Phase equilibria in the ternary reciprocal system Li, Ba // BO2, F and growth of bulk β-BaB2O4 crystals

In order to find the optimum solvent for the growth of nonlinear optical β-BaB2O4 crystals, the phase relationships in the ternary reciprocal system Li, Ba // BO2, F have been studied using solid state synthesis, differential thermal analysis and X-ray powder diffraction. Isothermal and polythermal sections of the system Li, Ba // BO2, F are reported. In the studied system, the following compounds are formed: LiBa2B5O10 (melts by peritectic reaction at 930°C, i.e. 1203 K) and LiBaF3 (melts incongruently at 850°C, i.e. 1123 K). Visual polythermal analysis of seeding and growth of β-BaB2O4 crystals in this system was carried out. The primary crystallization field of β-BaB2O4 was defined. Using the top-seeded pulling technique, a β-BaB2O4 crystal of 93 mm in diameter, 34 mm in height and 520 g in weight has been grown.

Effect of Ag on the primary phase field of the high-Tc (Bi,Pb)-2223 superconductor

The subsolidus equilibria and the primary phase field (crystallization field) of the 110 K high-Tc (Bi,Pb)-2223 ([Bi,Pb]:Sr:Ca:Cu) phase have been determined in the presence of Ag under a 92.5% Ar/7.5% O2 atmosphere (volume fraction). A total of 29 six-phase volumes that include both the (Bi,Pb)-2223 and Ag phases was observed. These subsolidus volumes are similar to those observed without the presence of Ag. The compositional range of initial melts of these volumes (mole fraction basis) covers BiO1.5 from 5.6% to 25.3%, PbO from 0.4% to 13.8%, SrO from 8.4% to 31.9%, CaO from 12.2% to 33.3%, CuO from 21.7% to 40.9%, and AgO0.5 from 1.2% to 6.3%. Based on these data, the primary crystallization field for the (Bi,Pb)-2223 phase in the presence of Ag was constructed using the convex hull technique. A section through this “volume” was portrayed by holding the AgO0.5, SrO, and CaO components at the median value of the 29 compositions while allowing projection on the other three axes (BiO1.5, PbO, and CuO). The net effect of Ag on the melt composition is a reduction in the PbO concentration and an increase in the SrO content. Applications of the liquidus data are also discussed.

X-Ray Characterization of Phase Equilibria of the Raveau and 2212 Phases in the Bi-Sr-Ca-Cu-0 System

Phase equilibria of two superconductor phases, namely the 20K Raveau phase (Bi2.2-xSr1.8+xCuOz, currently referred to as the 11905 phase) and the 80K 2212 phase of the Bi-Sr-Ca-Cu-0 system were investigated. The amount of Ca-substitution of the Raveau solid solution was determined and the solid solution region can be approximately described as Bi2.2+xSr1.8-X-Y CayCu1±x/2Ow (referred to as the Ca-Raveau phase or the 119x5, ‘ with 0<x<0.15, 0<y<0.5. To determine the melting equilibria of the 2212 phase, a procedure involving the use of a wicking technique to capture the melt was applied. X-ray powder diffraction (XPD) and quantitative energy dispersive x-ray spectroscopy (EDS) were used to analyse the phases present in the residual and melt, respectively. The approximate primary crystallization field of the incongruently melting 2212 phase was illustrated.