A structural phase transition between the cubic (space group, Fm3m) and tetragonal (space group, P4,lnmc) phases in a zirconia-ceria solid solution (Zr, -,Ce,O,) has been observed by Raman spectroscopy. The cubic-tetragonal (c-t") phase boundary in compositionally homogeneous samples exists at a composition X , (0.8 < X , c 0.9) at room temperature, where t" is defined as a tetragonal phase whose axial ratio c/a equals unity. The axial ratio c/a decreases with an increase of ceria concentration and becomes 1 at a composition Xg (0.65 < Xh c 0.7) at room temperature. The sample with a composition between X , and X i is t"-ZrO,. By Raman scattering measurements at high temperatures, the tetragonal (t") + cubic and cubic + tetragonal phase transitions occur above 400°C in Zro,2Ceo.802 solid solution.

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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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