Infrared-active phonons of LaMnO3 and CaMnO3

The infrared absorption spectra of polycrystalline LaMnO3 and CaMnO3 measured in the frequency range of the transverse optical phonons are reported, discussed, and compared with calculations of the lattice dynamics. For LaMnO3 the measured spectrum is consistent with the expected orthorhombic structure. For CaMnO3 the spectrum reflects a symmetry lower than that of a cubic perovskite. We find a close correspondence between the spectra of the two materials which suggests a similarity in their structures.