SYNTHESIS OF STOICHIOMETRIC LEAD MOLYBDATE PBMOO4 - AN X-RAY-DIFFRACTION, FOURIER-TRANSFORM INFRARED-SPECTROSCOPY, AND DIFFERENTIAL THERMAL-ANALYSIS STUDY

The PbO/MoO3 system with 47%:53%, 53%:47%, and 50%:50% molar ratios at various processing temperatures has been studied with x-ray diffracti on (XRD), Fourier transform infrared spectroscopy (FTIR), and differen tial thermal analysis (DTA) methods. It is found that in addition to t he crystallization of primary PbMoO4 phase, subphases such as Pb2MoO5 and PbMo2O7 are also formed. The remaining PbO and MoO3 are detected a t certain stages of the thermal process due to localized powder inhomo geneity. Physical processes, such as sublimation, eutectic melting, so lid to liquid, and liquid to vapor transformations are also investigat ed. In particular, evaporations of excessive PbO or MoO3 in the nonsto ichiometric PbO/MoO3 can be correlated to thermal processing parameter s. The current study has led to the following three processing guideli nes to obtain stoichiometric PbMoO4: (i) for high temperature applicat ion, such as the Czochralski melt growth, it is suggested an excessive MoO3 (a few mol%) must be included and a slow heating rate should be employed; (ii) for low temperature synthesis, the stoichiometric PbO-M oO3 can be used, but with a fast heating rate; and (iii) PbO-rich PbO/ MoO3 system is not recommended in PbMoO4 synthesis.