Physical and physicochemical processes accompanying powder synthesis, growth of PbMoO4 crystals, and their annealing in various media:: I.: Solid-state mechanism of the formation of the Pb2,MoO5 microheterogeneous phase in PbMoO4 crystals

In this study, the first of the proposed cycle, the conditions and the mechanism of nucleation and formation of particles of the Pb2MoO5 phase in PbMoO4 crystals, which are due to the physicochemical features of the heating, melting, and solidification of PbMoO4, are considered. It is shown that preferred evaporation of one of the composite components of this compound, MoO3, leads to the violation of the initial stoichiometry and formation of excess PbO in a charge at the synthesis stage and in a melt during the crystal growth. The formation of the Pb2MoO(5) phase in crystals with excess PbO occurs during their postgrowth cooling at temperatures below 930 degrees C (eutectics between PbMoO4 and Pb2MoO5). The results of the differential thermal analysis, X-ray diffraction analysis, high-temperature powder diffraction study, and annealing of crystals in specific media confirm the solid-state mechanism of the formation of the Pb2MoO5 phase in PbMoO4 crystals. (c) 2005 Pleiades Publishing, Inc.