Atomic Ordering of Two Neighboring Transition Metals-Cu and Zn from Binary CuZn to Ternary CuZnSb.

A new ternary compound CuZnSb was synthesized by high temperature solid state synthesis and characterized by single crystal X-ray diffraction and energy dispersive X-ray analysis. The ternary CuZnSb crystallizes in the tetragonal crystal system with the space group P4/ nmm (129), and its unit cell contains 10 atoms which are distributed over 4 independent crystallographic positions. The structure is built up with [CuSb] slabs that correspond to the unit cells of CuSb and planar 4 nets of Zn atoms. The planar nets of Zn atoms are interspersed between two adjacent [CuSb] slabs. The structure can be viewed as alternating units of CuSb and CsCl type β'-brass (CuZn) structures in the [001]. An unusual atomic ordering of two neighboring transition metals Cu and Zn is observed and is confirmed by first principle calculations. The atomic ordering of Cu and Zn is retained from binary β'-brass structure (CuZn) to ternary CuZnSb. Total energy calculations confirmed the experimental model of Cu/Zn ordering to be the most stable in the structure of CuZnSb. The calculated density of states (DOS) and crystal orbital Hamiltonian population (COHP) explain the stability and bonding characteristics in the structure of CuZnSb. The implication of the persistent Cu/Zn ordering in ternary phases for materials design is emphasized.