New group V κ-phases

New κ-phases (P. Rautala and J.T. Norton, Trans. AIME, 194 (1952) 1045; A. Hårsta and S. Rundqvist, J. Solid State Chem., 70 (1987) 210) were discovered and crystallographically characterized in the Zr-Ta-S, Zr-Nb-S, Zr-V-S, Hf-Nb-S, and Hf-V-S systems. A κ-phase was also identified in the Hf-Ta-S system through Guinier powder diffraction. These compounds are the first examples of the κ-phase structure containing the Group V transition metals, Ta, Nb, and V. The Ta and Nb κ-phases exhibit the largest volumes (by about 13%) and the largest amounts of second row nonmetal per formula unit of the known κ-phases. X-ray single-crystal diffraction experiments were used to determine metal site occupancies in these κ-phases, and it was found that statistical mixing of the metals primarily on one site occurred for the Ta and Nb compounds. Refinements of the X-ray intensity data indicated that the octahedral nonmetal sites (denoted X2) are less than fully occupied by sulfur in the Ta and Nb κ-phases and less than fully occupied by oxygen in the V κ-phases. Combined neutron and X-ray powder refinements reliably determined that these nonmetal X2 sites are occupied by a mixture of sulfur, oxygen, and vacancies in the Zr-Nb-S and Zr-Ta-S κ-phases. The κ-phases in the Zr-Nb-S (G. Marking et al., Phys. Rev. B, 48 (1993) 16630) and Hf-Nb-S systems were found to be superconductors with T_cs of 10.35 K and between 6 and 7 K respectively.