title: 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.
authors.affiliation: High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India.
authors.forename: Pallavi S
authors.initials: PS
authors.lastname: Malavi
authors.forename: S
authors.initials: S
authors.lastname: Karmakar
authors.forename: Debjani
authors.initials: D
authors.lastname: Karmakar
authors.forename: A K
authors.initials: AK
authors.lastname: Mishra
authors.forename: H
authors.initials: H
authors.lastname: Bhatt
authors.forename: N N
authors.initials: NN
authors.lastname: Patel
authors.forename: Surinder M
authors.initials: SM
authors.lastname: Sharma