LAUSR

Abstract X-ray diffraction, Raman scattering and infrared spectroscopy were used to investigate the orthorhombic-to-monoclinic polymorphic transformation of LaTaTiO 6 ceramics, induced at high temperatures. For sake of comparison, Ln TaTiO 6 ceramics for various lanthanides ( Ln ), including La, were prepared by the solid-state reaction method. Phase-pure orthorhombic ( Pnma space group) and monoclinic ( C 2/ c space group) structures were obtained for LaTaTiO 6 at sintering temperatures of 1300 °C and 1400 °C, respectively. The Raman spectrum of the orthorhombic LaTaTiO 6 appeared to be very close to that of PrTaTiO 6 , which crystallizes within the aeschynite structure. Raman and infrared spectra of monoclinic LaTaTiO 6 ceramics are reported for the first time. Polarized Raman spectroscopy allowed determining (and assigning) all the non-polar modes of the material into the C 2/ c monoclinic phase. Infrared reflectivity spectra revealed the main polar modes that contribute to the dielectric response. The intrinsic dielectric parameters obtained by this procedure match well with those found by microwave techniques in ceramics prepared at relatively high sintering temperatures – which must belong to the described monoclinic structure.