TY - JOUR
T1 - Effect of Ca doping on the optical properties of La 1.2Sr 1.8Mn 2O 7
AU - Her, J. L.
AU - Liu, H. L.
AU - Shen, C. H.
AU - Liu, R. S.
AU - Sheu, H. S.
N1 - Funding Information:
We would like to gratefully acknowledge financial support from the National Science Council of Republic of China under Grant Nos. NSC 94-2112-M-003-002 and 94-2120-M-007-013, and the National Taiwan Normal University under Grant No. ORD93-B.
PY - 2006
Y1 - 2006
N2 - We present x-ray-diffraction, infrared reflectivity, and Raman-scattering measurements of La1.2 (Sr1.8-x Cax) Mn2 O7 as a function of temperature and doping (x=0.0, 0.4, 0.6, and 0.8). At room temperature, x-ray-diffraction data show that the replacement of Sr ions with smaller Ca ions causes a shrinkage of the unit-cell volume. The far-infrared conductivity spectra of all doped samples are typical of an insulator, showing only phonons. When doped with Ca on Sr and a corresponding systematic reduction in Curie temperature (Tc), there is a suppression of the low-frequency optical spectral weight. For the x=0.0 compound, the Raman-active phonon associated with the internal stretching of the oxygen atoms in Mn O6 octahedra shows a noticeable hardening below Tc. A polaron transport can be attributed to the observed frequency shifts. Interestingly, this hardening is reduced as the Ca content increases. These observations suggest that Ca doping disrupts the effects of the double-exchange interaction on the lattice degree of freedom, thereby accounting for the characteristic changes in the phase diagram.
AB - We present x-ray-diffraction, infrared reflectivity, and Raman-scattering measurements of La1.2 (Sr1.8-x Cax) Mn2 O7 as a function of temperature and doping (x=0.0, 0.4, 0.6, and 0.8). At room temperature, x-ray-diffraction data show that the replacement of Sr ions with smaller Ca ions causes a shrinkage of the unit-cell volume. The far-infrared conductivity spectra of all doped samples are typical of an insulator, showing only phonons. When doped with Ca on Sr and a corresponding systematic reduction in Curie temperature (Tc), there is a suppression of the low-frequency optical spectral weight. For the x=0.0 compound, the Raman-active phonon associated with the internal stretching of the oxygen atoms in Mn O6 octahedra shows a noticeable hardening below Tc. A polaron transport can be attributed to the observed frequency shifts. Interestingly, this hardening is reduced as the Ca content increases. These observations suggest that Ca doping disrupts the effects of the double-exchange interaction on the lattice degree of freedom, thereby accounting for the characteristic changes in the phase diagram.
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U2 - 10.1063/1.2158499
DO - 10.1063/1.2158499
M3 - Article
AN - SCOPUS:30844435278
SN - 0021-8979
VL - 99
JO - Journal of Applied Physics
JF - Journal of Applied Physics
IS - 1
M1 - 013905
ER -