Crystal growth and thermodynamic investigation of Bi2M2+O4 (M = Pd, Cu)

Abstract

Phase equilibria that are relevant for the growth of Bi₂MO₄ have been studied experimentally, and the ternary phase diagrams of Bi₂O₃–PdO₂–Pd and Bi₂O₃–Cu₂O–CuO and its isopleth section Bi₂O₃–CuO were redetermined. It is shown that every melting and crystallization process is always accompanied by a redox process at the phase boundary and that for both title compounds, the valence of the transition metal is lowered during melting. Vice versa, during crystal growth, O₂ must be transported through the melt to the phase boundary. Based on these new insights provided by our thermodynamic studies, Bi₂CuO₄ single crystals with a length of up to 7 cm and a diameter of 6 mm were grown by the OFZ technique to be used for investigations of magnetic, electronic and thermal transport properties. The grown crystals were characterized by powder X-ray diffraction, Laue, magnetization and specific heat measurements.