Effect of doping and oxygen vacancies on the octahedral tilt transitions in the BaCeO3 perovskite

TL;DR

This study investigates how Y doping and hydration influence structural phase transitions in BaCeO3, revealing that doping raises transition temperatures while dehydration lowers them, linked to bond length changes and vacancy effects.

Contribution

It provides new insights into how doping and hydration alter phase transition temperatures and mechanisms in BaCeO3 perovskite materials.

Findings

Y doping increases the rhombohedral-orthorhombic transition temperature.

Dehydration significantly lowers the transition temperature.

Bond length changes and vacancy ordering explain the observed effects.

Abstract

We present a systematic study of the effect of Y doping and hydration level on the structural transformations of BaCeO3 based on anelastic spectroscopy experiments. The temperature of the intermediate transformation between rhombohedral and orthorhombic Imma phases rises with increasing the molar fraction x of Y roughly as (500 K)x in the hydrated state, and is depressed of more than twice that amount after complete dehydration. This is explained in terms of the effect of doping on the average (Ce/Y)-O and Ba-O bond lengths, and of lattice relaxation from O vacancies. The different behavior of the transition to the lower temperature Pnma orthorhombic phase is tentatively explained in terms of progressive flattening of the effective shape of the OH ion and ordering of the O vacancies during cooling.