Large structural heterogeneity in submicrometer BaTiO3 revealed via Eu⁺³ photoluminescence study

Abstract

Apart from being a model ferroelectric, BaTiO3 and its derivatives are materials of considerable technological importance in the capacitor industry and as a potential Pb-free piezoelectric. Here, we have examined BaTiO3 for its propensity to stabilize local low symmetry distortions and induce structural heterogeneity for two different situations, namely, (1) by introducing inhomogeneous lattice strain and (2) by restricting the average grain size to the submicrometer regime. We have introduced Eu⁺³ ions in BaTiO3 in a very dilute concentration to act as local probes. Our strategy relies on exploiting the great sensitivity of the 5D0 → 7F2 transition of Eu⁺³ with regard to the variation in the asymmetric distribution of the ligand field around itself to probe the structural heterogeneity developed in BaTiO3. The Eu⁺³ photoluminescence signal revealed a remarkable increase in the local structural heterogeneity in submicrometer (∼0.4 μm) sized BaTiO3. This manifests as an ∼170% increase in the intensity of the 7F2 band with respect to the structure insensitive 7F1 band. Although to a lesser extent, a similar scenario was observed when the large grain BaTiO3 develops residual strain. The structural insights presented here can be helpful in explaining the properties of BaTiO3-based multilayered ceramics wherein the two conditions of submicrometer size and residual strain is a common occurrence.