Intrinsic reasons for variations in dielectric properties of Ba6-3x R8+2x Ti18O54(R = La-Gd) solid solutions

Studies Of the temperature coefficient of permittivity of Ba6-3xR8+2xTi18O5 4 (R = La-Gd) solid solutions revealed a high degree of correlation with th e ratio of mean radii (gamma(A)/r(B)) Of A- and B-site ions. Single-crystal X-ray diffraction analyses of La, Sm and Pr analogues showed that r(A)/r(B ) can be further correlated to tilting of the TiO6 octahedra in the network of the Ba8-3xR8+2xTi18O54 crystal structure. Changes in the rating of the octahedra induce changes in the crystal field and subsequently, changes in the temperature coefficient of permittivity as well as dielectric loss. Var iations in dielectric properties are limited by the flexibility of the crys tal structure. Variations in the tilting of the octahedra resulting from ch anges in the composition are highly anisotropic, which explains the markedl y high electrical anisotropy of Ba6-3xR8+2xTi18O54 solid solutions.