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Microstructural design is a widespread approach to tailor the properties of functional materials with the size effect being an effective constraint that modifies physical phenomena. In this work, we investigate the grain size effect on the properties and the electric field induced phase transformation behavior in barium titanate. A broad range of unimodal average grain size distribution between 0.4 and 15 μm was successfully sintered avoiding abnormal grain growth. Samples with a grain size close to the range of 1–2 μm, balancing microstructural strain, presence, and mobility of domain walls to allow the field induced crystal phase transformation, showed optimal electromechanical and dielectric properties. By means of in situ high energy x-ray diffraction and a high-resolution multianalyzer detector, we distinguish and quantify a tetragonal–orthorhombic phase transformation induced by an electric field, providing unambiguous proof of this induced phase transformation. These results contribute to the understanding of fundamental questions about the piezoelectric effect in barium titanate and consequently other similar systems. [ABSTRACT FROM AUTHOR]

Piezoelectric applications such as ultrasonic motors, transformers and therapeutic ultrasonics demand high power generation with low losses, which is facilitated by "hard" ferroelectrics. Hardening of piezoelectric properties, characterized by high mechanical quality factor (Qm), is usually achieved by doping with lower valence elements, thereby tailoring the domain wall dynamics. In the present study, we demonstrate a hardening mechanism by developing composites of 0.94(Na1/2Bi1/2)TiO3-0.06BaTiO3 (NBT-6BT) with ZnO inclusions, as an alternative to chemical modifications. A decrease in the saturation polarization and total strain, higher internal bias fields, lower hysteretic losses and a two-fold increase in Qm are observed in comparison to NBT-6BT. The composite with 0.1 mole ratio of ZnO exhibits the highest Qm of 320 with d33=125 pC/N and Kp=0.29. A one-to-one correspondence between the increase in Qm and the decrease in the domain wall mobility is established from the ac field dependence of permittivity, in the framework of the Rayleigh law. A further increase in ZnO content beyond a mole ratio of 0.1 reduces Qm, but retains it at a higher level, as compared to NBT-6BT. The results are explained based on the poling-induced strain incompatibility between the matrix and the hard ZnO phase. This composite approach is therefore considered a generic hardening concept and can be extended to other ferroelectric systems. [ABSTRACT FROM AUTHOR]

The lattice strain and domain switching behavior of xBiScO3-(1-x)PbTiO3 (x=0.40) was investigated as a function of cyclic field and grain orientation by in situ X-ray diffraction during application of electric fields. The electric field induced 200 lattice strain was measured to be five times larger than the 111 lattice strain in pseudorhombohedral xBiScO3-(1-x)PbTiO3 (x=0.40). It is shown that the anomalous 200 lattice strain is not an intrinsic phenomenon, but arises primarily due to stress associated with the reorientation of the 111 domains in dense polycrystalline ceramic. [ABSTRACT FROM AUTHOR]