HIGH PRESSURE BEHAVIOR OF MANGANITES BY INFRARED AND RAMAN SPECTROSCOPY

Abstract

The effect of hydrostatic pressure on the properties of the La 0.75 Ca 0.25 MnO 3 manganite have been studied by means of spectroscopic techniques. Raman and infrared (IR) spectra of this pseudocubic manganese perovskite have been collected for the first time over a wide pressure range (0–14 GPa) using a diamond anvil cell. Preliminary results have been obtained also in the case of the Sr 1.5 La 0.5 MnO 4 layered perovskite. The Raman measurements allow us to follow the pressure evolution of the phonon spectrum of the MnO 6 octahedron vibrational modes. Through the IR measurements we study the pressure dependence of the high-frequency octahedron stretching mode and of the broad background associated to polaronic absorption. Raman results show an abrupt discontinuity at P *~7.5 GPa in both frequency and width of some of the observed phonons. The infrared absorption measurements shows a remarkable increase of the polaronic absorption which do not completely screen the phonon peak even at the maximum pressure. Our results, which are in agreement with recent high pressure diffraction data, do not support the possibility of obtaining a metallization transition in the La 0.75 Ca 0.25 MnO 3 manganite at high pressure.