An intermediate antipolar phase in NaNbO3NaNbO_{3} under compression

The crystal structure and vibration spectra of sodium niobate NaNbO$_3$ have been studied by means of neutron diffraction, X-ray diffraction and Raman spectroscopy at high pressures. An isostructural phase transformation from the initial antiferroelectric phase to an intermediate antiferroelectric phase HP-I have been observed under 2 GPa. This transformation is caused by complex reorientations of NbO$_6$ octahedra. Subsequent structural phase transition from the phase HP-I to an orthorhombic phase HP-III have been detected at pressures above 10 GPa. This transition leads to suppression of an antiferroelectric state of NaNbO$_3$. The observed phase transitions are accompanied by anomalies in lattice parameters compression

Structural, magnetic and vibrational properties of multiferroic GaFeO3GaFeO_{3} at high pressure

The crystal, magnetic structure and vibrational spectra of multiferroic GaFeO$_3$ have been studied by means of neutron, X-ray powder diffraction and Raman spectroscopy at pressures up to 6.2 and 42 GPa, respectively. A presence of Fe/Ga antisite disorder leads to a formation of the ferrimagnetic ground state with the Néel temperature T$_N$ = 292 K at ambient pressure. Upon compression, the magnetic ground state symmetry remains the same and the Néel temperature increases with a pressure coefficient (1/T$_N$)(dT$_N$/dP) = 0.011(1) GPa$^{−1}$. Application of high pressure above 21 GPa leads to a gradual structural phase transition from the polar orthorhombic Pc2$_1$n phase to nonpolar orthorhombic Pbnm phase. It is accompanied by anomalies in the pressure behaviour of several Raman modes. Pressure dependencies of lattice parameters and Raman modes frequencies in the observed structural phases were obtained

Competing magnetic and structural states in multiferroic YMn2{_2}O5{_5} at high pressure

The magnetic, structural, and vibrational properties of YMn${_2}$O${_5}$ multiferroic have been studied bymeans of neutron, x-ray powder diffraction, and Raman spectroscopy at pressures up to 6 and 30 GPa,respectively. Application of high pressure,P >1 GPa, leads to a gradual suppression of the commensurate andincommensurate antiferromagnetic (AFM) phaseswith a propagation vector q = (1/2,0,q${_z}$∼1/4) and appearanceof the commensurate AFM phase with q = (1/2,0,1/2). This observation is sharply contrasting to general trendtowards stabilization of commensurate AFM phase with q = (1/2,0,1/4) found in other RMn${_2}$O${_5}$ compoundsupon lattice compression. At P ∼ 16 GPa a structural phase transformation accompanied by anomalies in latticecompression and pressure behavior of vibrational modeswas observed. The comparative analysis of high-pressureand R-cation radius variation effects clarified a role of particular magnetic interactions in the formation of themagnetic states of RMn${_2}$O${_5}$ compounds