Single crystal growth in series of layered oxyselenide Sr₂MCu₂Se₂O₂ (M = Co, Ni) by melt-solidification method

Single crystals of layered oxychalcogenide Sr₂MCu₂Se₂O₂ (M = Co, Ni) have been successfully grown by the melt-solidification method. Thermal analysis and X-ray diffraction measurement results revealed that these compounds are congruent melting under a sealed environment similar to Sr₂ZnCu₂Se₂O₂, while melting points are slightly different. The plate-like single crystals on the order of mm² were obtained by melt solidification. The anisotropy of resistivity in Sr₂CoCu₂Se₂O₂ showed that the resistivity in the c-axis direction was about 200 times higher than in the a(b)-axis direction, reflecting the two-dimensional crystal structure. These results indicate that there are several congruent melting layered mixed-anion compounds, even though they have complex crystal structures with multiple components. Thus, the single crystal growth method by melt-solidification under a sealed environment has the potential to be applied to other relative compounds.