FIRST-PRINCIPLES DETERMINATION OF A FERROELECTRIC INSTABILITY IN SRHFO3

Zone-center TO phonon frequencies and eigenvectors of cubic SrHfO3 are determinated, by calculating atomic forces, in the framework of the l ocal density approximation to density functional theory to sense the p resence of possible lattice instabilities. The results are compared wi th parallel calculations made on SrTiO3. An unstable zone-center phono n mode is obtained for both SrHfO3 and SrTiO3, but with quite differen t displacement patterns. As in SrTiO3, an unstable mode suggests the p resence of a temperature-dependent ''soft'' mode in SrHfO3 which shoul d be further confirmed by experimental measurements.