CuMn₂O₄: properties and the high-pressure induced Jahn-Teller phase transition

Abstract

Single crystal x-ray diffraction, x-ray photoelectron spectroscopy and magnetic susceptibility measurements at normal pressure have shown that, in spite of two Jahn-Teller active ions in CuMn2O4, the crystal is cubic with partly inverse spinel structure, the inversion parameter being \mbox{$x = 0.8$}. The cation configuration at normal pressure was determined as Cu0.2+Mn2+0.8[Cu2+0.8Mn3+0.2Mn4+1.0]O4. The high-pressure behaviour of the crystal was investigated up to 30 GPa using the energy dispersive x-ray diffraction technique and synchrotron radiation. A first-order phase transition connected with a tetragonal distortion takes place at Pc = 12.5 GPa, the c/a ratio being 0.94 at P = 30 GPa. The high-pressure phase has been described in terms of ligand field theory and explained by the changes to the valence and electronic configuration of the metal ions, leading to the formula Cu2+0.2Mn3+0.8[Cu2+0.8Mn3+1.2]O4. The electron configuration of the tetrahedrally coordinated Cu2+ and Mn3+ is (e4)t5 and e2t2, respectively. On the other hand, the electron configuration of Cu2+ located at octahedral sites is (t62g)e3g. While six electrons with antiparallely aligned spins occupy the triplet (t62g), three electrons on the orbital eg can be distributed in two ways (double degeneracy): (dx2-y2)1(dz2)2 and (dx2-y2)2(dz2)1. The first alternative leads to an axially elongated octahedron; the second one causes flattening of the octahedron. The contraction of the c axis indicates, that in the high-pressure phase the second configuration with unpaired electron on the dz2 orbital occurs. A similar effect of the octahedral contraction brings the orbital degeneracy of Mn3+ with the t32ge1g distribution. It follows that at high pressure the ligand field forces the two metals to take the valences that they show in the parent oxides CuO and Mn2O3.

High-Pressure Energy Dispersive X-Ray Diffraction Investigation of Lithium-Manganese Spinel

“…This observation is contradictive to described for the Mn 3+ silicate, where the stronger compression of the long bonds, relative to short bonds, leads to a smaller compressional overbonding, and acts against the Jahn-Teller distortion [15]. However, presented results coincide with the pressureinduced lowering of symmetry observed for any spinels with the Jahn-Teller Mn 3+ ion [16]. Fig.…”

In situ high-temperature X-ray and neutron diffraction of Cu–Mn oxide phases

“…From Table 4, it can be seen that for Cu ) tetra increase as temperature increases from room temperature to high temperature, which demonstrates that reaction (2) proceeds to the right as temperature increases. Many models have been proposed for the cation distribution, but there is no clear consensus which one is more accurate [2,6,11,14,22,29,33]. Clearly, the site exchange based on Eq.…”

“…At high temperatures, the thermal factor may be assumed to play a key role in determining the equilibrium state of Cu x Mn 3-x O 4 solid solutions. Waskowska et al [2] mentioned that the amount of distorting ions is the key to crystal symmetry in Cu x Mn 3-x O 4 . The critical fraction of distortive ions on octahedral sites should be about 55%.…”

“…Copper-manganese oxides, Cu x Mn 3-x O 4 ,C u 1-x Mn 1?x O 2 , have interesting physical and catalytic properties [1][2][3][4][5][6][7][8]. For example, Cu-Mn oxide-based catalysts were proposed for the removal of air pollutants like carbon monoxide and nitrous oxides from exhaust gas [3,9].…”

New Nanocrystalline Cu/MnOx Catalysts Prepared from Supercritical Antisolvent Precipitation

“…The corresponding C(1s) spectrum of the precursor exhibited two components at binding energies of 284.7 eV and 288.4 eV, reflecting the two nonequivalent carbon atoms in the acetate species. After calcination, we detected the development of a new lower binding energy feature in the Cu(2p) spectrum, assigned to Cu + [20] with significant contributions from Cu 2 + . The Cu + /Cu 2 + molar ratio was calculated from the Cu(2p) spectrum to be 0.20:1, which was consistent with the reported value of the partly inverse spinel structure, CuMn 2 O 4 , in which the ratio was 0.25:1.…”