New Representatives of the NbAs₂ and ZrAs₂ Structures

Abstract

THE monoclinic unit cell and the space group of NbAs₂ and isomorphous TaAs₂ have recently been determined by Saini et al.¹. In the course of an examination of transition-element polycompounds I observed this structure also in VP₂, VAs₂, NbP₂, TaP₂, MoAs₂, α-WP₂ (low-temperature modification) and WAs₂. The titanium-group phosphides TiP₂, ZrP₂ and HfP₂, on the other hand, were found to be isostructural with the orthorhombic ZrAs₂ (ref. 2) and HfAs₂ (ref. 3). This structure is referred to as PbCl₂ (C23) type. However, in these titanium-group pnictides anion–anion bonds seem to be important so that I prefer to distinguish this variety from the ionic PbCl₂ type by using a different name. The lattice constants, as derived from powder patterns, are listed in Table 1.