Crystallization of BaTiO, from an X-ray amorphous, metal organic precursor was investigated by comparing samples heated in O,, air, argon, and CO,. It is evident that an intermediate barium titanium oxycarbonate phase forms between 500" and 620°C and that BaTiO, forms directly by the endothermic decomposition of this phase between 635" and 700°C. From thermodynamic calculations, thermal analysis, X-ray diffraction, and Raman spectroscopy, it is concluded that the intermediate oxycarbonate is a highly disordered, metastable, and weakly crystalline phase with a stoichiometry close to Ba,Ti,O,CO,.

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In as-sintered silicon nitride with yttria as a sintering aid, the intergranular glassy phase contains Y, Si, O, and N. Results of crystallization of partly crystalline, as-quenched melt samples containing 28–40 mol% Y2O3 in the Y2O3–SiO2 system are presented. Three different compositions were melted in tungsten crucibles at 2100 °C in 1 and 50 atm nitrogen and heat treated in air in the temperature range of 1200 to 1600 °C. Phase identification by x-ray diffraction (XRD) and transmission electron microscopy (TEM) showed crystallization to β, γ, and δ polymorphs of Y2Si2O7.