Pressure and temperature dependence of optical phonons in La0.75Ca0.25MnO3 Original Research Article

We present the results of extensive studies on Raman and infrared active phonons in the La0.75Ca0.25MnO3 manganite over a wide temperature (100–320 K) and pressure (0–14 GPa) range. The analysis of the temperature dependent data allows to identify a clear spectroscopic signature of the insulator to metal transition. Indeed the abrupt reduction of the effective electron–phonon interaction on entering the metallic phase determines a change in slope in the temperature dependence of the Jahn–Teller phonon line width. The analysis of the pressure dependent data shows that the octahedral Jahn–Teller distortion, and consequently the electron–phonon interaction, is strongly reduced only in the low-pressure regime. At very high pressure, the onset of a pressure-activated localizing mechanism efficiently contrasts the natural delocalizing tendency of pressure. We finally guess that this effect could be attributed to charge-localizing antiferromagnetic interactions activated by the strong lattice compression.