We perform a combination of diffraction and diffusion of neutron and high-resolution x-ray experiments on the ${\mathrm{Sr}}_{1-x}{\mathrm{Ba}}_x{\mathrm{TiO}}_3$ system as well as dielectric susceptibility and polarization measurements. We show the ${\mathrm{SrTiO}}_3$-type antiferrodistortive phase up to a concentration of barium $x_c\approx 0.094:$ 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 $(x<\mathrm{}{x}_c)$ and one with a succession of three ${\mathrm{BaTiO}}_3$-type ferroelectric phase transitions $(x>\mathrm{}{x}_c).\mathrm{}$ 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.

• Received 18 December 2001

DOI:https://doi.org/10.1103/PhysRevB.65.224104