Solid-Phase Synthesis and Structural Features of Compound Cu₃NaS₂

Abstract―Compound Cu₃NaS₂ has been prepared by solid-phase reactions from copper and sodium sulfides Cu₂S and Na₂S. It has been shown that compound Cu₃NaS₂ has hexagonal structure with lattice parameters a = 13.9398 ± 23 Å and c = 21.4637 ± 74 Å. After 6 months after synthesis, compound Cu₃NaS₂ spontaneously transforms at ambient temperature from hexagonal structure into phase with face-centered cubic (FCC) lattice. The dimension of coherent-scattering regions (CSR) for the FCC phase determined from the broadening of diffraction lines varies from ~25 nm at ambient temperature to ~110 nm at 500°C. DSC curves show anomalies at temperatures of 108 and 436°C corresponding to endothermal reversible transitions without change in the type of crystal lattice. The authors consider these anomalies to be due to redistribution of copper and sodium cations over possible crystallographic positions.