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Temperature dependence of the dielectric constant and longitudinal acoustic wave velocity were studied in betaine phosphite-betaine phosphate single crystals (BPI1-xBPx: x = 0-0.1) in temperature regions of antiferrodistortive (Tc1) and ferroelectric (Tc2) phase transitions. The admixture of BP to BPI leads to increase of the antiferrodistortive phase transition temperature Tc1(x) (Tc1(0.1) = 360 K, Tc1(0) = 355 K) and decrease of the dielectric anomaly at Tc1(x). The nonlinear temperature dependence of the inverse dielectric constant in the antiferrodistortive phase, the electric field effect on the dielectric constant and acoustic anomalies at the ferroelectric phase transition are described in the frames of the Landau-Ginzburg-Devonshire-type thermodynamic model with the biquadratic coupling between nonpolar and polar order parameters. [ABSTRACT FROM AUTHOR]

Perovskites PbBO3 with multiple substitutions in the B-positions were synthesized. Ceramic samples with n = 2-6 (n is the number of different B-ions) were studied using X-ray diffraction, and measurements of dielectric permittivity at frequencies 12 Hz-100 kHz and temperatures 77-450 K. It has been shown that the samples are of the perovskite structure, they undergo phase transitions from disordered to ordered phase, and their dielectric behavior is typical for relaxors. The order-disorder phase transitions proceed with the unit cell doubling. Based on this and in accordance with random site model, the B-ion distribution over two sublattices is discussed. [ABSTRACT FROM AUTHOR]

Polycrystalline films of betaine phosphite (BPI) and triglycine sulphate (TGS) were grown by the evaporation method on different substrates (α-SiO2, α-Al2O3 and LiNbO3 with interdigital transducers, and Al/SiO2). Large (∼1 mm in BPI and ∼0.2 mm in TGS) single-crystalline blocks were visualized in a polarizing microscope in the reflection mode. Blocks are characterized by preferable in-plane orientation of the ferroelectric axis. Temperature dependences of the BPI and TGS film capacity at frequencies 120 Hz-1 MHz exhibit a strong maximum at the temperature of the ferroelectric phase transition of bulk crystals. The effect of a bias electric field on the dielectric constant and losses was studied. Description of dielectric properties is carried out using Landau-Ginsburg-Devonshire model with account of film-substrate interaction. Low frequency conductivity in BPI films is related to DC conductivity due to thermo-activation process with activation energy Eact ∼ 0.1 eV. AC conductivity associated with the hoping mechanism and the combination DC and AC conductivity was found in TGS films on Al/SiO2 substrates and α-Al2O3 substrates correspondingly. [ABSTRACT FROM AUTHOR]

A number of novel protein amino acid-based single crystals were grown from aqueous solutions and their dielectric and pyroelectric properties were studied in a temperature range 140-340 K. It was shown that some of the crystals such as L-His· (H3P04)2, L-Tyr· HCl, L-Ala2H3PO3· H2O have pyroelectric figure-of-merit comparable to those of TGS. Anomalous dielectric properties of DL-Ser2· H2S04· H2O single crystals were observed in a temperature range 260-270 K revealing a first-order phase transition to an incommensurate phase. [ABSTRACT FROM AUTHOR]

The article examines the phase transitions and dielectric relaxation in incipient ferroelectrics SrTiO3, KTaO3 and CaTiO3 with perovskite structure. The role of quantum fluctuations in the suppression of ferroelectric phase transition is studied. The transformation of Arrhenius classical thermally activated regime into quantum tunneling is also discussed.

Dielectric relaxation in SrTiO3 ceramic samples doped with Mn and (Mg1/3Nb2/3) was studied in a frequency range of 10 Hz-1 MHz at temperatures between 4.2 and 300 K. Debye relaxation was found in all the samples. The evolution from thermally activated Arrhenius regime to quantum tunneling was observed. The structure of impurity centers and parameters of thermally activated and tunneling processes ate discussed. [ABSTRACT FROM AUTHOR]