Synthesis, crystal structure, and thermal stability of new borates Na3REB2O6 (RE = Pr, Sm, Eu)

Subsolidus phase equilibrium of Na2O–Sm2O3–B2O3 system has been investigated mainly by solid-state reaction and powder X-ray diffraction method. There are nine definite three-phase regions and three ternary compounds determined under present experimental conditions. A novel compound Na3SmB2O6 was found and confirmed in this system, along with its two homogeneous compounds Na3REB2O6 (RE = Pr, Eu) synthesized for the first time. The indexing results showed that all three compounds crystallize in the monoclinic space group P21/c (No.14) with the same structure type as both Na3NdB2O6 and Na3GdB2O6. The lattice parameters (a, b, and c) of new borates Na3REB2O6 (RE = Pr, Sm, Eu) decrease linearly with a decreasing radius of RE ion, which obeys the Lanthanide-contraction rule. The existence of a trigonal BO3 group in the Na3REB2O6 (RE = Pr, Sm) compounds was confirmed by analysis of their infrared absorption spectra. Thermal stabilities of the three new borates have been investigated.

Equilibrium phase diagrams for the systems PbO–SrO–CuO and PbO–CaO–SrO

In order to obtain essential information on the formation process of the high-Tc phase in the Bi, Pb–Sr–Ca–Cu–O system, subsolidus phase equilibrium in the systems PbO(PbO2)–SrO–CuO and PbO(PbO2)–CaO–SrO has been studied, mainly by XRD analysis. A pseudoternary Pb–Sr–Cu–O solid solution was newly found. This solid solution has a wide solubility range including its typical composition Pb2.03Sr3Cu0.73O7.70. It has a hexagonal structure with lattice parameters a = 10.11 and c = 7.11 in AU. Composition dependences of the lattice parameters and the decomposition (incongruent melting) temperature of (Ca1−xSrx)2PbO4 solid solution are also reported.

Equilibrium phase diagram for the system PbO-CaO-CuO

In order to obtain essential information on the formation process of the high-Tc phase in the Bi, Pb-Sr-Ca-Cu-O system, phase equilibria in the system PbO-CaO-CuO have been studied, mainly by x-ray diffraction analysis and thermal analysis. Temperature versus composition diagrams were established for the systems PbO-CuO(Cu2O) and PbO(PbO2)–CaO in air. Three invariant points were detected in these systems: a eutectic reaction (PbO + Ca2PbO4 = L) at 847 ± 6°C, a peritectic reaction (Ca2PbO4 = L + CaO) at 980 ± 2°C, and a eutectic reaction (PbO + CuO = L) at 789 ± 3°C. For the system PbO(PbO2)-CaO-CuO, subsolidus phase equilibrium in air was established. The liquidus was also examined at 780, 800, and 820°C, and a ternary (PbO-Ca2PbO4-CuO) eutectic point was detected at 772 ± 6°C.

Subsolidus solubility between : a hydrothermal investigation

SummaryThe subsolidus phase equilibrium of the lithiophilite-tephroite system was studied in the temperature range 500 to 900° C. The solubility of tephroite in lithiophilite is limited and increases with temperature. The reaction is very sluggish and has peculiar kinetic properties. No reverse solubility was observed. Similar asymmetry was found in the LiMgPO4-forsterite system of which a preliminary study was made. Apparent absences of silicate phosphate olivine solid solutions in nature are related to our experimental findings and to geological factors.