Thermal and dielectric behaviour of pure and doped Na0.5Bi0.5TiO3 at low temperatures

Low-temperature (4.2 to 300 K) thermal conductivity measurements of undoped NET crystals and of Ba, Mn and Nb doped NBT are presented for the first ti me. First low-temperature dielectric measurements of NET single crystals ar e also presented. It is shown that a nearly temperature independent regime (platt au) of thermal conductivities lambda appears, as in glasses. This pl ateau correlates with an anomaly in the CexptT-3 curve. These non-Debye low -temperature features are observed in polycrystalline as well as crystallin e samples, so they cannot be related to grain boundary mechanisms. Introduc ing substitutional impurities into crystalline or polycrystalline NET has o nly a small influence on the temperature dependence of the thermal conducti vity at low temperatures (the plateau region exists in all samples). This f act indicates that this anomaly is related rather to intrinsic mechanisms a nd not to impurity doping. Strong temperature and frequency dependences of the dielectric permittivity were observed. A low-temperature loss anomaly w as reported. This anomaly al ises from dielectric relaxation which can be c onnected with polarons localised on defects (oxygen vacancies) and/or on tw inning walls between rhombohedral domains and on rhombohedral-another phase (probably tetragonal) interphases.