Geometric Analysis and Formability of the Cubic A2BX6 Vacancy Ordered Double Perovskite Structure
Anjie Cheng
Chenyang Lyu
Tianyi Shi
Ziheng Wang
Robert Palgrave
10.26434/chemrxiv.12601538.v1
https://chemrxiv.org/articles/preprint/Geometric_Analysis_and_Formability_of_the_Cubic_A2BX6_Vacancy_Ordered_Double_Perovskite_Structure/12601538
<p>A geometric analysis of the cubic A<sub>2</sub>BX<sub>6</sub>
structure commonly formed by metal halides is presented. Using the ‘hard sphere’
approximation, where the ions are represented by spheres of a fixed radius, we
derive four limiting models that each constrain the distances between
constituent ions in different ways. We compare the lattice parameters predicted
by these four models with experimental data from the Inorganic Crystal
Structure Database (ICSD). For the fluorides, the maintenance of the AX bond
length at the sum of the A and X radii gives the best approximation of the
lattice parameter, leading to structures with widely separated BX<sub>6</sub>
octahedra. For the heavier halides, a balance between forming an A site cavity
of the correct size, and maintaining suitable anion-anion distances determines
the lattice parameter. It is found that in many A<sub>2</sub>BX<sub>6</sub>
compounds of heavier halides, the neighbouring octahedra show very significant
anion-anion overlap, meaning that the commonly used description of these
materials of having isolated BX<sub>6</sub> octahedra is misleading. We use the
geometric models to derive formability criteria for vacancy ordered double
perovskites. </p>
2020-07-03 10:47:24
K2PtCl6
vacancy ordered perovskite