Low temperature structural and transport studies of La0.175Pr0.45Ca0.375MnO3-δ

The temperature (T) dependent x-ray diffraction (XRD) and resistivity measurements of La_0.175Pr_0.45Ca_0.375MnO_3-δ (LPCMO) have been performed down to 2K to understand the structural and transport properties. From room temperature down to 220K, LPCMO exists in orthorhombic phase with Pnma structure and at T~220K, it transforms to charge ordered (CO) monoclinic phase with P2₁/m structure and remains as it is down to 2K. The CO phase is evident from the occurrence of weak but well defined superlattice peaks in the XRD pattern. This structural transformation is of first order in nature as evident from the phase coexistence across the transition region. These results thus clearly illustrate that LPCMO undergoes a first order structural phase transition from charge disordered orthorhombic phase to CO monoclinic phase at ~220K, consistent with temperature dependent resistivity results. Our structural analysis of T dependent XRD data using Rietveld refinement infers that below 220K, LPCMO forms commensurate CO monoclinic P2₁/m structure with four times structural modulation.