PREPARATION, THERMAL CHARACTERIZATION AND X-RAY POWDER DIFFRACTION OF Ba2REF7 SUPERSTRUCTURE PHASES (RE EQUVLNT Dy-Lu, Y).

Article abstract of DOI:10.1016/0022-5088(80)90101-0

Thermal analyses on samples of the composition (Ba, RE)F//2//,//3//3 revealed seven new compounds Ba//2REF//7 (RE EQUVLNT Dy-Lu, Y). They are stable only above about 940 degree C but can be quenched after annealing for several days at 950-1000 degree C. These phases, which are metastable at room temperature, were characterized by X-ray powder diffraction. A tetragonal distortion of the fluorite parent structure was detected, analogous to that in the Ln//3F//7, Ca//2REF//7, and Sr//2REF//7 phases. In contrast, however, the superstructure is not fully pronounced and only tripling along the c axis is observed.