Influence of hydration and dopant ionic radius on the elastic properties of BaZrO3

The influence of point defects (acceptor dopants, oxygen vacancies, protonic defects) on the macroscopic elastic properties of acceptor-doped BaZrO3 ceramics is investigated. Ultrasonic pulsed echo time of flight measurements are used to study the impact of dopant size, concentration and degree of hydration. Ceramics of BaXxZr1-xO3-x/2+δH2δ with X = Y, Sc and 0.05 ≤ x ≤ 0.2 were prepared by solid state reactive sintering with NiO sintering aid, added to achieve mechanical robustness sufficient for high-degree (58–71%) hydration without disintegration. Introduction of the dopants causes linear decrease in the Young's and shear moduli. By comparing the rate of decrease upon doping with Y3+ and Sc3+, the contribution of the lattice expansion was separated from the contribution of vacancy formation. Dissociative water incorporation also decreases the elastic moduli, however, for the case of Sc-doping the effect of hydration on the elastic moduli is much larger. All experimental data agree well with predictions by ab initio calculations.