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Based on measurements of spontaneous linear birefringence, the phase diagram of Rb1-x(NH4)xH2AsO4 has been completed. The ferroelectric compounds (x 0.46) are strongly first-order.

A-/b- and c-axis oriented SrBi2Ta2O9 thin films were grown on the MgO(110) and MgO(100) substrates, respectively, by rf magnetron sputtering deposition method. Optical anisotropy was shown in the infrared reflectance spectra for the SrBi2Ta2O9 thin films. Quadratic electro-optic effects were observed only in the a-/b-axis oriented films. The effective quadratic electro-optic coefficient was about 3.8 ×10-17 m2/V2.

The electrical properties of sol–gel deposited BaTiO3 thin films on Si(100) and SiO2-buffered Si(100) substrates were investigated. The dielectric constant measured as a function of frequency was fitted using the space charge relaxation model. The effective dielectric constant (ε') and dissipation factor (tan δ) were determined in the accumulation region from the results of capacitance–voltage ( C–V ) measurements at room temperature, at 1 MHz. Values of 23–185 and 0.02–0.08 were determined, respectively. The density of the interfacial surface states (N ss), calculated from the width of the memory window of the C–V curve, was of the order of 1011–1012 eV-1 cm-2. The leakage current densities for BaTiO3 films deposited on Si and SiO2-buffered Si substrates were 22–57 nA/ cm2 and 0.85–4 nA/ cm2, respectively, at an applied field of 100 kV/cm. The dielectric breakdown strength exceeded 1 MV/cm for all films.

Experimental results on mixed crystals of K1-x (NH4) x H2PO4 and KH2P1-x As x O4 are reported as a function of concentration (for x\lesssim0.13) and explained by the modified proton lattice coupled model. Some physical properties of the mixed crystals obtained from measurement of the Curie constants, spontaneous polarizations, and specific heats are related to the role of impurities in the phase transition of the crystals. We found that the interaction energy beween host and impurity is negative for mixed crystal with ADP impurities. This indicates that in this mixed crystal, there is competition between ferroelectric and antiferroelectric exchange interactions.

The infrared reflectances of the single crystal (NH4)2SO4 have been measured as functions of temperature and crystallographic axis. It is observed that the asymmetric streching internal mode (ν3) of SO4 2 ions which has triple degeneracy at room temperature is split into two modes around the phase transition temperature along each axis, but only along the ferroelectric c-axis these two modes are split again into three modes far below the transition temperature. The triplet asymmetric bending mode (ν4) of NH4 + ions shows no apparent change except the splitting of the peak into two in the c-axis polarized light below transition temperature. The optical constants, the mode parameters and the oscillator strengths are calculated by using Kramers-Kronig relations and the results are interpreted physically.