Structural, magnetic, infrared and Raman studies of La0.8SrxCa0.2-xMnO3 (0 ≤ x ≤ 0.2)

We report the results of magnetic, X-ray powder diffraction, infrared and temperature dependent Raman spectra of the La0.8Sr x Ca0.2-x MnO3 (0 ≤ x ≤ 0.2) manganite. The structure refinement using the Rietveld method indicates that the partial substitution of strontium for calcium (for x ≥ 0.15) modifies the orthorhombic structure of the CaMnO3 perovskite towards a rhombohedral phase. Magnetic measurement confirms the increase in the Curie temperature from 180 K for La0.8Ca0.2MnO3 to 307 K for La0.8Sr0.2MnO3, respectively. It is argued that the substitution with the larger Sr2+ ion strengthens the double-exchange interaction and gives rise to the observed increase of transition temperatures. All manganites show two IR active vibrational modes around 400 and 600 cm−1. Moreover, when x ≤ 0.1, the absorption band around 400 cm−1 splits into two peaks. In addition, we have analyzed the frequencies and widths of the observed Raman modes as a function of temperature for all samples with various Sr content. The mode splitting is attributed to both magnetic ordering and large orthorhombic distortion in doped rhombohedral manganites.