Structural evolution and polar order in Sr1-xBaxTiO3 -: art. no. 224104

We perform a combination of diffraction and diffusion of neutron and high-resolution x-ray experiments on the Sr1-xBaxTiO3 system as well as dielectric susceptibility and polarization measurements. We show the SrTiO3-type antiferrodistortive phase up to a concentration of barium x(c)approximate to0.094: the progressive substitution of Sr by Ba leads to a monotonic decrease and to a vanishing of the oxygen octahedra tilting. The critical concentration x(c) separates the phase diagram in two regions, one with a sole antiferrodistortive phase transition (x<x(c)) and one with a succession of three BaTiO3-type ferroelectric phase transitions (x>x(c)). Inside the nonferroelectric antiferrodistortive phase a local polarization is observed, with a magnitude which is comparable to the values of the spontaneous polarization observed in the ferroelectric phases of the rich in barium-compounds. In these compounds a relative shift of Ti and Ba from the oxygen skeleton is measured and the spontaneous (long-range) polarization calculated from structural refinements. Its concentration and temperature evolution is in qualitative agreement with the values deduced from our dielectric susceptibility study.