- Email: [email protected]
Ab initio molecular dynamic study of structure and atomic motions in SrCoO3-x and SrCo0.875Mo0.125O3-x
Materials Today: Proceedings xxx (xxxx) xxx
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Ab initio molecular dynamic study of structure and atomic motions in SrCoO3-x and SrCo0.875Mo0.125O3-x Igor Gainutdinov a,⇑, Alexander Nemudry a, Igor Zilberberg b a b
Institute of Solid State Chemistry and Mechanochemistry SB RAS, Kutateladze, 18, Novosibirsk 630128, Russia Boreskov Institute of Catalysis SB RAS, Novosibirsk 630090, Russia
a r t i c l e
i n f o
Article history: Received 4 November 2019 Received in revised form 15 December 2019 Accepted 19 December 2019 Available online xxxx Keywords: Perovskites Non-stoichiometric oxides Molecular dynamic Density functional theory Ab initio calculations Effective charge
a b s t r a c t We performed ab initio molecular dynamic simulations for SrCoMoO1-x and SrCo0.875Mo0.125O1-x (x = 0, 0.125, 0.25) compounds with VASP package. The Mo doping cause ‘‘contraction” of structure with lowering the volume of studied system and lowering the thermal expansion up to 2 times. Analysis of inner ionic motions showed that vacancies may move both to Co cation neighbor and Mo neighbor despite the Mo effective charge is about +2.6e but Co charge about +1.6e. The effective charges of ions during vacancy motion vary only by a small amount. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the III All-Russian Conference (with International Participation) Hot Topics of Solid State Chemistry: From New Ideas to New Materials.
1. Introduction Oxides with perovskite structure SrCo1-yFeyO3-x are ancestors of wide range of technologically important substances, which due to high oxygen mobility used as oxide ionic conductors in fuel cells, oxygen selective membranes, etc. One of the most significant disadvantages is that these compounds are not stable enough at low partial pressures of oxygen and in the CO2 atmosphere. There are also first order phase transitions with a change in volume, which complicates their technological application due to mechanical instability during temperature cycling. In addition, lowtemperature structural modifications usually have low ionic conductivity what limiting from below the temperature of operation for these devices. One of the widely used effective methods to overcome the above difficulties is doping these compounds by high valence cations (Mo, W, Nb, Ta). Recently we reported experimental results of influence of Mo doping on properties of Ba0.5Sr0.5Co0.8Fe0.2O3-x and SrFeO3-x system [1] and the results of an extensive ab initio study of the effect of doping by various cations on the ground state of SrFeO3 and SrCoO3 systems [2]. We observed increasing the sta⇑ Corresponding author. E-mail address: [email protected] (I. Gainutdinov).
bility of substances in different atmospheres and suppression of undesirable structural phase transitions while maintaining sufficiently high oxygen permeability. Accordingly, the mechanism of influence of dopants on the properties of these oxides is of interest. And also, the actual reason for the abnormally high mobility of oxygen in these compounds is still a question. Despite considerable progress in understanding microscopic processes and the structure of these compounds, usually experimental data are obtained at relatively low temperatures, usually below the technological operating temperature. Direct experimental study of the structure of the high-temperature state and the mechanism of oxygen transport is difficult. However, to clarify this issue, it is possible to use computer simulation methods, in particular - the method of molecular dynamics. The classical molecular dynamics method has main problem the type of interatomic interaction potential which should describe interactions correctly. Usually for calculations of ionic systems, including cobaltite or strontium ferrite, interatomic potentials take into account electrostatic interaction of ions and repulsion of the ion cores taken in the form of the Born-Mayer potential (simple inverse-exponent V = Aexp(-r/B)) – see, for example [3–6]. This kind of potential has a spherical symmetry. Also, the charges on the ions are taken constant, and these both simplification lead to significant coarsening of model.
https://doi.org/10.1016/j.matpr.2019.12.150 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the III All-Russian Conference (with International Participation) Hot Topics of Solid State Chemistry: From New Ideas to New Materials.
Please cite this article as: I. Gainutdinov, A. Nemudry and I. Zilberberg, Ab initio molecular dynamic study of structure and atomic motions in SrCoO3-x and SrCo0.875Mo0.125O3-x, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.150
2
I. Gainutdinov et al. / Materials Today: Proceedings xxx (xxxx) xxx
Modern software packages for first principles calculations by the density functional theory (DFT) method allow producing the so-called ab initio modeling, or quantum molecular dynamics. Due to the availability of the method the number of works on the study of oxides using the first-principle molecular dynamics in recent years is growing [7–9]. Ab initio modeling is free from the above disadvantages of classical molecular dynamics; all possible effects associated with the structure of bonds between atoms in this method are taken into account correctly. But there are limitations related to the amount of calculations required. Even with supercomputer systems, we can hardly get any meaningful result (especially for diffusion or restructuring) on systems containing more than 50 atoms. However, with this method we can qualitative analyze microscopic picture and this will help us to better understand the overall process of ionic motions in oxide and help in further design more relevant interatomic interaction potentials for ‘‘large” simulations by the classical molecular dynamic’s method.
Ab initio molecular dynamic simulations for SrCoO3-x and SrCo0.875Mo0.125O3-x (x = 0, 0.125, 0.25) compounds with VASP package was performed [10–11]. The system contained of 2x2x2 elementary cells, 40 ions. For composition x = 0.125, 0.25 some oxygen atoms (one and two respectively) were removed from the system. In the molybdenum doped systems one of the cobalt atoms was replaced by molybdenum. Calculations were performed with PAW PBE pseudopotentials in gamma point only approach in periodic boundary conditions. Ab initio molecular dynamic simulation was performed with time step (VASP parameter POTIM) dt = 3*10-16 sec, overall run length was 8000 steps, i.e. our systems was modelled in time interval 2.4*10-12 sec. The characteristic time per atomic oscillation around the equilibrium position was 50–80 steps. The system was modeled under NPT conditions with external pressure p = 0. Langevin thermostat with GAMMA parameter (friction parameter)
4,31
4,31
4,26
4,26
4,22 4,17
4,17
4,12
4,12
4,07
4,07
4,02
4,02
3,97
3,97
3,91
3,91
800 900 1000 1100 1200 1300 1400
T, K
x=3.0 x=2.875 x=2.75
4,22
SrCoOx
I
V, A3
2. Computation details
SrCo0.875Mo0.125Ox
800
900 1000 1100 1200 1300
T, K
Fig. 1. ‘‘Effective” cell dimension aeff for pure SrCoOx and for Mo doped one for different oxygen stoichiometry – x = 3.0 (squares), x = 2.875 (triangles) and x = 2.75 (stars).
Fig. 2. Amplitude of vibrations A(m) in dependence of temperature for SrCoOx (left) and for SrCo0.875Mo0.125Ox (right) for different oxygen stoichiometry – x = 3.0 (upper line), x = 2.875 (middle) and x = 2.75 (bottom).
Please cite this article as: I. Gainutdinov, A. Nemudry and I. Zilberberg, Ab initio molecular dynamic study of structure and atomic motions in SrCoO3-x and SrCo0.875Mo0.125O3-x, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.150
3
I. Gainutdinov et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 3. Jump of oxygen ion from Mo neighbor to Co. From 1) through 2) to 3) state – overall motion time is about 1e-14 sec. Blue – Mo, red – O, green – Sr, rose – Co. Moved Oxygen ion marked by triangle. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
equal to 10 ps1 for all types of atoms and for unit cell shape was used to maintain the temperature. System was equilibrated during 1000 time steps and this time was enough. 3. Results To estimate the degree of change in the volume of the system, we calculated some effective ‘‘cell dimension” aeff.
aeff ¼
ffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1p 3 2
ð1Þ
Here V is the system volume, the cube root of the volume is the size of a cube of equal volume, 1/2 - since our system contains 2x2x2 unit cell of the initial perovskite, then 1/2 of this length the size of the corresponding cubic elementary cell that would be observed by some experimental method (for example, by Xray diffractometry) if it would be performed with our model substance. The dependence of this value on the temperature is shown in Fig. 1. As can be seen from the figure, the system expands with increasing temperature. Molybdenum doping leads to some compression of the substance and almost halves the coefficient of thermal expansion. Obtained values of the coefficients of thermal expansion 40*10-6 1/K for SrCoO3-x and 20*10-6 1/K for SrCo0.875Mo0.125O3-x are in agreement with literature data [12,13]. The velocity autocorrelation function (VAF) (2)
VAF ðsÞ ¼
XN XJend i¼1
j¼Jstart
! ! tj i v tj þ s i
v
ð2Þ
allows to calculate the vibrational characteristics in the form of VAF expansion in a series of cosines A(m), where frequency m = pns/T (n – natural number, s – time shift in formulae for VAF(s), T – overall time of observation) which can be considered as oscillation spectrum
VAF ðsÞ ¼
XNcos n¼1
AðmÞcosð
pns T
Þ
ð3Þ
This quantity, A(m), for different stoichiometry in SrCoOx (left) and SrCo0.875Mo0.125Ox (right) and in dependence of temperature is pictured on the map plot (Fig. 2). As one can see, the spectrum of oscillations with increasing temperature regularly becomes wider, the amplitude of oscillations increases. For Mo doped compounds one can observe some low-frequency shoulders, which can correspond to more slowly vibrations of more massive Mo ion. But at 900 K we observe some peculiarities – vibrational spectra have the same width as a high-temperature one, and have lowfrequency peaks. A detailed examination of the trajectories of the system at this temperature shows that the dynamics of the movement of atoms has a certain feature - apparently, the ions ‘‘feel” the proximity of the structural phase transition and try to overcome the barriers, which due to the proximity to the structural transition at this temperature are reduced and broadened. And in these attempts ions
Table 1 Energy of system, charges of ions involved in motion and Co magnetic moments for three consequent configuration during O ion’s motion. Parameter
1)
2)
3)
Total energy of system, eV Charge of moving oxygen ion, e Charge of Mo ion, e Charge of Co ion, e Charge of Sr ion, e Magnetic moment of Co, mB
224,067 1,26 +2,65 +1,48 +1,56 2,99
243,031 1,18 +2,62 +1,51 +1,56 2,51
244,62 1,15 +2,67 +1,51 +1,60 2,88
are ‘‘hanging” on ridges of barriers or in close proximity to them. In fact, the appearance of low-frequency peaks means the appearance of large-scale and long-term (relative to the characteristic oscillation times in the system at a given temperature) fluctuations preceding the phase transition. During molecular dynamic run we observe several jumps of oxygen ions from one position to another. We cannot accumulate enough statistical data and obtain a dependence of diffusion coefficient from temperature in this investigation but some data about ions involved in elementary diffusion act pictured on Fig. 3 are presented in Table 1. This data illustrates one principle which we must take into account – no significant changes in effective charges was observed during oxygen motion from Mo ion to Co ion. And secondary – we should construct classic MD interatomic potentials with effective charges values - overestimation of charges will give us a deeper and more narrow interatomic potential, and hence, more localized ionic motion that will lower ionic mobility in such model.
CRediT authorship contribution statement Igor Gainutdinov: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Visualization, Writing - original draft. Alexander Nemudry: Supervision, Validation. Igor Zilberberg: Supervision, Validation, Writing - review & editing.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements This work was supported by the Russian Science Foundation (grant No. 18-13-00059).
Please cite this article as: I. Gainutdinov, A. Nemudry and I. Zilberberg, Ab initio molecular dynamic study of structure and atomic motions in SrCoO3-x and SrCo0.875Mo0.125O3-x, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.150
4
I. Gainutdinov et al. / Materials Today: Proceedings xxx (xxxx) xxx
References [1] E.V. Shubnikova, O.A. Bragina, A.P. Nemudry, J. Ind. Eng. Chem. 59 (2018) 242– 250. [2] I. I. Gainutdinov, A. P. Nemudry, I. L. Zilberberg, Materials Today: Proceedings, V 12 P 1 (2019) 21–24 [3] Jiehua Wang, Lijia Zhou, Yanhui Wang, Xu. Jungu, Xiaoyan Yang, Xiaojun Kuang, J. Solid State Chem. 268 (2018) 16–21. [4] Mai Thi Lan, Tran Thuy Duong, Nguyen Viet Huy, Nguyen Van Hong, Mater. Res. Express 4 (2017) 035202. [5] Stevin S. Pramana, Tom Baikie, Tao An, Matthew G. Tucker, Wu. Ji, Martin K. Schreyer, Fengxia Wei, Ryan D. Bayliss, Christian L. Kloc, Timothy J. White, Andrew P. Horsfield, Stephen J. Skinner, J. Am. Chem. Soc. 138 (2016) 1273– 1279.
[6] Weixuan Li, Xiang Chen, Zexi Zheng, Youping Chen, Comput. Mater. Sci. 112 (2016) 107–112. [7] Michel Sassi, Tiffany Kaspar, Kevin M. Rosso, R. Steven, Spurgeon Scientific Reports 9 (2019) 8190. [8] Qingping Zhang, Wu. Xiusheng, Eerjun Kan, Curr. Appl Phys. 16 (2016) 1094– 1099. [9] FengLia HongWua, Phys. Lett. A 383 (2019) 210–214. [10] G. Kresse, J. FurthmuËller, Phys. Rev. B: Condens. Matter Mater. Phys. 54 (1996) 11169–11186. [11] J.P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 78 (1997) 1396. [12] T. Nagai, W. Ito, T. Sakon, Solid State Ionics V 177 (2007) 3433–3444. [13] V.S. Kharton, Li Shuangbao, A.V. Kovalevsky, E.N. Naumovich, Solid State Ionics 96 (1997) 141–151.
Please cite this article as: I. Gainutdinov, A. Nemudry and I. Zilberberg, Ab initio molecular dynamic study of structure and atomic motions in SrCoO3-x and SrCo0.875Mo0.125O3-x, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.150
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Ab initio molecular dynamic study of structure and atomic motions in SrCoO3-x and SrCo0.875Mo0.125O3-x Igor Gainutdinov a,⇑, Alexander Nemudry a, Igor Zilberberg b a b
Institute of Solid State Chemistry and Mechanochemistry SB RAS, Kutateladze, 18, Novosibirsk 630128, Russia Boreskov Institute of Catalysis SB RAS, Novosibirsk 630090, Russia
a r t i c l e
i n f o
Article history: Received 4 November 2019 Received in revised form 15 December 2019 Accepted 19 December 2019 Available online xxxx Keywords: Perovskites Non-stoichiometric oxides Molecular dynamic Density functional theory Ab initio calculations Effective charge
a b s t r a c t We performed ab initio molecular dynamic simulations for SrCoMoO1-x and SrCo0.875Mo0.125O1-x (x = 0, 0.125, 0.25) compounds with VASP package. The Mo doping cause ‘‘contraction” of structure with lowering the volume of studied system and lowering the thermal expansion up to 2 times. Analysis of inner ionic motions showed that vacancies may move both to Co cation neighbor and Mo neighbor despite the Mo effective charge is about +2.6e but Co charge about +1.6e. The effective charges of ions during vacancy motion vary only by a small amount. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the III All-Russian Conference (with International Participation) Hot Topics of Solid State Chemistry: From New Ideas to New Materials.
1. Introduction Oxides with perovskite structure SrCo1-yFeyO3-x are ancestors of wide range of technologically important substances, which due to high oxygen mobility used as oxide ionic conductors in fuel cells, oxygen selective membranes, etc. One of the most significant disadvantages is that these compounds are not stable enough at low partial pressures of oxygen and in the CO2 atmosphere. There are also first order phase transitions with a change in volume, which complicates their technological application due to mechanical instability during temperature cycling. In addition, lowtemperature structural modifications usually have low ionic conductivity what limiting from below the temperature of operation for these devices. One of the widely used effective methods to overcome the above difficulties is doping these compounds by high valence cations (Mo, W, Nb, Ta). Recently we reported experimental results of influence of Mo doping on properties of Ba0.5Sr0.5Co0.8Fe0.2O3-x and SrFeO3-x system [1] and the results of an extensive ab initio study of the effect of doping by various cations on the ground state of SrFeO3 and SrCoO3 systems [2]. We observed increasing the sta⇑ Corresponding author. E-mail address: [email protected] (I. Gainutdinov).
bility of substances in different atmospheres and suppression of undesirable structural phase transitions while maintaining sufficiently high oxygen permeability. Accordingly, the mechanism of influence of dopants on the properties of these oxides is of interest. And also, the actual reason for the abnormally high mobility of oxygen in these compounds is still a question. Despite considerable progress in understanding microscopic processes and the structure of these compounds, usually experimental data are obtained at relatively low temperatures, usually below the technological operating temperature. Direct experimental study of the structure of the high-temperature state and the mechanism of oxygen transport is difficult. However, to clarify this issue, it is possible to use computer simulation methods, in particular - the method of molecular dynamics. The classical molecular dynamics method has main problem the type of interatomic interaction potential which should describe interactions correctly. Usually for calculations of ionic systems, including cobaltite or strontium ferrite, interatomic potentials take into account electrostatic interaction of ions and repulsion of the ion cores taken in the form of the Born-Mayer potential (simple inverse-exponent V = Aexp(-r/B)) – see, for example [3–6]. This kind of potential has a spherical symmetry. Also, the charges on the ions are taken constant, and these both simplification lead to significant coarsening of model.
https://doi.org/10.1016/j.matpr.2019.12.150 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the III All-Russian Conference (with International Participation) Hot Topics of Solid State Chemistry: From New Ideas to New Materials.
Please cite this article as: I. Gainutdinov, A. Nemudry and I. Zilberberg, Ab initio molecular dynamic study of structure and atomic motions in SrCoO3-x and SrCo0.875Mo0.125O3-x, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.150
2
I. Gainutdinov et al. / Materials Today: Proceedings xxx (xxxx) xxx
Modern software packages for first principles calculations by the density functional theory (DFT) method allow producing the so-called ab initio modeling, or quantum molecular dynamics. Due to the availability of the method the number of works on the study of oxides using the first-principle molecular dynamics in recent years is growing [7–9]. Ab initio modeling is free from the above disadvantages of classical molecular dynamics; all possible effects associated with the structure of bonds between atoms in this method are taken into account correctly. But there are limitations related to the amount of calculations required. Even with supercomputer systems, we can hardly get any meaningful result (especially for diffusion or restructuring) on systems containing more than 50 atoms. However, with this method we can qualitative analyze microscopic picture and this will help us to better understand the overall process of ionic motions in oxide and help in further design more relevant interatomic interaction potentials for ‘‘large” simulations by the classical molecular dynamic’s method.
Ab initio molecular dynamic simulations for SrCoO3-x and SrCo0.875Mo0.125O3-x (x = 0, 0.125, 0.25) compounds with VASP package was performed [10–11]. The system contained of 2x2x2 elementary cells, 40 ions. For composition x = 0.125, 0.25 some oxygen atoms (one and two respectively) were removed from the system. In the molybdenum doped systems one of the cobalt atoms was replaced by molybdenum. Calculations were performed with PAW PBE pseudopotentials in gamma point only approach in periodic boundary conditions. Ab initio molecular dynamic simulation was performed with time step (VASP parameter POTIM) dt = 3*10-16 sec, overall run length was 8000 steps, i.e. our systems was modelled in time interval 2.4*10-12 sec. The characteristic time per atomic oscillation around the equilibrium position was 50–80 steps. The system was modeled under NPT conditions with external pressure p = 0. Langevin thermostat with GAMMA parameter (friction parameter)
4,31
4,31
4,26
4,26
4,22 4,17
4,17
4,12
4,12
4,07
4,07
4,02
4,02
3,97
3,97
3,91
3,91
800 900 1000 1100 1200 1300 1400
T, K
x=3.0 x=2.875 x=2.75
4,22
SrCoOx
I
V, A3
2. Computation details
SrCo0.875Mo0.125Ox
800
900 1000 1100 1200 1300
T, K
Fig. 1. ‘‘Effective” cell dimension aeff for pure SrCoOx and for Mo doped one for different oxygen stoichiometry – x = 3.0 (squares), x = 2.875 (triangles) and x = 2.75 (stars).
Fig. 2. Amplitude of vibrations A(m) in dependence of temperature for SrCoOx (left) and for SrCo0.875Mo0.125Ox (right) for different oxygen stoichiometry – x = 3.0 (upper line), x = 2.875 (middle) and x = 2.75 (bottom).
Please cite this article as: I. Gainutdinov, A. Nemudry and I. Zilberberg, Ab initio molecular dynamic study of structure and atomic motions in SrCoO3-x and SrCo0.875Mo0.125O3-x, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.150
3
I. Gainutdinov et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 3. Jump of oxygen ion from Mo neighbor to Co. From 1) through 2) to 3) state – overall motion time is about 1e-14 sec. Blue – Mo, red – O, green – Sr, rose – Co. Moved Oxygen ion marked by triangle. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
equal to 10 ps1 for all types of atoms and for unit cell shape was used to maintain the temperature. System was equilibrated during 1000 time steps and this time was enough. 3. Results To estimate the degree of change in the volume of the system, we calculated some effective ‘‘cell dimension” aeff.
aeff ¼
ffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1p 3
ð1Þ
Here V is the system volume, the cube root of the volume is the size of a cube of equal volume, 1/2 - since our system contains 2x2x2 unit cell of the initial perovskite, then 1/2 of this length the size of the corresponding cubic elementary cell that would be observed by some experimental method (for example, by Xray diffractometry) if it would be performed with our model substance. The dependence of this value on the temperature is shown in Fig. 1. As can be seen from the figure, the system expands with increasing temperature. Molybdenum doping leads to some compression of the substance and almost halves the coefficient of thermal expansion. Obtained values of the coefficients of thermal expansion 40*10-6 1/K for SrCoO3-x and 20*10-6 1/K for SrCo0.875Mo0.125O3-x are in agreement with literature data [12,13]. The velocity autocorrelation function (VAF) (2)
VAF ðsÞ ¼
XN XJend i¼1
j¼Jstart
! ! tj i v tj þ s i
v
ð2Þ
allows to calculate the vibrational characteristics in the form of VAF expansion in a series of cosines A(m), where frequency m = pns/T (n – natural number, s – time shift in formulae for VAF(s), T – overall time of observation) which can be considered as oscillation spectrum
VAF ðsÞ ¼
XNcos n¼1
AðmÞcosð
pns T
Þ
ð3Þ
This quantity, A(m), for different stoichiometry in SrCoOx (left) and SrCo0.875Mo0.125Ox (right) and in dependence of temperature is pictured on the map plot (Fig. 2). As one can see, the spectrum of oscillations with increasing temperature regularly becomes wider, the amplitude of oscillations increases. For Mo doped compounds one can observe some low-frequency shoulders, which can correspond to more slowly vibrations of more massive Mo ion. But at 900 K we observe some peculiarities – vibrational spectra have the same width as a high-temperature one, and have lowfrequency peaks. A detailed examination of the trajectories of the system at this temperature shows that the dynamics of the movement of atoms has a certain feature - apparently, the ions ‘‘feel” the proximity of the structural phase transition and try to overcome the barriers, which due to the proximity to the structural transition at this temperature are reduced and broadened. And in these attempts ions
Table 1 Energy of system, charges of ions involved in motion and Co magnetic moments for three consequent configuration during O ion’s motion. Parameter
1)
2)
3)
Total energy of system, eV Charge of moving oxygen ion, e Charge of Mo ion, e Charge of Co ion, e Charge of Sr ion, e Magnetic moment of Co, mB
224,067 1,26 +2,65 +1,48 +1,56 2,99
243,031 1,18 +2,62 +1,51 +1,56 2,51
244,62 1,15 +2,67 +1,51 +1,60 2,88
are ‘‘hanging” on ridges of barriers or in close proximity to them. In fact, the appearance of low-frequency peaks means the appearance of large-scale and long-term (relative to the characteristic oscillation times in the system at a given temperature) fluctuations preceding the phase transition. During molecular dynamic run we observe several jumps of oxygen ions from one position to another. We cannot accumulate enough statistical data and obtain a dependence of diffusion coefficient from temperature in this investigation but some data about ions involved in elementary diffusion act pictured on Fig. 3 are presented in Table 1. This data illustrates one principle which we must take into account – no significant changes in effective charges was observed during oxygen motion from Mo ion to Co ion. And secondary – we should construct classic MD interatomic potentials with effective charges values - overestimation of charges will give us a deeper and more narrow interatomic potential, and hence, more localized ionic motion that will lower ionic mobility in such model.
CRediT authorship contribution statement Igor Gainutdinov: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Visualization, Writing - original draft. Alexander Nemudry: Supervision, Validation. Igor Zilberberg: Supervision, Validation, Writing - review & editing.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements This work was supported by the Russian Science Foundation (grant No. 18-13-00059).
Please cite this article as: I. Gainutdinov, A. Nemudry and I. Zilberberg, Ab initio molecular dynamic study of structure and atomic motions in SrCoO3-x and SrCo0.875Mo0.125O3-x, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.150
4
I. Gainutdinov et al. / Materials Today: Proceedings xxx (xxxx) xxx
References [1] E.V. Shubnikova, O.A. Bragina, A.P. Nemudry, J. Ind. Eng. Chem. 59 (2018) 242– 250. [2] I. I. Gainutdinov, A. P. Nemudry, I. L. Zilberberg, Materials Today: Proceedings, V 12 P 1 (2019) 21–24 [3] Jiehua Wang, Lijia Zhou, Yanhui Wang, Xu. Jungu, Xiaoyan Yang, Xiaojun Kuang, J. Solid State Chem. 268 (2018) 16–21. [4] Mai Thi Lan, Tran Thuy Duong, Nguyen Viet Huy, Nguyen Van Hong, Mater. Res. Express 4 (2017) 035202. [5] Stevin S. Pramana, Tom Baikie, Tao An, Matthew G. Tucker, Wu. Ji, Martin K. Schreyer, Fengxia Wei, Ryan D. Bayliss, Christian L. Kloc, Timothy J. White, Andrew P. Horsfield, Stephen J. Skinner, J. Am. Chem. Soc. 138 (2016) 1273– 1279.
[6] Weixuan Li, Xiang Chen, Zexi Zheng, Youping Chen, Comput. Mater. Sci. 112 (2016) 107–112. [7] Michel Sassi, Tiffany Kaspar, Kevin M. Rosso, R. Steven, Spurgeon Scientific Reports 9 (2019) 8190. [8] Qingping Zhang, Wu. Xiusheng, Eerjun Kan, Curr. Appl Phys. 16 (2016) 1094– 1099. [9] FengLia HongWua, Phys. Lett. A 383 (2019) 210–214. [10] G. Kresse, J. FurthmuËller, Phys. Rev. B: Condens. Matter Mater. Phys. 54 (1996) 11169–11186. [11] J.P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 78 (1997) 1396. [12] T. Nagai, W. Ito, T. Sakon, Solid State Ionics V 177 (2007) 3433–3444. [13] V.S. Kharton, Li Shuangbao, A.V. Kovalevsky, E.N. Naumovich, Solid State Ionics 96 (1997) 141–151.
Please cite this article as: I. Gainutdinov, A. Nemudry and I. Zilberberg, Ab initio molecular dynamic study of structure and atomic motions in SrCoO3-x and SrCo0.875Mo0.125O3-x, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.150