Effect of phonon anharmonicity on ferroelectricity in EuxBa1−xTiO3

Abstract

Investigating the competition between ferroelectric ordering and quantum fluctuations is essential to tailor the desired functionalities of mixed ferroelectric and incipient ferroelectric systems, like, (Ba,Sr)TiO3 and (Eu,Ba)TiO3. Recently, it has been shown that suppression of quantum fluctuations increases ferroelectric ordering in (Eu,Ba)TiO3 and since these phenomena are coupled to crystallographic phase transitions it is essential to understand the role of phonons. Here, we observe that the unusual temperature dependence of phonons in BaTiO3 gets suppressed when Ba2+ is replaced by Eu2+. This manifests in a decrease in the cubic-to-tetragonal (i.e., para-to-ferroelectric) phase transition temperature (by 150 K) and a complete suppression of tetragonality of the lattice (at room temperature by 40% replacement of Ba2+ by Eu2+). We have quantified the anharmonicity of the phonons and observed that the replacement of Ba2+ by Eu2+ suppresses it (by 93%) with a resultant lowering of the ferroelectric ordering temperature in the EuxBa1-xTiO3. This suggests that tuning phonon anharmonicity can be an important route to novel ferroelectric materials.