X-Ray Investigations and Determination of the Dielectric Properties of the Compound Ba_4.5Gd₉Ti₁₈O₅₄

The composition of the Gd variant of the Ba_6-xR_8+2/3xTi₁₈O₅₄ family of solid solutions ( R=rare earth) was determined by investigating its high temperature phase relations and by wavelength-dispersion spectroscopic analysis. The composition of the compound was determined to be Ba_4.5Gd₉Ti₁₈O₅₄, which corresponds to x=1.5 without a detectable solid solubility range. The intensities of the diffraction lines are not in accordance with published values in the powder diffraction file (No. 43–233). An investigation of the thermal stability revealed that Ba_4.5Gd₉Ti₁₈O₅₄ starts to decompose at a temperature around 1350° C. It decomposes into a Gd₂Ti₂O₇, BaTi₂O₅ solid solution with Gd₂O₃, and probably Ba₄Ti₁₃O₃₀. However, during slowly cooling metastable BaTi₂O₅(ss) also decomposes into Ba₆Ti₁₇O₄₀ and BaTiO₃ solid solution with Gd₂O₃. Single phase Ba_4.5Gd₉Ti₁₈O₅₄ ceramics displayed a dielectric constant (ε _r) of 76.1, a Qxf-value of 2050 and a temperature coefficient of the resonant frequency (τ _f) of -35 ppm/K.