Structural evolution of theCuGaO2delafossite under high pressure

Abstract

We have performed pseudopotential calculations and x-ray-diffraction and x-ray-absorption measurements on the CuGaO 2 delafossite under high pressure. We have completely characterized the structural behavior of the low pressure phase. We have found out that the a axis is more compressible than the c axis, and as a consequence the oxygen octahedra defined by the gallium environment tend to become more regular under high pressure. We have determined the internal parameter describing the oxygen position inside the unit cell, and seen that it is nearly constant when pressure is applied. We have observed an irreversible phase transition affecting the copper environment but not the gallium one. Such phase transition begins at 24Ϯ2 GPa and is completed at 28Ϯ2 GPa.

Effect of Spin Dilution on the Magnetic State of Delafossite CuFeO2 with an S = 5/2 Antiferromagnetic Triangular Sublattice

“…Figure 5 shows the composition-dependent Raman spectra of single phase of CuFe 1−x Sc x O 2 (0 ≤ x ≤ 0.25) at room temperature. All the samples showed two Raman active modes in agreement with earlier results on CuFeO 2 [26] and CuCrO 2 [27], CuGaO 2 [25]. These bands are identified as σ (A 1g ) at 692 cm −1 and σ (E g ) at 351 cm −1 , respectively, and it has been suggested that these vibrations may be associated with the spectral features of edge-sharing Fe III O 6 octahedra and possibly the O-Cu − -O linear bond [28].…”

“…Since there is only one mode of each symmetry, the exact eigenvector is determined without any lattice dynamical model required. Pellicer-Porres et al [25] had discussed the phonon dispersion at the zone center for CuGaO 2 delafossite. They proposed that the inversion center is lost along the direction of (T ) direction and the symmetry is reduced from D 3d to C 3v .…”

Multiferroic CuCrO2 under high pressure: In situ X-ray diffraction and Raman spectroscopic studies

“…Ab-initio band structure calculations and optical absorption measurements on CuAlO 2 and CuScO 2 thin films indicate the stability of CuAlO 2 , an indirect band gap semiconductor upto 20 GPa whereas CuScO 2 shows phase transition beyond 13 GPa to an unidentified phase [35]. Calculated phonon frequencies for CuGaO 2 and CuAlO 2 under pressure have indicated the dynamical instability of a transverse acoustic phonon to be the cause of pressure induced phase transition [27,28] in these materials. Recent first principles calculations determined the critical pressure of transition for delafossite CuAlO 2 to a leaning delafossite with a higher band gap, to be 60…”

“…Raman scattering measurements on CuAlO 2 [27] and CuGaO 2 [28] have reported that these compounds transform to unresolved structures above 34 and 26 GPa respectively. Energy dispersive x-ray diffraction and in-situ x-ray absorption near edge structure (XANES) measurements on CuGaO 2 under pressure confirm changes in copper environment leaving the environment of other cation unchanged [29].…”

“…However, anisotropic axial compressibility seems to be a common feature of all the copper delafossites with R3m structure resulting into the regularization of oxygen octahedra as compared to the distorted octahedra at ambient conditions [27][28][29][30][31][32][33][34]. To get more insight into the compression behaviour of these compounds, in this manuscript, we report the synthesis, characterization and high pressure investigations of CuCrO 2 by in-situ x-ray diffraction and Raman spectroscopic measurements.…”