DISORDER AND THERMAL TRANSPORT IN UNDOPED KTAO(3)

The thermal conductivity of nominally pure KTaO3 exhibits an unexpecte d strong phonon scattering around 8 K. The question arises whether thi s scattering is related to the distorted microregions observed by othe r experiments. We have investigated a set of undoped single crystals g rown by different methods. By comparison with doped specimens, it is s uggested that acoustic phonons we coupled to the soft optic mode via t he local disorder. From complementary dielectric permittivity and elec tron paramagnetic resonance experiments, oxygen vacancies and rhombic Fe3+ appear to be incontestable candidates to account for the distorte d microregions.