerfuel,su chascngorlpg,areputintouse,topreventairfrombeingpolluted.waterintherive rsiscleanagain.whereveryougo,youcanseegreentrees,grassandbeautifulflow ers.allthesemakelifeinbeijingmoreconvenient,pleasantandcolorful.beijingis stilladvancingtothebrightfuture.关于北京北京有3000多年的历史，近1300万人口和许多名胜古迹。 近年来，北京发展得很快。 你能看到更多的博物馆、公园和购物中心，比比皆是。 北京已建成越来越多的高速公路和过街天桥。 还有，更多的公共汽车投入使用，它们都使用环保燃料，以防空气受到污染。 河水又变得清澈了。 无论你走到哪里，你都能看到绿树、青草和美丽的花朵。
个人事迹简介 我是来自计算机与与软件学院的学生，现在为青年志愿者协会的干事，在班级担任生活委员。在过去的一年里，我注重个人能力的培养积极向上，热心公益，服务群众，奉献社会，热忱的投身于青年支援者的行动中！一年时间虽短，但在这一年的时间里，作为一名志愿者，我确信我成长了很多，成熟了很多。“奉献、友爱、互助、进步”这是我们志愿者的精神，在献出爱心的同时，得到的是帮助他人的满足和幸福，得到的是无限的快乐与感动。路虽漫漫，吾将上下而求索！在以后的日子里，我会在志愿者事业上做的更好。 在思想上，我积极进取,关心国家大事，并多次与同学们一起学习志愿者精神,希望我们会在新的世纪里继续努力,发扬我国青年的光传统,不懈奋斗,不断创造,奋勇前进,为实现中华民族的伟大复兴做出了更大的贡献。 在学习上刻苦认真，抓紧时间，不仅学习好学科基础知识，更加学好专业课知识，在课堂上积极配合老师的教学，乐意帮助其它同学，有什么好的学习资料，学习心得也与他们交流，希望大家能共同进步。在上一个年度总成绩在班级排名第四，综合考评在班级排名第二。在工作中，我认真负责，出色的完成老师、同学交给的各项任务，所以班级人际关系良好。
此外参加了学院组织的活动，并踊跃地参加，发挥自己的特长，为班级争得荣誉。例如：参加校举办的大合唱比赛并获得良好成绩；参加了计算机与软件学院党校学习并顺利结业；此外,参加了计算机与软件进行的“计算机机房义务打扫与系统维护”的活动。在这些活动中体验到了大学生生活的乐趣。 现将多次参与各项志愿活动汇报如下：2013年10月26日，参加计算机与软件学院团总支实践部、计算机与软件学院青年志愿者协会组织“志愿者在五福家园的健身公园开展义务家教招新活动”；2013年11月7日，参加组成计算机与软件学院运动员方阵在田径场参加学院举办的学校运动会；2013年12月5日，参与学校学院组织的”一二．五“大合唱比赛；2014年3月12日，参加由宿舍站长组织义务植树并参与植树活动；2014年3月23日，在计算机与软件学院团总支书记茅老师的带领下，民俗文化传承协会、计算机与软件学院青年志愿者协会以及学生会的同学们参观了“计算机软件学院的文化素质教育共建基地--南京市民俗博物馆”的活动；2014年3月26日，参加有宿舍站长组织的“清扫宿舍公寓周围死角垃圾”的活动；2014年4月5日，参加由校青年志愿者协会、校实践部组织的“南京市雨花台扫墓”活动，2014年4月9日，作为班级代表参加计算机软件学院组织部组织的“计算机应用office操作大赛”的活动。 在参与各项志愿活动的同时，我的学习、工作、生活能力得到了提高和认可，丰富生活体验，提供学习的机会，提供学习的机会。
介绍北京的英语作文介绍北京的高 中英语作文 作为中国的首都,北京已成为中国最受 欢迎的城市,所以越来越多的人想参观北京。你对北京的了解有多少呢?下面，X帮你整理了介绍北京的高中英语作文，希望你喜欢! 介绍北京的高中英语作文篇 1 As the captain of China，Beijing has been the most popular city of china。So more and more people want to visit Beijing. I think the best time to visit Beijing is spring ,for the weather of that time is very fine ,neither too hot nor too cold . The warm wind will make you fell people visit Beijing for it's beautiful sence and cultural inheritance . If you want to have a enjoyable journey ,I suggest you to pay a visit to
the Great Wall,the Summer Palace ,the Olympic Park and many other you feel tired after one day's journey ,you can taste the "Zha Jiang Mian",a kind of traditional food in Beijing. There are many other things you can do in Beijing,as shopping in the big shopping mall,visit the different kinds park ,visit the"Si He Yuan"and so on. I hope you can have a happy time in Beijing. 介绍北京的高中英语作文篇 2 Beijing is a metropolis in northern China and the capital of the People's Republic of China. It is one of the four municipalities of the PRC, which are equivalent to provinces in China's administrative structure. Beijing is one of the Four Great Ancient Capitals of China. The municipality of Beijing borders Hebei Province to the north, west, south,
《个人事迹简介》 个人事迹简介（一）： 李维波，男，中共党员，自2003年应聘农电工以来，他就把自己的一切奉献给了他热爱的电力事业。在多年的工作中爱岗敬业，勤勤恳恳，任劳任怨。2003年至2007年先后担任过xx供电所线损管理员、用电检查管理员、两率管理员、线路工作负责人;2007年调到xx供电所任用电检查管理员、客户经理;2009年5月调到xx供电所任营销员兼用电检查管理员。 刚踏入电力工作的时候，他还是个电力行业的门外汉，可他深深的明白：知识改变思想!思想改变行动!行动决定命运这句话，明白在当今学习的社会里，对于电力更就应不断的吸取新的知识，更新新的观念，以满足时代对于电力的更高的要求。正是这样他透过自己的努力学习，一步步的从门外汉变成了此刻的技术骨干。 一、加强政治学习，提高理论思想水平 多年以来，他在工作中始终坚持学习邓小平理论和三个代表重要思想。他深知：一个人只有有了与时俱进的思想做指导，人的认识才会提高，思想才能净化，行为也才能与时代同步，与社会同步，与发展同步，也才能成为社会发展的推动者、有作为者，正因为如此，他严格要求自己，认真学习思想理论方面的知识，抓紧一切时间学习，认真听，做好笔记，写好心得，并且用三个代表思想来约束自己，不断提高自身的修养，从而真正实践党的全心全意为人民服务的宗旨。 二、加强专业知识的学习，提高专业技术 在当今信息化的时代，科学技术飞速发展，尤其在电力行业这个技术密集型企业中，学习显得尤为重要。从踏进电力企业的大门开始，他就自觉学习专业知识，以书本为老师，阅读各方面的相关书籍，不断丰富自己的理论基础;以老同志为师傅，细心观察他们的实际操作，不断丰富自己的实践经验;以实践为老师，从中加深对知识的理解和领会。从2003年开始，学会了计算机普通操作，掌握了电力安全方面相关知识、电工基础知识、供电营业规则，参加局每年安规考试多次得到全局前十名，2005年农电体制改革考试应知和应会总分全局第5名。 三、发扬三千精神，做好优质服务 2007年，xx所因滩坑移民影响，电费回收率难以上升，应对电费回收的复杂严峻形势，