Infrared properties of perovskite manganites La1−xCaxMnO3 with 0.25 ≤ x ≤ 0.45

The systematical investigations of infrared phonon spectra were performed on the perovskite manganites La1−xCaxMnO3 with 0.25 ≤ x ≤ 0.45. Both frequency shift of stretching mode and effective number of carriers neff∗(T) change dramatically near the Curie temperature for all compounds. Moreover, Ca concentration dependences of variations of the phonon frequencies and neff∗(T) shows their extreme values around x = 0.35 and 0.40 respectively at the measuring temperatures. With the varying Ca concentration, the competition between the strong Jahn-Teller coupling and the magnetic double exchange interaction may be responsible for those results.