Far-infrared reflectivity properties of BaTiO3 ceramics

Far-infrared and infrared reflectivity measurements have been made on pure BaTiO3, BaTiO3 doped with 5 mol% LiF and (Ba,Ca,Pb)TiO3 at room temperature in the range between 50 and 1000 cm-l. A fitting procedure, based on a four-parameter model, and Kramers-Kronig analysis of the spectra were performed and the optical parameters of the observed ionic oscillators determined. Group theory analysis has been done and the number of experimentally observed active modes was compared with theoretical predictions. It was shown that the high frequency dielectric permittivity increases from 1.88 to 5.13 for pure BaTiO3 sintered at 1320 °C for 2 to 10h, respectively. It is also shown that infrared optical reflectivity measurements could give useful results for boundary cases when it is difficult to distinguish if a sample has a cubic or tetragonal structure. Reflectivity data and its numerical analysis can also give information on the degree of the sintering process and density of the samples.