Investigating the composition-microstructure-property relationship in two dimensions in a new class of compositionally complex solid electrolytes

This study investigates the synergistic composition-microstructure-property relationships in a new class of compositionally complex perovskite oxides (CCPOs) as Li-conductive solid electrolytes. A matrix of compounds with formula (Li0.375Sr0.4375)(Ta0.75(1-y)Nb0.75yZr0.25(1-z)Hf0.25z)O3-δ (y, z = 0, 0.5, or 1) are synthesized and characterized. Correlations among composition, structural distortion, microstructure, interfaces, and ionic conductivity are systematically investigated. It is found that Nb5+ substitution in B sites promotes densification and grain growth, while Hf4+ addition expands crystal lattice, which boost interface and bulk ionic transport, respectively. Notably, (Li0.375Sr0.4375)(Ta0.375Nb0.375Hf0.25)O3-δ achieves an improved ionic conductivity of ~0.336 mS/cm, occurring concurrently with a large BO6 distortion that enhances bulk ionic conduction and a large grain size that reduces the total grain boundary resistivity. This work represents the first in-depth experimental investigation of the composition-microstructure-property relationship of compositionally complex ceramics (CCCs) in two compositional dimensions, and it exemplifies a pathway to tailor properties in multiple compositional dimensions.