Bismuth-induced dielectric relaxation in the (1-x)La(Mg1/2Ti1/2)O3-xBi(Mg1/2Ti1/2)O3 perovskite system

The temperature variation of the dielectric permittivity and loss of the solid solutions (1-x)La(Mg1/2Ti1/2)O3-xBi(Mg1/2Ti1/2)O3 [(1-x)LMT-xBMT] (0≤x≤0.3) measured at radio, microwave, and far infrared frequency ranges has been analyzed in comparison with that observed in other bismuth-containing and bismuth-free perovskite ceramics based on LMT. It has been found that the low temperature dielectric response of the (1-x)LMT-xBMT compositions with x≥0 is frequency dependent over a wide range from radio to microwave frequencies. The considerable compositional growth of the dielectric permittivity and loss associated with the amount of bismuth in the system was revealed to be not contributed by the lattice polar phonon modes. The effect was suggested to be related to the low-temperature dielectric relaxation process due to a hopping movement of charge carriers in crystallographic A-sites of the perovskite lattice. Particular role of local lattice distortions caused by the anisotropic chemical bonds involving bismuth 6s2 electrons in a localization of hopping charge carriers in perovskites and other oxygen-octahedral compositions is considered. The characteristic features of the Bi-induced dielectric relaxation and those typical of the ferroelectric relaxors are compared and discussed