Abstract
Synthetic chalcomenite-type cupric selenite CuSeO3∙2H2O has been studied at room temperature under compression up to pressures of 8 GPa by means of single-crystal X-ray diffraction, Raman spectroscopy, and density-functional theory. According to X-ray diffraction, the orthorhombic phase undergoes an isostructural phase transition at 4.0(5) GPa with the thermodynamic character being first-order. This conclusion is supported by Raman spectroscopy studies that have detected the phase transition at 4.5(2) GPa and by the first-principles computing simulations. The structure solution at different pressures has provided information on the change with pressure of unit–cell parameters as well as on the bond and polyhedral compressibility. A Birch–Murnaghan equation of state has been fitted to the unit–cell volume data. We found that chalcomenite is highly compressible with a bulk modulus of 42–49 GPa. The possible mechanism driving changes in the crystal structure is discussed, being the behavior of CuSeO3∙2H2O mainly dominated by the large compressibility of the coordination polyhedron of Cu. On top of that, an assignation of Raman modes is proposed based upon density-functional theory and the pressure dependence of Raman modes discussed. Finally, the pressure dependence of phonon frequencies experimentally determined is also reported.
Highlights
Compounds containing divalent copper (Cu2+ ) have very interesting physical properties that are mainly related to the typical low-symmetry distortion around the Cu2+ ion [1]
Our SC-XRD experiments at ambient conditions confirmed that CuSeO3 ·2H2 O crystallizes in the orthorhombic space group P21 21 21 (Number 19)
As described by Robinson et al [5] and shown in Figure 1, the structure is composed of chains containing polyhedra with Cu in square pyramidal coordination alternating with SeO3 units
Summary
Compounds containing divalent copper (Cu2+ ) have very interesting physical properties that are mainly related to the typical low-symmetry distortion around the Cu2+ ion [1]. It has the additional interest of containing water molecules [3] that is known to influence the chemical and physical properties of materials [4]. By a bridge contact, which is very weak in comparison with the strong (covalent) H-O bond within. The adjacent chains are connected by H atoms weakly bonded to O atoms (not belonging to water) by the water molecule. Another interesting feature of the crystal structure is the existence of empty a bridge contact, which is very weak in comparison with the strong (covalent) H-O bond within the cavities in the structure
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