Chemical Descriptors of Yttria-Stabilized Zirconia at Low Defect Concentration: An ab Initio Study

Abstract

Keywords: solid oxide fuel cell, yttria stabilised zirconia, cubic zirconia, bixbyite yttria, ab initio, density functional theory, empirical potential, Born-Mayer-Huggins, point charge model, phonons, harmonic approximation. been observed in either X-ray or neutron diffraction experiments. The prediction of local defect structure and the interaction between defects is therefore of great interest. This has not been possible to date as the number of possible defect topologies is very large and to perform reliable total energy calculations for all of them would be prohibitively expensive. Previous theoretical studies have only considered a selection of representative structures. In this study, a comprehensive search for low energy defect structures using a combined classical modelling and density functional theory approach is used to identify the low energy isolated defect structures at the dilute limit, 3.2mol%. Through analysis of energetics computed using the best available Born-Mayer-Huggins empirical potential model, a point charge model, DFT, and a local strain energy estimated in the harmonic approximation, the main chemical and physical descriptors that correlate to the low energy DFT structures are discussed. It is found that the empirical potential model reproduces a general trend of increasing DFT energetics across a series of locally strain relaxed structures, but is unreliable both in predicting some incorrect low energy structures, and 3 in finding some meta-stable structures to be unstable. A better predictor of low energy defect structures is found to be the total electrostatic energy of a simple point charge model calculated at the unrelaxed geometries of the defects. In addition, the strain relaxation energy is estimated effectively in the harmonic approximation to the imaginary phonon modes of undoped c-ZrO 2 , but is found to be unimportant in determining the low energy defect structures. These results allow us to propose a set of easily computed descriptors that can be used to identify the low energy YSZ defect structures, negating the combinatorial complexity and number of defect structures that need to be considered. Abstract

Unexpectedly large energy variations from dopant interactions in ferroelectric HfO2 from high-throughput ab initio calculations

“…41,42 As pointed out in the last paragraph, each of the three processing techniques reveals different dopant distributions, which only in one case represents the thermodynamic equilibrium configuration with the lowest energy. Doping of HfO 2 [25][26][27][43][44][45] and ZrO 2 46 was extensively researched utilizing the density functional theory (DFT) and using cluster expansion 30,33,47 or high-throughput calculations 48 under the premise that the lowestenergy structure is realized in thin films. Although all these studies attempt to answer the question of phase stabilization with doping, they do not consider the energy variation from the doping distribution enforced and biased by the processing technique.…”

Revisiting the Temperature Dependent Ionic Conductivity of Yttria Stabilized Zirconia (YSZ)

“…Simulations on defect interaction often con-sidered defect pairs and found that energies are lower for an Y ion in the NNN (next nearest neighbor) cation shell of an oxygen vacancy, compared to Y in the NN (nearest neighbor) cation tetrahedron of the vacancy or interaction-free vacancies, even though calculated absolute values of defect interaction energies vary considerably. 11,13,18,19,22,24 This defect interaction also strongly depends on the dopant ion. 15,23,24 Defect energies were further calculated for more extended defects of several dopant ions and oxygen vacancies, [30][31][32] and such studies as well as experimental data 33 showed the relevance of vacancy-vacancy interaction.…”

Third-order nonlinear optical susceptibility of crystalline oxide yttria-stabilized zirconia

“…First, we focused on the static non-linear optical properties of pure c-ZrO 2 aiming at a reliable estimation of the order of magnitude of its third order NLO responses in idealized conditions to be used as a guide for our qualitative conclusions. Since little is known about the true local atomistic structure of YSZ, to circumvent the challenging task [25,26] of determining the most stable local crystal structure of each system considered, the second step comprised computations addressing the importance of the vacancy/dopant distribution on the third order susceptibilities. For this task, we chose two doping concentrations of 3.2 and 33 %mol.…”

“…These are the pure Perdew, Burke, and Ernzerhof (PBE) [31] exchange-correlation functional, its hybrid counterpart PBE0 [32] and the Becke, three-parameter, Lee-Yang-Parr exchange-correlation functional (B3LYP). [33] The first two functionals, namely PBE and PBE0, have been used in previous studies, [25,34] involving the structural and electronic properties of YSZ while the popular B3LYP, was chosen in order to check the robustness of the results. All periodic calculations have been performed at the static limit with a developer s version of CRYSTAL17 software [35] that allows analytic computations of non-linear optical (NLO) properties of infinite periodic systems.…”

“…In the case of 3.2%mol. in Y 2 O 3 , we considered the ten most stable nonequivalent configurations reported by Parkes et al [25] the crystal structures of which were built upon a doped 2 × 2 × 2 super cell of c-ZrO 2 , optimized with the PBE functional.…”