HF5COAS3, THE FIRST HF RICH HAFNIUM COBALT ARSENIDE - INTERCALATION OF CO VS A CO AS EXCHANGE/

Hf5CoAs3 was prepared by are-melting of HfAs, Hf and Co. This new arse nide crystallizes in the orthorhombic space group Pnma with cell dimen sions of a=17.327(5)Angstrom, b=3.685(4)Angstrom, c=10.370(4)Angstrom, V=662(1)Angstrom(3). Its crystal structure is isostructural to the st ructure of Hf5CoP3. The Co and As atoms both are located in trigonal p rismatic voids of the Hf substructure. The Hf atoms form double channe ls, each of which is filled with an infinite -Co-As-zigzag chain. Thes e double channels are interconnected via bonding Hf-Hf interactions to form the three-dimensional Hf substructure. Since adding more Co occu rs with significantly enlarged cell dimensions, it is concluded that t he additional Co atoms are included in the structure of Hf5CoAs3, as N i is in case of Hf5Ni1+xP3. The densities of states obtained by Extend ed Huckel calculations and the Pauli paramagnetism experimentally obta ined point to metallic behavior of Hf5CoAs3. (C) 1998 Elsevier Science S.A.