X-Ray Investigations and Determination of the Dielectric Properties of the Compound Ba_<4.5>Gd_9Ti_<18>O_<54>

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The composition of the Gd variant of the Ba_<6-x>R_<8+2/3x>Ti_<18>O_<54> 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_<4.5>Gd_9Ti_<18>O_<54>, 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_<4.5>Gd_9Ti_<18>O_<54> starts to decompose at a temperature around 1350℃. It decomposes into a Gd_2Ti_2O_7, BaTi_2O_5, solid solution with Gd_2O_3, and probably Ba_4Ti_<13>O_<30>). However, during slowly cooling metastable BaTi_2O_5(ss) also decomposes into Ba_6Ti_<17>O_<40> and BaTiO_3 solid solution with Gd_2O_3. Single phase Ba_<4.5>Gd_9Ti_<18>O_<54> 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.
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1996-01-15