For tetragonal barium titanate (BaTiO3) single crystals, an electric field (E-field) applied along the [111]c direction can induce an engineered-domain configuration in these crystals. In this study, such engineered-domain configurations of different domain sizes were induced in BaTiO3 single crystals, and their piezoelectric properties were investigated as a function of domain size. Prior to this study, the dependences of the domain configuration on the temperature and E-field were investigated using a polarizing microscope in order to understand the optimum poling condition for fine- and coarse-domain configurations. We found that above the Curie temperature (TC) of 132.2 °C, when an E-field above 6.0kV∕cm was applied along the [111]c direction, an engineered domain with a fine-domain configuration appeared. Moreover, it was also found that this fine-domain configuration remained stable at room temperature without the E-field. On the other hand, the coarse-domain configuration was obtained upon poling at just below TC. Finally, the piezoelectric properties of 31 resonators with different domain sizes of 40–5.5μm were measured. As a result, it was found that the piezoelectric properties, such as d31 and k31, increased significantly with decreasing domain size.

No abstract

A size effect on crystal structure has been investigated for barium titanate (BaTiO3) nanoparticles of 40-, 140-, and 430-nm sizes, by means of neutron and high-resolution synchrotron x-ray powder-diffraction and Raman-scattering techniques. These samples were prepared by a modified two-step thermal decomposition method from barium titanyl oxalate, resulting in very few lattice impurities. Rietveld analysis of the neutron-diffraction data for the 430-nm- and 140-nm-sized BaTiO3 particles was performed assuming a single phase of tetragonal (P4mm) structure. The axial ratio c∕a of tetragonal BaTiO3 decreases with a decrease in particle size from 430 to 140 nm. Barium titanate particles with a size of 40 nm consist of (1) tetragonal crystals (83 wt %) with a large cell volume and an axial ratio of unity c∕a=1.000(5) and of (2) a hexagonal phase (P63mmc, 17 wt %) with a large unit-cell volume. Rietveld and maximum-entropy method analyses suggest that there exist atomic displacements from the ideal site of a cubic structure and a spontaneous polarization of the tetragonal phase even in the 40-nm-sized BaTiO3 particles. The nuclear-density distribution of the 140-nm-sized particles with a high dielectric constant does not exhibit a large positional disorder, while the Ba atom of tetragonal BaTiO3 in the 40-nm-sized particles has a smaller atomic displacement parameter.

Barium titanate (BaTiO 3 ) ceramics with various grain sizes were prepared by a conventional sintering method and a two-step sintering method. The permittivity of the ceramics increased with decreasing the grain size down to 1.1 mm on average. The BaTiO 3 ceramics with an average grain size of 1.1 mm had a high permittivity of 7,700. The transmission electron microscopy (TEM) observation revealed that the 90 domain density increased with decreasing the grain size. The domain size of the ceramics with the highest permittivity of 7,700 was approximately 100 nm. From an ultra wide range dielectric spectroscopy, it was found that the high domain density enhanced the orientational polarizability due to the domain-wall vibration and the ionic polarizability due to the lattice vibration. It was clarified that the increase of the permittivity with decreasing the grain size was due to the domain size effect.

High density, almost impurity-free and defect-free barium titanate ͑BaTiO 3 ͒ fine particles with various sizes from 20 to 1000 nm were prepared by the two-step thermal decomposition of barium titanyl oxalate and postheating treatment. The crystal structures of these particles were investigated as a function of the size and the temperature using synchrotron radiation x-ray diffraction ͑XRD͒ measurement. As a result, the size-induced ferroelectric ͑tetragonal-cubic͒ phase transition observed at around 30 nm. Moreover, the temperature dependence of the crystal structures revealed that one phase transition at 135°C separated into two kinds of phase transition behaviors with decreased particle sizes, i.e., the tetragonal-cubic phase transition temperature was constant at 135°C despite particle sizes while the cell volume expansion temperature shifted to low temperature with decreasing particle sizes. Moreover, the temperature dependence of Raman scattering spectra clarified that the temperature at a discontinuous change of damping factor was almost consisted with the cell volume expansion temperature from the XRD measurement. These results suggested that the phase transition behavior of the BaTiO 3 nanoparticles was quite different from that of the BaTiO 3 single crystals.

Nanostructures of barium titanate (BaTiO3) nanoparticles were analyzed using a composite structure model. It was found that BaTiO3 nanoparticles had a composite structure consisting of (i) inner tetragonal core, (ii) gradient lattice strain layer (GLSL), and (iii) surface cubic layer. The crystal structure of each region did not depend on particle size while the volume fraction of the GLSL and the surface cubic layer increased with decreasing the particle size. These results suggested that the size effect of BaTiO3 nanoparticles originated from the composite structure.

Ultrawide range dielectric spectra from the kilohertz to terahertz range of BaTiO3 (BT), Ba(Zr0.25Ti0.75)O3 (BZT), (Ba0.6Sr0.4)TiO3 (BST), and SrTiO3 ceramics were presented by analyzing dielectric permittivity and IR reflectivity data. It was found that the permittivity of the ST was determined only by the ionic polarization while that of the BT was determined by the ionic polarization as well as the dipole polarization due to the domain contribution. The high permittivity of the BZT ceramics was attributed to the dipole polarization of polar nanoregions in the relaxors. The dipole and ionic polarizations overlapped in the BST.

[110]-oriented barium titanate (BaTiO3) ceramics were prepared by templated grain growth (TGG) method using [110]-oriented BaTiO3 platelike particles as a template and hydrothermal BaTiO3 sphere particles with different particle sizes as a matrix. The degree of orientation along the [110] direction, F110, was measured using an X-ray diffraction (XRD) pattern by the Lotgering method. To obtain both a high density and a high F110, the preparation conditions were optimized as functions of matrix particle size, volume fraction of the template to the matrix, and sintering temperature. As for the results, BaTiO3-grain-oriented ceramics with a high density of more than 96% were successfully prepared despite various F110 values from 0 to 98%. Scanning electron microscopy (SEM) revealed that their average grain sizes were always approximately 75 µm despite various F110 values and there were no anisotropic microstructures. These grain-oriented BaTiO3 ceramics were poled at 100 °C, and their piezoelectric properties were measured using a resonance–antiresonance method and a piezo d33 meter for d31 and d33 piezoelectric constants. As for the results, the d31 values were almost constant at -50 pC/N despite various F110 values, while the d33 values increased with increasing F110 values, and at around an F110 of 85%, d33 reached a maximum of 788 pC/N.