Single Crystal Growth of Tl₂Ba₂CaCu₂O₈ and Tl₂Ba₂Ca₂Cu₃O₁₀ and Low Temperature X-ray Single Crystal Experiment of Tl₂Ba₂Ca₂Cu₃O₁₀

Abstract

Large, thick single crystals of Tl₂Ba₂CaCu₂O₈ and Tl₂Ba₂CaCu₃O₁₀ have been successfully grown using a self-flux method in the BaO-CaO-CuO system. The former crystals are grown by a heating and cooling cycle from a mixture of raw reagents and the latter are obtained from a mixture of the flux and Tl₂Ba₂CaCu₃O₁₀ powder in both systems. It is formed that well-developed single crystals with polyhedral habits can be grown under coexisting condition of liquid and solid. X-ray single crystal experiment of Tl₂Ba₂CaCu₃O₁₀ (Tc=117K) has been carried out at 290, 130, 120, 115 and 90K using a four-circle diffractometer with a blowing system of cold N₂ gas. In the CuO₅ square-pyramid, the distance from copper to apical oxygen and the coordination volume abruptly increase at the superconducting critical temperature. The refined site-occupancies and crystallochemical requirement result in the chemical formula of this crystal being Tl³⁺_1.806Ba²⁺₂(Ca²⁺_0.848Tl³⁺_0.152)₂Cu²⁺₂(Cu²⁺_0.722Cu³⁺_0.278)O²⁻₁₀.