High-pressure behavior of LaxSr2-xMnO4 layered manganites investigated by Raman spectroscopy and x-ray diffraction -: art. no. 224102

Raman spectra and x-ray diffraction patterns of La0.5Sr1.5MnO4 and Sr2MnO4 layered manganites have been collected over a wide pressure range (0-20 GPa) using a diamond anvil cell. The pressure dependence of both phonon peaks and lattice parameters, as well as the mode-Gruneisen parameters, have been determined. The comparative analysis of the results allows us to give a reliable assignment for the four phonon modes observed in the Raman spectra and in particular to identify the peak at higher frequency as a Jahn-Teller phonon. The comparison between the pressure dependence shown by doped and pure samples evidences the role played by the Jahn-Teller octahedral distortion on the lattice structural and dynamical properties. A progressive pressure-induced reduction of the Jahn-Teller distortion has also been observed in the doped sample. Finally, taking into account of recent results obtained by infrared spectroscopy on high-pressure pseudocubic and layered manganites, the role of lattice dimensionality on the pressure-induced charge delocalization has been discussed.