X-ray and neutron diffraction study of tetragonal barium titanate

Abstract

An attempt is made to differentiate between the three previously proposed models of the structure of tetragonal BaTiO3. In the new model, the serious parameter-interaction problem was avoided by the use of both neutron and X-ray diffraction data collected from c-domain single crystals. The result of the refinement gave the displacement of the Ti atom from its cubic position as 0.0135 ± 0.0004 Å; the R value was 0.027 and 0.024 for the neutron and X-ray data respectively. The analysis also showed that the temperature parameters, B33, along the c axis are approximately independent of mass; B33 = 0.32 ± 0.03 Å2 from X-ray and 0.33 ± 0.04 Å2 from neutron diffraction. The average value obtained for the B11 temperature parameters, B11 = 0.50 Å2, is considerably higher than the B33 value, which thus clearly indicates the existence of low frequency optic modes at room temperature.