High pressure Raman study of La1-xCaxMnO3-delta manganites

We report a high-pressure Raman study on two members of the La1-xCaxMnO3-delta manganite family (x = 0.20, delta = 0 and delta = 0.08). The results obtained for the delta = 0 sample show a different behavior in the low and high pressure regime which is ascribed to the onset of a new pressure-activated interaction previously invoked in other manganite compounds. The comparison of our results with literature data gives further support to the identification of the Jahn-Teller sensitive stretching mode and shows that pressure-induced octahedral symmetrization is more effective in systems exhibiting a lower metallic character. On the contrary the new interaction sets in at a pressure which decreases on increasing the metallic character of the system indicating an important role of the Mn-Mn hopping integral in its activation.