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 diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and differential thermal analysis (DTA) methods. It is found that in addition to the crystallization of primary PbMoO₄ phase, subphases such as Pb₂MoO₅ and PbMo₂O₇ are also formed. The remaining PbO and MoO₃ are detected at certain stages of the thermal process due to localized powder inhomogeneity. Physical processes, such as sublimation, eutectic melting, solid to liquid, and liquid to vapor transformations are also investigated. In particular, evaporations of excessive PbO or MoO₃ in the nonstoichiometric PbO/MoO₃ can be correlated to thermal processing parameters. The current study has led to the following three processing guidelines to obtain stoichiometric PbMoO₄: (i) for high temperature application, 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–MoO₃ can be used, but with a fast heating rate; and (iii) PbO-rich PbO/MoO₃ system is not recommended in PbMoO₄ synthesis.