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We had investigated the pressure-induced phase transition phenomenon in the perovskite-like material Nd 2 Ti 2 O 7 compound. The structural and vibrational properties of a layered Nd 2 Ti 2 O 7 have been studied by means of X-ray diffraction and Raman spectroscopy at pressures up to 30 GPa. The gradual structural phase transition from the initial monoclinic P2 1 C 2 2 phase to the monoclinic P2 C 2 1 phase was observed at P ∼ 19 GPa. This pressure-induced phase transition is accompanied by anomalies in the pressure behavior of unit cell parameters and vibrational modes. The role of pressure application as a trigger for a significant rotation of the TiO 6 octahedra, alterations in interatomic distances, and the displacement of Nd atoms were discussed. • Structural and vibration properties of perovskite-like layered Nd 2 Ti 2 O 7 was studied at pressures up to 30 GPa. • The structural phase transition in Nd 2 Ti 2 O 7 was observed at P = 19.2 GPa. • The suppression of the ferroelectric phase of Nd 2 Ti 2 O 7 was discussed. • The bulk modulus of both phases were calculated. [ABSTRACT FROM AUTHOR]

The structural and luminescence properties of chalcogenide semiconductor Ca x Ba 1− x Ga 2 S 4 solid solutions ( x =0.1–0.9) doped with 7 at% of Eu 2+ ions were studied at room temperature. It was found, that the crystal structure of Ca x Ba 1− x Ga 2 S 4 solid solutions varies with the amount of Ca 2+ cations and phase transition from cubic to orthorhombic takes place with increase of x value. Ca x Ba 1− x Ga 2 S 4 :Eu 2+ solid solutions exhibit intense photoluminescence in cyan to yellow spectral region depending on x due to 5d→4f electron–dipole transitions in Eu 2+ ions. The peak position of the emission band shifts from 506 nm for x =0.1 to 555 nm for x =0.9 and the full width at half maximum of the emission band varies from 62 nm to 72 nm depending on the symmetry of the crystal lattice. The PL excitation spectrum of Ca x Ba 1− x Ga 2 S 4 :Eu 2+ covers the range at half maximum from 310 nm to 480 nm for x =0.1 and to 520 nm for x =0.9. It was shown that long-wavelength shift is caused by influence of the growing crystal field strength on Eu 2+ ions. [ABSTRACT FROM AUTHOR]

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 Pc 2 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. [ABSTRACT FROM AUTHOR]

Highlights: [•] The detailed P–T phase diagram of BiMnO3 was established. [•] We found three monoclinic modifications of BiMnO3 at pressure and temperature. [•] A suppression of monoclinic C2/c phase have been observed under pressure. [•] We found a new orthorhombic Imma phase of BiMnO3 at P >20GPa. [Copyright &y& Elsevier]