Suppression of Lattice Doubling in Quasi-Skutterudite La 3 Rh 4 Sn 13 : A Comparison of Temperature and Hydrostatic Pressure Routes.

We present structural properties at different temperatures and high-pressure (HP) of La ₃ Rh ₄ Sn ₁₃ which is one of the interesting systems in the Remika phase RE ₃ Rh ₄ Sn ₁₃ (RE=Sr, Ca, La, Pr, Ce) quasi-skutterudite series using synchrotron diffraction. Data at ambient conditions revealed the presence of several weak reflections, which could be accounted only with a superlattice I* structure (I4 ₁ 32) with lattice parameter a~19.457 Å. However, above 350 K, a complete suppression of the weak superlattice reflections of the I* structure is observed. Data at higher temperatures is found to be well described by the I structure (Pm-3n) having half the lattice parameter compared to the I* structure. HP-XRPD at ambient temperature showed that pressures greater than 7.5 GPa result in similar suppression of the weak I* superlattice reflections. Data at higher pressures is found to be well described by the I structure (Pm-3n), similar to the high-temperature phase. HP Raman measurements demonstrated changes that seem to be consistent with a locally more ordered structure as in the case of the I*→I transition. Our findings on La ₃ Rh ₄ Sn ₁₃ open up new avenues to study unexplored HP phenomena, especially the superconductivity in these Remika phase quasi-skutterudites.
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