Investigation of structural, dielectric, and magnetic properties of hard and soft mixed ferrite composites J. Appl. Phys. 112, 054323 (2012) Growth and ferromagnetic resonance of yttrium iron garnet thin films on metals Appl. Phys. Lett. 101, 082405 (2012) Magnetoelectric effects at microwave frequencies on Z-type hexaferrite Appl. Phys. Lett. 101, 062406 (2012) Temperature and frequency dependent giant magnetodielectric coupling in DyMn0.33Fe0.67O3 J. Appl. Phys. 112, 013920 (2012) Structure refinement and dielectric relaxation of M-type Ba, Sr, Ba-Sr, and Ba-Pb hexaferritesThe power loss of MnZn ferrites and its relation to average grain size and grain boundary properties was investigated. The power loss was found to be dependent on the average grain size and on the highly electrically resistive grain boundaries which are formed by introduction of aliovalent ions in the outer grain region of a MnZn ferrite. Analysis of ac impedance data, assisted by Auger electron spectroscopy, elucidated the chemical and electrically diversity of doped and undoped samples and its influence on eddy current loss.

Grain growth and semiconductivity of donor-doped BaTiO 3 ceramics with an excess of BaO and additions of SiO 2 or B 2 O 3 were studied. The microstructures and electrical measurements on sintered samples revealed that their electrical properties are related to the microstructure development of the sintered samples. Samples heated with an excess of BaO developed a normal microstructure during sintering, as a consequence of normal grain growth (NGG), and were yellow and insulating. In contrast, samples with an excess of BaO and an addition of SiO 2 or B 2 O 3 exhibited anomalous grain growth (AGG) and were dark blue and semiconducting after sintering. When some BaTiO 3 seed grains were embedded in a sample of donor-doped BaTiO 3 with an excess of BaO (without SiO 2 or B 2 O 3 ), AGG was observed, i.e., some seed grains grew into large grains and were blue and semiconducting. An explanation is given for why AGG is responsible for the oxygen release and the formation of semiconducting grains in donor-doped BaTiO 3 and not NGG.

Donor-doped BaTiO3 ceramics were prepared by adding PbO B2O3 SiO2 as a sintering aid. Semiconducting BaTiO3 was obtained at a sintering temperature of 1100 °C. The sintered samples exhibit the Positive Temperature Coefficient of Resistivity (PTCR) effect, which depends on the amount of liquid phase, the concentration of the donor-dopant, and the sintering temperature. The cold resistivity of the samples decreases when the sintering temperature increases. The increase of the grain boundary resistivity and hence of the cold resistivity at lower sintering temperatures was explained by applying the diffusion grain boundary layer model.

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