Yoshihito Tachi

Giant electromechanical coupling factor of k31 mode and piezoelectric d31 constant in Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 piezoelectric single crystal

High-quality and large piezoelectric single crystals of Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 (PZNT91/09) fabricated by the Bridgman method were investigated regarding the material constants and their temperature dependence. The single crystals poled along [001] of the original cubic direction possess high piezoelectric constants such as g33 and g31 as well as high dielectric constant e33T/e0 (4600), electromechanical coupling factor of the k33 mode (95.3%) and d33 (2500 pC/N). In particular, since k31 and d31 reach 80.8% and -1700 pC/N, respectively, the crystals can be applied for use in sensors and actuators with high performance. Based on the temperature dependence, we inferred that there is a relatively large difference in the elastic compliance (s11E) between rhombohedral and tetragonal phases. The cause of the high piezoelectricity in rhombohedral PZNT91/09 single crystals is thought to be the mechanical softness which leads to easy deformation by the poling field in comparison with the tetragonal phase.

Poling and Depoling Effects on Dielectric Properties and Domain Structures in Relaxor 24Pb(In1/2Nb1/2)O3–46Pb(Mg1/3Nb2/3)O3–30PbTiO3 near a Morphotropic Phase Boundary Composition

The temperature dependence of the complex relative permittivity in a relaxor ferroelectric solid solution 24Pb(In1/2Nb1/2)O3–46Pb(Mg1/3Nb2/3)O3–30PbTiO3 (PIN–PMN–PT) crystal poled and depoled was measured from room temperature to 200 °C at various frequencies. The poled sample exhibits transitions from the ferroelectric (FE) phase to the relaxor (RE) phase on heating, and after that, the depoled one exhibits those from the RE phase to the glassy freezing phase on cooling. An RE-type dielectric dispersion with a weak frequency (f) dependence was observed. Such a dielectric dispersion in the RE state was found to be based on tweed domain structures observed by polarization light microscopy (PLM) and piezoelectric force microscopy (PFM) due to the competition between the antiferroelectric (AFE) and FE coupling in the RE state. The temperature dependence of complex permittivity with resonance- and relaxor-type dielectric dispersions in the poled and depoled samples was characterized by hierarchical domain structures.

Study of Slow Lattice Dynamics in Relaxor Ferroelectric PMN–30%PT by Neutron Spin Echo Technique

We have used the neutron spin echo technique to characterize the dynamics of polar nanoregions (PNRs) in the relaxor ferroelectric (1- x )Pb(Mg 1/3 Nb 2/3 )O 3 – x PbTiO 3 (PMN– x PT) with x =30% ( T C ∼400 K). We measured the normalized intermediate scattering function I ( Q , t )/ I ( Q ,0) for a butterfly-shaped diffuse scattering around the (100) Bragg point, which is associated with atomic shifts, i.e., polarizations in PNRs. For T ≥500 K, I ( Q , t )/ I ( Q ,0) shows a peak structure at 0.5 ns, which is ascribed to the coexistence of echo signals from a relaxation mode and those from a low-frequency vibrational mode with ω∼26 µeV. Such a low-frequency vibrational mode for directions indicate a flat free-energy surface between the rhombohedral and tetragonal phases. On cooling below 450 K, the peak structure in I ( Q , t )/ I ( Q ,0) disappears and diffuse scattering intensity increases, which indicates that the condensed or pinned low-frequency mode for directions is the origin of PNRs.

Domain switching in nanometer scale in Bismuth-based relaxor solid solution

Microscopic piezoresponse force microscopy observation in 0.9967(Na1/2Bi1/2)TiO3(NBT)-0.0033BaTiO3(BT) rhombohedral (001) plate reveals two kinds of piezoresponse images, one with domain switching characterized with superior piezoresponsibility and the other without one, whereas macroscopic observation reveals non-switching of domain. Such microscopic remarkable difference of domain switching depends on coercive field caused by localized nucleation of domains with reversed polarization. Such coercive fields depend on relaxor states induced by random fields due to built-in charge disorder resulting from lattice defects at A-site and oxygen vacancies in ABO3 perovskite. The random fields based on lattice defects on {110} plane lower activation barrier for domain switching, leading to nucleation and growth of domains, while for non-switching of domains, oxygen vacancies on {110} and/or {001} plane play a role as clamping center for restriction of domain switching.