Barium titanate ͑BaTiO 3 , BT͒-bismuth magnesium titanium oxide ͓Bi͑Mg 0.5 Ti 0.5 ͒O 3 , BMT͔ system ceramics were prepared in an ambient atmosphere in order to increase the Curie temperature ͑T c ͒ of BT above 132°C. A single perovskite phase was observed for BT-BMT ceramics with BMT compositions less than 50 mol %, and their relative densities were greater than 94%. Synchrotron measured x-ray diffraction patterns revealed that all the cations in the ceramics were homogeneously distributed. The temperature dependence of the dielectric properties revealed that the BT-BMT system ceramics exhibited relaxorlike characteristics with a dielectric maximum temperature as high as 360°C for the 0.5BT-0.5BMT ceramic. The apparent piezoelectric constant ͑d ‫ء‬ ͒ was 60 pC/N for the 0.4BT-0.6BMT ceramic. Based upon these results, the BT-BMT system shows potential as a new type of lead-free material for high T c piezoelectric applications.

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Barium titanate (BaTiO 3 , BT)bismuth magnesium titanium oxide (Bi(Mg 0.5 Ti 0.5 )O 3 , BMT) solid solution system ceramics were prepared using nanoparticles in atmosphere to enhance Curie temperature (Tc) of BT, 132°C, to much higher temperature. Optimization of calcination and sintering conditions resulted in a formation of a perovskite single-phase, and their densities were always greater than 94%. The synchrotron XRD measurement revealed that the all ions in the ceramics had almost homogeneous distribution. Temperature dependence of dielectric property revealed that the BTBMT system ceramics was typical relaxor materials, and for the 0.5BT0.5BMT ceramics, the dielectric maximum was clearly observed at 360°C. Finally, their apparent piezoelectric constant (d*) were measured by electric-field dependence of strain at room temperature, and the d* value was measured at around 60 pm/V for the 0.4BT0.6BMT ceramics.

In this contribution, we present our study on disc-shaped and homogeneously poled piezoelectric ceramic transformers working in planar-extensional vibration modes. Transformers are designed with electrodes divided into wedge, axisymmetrical ring-dot, moonie, smile, or yin-yang segments. Transformation ratio, efficiency, and input and output impedances were measured for low-power signals. Transformer efficiency and transformation ratio were measured as a function of frequency and impedance load in the secondary circuit. Optimum impedance for the maximum efficiency has been found. Maximum efficiency and no-load transformation ratio can reach almost 100% and 52 for the fundamental resonance of ring-dot transformers and 98% and 67 for the second resonance of 2-segment wedge transformers. Maximum efficiency was reached at optimum impedance, which is in the range from 500 Ω to 10 kΩ, depending on the electrode pattern and size. Fundamental vibration mode and its overtones were further studied using frequency-modulated digital holographic interferometry and by the finite element method. Complementary information has been obtained by the infrared camera visualization of surface temperature profiles at higher driving power.