Estimation of the compressibility of Na0.5Bi0.5TiO3and related perovskite-type titanates

We report on the estimation of the compressibility of Na 0.5 Bi 0.5 TiO 3 and its constituent polyhedra through two different approaches: the so-called polyhedral approach and that based on the pressure dependence of particular Raman-active modes. In order to investigate the reliability of the results obtained for Na 0.5 Bi 0.5 TiO 3 , the two approaches have also been applied to perovskite-type titanates, ATiO 3 (A = Ca, Ba, Sr, Pb), and the results are compared with compressibility data reported in the literature. The comparative study shows that (i) ATiO 3 compressibilities are overestimated by the polyhedral approach, but can be roughly corrected by an empirical scaling factor, (ii) the A cation has a smaller influence in the compressibility than would be expected in view of the weakly bonded large AO 12 polyhedra, (iii) TiO 6 compressibilities deduced from Raman spectra are remarkably uniform among different titanates ((4.3±0.2)×10 -3 GPa -1 ), (iv) the Raman approach yields compressibilities within 10% of the experimental values.