X-RAY-INVESTIGATIONS AND DETERMINATION OF THE DIELECTRIC-PROPERTIES OF THE COMPOUND BA4.5GD9TI18O54

The composition of the Gd variant of the Ba(6-x)R(8+2/3x)Ti(18)O(54) f amily of solid solutions (R = rare earth) was determined by investigat ing its high temperature phase relations and by wavelength-dispersion spectroscopic analysis. The composition of the compound was determined to be Ba4.5Gd9Ti18O54, which corresponds to x = 1.5 without a detecta ble solid solubility range. The intensities of the diffraction lines a re not in accordance with published values in the powder diffraction f ile (No. 43-233). An investigation of the thermal stability revealed t hat Ba4.5Gd9Ti18O54 starts to decompose at a temperature around 1350 d egrees C. It decomposes into a Gd2Ti2O7, BaTi2O5 solid solution with G d2O3, and probably Ba4Ti13O30. However, during slowly cooling metastab le BaTi2O5(ss) also decomposes into Ba6Ti17O40 and BaTiO3 solid soluti on with Gd2O3. Single phase Ba4.5Gd9Ti18O54 ceramics displayed a diele ctric constant (epsilon(r)) of 76.1, a Qxf-value of 2050 and a tempera ture coefficient of the resonant frequency (tau(f)) of -35 ppm/K.