Critical concentrations in Ba-doped incipient ferroelectric SrTiO3

Temperature-induced variations of light refraction and dielectric permittivity in single-crystal Sr1−x BaxTiO3 (x=0.02, 0.05, 0.07, and 0.14), Sr1−x CaxTiO3 (x=0.014), and in nominally pure strontium titanate have been studied within the 17–300 K temperature range. The spontaneous polar contribution to the refractive index has been isolated. It was used to calculate the temperature and concentration dependences of the polarization autocorrelation function 〈P s 2〉 in the Sr1−x BaxTiO3 system. For x⩽0.07, the polarization P s=〈P s 2 〉1/2 varies proportional to (x−x g)1/2, where x g=0.0027 is the new critical concentration in Sr1−x BaxTiO3, below which short-range polar order vanishes.