PROCEEDINGS OF THE SHEVCHENKO SCIENTIFIC SOCIETY

Chemical Sciences

Архів / Том LIII 2018

Olga ZHAK

Ivan Franko National University of Lviv, Kyryla and Mefodia Str., 6, 79005 Lviv, Ukraine

DOI: https://doi.org/10.37827/ntsh.chem.2018.53.024

CRYSTAL STRUCTURE OF THE ARSENIDE HfNiAs

Crystal structure of the earlier known ternary arsenide with equimolar composition HfNiAs was refined by X-ray powder diffraction method and atomic positional parameters were determined: space group Pnma, TiNiSi-type structure, lattice parameters а = 0.64000(6) nm, b = 0.38050(3) nm, с = 0.73378(6) nm, residual values are RI = 0.0428, RP = 0.0413, RwP = 0.0554. Starting materials for the samples preparation were powders of hafnium, nickel, and grey arsenic, all with the stated purity not less than 99.95 mass %. Mixtures of the constituents in the stoichiometric ratio were pressed into pellets. The pellets were placed within evacuated fused silica tubes which were slowly heated to 1070 K (200 K per day), kept at this temperature over 100 h, and then cooled to room temperature by shutting off the furnace. The sintered samples were melted in arc furnace, then sealed again in evacuated silica tubes, annealed at 1070 K during 1000–1200 h, and quenched in cold water without breaking the tubes. All samples have been studied by X-ray phase and structural analysis using DRON-3M diffractometer (CuKα-radiation). For all calculations the WinCSD software has been used. Crystal structure of the ternary arsenide HfNiAs was found to be isotypic with the TiNiSi type, fully ordered ternary derivative of the orthorhombic Co2Si (or anti-PbCl2) binary structure. In the structure of the HfNiAs compound all atoms are ordered in the three Wyckoff sites 4c (x ¼ z) of the space group Pnma. Arsenic atoms have trigonal-prismatic coordination in the HfNiAs structure. It should be mentioned, that trigonal prisms formed by only atoms of metals are the most common type of coordination of arsenic and phosphorus atoms in the crystal structures of the intermetallic compounds. Interatomic distances in the structure of the arsenide HfNiAs are nearly the same as the respective sum of the atomic radii of the pure components. Distances reducing being observed between atoms of metals and arsenic dNi–As = 0.2402(7) nm, and dHf–As = 0.2707(7) nm are less than 2.5 % of the respective sum of the atomic radii values, so can indicate predominantly metallic type of bonding between metals and arsenic atoms. Peculiarities of the HfNiAs structure and TiNiSi type structure as derivative of the Co2Si-type have been discussed.

Key words: crystal structure, transition metal, hafnium, nickel, arsenide.

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How to Cite

Zhak O. CRYSTAL STRUCTURE OF THE ARSENIDE HfNiAs Proc. Shevchenko Sci. Soc. Chem. Sci. 2018 Vol. LIII. P. 24-30.

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