Thermal Expansion and Pressure-Temperature Phase Diagrams of Pb3(VO4)2 and Pb3(PO4)2 Crystals
1981 年 50 巻 5 号 p. 1592-1594
詳細
1981 年 50 巻 5 号 p. 1592-1594
The experimental results of dilatation and the temperature-pressure phase diagrams for Pb3(VO4)2 and Pb3(PO4)2 crystals are presented. The pressure coefficients of transition temperatures between the trigonal and the nonpolar monoclinic phases dT1⁄dp and between the nonpolar and polar monoclinic phases dT2⁄dp for Pb3(VO4)2 were −12.1 and 20.2 deg/kbar, respectively. The intermediate monoclinic phase II of Pb3(VO4)2 vanishes at a triple point of 3 kbar and 65°C. The dT1⁄dp for Pb3(PO4)2 was −9.8 deg/kbar, but no triple point was observed. The entropy change estimated for Pb3(VO4)2 on the basis of obtained data suggests that the transition mechanism in this crystal is likely to be of the order-disorder type.
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