Lattice modes in paraelectric La1/2Na1/2TiO3 by infrared and Raman spectroscopy.

The lattice dynamics of La(1/2)Na(1/2)TiO(3) single crystal have been investigated by far-infrared and Raman scattering spectroscopy. Far-IR reflectivity spectra revealed Slater, Last and Axe modes near 140, 190 and 555 cm(-1), respectively. The frequency of the Slater mode decreases by about 10% on cooling, which is enough to account for the observed increase of the low-frequency permittivity. The results allowed us to discuss the reasons for the suppressed ferroelectricity of the material. Temperature evolution of the Raman scattering intensity of an oxygen octahedra bending mode near 455 cm(-1) suggests a second-order phase transition towards the perovskite aristotype phase near 870 K.