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

Abstract

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 CoFe 2 O 4 spinel. CoFe 2 O 4 adopts a distorted tetragonal spinel structure at one atmosphere. At a pressure of ϳ32.5 GPa, both x-ray diffraction and Raman spectroscopy indicate that CoFe 2 O 4 transforms to the orthorhombic CaFe 2 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 94͑12͒ and 145͑16͒ GPa, respectively, with KЈϵ4. 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.

Raman study of NiFe2O4 nanoparticles, bulk and films: effect of laser power

“…[18] The value of ϒ i of of 0.42 for the 703 cm −1 mode is taken on the basis of the value for CoFe 2 O 4 obtained from high-pressure Raman studies. [19] The two compounds matches well in structural and other properties and, hence, to the first approximation we assume the Gruneisen parameter for the two compounds have similar values. Here a represents difference in lattice parameter of the nanoparticles compared to the bulk value (a 0 ) and ω i denotes Raman mode position.…”

Dependence of magnetic properties on crystallite size of CoFe2O4nanoparticles synthesised by auto-combustion method

“…As for CoFe 2 O 4 , there are five Raman active modes (Ag þ Eg + 3F 2g ) and four infrared modes (4F 1u ) [22,23]. Figure 4 shows the measured Raman spectra from 1000 to 100 cm À1 .…”

Pressure‐induced structural phase transitions in materials and earth sciences

“…In a similar way, MCr 2 O 4 spinels with M = Mg, Mn, and Zn are theoretically predicted to decompose above 19 GPa, 23 GPa, and 34 GPa, respectively [295]. However, a recent study has shown that ZnAl 2 O 4 is stable in the cubic spinel structure up to 43 GPa [296] [297,298].…”