COMPUTATIONAL SIMULATION OF IONIC CONDUCTION IN BIMEVOX

• Main Author: LA KILO (NIM : 30507008); Ketua tim Pembimbing : Prof. Dr. Ismunandar; Anggota tim pembimbing, AKRAM
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/14772
• Institution: Institut Teknologi Bandung

Computational simulation of ionic conductivity of BIMEVOX oxide which has a layered structure and high symmetry is such a challenge. The oxide has a potential to be used in solid oxide fuel cell, especially as the electrolyte, because it has a high ionic conductivity. However, at low temperature, y-Bi2VO5.5 becomes unstable, it will turn into Beta-phase then alpha-phase. To stabilize y-Bi2VO5.5 at the low temperature, partial substitution of V by ME (ME = metal ion as a dopant) to generate Bi2V1-x(ME)xO5.5, which is often called BIMEVOX, is carried out. In this research, simulation of ionic conduction in BIMEVOX and it parent compound, y-Bi2VO5.5 using by atomistic, Bond Valence Sum (BVS), molecular dynamic, and ab initio methods has been conducted. These four methods use GULP, JUMPITER, DLPOLY, and CASTEP codes, respectively. y-Bi2VO5.5 has vacancies in equatorial and apical sites in its perovskite-like layer. The vacancies are to enable migration of oxide ion to the vacant site. Structure of y-Bi2VO5.5 which is used as input is a structure with I4/mmm and P1 space groups. Structure <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> with P1 space group was made in a simple and super cell structures by creating vacancies in the equatorial site. Input with I4/mmm space group were simulated by atomistic method. In the structure with space group P1, the oxide ion <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> conductivity occurs in the perovskite-like layer which is simulated by atomistic, BVS, and ab initio methods. Atomistic simulation results indicate that presence of <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> intrinsic defect increase lattice energy of y-Bi2VO5.5 compared to single layer Aurivillius compound. y-Bi2VO5.5 predicted is stable when concentration of vacancies in apical site is less than 10%. Minimum energy is reached when the oxide ion vacancies at the equatorial site, and the results are in a good agremeent with experiment report (Abraham et al.). Maximum dopant concentrations of Cu2+, Ga3+, and Ta5+ which can partially substitute V5+ are 12.5%, 13%, and 65%, respectively. It is predicted that BICUVOX, BIGAVOX, and BITAVOX with dopant exceeded above concentration could not be prepared. Simulation result <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> using by Mott-Littleton method shows defect energies in region II are reached at concentrations of 10%, 10%, and 20% for Cu2+ (Bi2Cu0.1V0.9O5.35), Ga3+(Bi2Ga0.1V0.9O4.4), and Ta5+ (Bi2Ta0.2V0.8O5.5), respectively. These concentrations are in a good agreement with experimental results where highest ionic conductivity is obtained for each BIMEVOX. Study of molecular dynamic indicates that activation energies (Ea) for y-Bi2VO5.5, Bi2Cu0.1V0.9O5.35, and Bi2Ta0.2V0.8O5.5 are 0.19, 0.21, and 0.10 eV, respectively. The energies are in a good agreement with experimental results. For y-Bi2VO5.5, the activation energy is different to those of ab initio simulation, Ea = 0.38 eV. The difference was caused by V-O coordination in the perovskite-like layer in y-Bi2VO5,5, which are all tetrahedral in the ab initio method, and a mixture of tetrahedral, five-coordination, and octahedral in MD simulation. This showed that V-O coordination in perovskite-like layer of y-Bi2VO5,5 will be very strong to form coordination mixture. BVS calculation shows apical oxide ion migration to the vacant site in the equatorial site is difficult because it faces a large hindrance, as indicated by its BVS. In contrast, migration of oxide ions in the equatorial site is easier shown by its low BVS value. The BVS maximum of oxide ion in equatorial site are less than oxide valence, so it can be said that y-Bi2VO5,5 is ionic conductor material. Ease of oxide ions migration in the equatorial site is supported by atomistic simulation, in which ion migration energy barrier is lower than the oxide ion migration energy of oxide from apical position to the vacant position in the equatorial site. <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> Therefore, active trajectory in y-Bi2VO5.5 compound is the trajectories of oxide ion in equatorial site of perovskite-like layers.