$\beta \mathrm{-}\mathrm{HfCuGe}\mathrm{—}\mathrm{A}$ new polymorph of HfCuGe with a novel structure type

Abstract

The structure and elementary physical properties of a new intermetallic compound, $\beta \mathrm{-}\mathrm{HfCuGe}$, are reported. $\beta \mathrm{-}\mathrm{HfCuGe}$ has a tetragonal structure (space group I4/mmm) with lattice constants of a=3.7634(11)Å and c=13.499(4) Å. The structure, which consists of double layers of Hf stacked with edge-sharing CuGe₄ squares, is not typical for intermetallic compounds and appears to be a new structure type. The compound is a weak paramagnet and a normal metal down to 0.4 K.

Introduction

There are four previously reported compounds in the Hf–Cu–Ge ternary system. The 1:1:1 compound HfCuGe crystallizes in the TiNiSi structure type (space group Pnma) [1], Hf₂CuGe₄ crystallizes in space group Cmcm [2], Cu₄Hf₃Ge₂ crystallizes in the Fe₂P structure type with the space group $\mathrm{P}\overline{6}2\mathrm{m}$ [3] and HfCuGe₂ crystallizes in space group P4/nmm [4]. Among these, HfCuGe₂ is a layered compound with alternating layers of Hf–Ge–Cu₂–Ge–Hf–Ge₂. Hf₂CuGe₄ also consists of layers but with a different stacking order. Fe₂P-type Cu₄Hf₃Ge₂ consists of alternating Cu–Ge and Cu–Hf layers. In none of these compounds are two layers of the same element adjacent. In the previously reported form of HfCuGe, which has the TiNiSi structure type, the layers include all three atom types. To the best of the authors’ knowledge the properties of those phases have not yet been reported.

Here we report the crystal structure and properties of a new phase in the Hf–Cu–Ge ternary system with the composition 1:1:1. This polymorph of HfCuGe crystallizes in a new structure type that is quite different from the known Hf–Cu–Ge compounds. The layers consist of edge sharing CuGe₄ squares alternating with two Hf metal layers; both structural components are unusual for ternary intermetallic compounds.