Synthesis and structural characterization of CuAl2O4 spinel with an unusual cation distribution

Abstract

A CuAl₂O₄ spinel with unusual cation distribution has been synthesized for the first time by the solid phase reaction of copper hydroxide and pseudo-boehmite with both stoichiometric (Cu/Al = 1/2) and non-stoichiometric (Cu/Al = 1/3) ratios. Instead of characterizing one cation for the determination of cations distribution as generally performed in previous literatures, both cations in the synthesized spinel have been characterized with ²⁷Al NMR for Al ions and EXAFS for Cu ions, respectively. The characterization data reveal that nearly all Al³⁺ ions are octahedrally coordinated while most Cu²⁺ occupy the tetrahedral sites, giving a (Cu_0.8)[Cu_0.2Al₂]O₄ spinel which has been supported by the Rietveld refinement. The unusual cation distribution, which has been rarely reported before, presents abnormal site occupancies in Cu-Al spinel oxide. Hence, the findings of this work may invoke further explorations on other spinel oxides for targeting novel distinctive properties and applications.