Cu2O behavior under pressure: an ab initio study

Abstract

We have performed density-functional theory calculations for three crystallographic phases (cuprite,CdI2, andCdCl2) of the cuprous oxide by using both the local-density approximation (LDA) and thePerdew–Burke–Ernzerhof generalized-gradient approximation. The latter gives a very gooddescription of the properties of the cuprite phase at room temperature. In particular, thebulk modulus and the elastic constants at zero pressure are in excellent agreement withexperiment. At 10 GPa (7 in LDA calculations), the transition from the cuprite to theCdI2 phase occurs, and the latter remains the phase having the smallest Gibbs energy up to themaximum pressure we have considered (20 GPa). We have also determined the elastic constants ofCu2O in the cuprite phase for various applied pressures. The results indicate that this structurebecomes unstable with respect to trigonal deformations before the transition to theCdI2 phase. On the other hand, no indication of instability with respect to tetragonaldeformations has been found. This kind of instability would occur at pressures greater thanthe phase transition pressure.