Intrinsic Reasons for Variations in Dielectric Properties of Ba6-3xR8+2xTi18O54(R=LA–Gd) Solid Solutions

TLDR: In this article, the temperature coefficient of permittivity of Ba6-3xR8+2xTi18O54 (R=La-Gd) solid solutions revealed a high degree of correlation with the ratio of mean radii (rA/rB) of A- and B-site ions.

Abstract: Studies of the temperature coefficient of permittivity of Ba6-3xR8+2xTi18O54 (R=La–Gd) solid solutions revealed a high degree of correlation with the ratio of mean radii (rA/rB) of A- and B-site ions. Single-crystal X-ray diffraction analyses of La, Sm and Pr analogues showed that rA/rB can be further correlated to tilting of the TiO6 octahedra in the network of the Ba6-3xR8+2xTi18O54 crystal structure. Changes in the tilting of the octahedra induce changes in the crystal field and subsequently, changes in the temperature coefficient of permittivity as well as dielectric loss. Variations in dielectric properties are limited by the flexibility of the crystal structure. Variations in the tilting of the octahedra resulting from changes in the composition are highly anisotropic, which explains the markedly high electrical anisotropy of Ba6-3xR8+2xTi18O54 solid solutions.