Incorporation and Conduction of Protons in Ca, Sr, Ba-Doped BaLaInO ₄ with Ruddlesden-Popper Structure

Abstract

The new phases BaLa _0.9M _0.1InO _3.95 (M = Ca ²⁺, Sr ²⁺, Ba ²⁺) with a Ruddlesden-Popper structure were obtained. It was established that all investigated samples were capable for the water uptake from the gas phase. The ability of water incorporation was due to not only by the presence of oxygen vacancies, but also due to the presence of La-O blocks in the structure. The degree of hydration of the samples was much higher than the concentration of oxygen vacancies and the composition of the samples appear to be BaLaInO _3.42(OH) _1.16, BaLa _0.9Ca _0.1InO _3.25(OH) _1.4, BaLa _0.9Sr _0.1InO _3.03(OH) _1.84, BaLa _0.9Ba _0.1InO _2.9(OH) _2.1. The degree of hydration increased with an increase in the size of the dopant, i.e., with an increase in the size of the salt blocks. It was proven that doping led to the increase in the oxygen ionic conductivity. The conductivities for doped samples BaLa _0.9M _0.1InO _3.95 were higher than for undoped composition BaLaInO ₄ at ~1.5 order of magnitude. The increase in the conductivity was mainly attributed to the increase of the carrier concentration as a result of the formation of oxygen vacancies during doping. The proton conductivities of doped samples increased in the order Ca ²⁺–Sr ²⁺–Ba ²⁺ due to an increase in the concentration of protons. It was established that all doped samples demonstrated the dominant proton transport below 450 °C.