6533b86ffe1ef96bd12cdaca

RESEARCH PRODUCT

Effect ofA-site andB-site substitution on the infrared reflectivity spectra ofLa1−yAyMn1−xBxO3(A=Ba,Sr;B=Cu,Zn,Sc;0<y<~0.3;0<~x<~0.1)manganites

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description

We have measured the infrared reflectivity spectra of ${\mathrm{La}}_{1\ensuremath{-}y}[\mathrm{Sr}(\mathrm{Ba}){]}_{y}{\mathrm{Mn}}_{1\ensuremath{-}x}[\mathrm{Cu}(\mathrm{Zn},\mathrm{Sc}){]}_{x}{\mathrm{O}}_{3}$ $(0lyl~0.3,0l~xl~0.10)$ manganites, in a wide frequency $(100\char21{}4000{\mathrm{cm}}^{\ensuremath{-}1})$ and temperature (80 K\char21{}300 K) range. The reflectivity spectra were analyzed by a fitting procedure based on a model that includes Drude, midinfrared electronic, and phonon oscillator contributions to the dielectric constant. Six infrared active ${(3A}_{u}$ and ${3E}_{u})$ modes of rhombohedral symmetry are clearly observed. We assigned all observed modes according to existing lattice dynamical calculations for the rhombohedral structure of ${\mathrm{LaMnO}}_{3}.$ A decrease of the rhombohedral distortion below the paramagnetic-ferromagnetic transition is manifested through a lowering or complete removal of the frequency difference between the ${A}_{u}$ and ${E}_{u}$ modes.