Synthesis, crystal structures, phase width and electrochemical performances of γ-brass type phases in Cu–Zn–Sn system

Abstract

Cu–Zn–Sn ternary phases were synthesized by high-temperature solid-state synthesis. Structural characterization was performed by means of X-ray diffraction and energy dispersive X-ray analysis. The ternary compounds were found to adopt γ-brass (Cu5Zn8) structure type. X-ray diffraction analyses show that γ-brass type phases in Cu–Zn–Sn system crystallize in P4¯3m space group (cP52, 215). Ternary Cu–Zn–Sn γ-brass type phases exist in an extended homogeneity range. The phase-pure ternary compounds are found to exist for compositions ranging between 48 and 70 atomic % Cu, between 15 and 46 atomic % Zn, and between 5 and 15 atomic % Sn. The phase width arises due to the statistical distribution of constituent elements, which is typical for intermetallic compounds. The Cu–Zn–Sn γ-brass structures consist of two compositionally different γ-clusters (consists of the four polyhedral shells: inner tetrahedron (IT), outer tetrahedron (OT), octahedron (OH), cuboctahedron (CO)) centered at high symmetric sites in a primitive cubic unit cell. The γ-brass cluster (A) at (0,0,0) site is Cu-rich, chemically more ordered than the cluster (B) present at (½,½,½). For A cluster, only IT site is mixed (Zn/Sn) and OT, OH, CO sites are exclusively occupied by Cu, throughout the entire homogeneity range. The B cluster is heavily disordered; only the OT site is exclusively occupied by Cu all over the phase region. For Zn rich region IT site is fully occupied by Zn, then mixed occupied between Cu and Zn at intermediate Zn-concentration, and completely occupied by Cu at Cu-rich side of the Cu–Zn–Sn phases. OH site is fully occupied by Zn at Zn rich side. The same site is mixed occupied between Cu, Zn and Sn for the composition at intermediate Zn-concentration and Cu/Sn at Zn poor side. CO site of B cluster is occupied by Zn and Sn. The electrochemical properties of four Cu–Zn–Sn based samples with different compositions were studied as an anode material for lithium and sodium-ion storage using galvanostatic charge-discharge cycles. Li-ion half-cells transpired excellent retention of charge capacity (>80%) with more than 99% Coulombic efficiency. The results further encourage the prospects of ternary Cu–Zn–Sn alloy anodes to utilize in real energy storage applications.