Optical investigation of La1-xCaxMnO3 and La1-xLixMnO3
An optical study has been made of La0·7Ca0·3MnO3 and La0·8Li0·2MnO3 in the infrared spectral region (100 cm-1 to 4000 cm-1). The transmission of all samples is negligible. The photoconductive response is also unmeasurable. The data reported are therefore restricted to reflectivity measurements. At room temperature, both materials exhibit similar ‘bending’ and ‘stretching’ phonon modes, associated with the MnO6 octahedra, at ~330 and ~580 cm-1, respectively. The ‘external’ phonon mode observed at ~170 cm-1, corresponding to the (La,Ca/Li) cations beating against the MnO6 octahedra, is slightly shifted between the two materials, as would be expected on the basis of the different compositions. At elevated temperature (~600°C) the intensity of the light reflected decreases across the infrared spectrum, and the ‘stretching’ mode moves to lower energy.