Structure and microwave dielectric properties of BaLa4Ti 4O15

BaLa₄Ti₄O₁₅ (BLT) is a compound with a Ti-deficient, layered perovskite-related structure. Dense BLT ceramics have been produced and their crystal structures and microstructures are investigated. The average macroscopic structure of BLT powder is considered to be hexagonal with space group, but there is some evidence in high-order x-ray diffraction peaks of asymmetry. Energy-dispersive x-ray analysis and Raman spectroscopy have illustrated that there is a heterogeneous distribution of constituent cations which may induce asymmetry as a result of the presence of two hexagonal phases of slightly different lattice parameter. Despite this inhomogeneity, BLT exhibits a microwave quality factor (Qf) of ∼44000 GHz, a relative permittivity (ε_r) of ∼45, and a temperature coefficient of resonant frequency (τ_f) of -2 ppm °C^-1. In addition, anisotropy in the properties of the ceramic has been observed, with ε_r found to be larger when measured normal to the pressing direction.