Crystal structure refinements of the κ phases in the Hf-Mo-Se and Hf-Mo-Ge systems

The crystal structures of κ-(Hf-Mo-Se) and κ-(Hf-Mo-Ge) were determined using X-ray single-crystal diffractometry. Both structures crystallize in the space groupP6₃/mmc (No. 194) with the unit-cell dimensionsa = 8.6995(4)A?,c = 8.6234(7)A? for κ-(Hf-Mo-Se) anda = 8.6394(4)A?,c = 8.6827(5)A? for κ-(Hf-Mo-Ge). The structures have been refined onF² toR(F²) values of 0.0784 and 0.0661, respectively. κ-(Hf-Mo-Se) and κ-(Hf-Mo-Ge) are isostructural with κ-(Hf-Mo-P) with a variable degree of hafnium substitution on the molybdenum sites of the structure. In κ-(Hf-Mo-Ge) germanium vacancies were found to occur on the trigonal prismatic 2c site and the phase was also found to contain oxygen on the octahedral 6g site. According to the final refinements the compositions are Hf_9+xMo_4?xSe withx = 0.40(2) and Hf_9+xMo_4?xGe_yO₂ withx = 0.25(2),y = 0.88(1), andz = 1.47(12).