New group V κ-phases

Abstract

New κ-phases (P. Rautala and J.T. Norton, Trans. AIME, 194 (1952) 1045; A. Harsta 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 Nh 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 2s of 10.35 K and between 6 and 7 K respectively.