Unfolding grain size effects in barium titanate ferroelectric ceramics

Grain size effects on the physical properties of polycrystalline ferroelectrics have been extensively studied for decades; however there are still major controversies regarding the dependence of the piezoelectric and ferroelectric properties on the grain size. Dense BaTiO3 ceramics with different grain sizes were fabricated by either conventional sintering or spark plasma sintering using micro- and nano-sized powders. The results show that the grain size effect on the dielectric permittivity is nearly independent of the sintering method and starting powder used. A peak in the permittivity is observed in all the ceramics with a grain size near 1μm and can be attributed to a maximum domain wall density and mobility. The piezoelectric coefficient d33 and remnant polarization Pr show diverse grain size effects depending on the particle size of the starting powder and sintering temperature. This suggests that besides domain wall density, other factors such as back fields and point defects, which influence the domain wall mobility, could be responsible for the different grain size dependence observed in the dielectric and piezoelectric/ferroelectric properties. In cases where point defects are not the dominant contributor, the piezoelectric constant d33 and the remnant polarization Pr increase with increasing grain size

MEMS Technologies for Energy Harvesting

The objective of this chapter is to introduce the technology of Microelectromechanical Systems, MEMS, and their application to emerging energy harvesting devices. The chapter begins with a general introduction to the most common MEMS fabrication processes. This is followed with a survey of design mechanisms implemented in MEMS energy harvesters to provide nonlinear mechanical actuations. Mechanisms to produce bistable potential will be studied, such as introducing fixed magnets, buckling of beams or using slightly slanted clamped-clamped beams. Other nonlinear mechanisms are studied such as impact energy transfer, or the design of nonlinear springs. Finally, due to their importance in the field of MEMS and their application to energy harvesters, an introduction to actuation using piezoelectric materials is given. Examples of energy harvesters found in the literature using this actuation principle are also presented

Ferroelectric, dielectric and piezoelectric properties13; of Pb1x2013;xCex(Zr0.60Ti0.40)O3, 0 xA3; x xA3; 0.08

The ferroelectric, dielectric and piezoelectric13; properties of compositions Pb1x2013;xCex (Zr0.60Ti0.40)O3,13; (x = 0.0, 0.01, 0.02, 0.04, 0.06 and 0.08) are studied. The13; above compositions are prepared from their constituent13; oxides, calcined at 900 C for 4 h and various phases13; present are characterized by X-ray diffraction (XRD)13; technique. The above powders are uniaxially pressed into13; circular compacts, sintered at 1,250 C for 2 h, electroded,13; poled at 2 kV/mm D.C. voltage and their electrical properties13; are measured. The XRD analysis shows the presence13; of rhombohedral phase up to 2 mol% ceria while tetragonal13; phase found at higher concentrations. It is observed that13; the ferroelectric, dielectric and piezoelectric properties13; increase with the addition of ceria with a maximum at13; 2 mol% and then decreases. The higher piezo properties13; associated with low ceria concentration are attributed to13; rhombohedral phase