High pressure structural and vibrational properties of the spin-gap system Cu₂PO₄(OH)

Abstract

The structural and vibrational properties of the spin-gapped system Cu(2)PO(4)(OH) have been investigated at room temperature under high pressure up to ~20 GPa by Raman scattering and synchrotron-based x-ray diffraction and infrared (IR) spectroscopic measurements. The orthorhombic phase (space group Pnnm, z = 4) remains stable up to at least 7 GPa where it undergoes a weakly first order structural transition (with negligible volume drop) to a monoclinic phase (space group P2(1)/n, z = 4) with an abrupt monoclinic distortion. Refinement of atomic positions has been performed for the low pressure phase. The conspicuous changes in the vibrational spectra (Raman as well as far-IR) confirm this phase transition. At further higher pressures the monoclinic angle increases rapidly and the system transforms irreversibly into a disordered phase. Detailed vibrational analyses have been performed in the orthorhombic phase and pressure-induced structural evolution has been correlated with the vibrational modes corresponding to the Cu-O bonds. A strong negative pressure dependence of hydroxyl mode frequencies (as observed from the mid-IR absorption spectra) supports the pressure-induced structural disordering at higher pressures.

Tuning photocatalytic performance of the near-infrared-driven photocatalyst Cu2(OH)PO4 based on effective mass and dipole moment

“…Due to the distorted polyhedrons, it may lead to a net dipole moment in such units, which can play an important role in photocatalysis, as reported before. 26,27 On the whole, the previous researched interests of CHP were mainly focused on its structure properties, including low-temperature structural phase transition, 28 vibrational properties, 29 and the magnetic behaviors of CHP, especially its low-dimensional quantum magnetic and so forth. 23,30,31 However, the photocatalytic performance, especially the NIR driven photocatalysis of Cu 2 (OH)PO 4 has been less investigated.…”

Raman spectroscopy and X‐ray diffraction of pressure‐induced reversible structure change in K2OsO2(OH)4

“…Based on the theory from Reynolds and Sternstein, 14 the distance of the O atoms is reduced and the electrostatic attraction of H···O increases when compressing, thus lengthening the O–H bond and reducing the stretching wavenumber. In addition, pressure‐induced softening of the OH stretching modes is accompanied by peak broadening and loss of intensity for many transition metal hydroxides 15–19 . Except from the distinct peak that denotes O–H symmetry stretching mode, we also noticed that there is a right shoulder at above 3000 cm −1 in Figure 3b, which is asymmetry stretching mode with higher wavenumber.…”

“…In addition, pressure-induced softening of the OH stretching modes is accompanied by peak broadening and loss of intensity for many transition metal hydroxides. [15][16][17][18][19] Except from the distinct peak that denotes O-H symmetry stretching mode, we also noticed that there is a right shoulder at above 3000 cm −1 in Figure 3b, which is asymmetry stretching mode with higher wavenumber. Asymmetry in the peak shape of the OH stretching modes suggests the existence of diverse disordered sites for H atoms.…”

Rational Design of (NH4)Cu[PO4] with a Spin Gapped, Distorted Honeycomb Layer

“…In addition, temperature affects the synthesis of the title compound. Lower synthesis temperature (such as 463 K) led to another known phase of Cu 2 PO 4 (OH) . Moreover, the reaction duration also affects the crystal size and quality of the title compound.…”