A structural phase transition in La2Ti2O7 at high pressure

High-pressure effects on the crystal structure and vibration spectra of the perovskite-like layered La2Ti2O7 compound were studied using X-ray diffraction and Raman spectroscopy at pressures up to 30 GPa. The crystal structure of the compound was measured by means of a neutron diffraction at room temperature and ambient pressure. At P = 17.3 GPa, phase transition from the initial monoclinic phase of P21 symmetry to the monoclinic phase of P2 symmetry has been observed. The pressure-induced phase transitions in La2Ti2O7 are accompanied by anomalies in the pressure dependences of the unit cell parameters, as well as the vibrational modes. The baric dependences of lattice parameters, unit cell volume and vibration frequencies were obtained; the bulk modules for initial and pressure-induced phases of La2Ti2O7 were calculated.