High pressure Raman study of La$_{1-x}$Ca$_x$MnO$_{3-\delta}$ manganites

TL;DR

This study investigates how high pressure affects the vibrational properties of La$_{1-x}$Ca$_x$MnO$_{3- ext{delta}}$ manganites, revealing a pressure-activated interaction and the influence of metallic character on structural changes.

Contribution

It provides new insights into pressure-induced interactions and octahedral symmetrization in manganites, highlighting the role of metallicity and Mn-Mn hopping.

Findings

Pressure activates a new interaction in manganites.

Pressure-induced octahedral symmetrization depends on metallic character.

Lower metallic systems show more effective octahedral symmetrization.

Abstract

We report on a high-pressure Raman study on two members of the La$_{1-x}$Ca$_x$MnO$_{3-\delta}$ 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 regimes 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 active 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 pressure which decreases on increasing the metallic character of the system indicating a relevant role of the Mn-Mn hopping integral in its activation.