Piezoelectric properties of barium titanate single crystals were investigated at room temperature as a function of crystallographic orientation. When a unipolar electric field was applied along [001], its strain vs electric-field curve showed a large hysteresis, and finally barium titanate crystal became to single-domain state with piezoelectric constant d 33 of 125 pC/N over 20 kV/cm. On the other hand, electric-field exposure below 6 kV/cm along [111] resulted in a high d 33 of 203 pC/N and a hysteresis-free strain vs electric-field behavior, which suggested the formation of an engineered domain configuration in a tetragonal barium titanate crystal. Moreover, when an electric field over 6 kV/cm was applied along [111], two discontinuous changes were observed in its strain vs electric-field curve. In situ domain observation and Raman measurement under an electric field suggested an electric-field-induced phase transition from tetragonal to monoclinic at around 10 kV/cm, and that from monoclinic to rhombohedral at around 30 kV/cm. Moreover, in a monoclinic barium titanate crystal, electric-field exposure along [111] resulted in the formation of another new engineered domain configuration with d 33 of 295 pC/N.

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A simple indentation technique for measuring the hardness‐to‐modulus ratio of elastic/plastic materials was developed. The method, which is based on measurement of the elastic recovery of the in‐surface dimensions of a Knoop indentation, allows ready evaluation of the hardness‐to‐modulus ratio to an accuracy better than 10%.

Fine particles of barium titanate single crystal with an average particle size of about 66 nm were prepared by a hydrothermal method. In the as-prepared sample, there was a large amount of the hydroxyl group and barium vacancy, and its crystal structure was assigned to cubic with an expanded lattice using a Rietveld method. The hydroxyl group desorbed with increasing calcination temperature, especially desorbing remarkably in the range from 200 to 300 °C. Above 700 °C, there was no hydroxyl group in the particle, and the crystal structure of the sample treated at 800 °C was assigned to tetragonal with tetragonality of 1.001 using a Rietveld method. The state of the lattice vibration was measured by an infrared reflection method, and analyzed using a nonlinear least-squares method with a four-parameter semiquantum model. As the result, the crystal structure of the as-prepared sample estimated using Fourier transform infrared and Raman was assigned to tetragonal. On the O6 octahedra deformation mode, the resonance frequency was independent of the concentration of the lattice hydroxyl group while the damping factor decreased with decreasing concentration of the lattice hydroxyl group. The role of the lattice hydroxyl group on the O6 octahedra deformation mode is discussed.