Polymorphism of Li_2CuZrO_4

摘要

Lithium zirconate is one of the ceramics being investigated for tritium breeding blankets of future thermonuclear fusion reactors. Copper doped ceramic was studied in order to evaluate a possible enhancement of the release of tritium generated from the nuclear reaction between lithium and neutrons. The study of the pseudo-binary Li_2ZrO_3-CuO diagram evidenced the existence of a Li_2ZrO_3 type solid solution and of a new polymorph variety of Li_2CuZrO_4, denoted γ. The γ Li_2CuZrO_4 lattice is orthorhombic, a = 5.861 A (l), b = 5.892 A (l) and c = 9.410A (2), F_(23) = 22 (0.00851, 123). The β <=> γ transition, was studied by X-ray thermo-diffractometry, dilatometry, and differential thermal analysis. The new γ phase is stable at low temperature and reversibly transforms into the β phase at 550°C. The β phase can be easily preserved at room temperature by quenching. Structures of the γ orthorhombic and β tetragonal polymorphs were refined using X-ray diffraction data on powder (Rietveld method) and on single crystal, respectively.