阅读说明：本技术 一种三元稀土氧化物复合点缺陷的预测方法 (Method for predicting defects of ternary rare earth oxide composite points ) 是由 刘斌 姚芸 赵娟利 范芸 赖梦玲 于 2021-09-03 设计创作，主要内容包括：本发明公开了一种三元稀土氧化物复合点缺陷的预测方法,涉及三元稀土氧化物技术领域,具体为S1、三元稀土氧化物缺陷模型的构建；S2、孤立点缺陷形成能计算和缺陷位置确定和S3、主导复合缺陷类型预测。该三元稀土氧化物复合点缺陷的预测方法,基于第一性原理计算,只需要知道三元稀土氧化物的基本晶体结构信息,不需要其它参数就可以计算出其化学计量比与非化学计量比的缺陷形成能,完成主导缺陷类型和浓度的预测,且采用的计算模拟方法,无需投入除了计算机之外的实验设备和原材料,费用低且效率高。(The invention discloses a method for predicting defects of a ternary rare earth oxide composite point, which relates to the technical field of ternary rare earth oxides, in particular to S1 construction of a ternary rare earth oxide defect model; s2, outlier defect formation calculation and defect location determination and S3, dominant composite defect type prediction. The method for predicting the defects of the composite points of the ternary rare earth oxide is calculated based on the first principle, only basic crystal structure information of the ternary rare earth oxide needs to be known, defect formation energy of stoichiometric ratio and non-stoichiometric ratio of the ternary rare earth oxide can be calculated without other parameters, the prediction of dominant defect types and concentration is completed, and the adopted calculation simulation method does not need to invest experimental equipment and raw materials except a computer, so that the cost is low and the efficiency is high.)

1. A method for predicting defects of a ternary rare earth oxide composite point is characterized by comprising the following steps: the method for predicting the defects of the ternary rare earth oxide composite points comprises the following operation steps:

s1, constructing a ternary rare earth oxide defect model:

constructing a ternary rare earth oxide complete structure supercell and carrying out structure optimization, constructing an isolated point defect structure supercell model, namely an isolated point defect model for short, based on the optimized supercell, and converting the ternary rare earth oxide supercell model into three-dimensional atomic coordinate information;

s2, isolated point defect formation energy calculation and defect position determination:

setting input parameters, carrying out structural optimization on all isolated point defect models, calculating defect formation energy of isolated point defects, and selecting the most stable defect position by comparing the sizes of all structural supercell formation energy of the same isolated point defect;

s3, predicting the dominant composite defect type:

considering all possible competitive phases, listing chemical potential limiting conditions of the ternary rare earth oxide, drawing a chemical potential phase diagram containing the competitive phases, and finding out a region where the ternary rare earth oxide can stably exist and boundary chemical potential conditions; therefore, possible defect chemical reactions and corresponding composite defect types under each chemical potential condition are written out, composite defect forming energy is obtained by calculating the defect chemical reaction capacity, and the type of the dominant composite defect and the concentration at different temperatures are predicted.

2. The method for predicting defects of a ternary rare earth oxide composite point according to claim 1, wherein: in the step S1, the ternary rare earth oxide complete structure supercell is subjected to structure optimization, and in the optimized ternary rare earth oxide complete supercell structure, an atom inside is removed to form an isolated vacancy defect model, one cation occupies another cation position to form an inverse structure defect model, and an atom is added to occupy a gap position to form a gap defect model.

3. The method for predicting defects of a ternary rare earth oxide composite point according to claim 2, wherein: for all isolated point defects, the valence states adopt the standard valence of the corresponding element, and for isolated point defect types with multiple possibilities, all possible structural supercells are constructed for the isolated point defects.

4. The method for predicting defects of a ternary rare earth oxide composite point according to claim 1, wherein: in the step S2, the calculation is based on the first principle of density functional.

5. The method for predicting defects of a ternary rare earth oxide composite point according to claim 1, wherein: in the step S2, the computing software used in the computation is VASP, which is called Vienna Ab-initio Simulation Package software.

6. The method for predicting defects of a ternary rare earth oxide composite point according to claim 1, wherein: the exchange correlation functional adopts a generalized gradient approximate PBEsol method, all calculations consider spin polarization, the truncation energy of the plane wave pseudopotential is set to be more than 500eV, and the convergence standard of the structure optimization is set to beAnd the calculation result of the system is ensured to reach sufficient calculation precision within controllable calculation amount.

7. The method for predicting defects of a ternary rare earth oxide composite point according to claim 5, wherein: the calculation method for all the processes is as follows:

generating k points by a Monkhorst-Pack method, and setting the grid density of the generated k points to be less thanThe method can simply and quickly generate the grid points and improve the calculation efficiency.

8. The method for predicting defects of a ternary rare earth oxide composite point according to claim 1, wherein: the chemical potential limiting conditions and the phase diagram need to consider all possible unitary, binary and ternary key competitive phases of the constituent elements of the ternary rare earth oxide material, the volume of a supercell is kept unchanged in the defect model structure optimization process, and relaxation is allowed to be carried out on all atomic positions.

9. The method for predicting defects of a ternary rare earth oxide composite point according to claim 1, wherein: in the step S2, the defect formation can be represented by formula E_f＝E_d+E_p+∑n_iμ_i+q(ΔE_F+E_VBM) Calculation of where E_dAnd E_pTotal energy of the supercell with and without defects, n_iIs the number of atoms, μ, to be removed or added_iIs the chemical potential of the corresponding element, q is the valence of the point defect, E_VBMEnergy level, Δ E, of the valence band maximum, abbreviated VBM_FIs based on the fermi level measured by the VBM.

10. The method for predicting defects of a ternary rare earth oxide composite point according to claim 1, wherein: in the step S3, the concentration at different temperatures is calculated as follows:

under the condition of thermodynamic equilibrium, the Arrhenius equation is used to calculate the concentration of various complex defects at different temperatures, namelyWherein N is_sAnd N_cRespectively the number of sites of composite defects in a unit volume and the number of equivalent arrangements, k_BIs Boltzmann constant, T is temperature, E_fIs the defect formation energy.

Technical Field

The invention relates to the technical field of ternary rare earth oxides, in particular to a method for predicting defects of a ternary rare earth oxide composite point.

Background

The material is the basis of various industries of national economy, along with the rapid development of modern industrial revolution, the requirement of the industry on the performance of novel inorganic non-metallic materials is higher and higher, and the ternary rare earth oxide becomes a novel material which is concerned by the scientific field in recent years due to the high-temperature structural stability and excellent mechanical/physical/chemical comprehensive performance of the ternary rare earth oxide, and has wide application prospects in the industry, for example, the ternary rare earth oxide is considered as a potential thermal barrier and ring barrier coating material due to the lower thermal conductivity and good high-temperature phase stability of the ternary rare earth oxide; the excellent ionic conductivity and defect accommodation capacity of the ternary rare earth oxide lead the ternary rare earth oxide to be widely applied to the fields including electrolyte materials of solid oxide fuel cells, solidified bodies of nuclear waste and the like, and the properties of ionic conductivity, radiation resistance, thermal conductivity and the like involved in the application of the ternary rare earth oxide can be explained through point defects, so that the analysis and the research of the point defects are necessary.

Although the research on the ternary rare earth oxide is more and more extensive, the experiment and theoretical calculation research related to the defects are not complete enough, the traditional defect theoretical research is mainly based on an isolated point defect model, and the predicted result and the experiment are contradictory due to the fact that the electric neutrality cannot be maintained, the defects cannot be ignored, and the defects interact with each other.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a method for predicting defects of a ternary rare earth oxide composite point, which solves the problems that the existing research on ternary rare earth oxide is more and more extensive, but the related experiments and theoretical calculation research on the defects are not complete enough, the traditional defect theoretical research is mainly based on an isolated point defect model, and the contradiction between the prediction result and the experiment is caused by the interaction of the defects because the electrical neutrality cannot be maintained and the defects are ignored.

In order to achieve the purpose, the invention is realized by the following technical scheme: a method for predicting defects of a ternary rare earth oxide composite point comprises the following operation steps:

s1, constructing a ternary rare earth oxide defect model:

constructing a ternary rare earth oxide complete structure supercell and carrying out structure optimization, constructing an isolated point defect structure supercell model, namely an isolated point defect model for short, based on the optimized supercell, and converting the ternary rare earth oxide supercell model into three-dimensional atomic coordinate information;

s2, isolated point defect formation energy calculation and defect position determination:

setting input parameters, carrying out structural optimization on all isolated point defect models, calculating defect formation energy of isolated point defects, and selecting the most stable defect position by comparing the sizes of all structural supercell formation energy of the same isolated point defect;

s3, predicting the dominant composite defect type:

considering all possible competitive phases, listing chemical potential limiting conditions of the ternary rare earth oxide, drawing a chemical potential phase diagram containing the competitive phases, and finding out a region where the ternary rare earth oxide can stably exist and boundary chemical potential conditions; therefore, possible defect chemical reactions and corresponding composite defect types under each chemical potential condition are written out, composite defect forming energy is obtained by calculating the defect chemical reaction capacity, and the type of the dominant composite defect and the concentration at different temperatures are predicted.

Optionally, in the step S1, the ternary rare earth oxide complete structure supercell is subjected to structure optimization, an atom in the optimized ternary rare earth oxide complete supercell structure is removed to form an isolated vacancy defect model, one cation occupies another cation position to form an inverse structure defect model, and an atom is added to occupy a gap position to form a gap defect model.

Alternatively, for all isolated point defects, the valency is taken to be the standard valency of the corresponding element, for which all possible structural supercells are constructed here for the various possible isolated point defect types.

Optionally, in the step S2, the calculations all adopt first-nature-principle calculations based on the density functional.

Optionally, in the step S2, the computing software used in the computing is VASP, which is called Vienna Ab-initio Simulation Package software.

Optionally, the exchange correlation functional adopts a generalized gradient approximation PBEsol method, all calculations consider spin polarization, the truncation energy of the plane wave pseudopotential is set to be more than 500eV, and the structure is optimizedHas a convergence criterion set asAnd the calculation result of the system is ensured to reach sufficient calculation precision within controllable calculation amount.

Optionally, the calculation method of all the processes is as follows:

generating k points by a Monkhorst-Pack method, and setting the grid density of the generated k points to be less thanThe method can simply and quickly generate the grid points and improve the calculation efficiency.

Optionally, the chemical potential limiting conditions and the phase diagram need to consider all possible unitary, binary and ternary key competitive phases of the constituent elements of the ternary rare earth oxide material, the volume of the supercell is kept unchanged in the defect model structure optimization process, and relaxation is allowed to be performed at all atomic positions.

Optionally, in the step S2, the defect formation can be represented by formula E_f＝E_d+E_p+∑n_iμ_i+q(ΔE_F+E_VBM) Calculation of where E_dAnd E_pTotal energy of the supercell with and without defects, n_iIs the number of atoms, μ, to be removed or added_iIs the chemical potential of the corresponding element, q is the valence of the point defect, E_VBMEnergy level, Δ E, of the valence band maximum, abbreviated VBM_FIs based on the fermi level measured by the VBM.

Optionally, in the step S3, the concentration at different temperatures is calculated as follows:

under the condition of thermodynamic equilibrium, the Arrhenius equation is used to calculate the concentration of various complex defects at different temperatures, namelyWherein N is_sAnd N_cRespectively the number of sites of composite defects in a unit volume and the number of equivalent arrangements, k_BIs Boltzmann constant, T is temperature, E_fIs in the shape of a defectAnd (4) becoming energy.

The invention provides a method for predicting defects of a ternary rare earth oxide composite point, which has the following beneficial effects:

1. the method for predicting the defects of the composite points of the ternary rare earth oxide is calculated based on the first principle, only basic crystal structure information of the ternary rare earth oxide needs to be known, defect formation energy of stoichiometric ratio and non-stoichiometric ratio of the ternary rare earth oxide can be calculated without other parameters, the prediction of dominant defect types and concentration is completed, and the adopted calculation simulation method does not need to invest experimental equipment and raw materials except a computer, so that the cost is low and the efficiency is high.

2. According to the method for predicting the defects of the composite points of the ternary rare earth oxide, the actual chemical environment of the material can be simulated by considering the competitive phase of the ternary rare earth oxide, and the most probable defect chemical reaction and the corresponding composite defect types in each chemical environment and the defect concentrations at different temperatures are predicted according to the actual chemical environment, so that a theoretical basis is provided for regulating and controlling the defect types in the experimental synthesis process, and the optimization of the physical properties of the material related to the defects is promoted.

Drawings

FIG. 1 is a schematic flow diagram of the present invention;

FIG. 2 is a chemical potential diagram of A-Zr-O according to the present invention;

FIG. 3 is a view of ternary rare earth zirconate A of the invention₂Zr₂O₇A schematic diagram of the formation energy of schottky defects, frenkel defects and cation inversion defects in (a ═ La, Pr, Pm, Eu);

FIG. 4 is a schematic diagram of the reaction equation of the dominant defect and its reaction enthalpy of formation in different chemical environments of the present invention;

FIG. 5 shows RE of the present invention₂Si₂O₇A schematic chemical potential diagram;

FIG. 6 shows RE of the present invention₂Si₂O₇The formation energy of the schottky, fern-kel and anti-structure composite defects of (a);

FIG. 7 shows Yb of the present invention depending on different chemical environments₂Si₂O₇And Lu₂Si₂O₇Dominant defect reaction inEquation and reaction enthalpy diagram thereof.

Detailed Description

Referring to fig. 1 to 7, the present invention provides a technical solution: a method for predicting defects of a ternary rare earth oxide composite point comprises the following operation steps:

s1, constructing a ternary rare earth oxide defect model:

constructing a ternary rare earth oxide complete structure supercell and carrying out structure optimization, constructing an isolated point defect structure supercell model, namely an isolated point defect model for short, based on the optimized supercell, and converting the ternary rare earth oxide supercell model into three-dimensional atomic coordinate information;

s2, isolated point defect formation energy calculation and defect position determination:

setting input parameters, carrying out structural optimization on all isolated point defect models, calculating defect formation energy of isolated point defects, and selecting the most stable defect position by comparing the sizes of all structural supercell formation energy of the same isolated point defect;

s3, predicting the dominant composite defect type:

considering all possible competitive phases, listing chemical potential limiting conditions of the ternary rare earth oxide, drawing a chemical potential phase diagram containing the competitive phases, and finding out a region where the ternary rare earth oxide can stably exist and boundary chemical potential conditions; therefore, possible defect chemical reactions and corresponding composite defect types under each chemical potential condition are written out, composite defect forming energy is obtained by calculating the defect chemical reaction capacity, and the type of the dominant composite defect and the concentration at different temperatures are predicted.

And S1, carrying out structural optimization on the ternary rare earth oxide complete structure supercell, removing an atom in the optimized ternary rare earth oxide complete supercell structure to form an isolated vacancy defect model, enabling one cation to occupy another cation position to form an inverse structure defect model, and adding an atom to occupy a gap position to form a gap defect model.

For all isolated point defects, the valence states adopt the standard valence of the corresponding element, and for isolated point defect types with multiple possibilities, all possible structural supercells are constructed for the isolated point defects.

In step S2, the calculations all use the first principle calculation based on the density functional.

In step S2, the computing software used in the computation is VASP, which is called Vienna Ab-initio Simulation Package software.

The exchange correlation functional adopts a generalized gradient approximate PBEsol method, all calculations consider spin polarization, the truncation energy of the plane wave pseudopotential is set to be more than 500eV, and the convergence standard of the structure optimization is set to be And the calculation result of the system is ensured to reach sufficient calculation precision within controllable calculation amount.

The calculation method for all the processes is as follows:

generating k points by a Monkhorst-Pack method, and setting the grid density of the generated k points to be less thanThe method can simply and quickly generate the grid points and improve the calculation efficiency.

And drawing chemical potential limiting conditions and a phase diagram, all possible unitary, binary and ternary key competitive phases of the composition elements of the ternary rare earth oxide material need to be considered, the volume of a supercell is kept unchanged in the structure optimization process of the defect model, and all atomic positions are allowed to be relaxed.

In step S2, defect formation can be represented by formula E_f＝E_d+E_p+∑n_iμ_i+q(ΔE_F+E_VBM) Calculation of where E_dAnd E_pTotal energy of the supercell with and without defects, n_iIs the number of atoms, μ, to be removed or added_iIs the chemical potential of the corresponding element, q is the valence of the point defect, E_VBMIs the top of the valence band, i.e. value band maximum, abbreviated as energy level of VBM,. DELTA.E_FIs based on the fermi level measured by the VBM.

In step S3, the concentrations at different temperatures are calculated as follows:

under the condition of thermodynamic equilibrium, the Arrhenius equation is used to calculate the concentration of various complex defects at different temperatures, namelyWherein N is_sAnd N_cRespectively the number of sites of composite defects in a unit volume and the number of equivalent arrangements, k_BIs Boltzmann constant, T is temperature, E_fIs the defect formation energy.

Case one:

construction A₂Zr₂O₇(A ═ La, Pr, Pm, Eu) complete structure supercell and carrying out structure optimization, based on the optimized perfect supercell, constructing a supercell model containing isolated point defect structure, and using A₂Zr₂O₇Converting the supercell model into three-dimensional atomic coordinate information, and optimizing A₂Zr₂O₇In the perfect supercell structure, one A, Zr atom and one O atom in the inner part are respectively deleted to form V_A、V_ZrAnd V_OVacancy defects; one A atom occupying the Zr position or one Zr atom occupying the A position, respectively, forms A_ZrAnd Zr_ATwo types of inverse structural defects; addition of an A, Zr and O atom at the interstitial position to form A, respectively_i、Zr_iAnd O_iThree gap defects, for A₂Zr₂O₇All isolated point defects in the structure have the valence state which adopts the standard valence of the corresponding element;

setting input parameters, carrying out structure optimization on all isolated point defect models, calculating defect formation energy of isolated point defects, selecting the most stable defect position by comparing the sizes of all structure supercell formation energy of the same isolated point defect, calculating by adopting a first principle based on a density functional theory, wherein the calculated software is VASP (Vienna Ab-initio Simulation Package) software, the exchange correlation functional adopts a GGA-PBEsol method with generalized gradient approximation, and all the calculations consider spin polesThe truncation energy of the plane wave pseudopotential is set to 520eV, and the convergence standard of the structure optimization is set to beThe calculation method generates k points by a Monkhorst-Pack method during calculation, the grid density of the generated k points is set to be 2 multiplied by 2, and the defect formation can be realized by a formula E_f＝E_d+E_p+∑n_iμ_i+q(ΔE_F+E_VBM) Calculation of where E_dAnd E_pTotal energy, n, of defective and non-defective supercells, respectively_iIs the number of atoms, μ, to be removed or added_iIs the chemical potential of the corresponding element, q is the valence of the point defect, E_VBMIs the energy level of the valence band top (VBM), Δ E_FIs the fermi level measured based on VBM;

consider all possible competing phases in the ternary rare earth zirconate: ternary phase A₂Zr₂O₇Binary phase A₂O₃、ZrO₂And a monophasic A, Zr and O₂Listing the chemical potential limiting conditions among the monobasic, binary and ternary phases in the ternary rare earth zirconate to obtain and draw A₂Zr₂O₇The chemical potential phase diagram containing the competitive phase finds out the area ABCD and the boundary chemical potential condition where the ternary rare earth zirconate can stably exist; therefore, possible defect chemical reactions and corresponding composite defect types under each chemical potential condition are written, composite defect forming energy is obtained by calculating the defect chemical reactions, and the type and the concentrations of the dominant composite defects at different temperatures are predicted, wherein the chemical potential limiting conditions are as follows:

schottky defect:

frenkel defect:

and (3) inverse structure defects:

under thermodynamic equilibrium conditions, the Arrhenius equation can be used to calculate the concentration of various complex defects at different temperatures:wherein N is_sAnd N_cRespectively the number of sites of composite defects in a unit volume and the number of equivalent arrangements, k_BIs Boltzmann constant, T is temperature, E_fFor defect formation energy, according to chemistryThe potential environment can be divided into two situations of stoichiometric ratio and non-stoichiometric ratio, wherein the non-stoichiometric condition can further subdivide the situation of different chemical environments according to relevant competitive phase excess, and the situation of rich ZrO₂And is rich in A₂O₃The dominant defects in the nonstoichiometric ratio under the conditions were as follows:

enriched ZrO₂Conditions are as follows:

rich in A₂O₃Conditions are as follows:

case two:

construction of RE₂Si₂O₇Carrying out structural optimization on the supercell with the complete structure, constructing a supercell model of an isolated point defect structure based on the optimized supercell, and combining RE (rare earth element)₂Si₂O₇Converting the supercell model into three-dimensional atomic coordinate information, and optimizing RE₂Si₂O₇In the complete supercell structure, deducting RE, Si and O to form V_RE、V_SiAnd V_OVacancy defects; one RE occupying Si position or one Si occupying RE respectively form RE_SiAnd Si_RETwo types of inverse structural defects; searching the whole potential energy surface to find out the gap configuration of each element with the lowest energy, thereby determining the gap position of each element, and adding RE, Si and O atoms at the gap position to form RE_i、Si_iAnd O_iThree kinds of gap defects, for RE₂Si₂O₇All isolated point defects in the structure have the valence state which adopts the standard valence of the corresponding element;

isolated point defect formation can be calculated and defect location determined: setting input parameters, carrying out structural optimization on all isolated point defect models, calculating defect formation energy of isolated point defects, and comparing all structural supercell formation energy of the same isolated point defectSelecting the most stable defect position, calculating by adopting a first principle based on a density functional, wherein the calculated software is VASP (Vienna Ab-initio Simulation Package) software, and RE (RE)₂Si₂O₇The prediction method of the composite point defect adopts a generalized gradient approximate GGA-PBEsol method to exchange a correlation functional, all the calculations consider spin polarization, the truncation energy of the plane wave pseudopotential is set to 520eV, and the convergence standard of the structure optimization is set to 520eVThe calculating method generates k points by a Monkhorst-Pack method during calculation, the grid density of the generated k points is set to be 2 multiplied by 2, the volume of the supercell is kept unchanged in the structural optimization process of the defect model, relaxation is allowed to be carried out on all atomic positions, and the defect formation can be carried out by a formula E_f＝E_d+E_p+∑n_iμ_i+q(ΔE_F+E_VBM) Calculation of where E_dAnd E_pTotal energy, n, of defective and non-defective supercells, respectively_iIs the number of atoms, μ, to be removed or added_iIs the chemical potential of the corresponding element, q is the valence of the point defect, E_VBMIs the energy level of the valence band top (VBM), Δ E_FIs the fermi level measured based on VBM;

consider all possible competing phases in ternary rare earth silicates: ternary phase RE₂Si₂O₇Binary phase RE₂O₃、SiO₂Monohydric phase RE, Si, O₂And in the binary phase RE₂O₃Ternary impurity phase RE produced in excess₂SiO₅ Listing chemical potential limiting conditions of the ternary double rare earth silicate, drawing a chemical potential phase diagram containing a competitive phase, finding out an area ABCD and a boundary chemical potential condition where the ternary double rare earth silicate can stably exist, accordingly, writing possible defect chemical reactions and corresponding composite defect types under each chemical potential condition, obtaining composite defect forming energy by calculating defect chemical reaction capacity, and predicting a leading composite defect forming energyThe type of defect and the concentration at different temperatures are combined, and the chemical potential limiting conditions are as follows:

ternary phase:

phase one:

binary phase:

ternary competitive phase:

schottky defect:

frenkel defect:

and (3) inverse structure defects:

under thermodynamic equilibrium conditions, the Arrhenius equation can be used to calculate the concentration of various complex defects at different temperatures:wherein N is_sAnd N_cRespectively the number of sites of composite defects in a unit volume and the number of equivalent arrangements, k_BIs Boltzmann constant, T is temperature, E_fFor defect formation energy, depending on the chemical potential environment, it can be divided into stoichiometric and non-stoichiometric conditions, wherein the non-stoichiometric condition can further subdivide the different chemical environments according to the relative competitive phase excess.

To summarize: based on the calculation of a first principle, only basic crystal structure information of the ternary rare earth oxide needs to be known, defect formation energy of the stoichiometric ratio and the non-stoichiometric ratio of the ternary rare earth oxide can be calculated without other parameters, prediction of leading defect types and concentrations is completed, the adopted calculation simulation method does not need to input experimental equipment and raw materials except a computer, the cost is low, the efficiency is high, the actual chemical environment of the material can be simulated by considering the competitive phase of the ternary rare earth oxide, the most possible defect chemical reaction and the corresponding composite defect types under each chemical environment and the defect concentrations under different temperatures are predicted according to the actual chemical environment, a theoretical basis is provided for regulation and control of the defect types in the experimental synthesis process, and optimization of physical properties related to the defects of the material is promoted.