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The ferroelastic phase transitions of KMgCl 3 crystal grown by the Czochralski method were investigated by direct observation using a polarizing microscope with varying temperature. The results showed that the KMgCl 3 crystal undergoes two pure ferroelastic phase transitions from cubic prototypic phase to tetragonal, and to orthorhombic structure at about 312 °C and 224 °C, respectively, and can be classified into m3mFmmm(p) species. The permissible domain walls of this species were analyzed by both the strain tensor and group theoretical method.

The relation between the phase transition temperature and unit cell volume in the (K 1-x Cs x ) 2 ZnCl 4 mixed crystals was studied. The phase transition temperature of A 2 BX 4 family is dependent on the size of cation and anion (FABRY and PEREZ-MATO). That is, the transition temperature of crystal decreases with increasing unit cell volume. In this study we investigated this property of mixed crystals with the increasing mixture ratio. From the current study, we obtained the result that in the mixed crystals (K 1-x Cs x ) 2 ZnCl 4 , the increase of x induces the increase of unit cell volume, so that T I decreases with increasing unit cell volume. In order to determine the distribution of the substituted Cs + , using the near IR and UV spectrophotometer, we investigated both the band gap energy and the type of transition.

Lead titanate thin films were prepared in-situ by RF magnetron sputtering method in the substrate temperature region of 550°C ∼ 650°C using Ti and Pb metal targets and oxygen gas. The films deposited at 650°C for 60 min - when the applied power to the Ti and Pb target and deposition pressure were 200 W, 40 W, and 1.8 x 10 -2 Torr, respectively - had stoichiometric composition ratio and shown X-ray diffraction patterns of tetragonal structure like that of the powder. For the application to the piezoelectric field effect transistor (PI-FET), the substrate of SiO 2 (50 nm)/p-Si(100) was used. Leakage current density of the thin film was 7 x 10 -8 A/cm 2 at 100 kV/cm, dielectric breakdown voltage was 1.8 MV/cm, and so it showed high insulator characteristics. Capacitance-voltage curve was measured as a function of pressure. The variation width of the capacitance was 6.5 pF at bias voltage of -4 volts, and the value increased linearly according to the pressure up to about 6 kgf/cm 2 , and was saturated at the pressure of 8 kgf/cm 2 .

The mixed crystal (K 1-x Cs x ) 2 ZnCl 4 with x = 0, 0.001, 0.01, 0.1, and 0.2 with optical quality has been grown by the Czochralski method. Using the Atomic Absorption Spectroscopy (AAS) and Energy Dispersive Spectroscopy (EDS), we determined the amount of Cs ion included in the mixed crystal. By using of DTA and DSC, we observed the change of T c and T i . The thermal hysteresis in the dielectric constants show strong dependence on the thermal process and on the amount of impurity which are explained by the influence of the thermal process and impurity, respectively on the creation, annihilation, and growth of discommensuration (DC).

Lead titanate powders and thin films were prepared by the sol-gel process of metal alkoxide solutions and solvents. From DSC measurements, phase transition temperature of crystallized PbTiO3 powders was obtained at about 484 °C. From XRD investigation, it was confirmed that the tetragonal phase of polycrystalline PbTiO3 thin films is formed by coating of concentrated solution on all of the substrates we used after heat treatment above 500 °C. It was found by SEM and ellipsometric analysis that the thin film coated with 0.25 M concentrated solutions once had an average thickness of about 720 A. Surfaces of thin films were crack-free, uniform, and its average grain size investigated by SEM was 0.6–0.8 μm. Band gap energy of PbTiO3 thin film coated on the Al2O3 (2243) substrate was 3.45 eV, which is assumed to be due to the direct band to band transition. Dielectric constant (ϵ) and dielectric loss (tan δ) of PbTiO3 thin film amounted to 60–70 and 0.01–0.02 in the region of 10 kHz ∼ 1 MHz at room temperature, respectively, and transition temperature was 486 °C at 1 MHz. From the hysteresis loop of PbTiO3 thin film, spontaneous polarization of 12 μC/cm2 and coercive filed of 45 kV/cm were obtained.