The structural pressure dependence of potassium titanyl phosphate (KTP) to 8 GPa

Abstract

The crystal structure of (KTP) has been determined as a function of pressure to 8 GPa at ambient temperature, using single-crystal x-ray diffraction techniques. The first-order isosymmetric phase transition, at 5.8 GPa, appears to have a strong effect on the compression mechanism of the structure: in the low-pressure phase the structure compresses by polyhedral tilting within the cross-linking chains while in the high-pressure phase relative translations and rotations of the chains themselves account for a significant proportion of the unit-cell volume reduction both at the transition and on further pressure increase. The distortion of the framework at the phase transition is accompanied by relatively large displacements of the potassium atoms to positions more closely related to the Pnan symmetry of the high-temperature phase. A comparison of the pressure-induced changes of the highly distorted octahedra with recent high-pressure optical measurements indicates that neither the lengths nor the orientations of the Ti - O bonds correlate, at least directly, with the observed variation of the second-harmonic-generating (SHG) power of the crystal. This strongly suggests that other regions of the structure may be important for the SHG properties. .

Evolution towards centrosymmetry of the nonlinear-optical materialRbTiOPO4in the temperature range 293–973 K: Alkaline displacements and titanyl deformations

“…34͒ or to the localization of Fe 3ϩ impurities. 35 The large displacement of the Rb ions from their room-temperature position 6,12 suggests 31 the second-order phase transition. 3 Contrary to the pressure study on KTP, 12 which shows that the displacement FIG.…”

Lattice dynamics and high-pressure Raman scattering studies of ferroelectricK2MgWO2(PO4)Mączka1, Paraguassu2, Filho3 et al. 2008Phys. Rev. B111150View full textAdd to dashboardCite

“…5,6 Pressure-dependent Raman and x-ray studies of KTP revealed a first-order phase transition at 5.5-5.8 GPa. [6][7][8] It was shown that this transition is purely displacive and it does not lead to any symmetry change, i.e., this transition is an isosymmetric phase transition. 8 It was also shown that KTP may exhibit a second phase transition near 10 GPa but nature of this transition was not established.…”

“…[6][7][8] It was shown that this transition is purely displacive and it does not lead to any symmetry change, i.e., this transition is an isosymmetric phase transition. 8 It was also shown that KTP may exhibit a second phase transition near 10 GPa but nature of this transition was not established. 7 The former studies showed that properties of KTP-type family of compounds can be greatly modified by replacement of K + ͑Ti 4+ ͒ or PO 4 3− by Rb + , Cs + , Tl + ͑Zr 4+ , Sn 4+ , Ge 4+ ͒ or AsO 4 3− , GeO 4 4− , SiO 4 4− .…”

Pressure induced phase transformations in NaZr2(PO4)3 studied by X-ray diffraction and Raman spectroscopy

“…This occurs due to distortion of polyhedral network without bond breaking but only altering their bond angles with greater change in large cation cavity [14]. Compounds with such polyhedral links including silica polymorphs [15][16][17][18], LiCsSO 4 [19], NaTiPO 5 and related compounds [20,21], perovskites [22][23][24], feldspars [25], zeolites [26][27][28] have been extensively studied experimentally to understand their structural behavior at high pressures. For example, the principal compression mechanism in the structure of KTiPO 5 with corner linked TiO 6 octahedra and PO 4 tetrahedra under pressure are changes in polyhedral angles and coordination environment of K atom [29].…”