First-principles study of structural, elastic, and bonding properties of pyrochlores

TL;DR

This study uses density functional theory to analyze the structural, elastic, and electronic properties of pyrochlore materials, revealing how atomic composition influences their bonding and thermal characteristics.

Contribution

It provides detailed first-principles calculations of lattice, elastic, and electronic properties for various pyrochlore compositions, highlighting covalency and ionicity variations.

Findings

Sound velocity decreases with heavier B ions.

Large anomalous dynamical charges for Ti, Zr, Hf.

Ionicity increases from Sn to Zr in pyrochlores.

Abstract

Density Functional Theory calculations have been performed to obtain lattice parameters, elastic constants, and electronic properties of ideal pyrochlores with the composition A$_2$B$_2$O$_7$ (where A=La,Y and B=Ti,Sn,Hf, Zr). Some thermal properties are also inferred from the elastic properties. A decrease of the sound velocity (and thus, of the Debye temperature) with the atomic mass of the B ion is observed. Static and dynamical atomic charges are obtained to quantify the degree of covalency/ionicity. A large anomalous contribution to the dynamical charge is observed for Hf, Zr, and specially for Ti. It is attributed to the hybridization between occupied $2p$ states of oxygen and unoccupied d states of the B cation. The analysis based on Mulliken population and deformation charge integrated in the Voronoi polyhedra indicates that the ionicity of these pyrochlores increases in the order Sn--Ti--Hf--Zr. The charge deformation contour plots support this assignment.