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(-1). A fitting procedure, based on a f our-parameter model, and Kramers-Kronig analysis of the spectra were perfor med and the optical parameters of the observed ionic oscillators determined . Group theory analysis has been done and the number of experimentally obse rved active modes was compared with theoretical predictions. It was shown t hat the high frequency dielectric permittivity increases from 1.88 to 5.13 for pure BaTiO3 sintered at 1320 degreesC for 2 to 10 h, respectively. It i s also shown that infrared optical reflectivity measurements could give use ful results for boundary cases when it is difficult to distinguish if a sam ple has a cubic or tetragonal structure. Reflectivity data and its numerica l analysis can also give information on the degree of the sintering process and density of the samples.