High-pressure x-ray diffraction and Raman spectroscopic studies of the tetragonal spinelCoFe2O4

In situ x-ray diffraction and Raman spectroscopy have been carried out to pressures of 93.6 and 63.2 GPa, respectively, to explore the pressure-induced phase transformation of ${\mathrm{CoFe}}_{2}{\mathrm{O}}_{4}$ spinel. ${\mathrm{CoFe}}_{2}{\mathrm{O}}_{4}$ adopts a distorted tetragonal spinel structure at one atmosphere. At a pressure of \ensuremath{\sim}32.5 GPa, both x-ray diffraction and Raman spectroscopy indicate that ${\mathrm{CoFe}}_{2}{\mathrm{O}}_{4}$ transforms to the orthorhombic ${\mathrm{CaFe}}_{2}{\mathrm{O}}_{4}$ structure, which remains stable to at least 93.6 GPa. The bulk modulus ${(K}_{0})$ of the tetragonal and the high-pressure polymorphs were calculated to be 94(12) and 145(16) GPa, respectively, with ${K}^{\ensuremath{'}}\ensuremath{\equiv}4.$ Upon release of pressure the orthorhombic phase persists and appears to be structurally metastable. At zero pressure, laser induced heating leads to a significant transformation back to the tetragonal phase. The high-pressure orthorhombic phase at one atmosphere is 14.7% denser than the tetragonal phase.