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The mechanical, microstructure and electrical properties of the ZnO-V 2 O 5-Mn 3 O 4 (ZVM)-based varistors were investigated at different sintering temperatures of 825-950 • C. The microstructure of the samples consists mainly of ZnO grains with Zn 3 (VO 4) 2 ,Z n V 2 O 4 and VO 2 as minor secondary phases. These minor phases disappeared for samples sintered at 950 • C. Energy-dispersive X-ray spectroscopic (EDS) analysis confirmed the above microstructure results. The sintered density is decreased linearly from 5.45 to 5.30 g cm −3 with an increase in the sintering temperature. The E B-andα-values of ZnO-based varistor can be controlled in a straightforward manner through the control of grain size. The breakdown field exhibited the highest value (2110 V cm −1) at 825 • Ci nt h e sintering temperature and the lowest value (1427 V cm −1)a t9 5 0 • C in the sintering temperature. The non-linear coefficient exhibited the highest value, reaching 19.81 at 875 • C and the lowest value, reaching 6.71 at 850 • C. As the average grain size increases both the longitudinal wave velocity and the longitudinal elastic modulus decrease while the ultrasonic attenuation increases and vice versa. Keywords. Ceramics; electrical properties; microstructure; varistors; ZnO-V 2 O 5-doped Mn 3 O 4 varistor; sintering.

Ba (1-x) Sr (x) TiO 3 ceramics, where x=0.05, 0.10, 0.15, and 0.20, were prepared by solid state reaction technique. X-ray diffraction analysis confirmed the formation of single phase perovskite structures. Mechanical properties such as ultrasonic attenuation, longitudinal wave velocity, and longitudinal elastic modulus were studied by an ultrasonic pulse echo technique at 2 MHz. Investigations of ceramic microstructures and mechanical properties showed its dependence on composition and sintering time. Increasing of Sr content, x, resulted in a decrease in bulk density and ultrasonic attenuation and an increase in velocity and modulus. Also, size of crystallites and c/a ratio were found to decrease with increasing of x, and increased with increasing of sintering time. High temperature ultrasonic studies showed, in addition to Curie phase transition, two relaxation peaks and its origin was investigated. The acquired structural and mechanical results were correlated and discussed.

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