E. V. Balashova

Ferroelectric betaine phosphite films: Growth, optical imaging, and dielectric properties

Polycrystalline films of betaine phosphite (BPI) were grown by evaporation method on SiO2 and LiNbO3 substrates with interdigital transducers. Large (∼1 mm) single-crystalline blocks were visualized in a polarizing microscope in the reflection mode. Temperature dependences of the film capacity at frequencies 120 Hz–1 MHz exhibit a strong maximum at the temperature of the ferroelectric phase transition of BPI bulk crystals. The effect of a bias electric field was studied. Temperature variations in dielectric permittivity and electric field effect are analyzed using a thermodynamic model accounting for the substrate-film interaction.

Dielectric and Acoustic Properties of Some Betaine and Glycine Compounds

Acoustic and dielectric properties of deuterated betaine arsenate (DBA), betaine phosphite (BPI) and glycine phosphite (GPI) have been studied in the vicinity of ferroelectric, antiferroelectric and improper ferroelastic phase transitions. The temperature dependences of the velocity and attenuation of acoustic waves and dielectric response, including the electric field effect on dielectric constant, have been studied. It is shown that the dielectric and acoustic properties of the crystals and some features of phase diagrams can be described in the framework of the Landau phenomenological theory with account of bilinear or biquadratic coupling between polar (polarization) and nonpolar (centrosymmetrical or non-centrosymmetrical structural) order parameters.

GROWTH, OPTICAL IMAGING AND DIELECTRIC PROPERTIES OF FERROELECTRIC BETAINE PHOSPHITE AND TRIGLYCINE SULPHATE FILMS

ABSTRACT 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.

Ultrasonic study of deuterated betaine phosphate crystals

Abstract The temperature dependences of velocity and attenuation of longitudinal acoustic waves in deuterated betaine phosphate crystals in the region of high-temperature and low-temperature phase transitions have been studied. The coupling coefficients and order parameter relaxation time have been determined.

Structural and Dielectric Properties of Glycine Phosphite Thin Films

Thin polycrystalline films of amino acid ferroelectrics glycine phosphite (GPI) have been prepared by evaporation method on NdGaO3(001) substrate with interdigital structure of electrodes deposited on the surface. Optical images of films obtained by means of polarized microscope in reflection mode have shown that the films consist of small single crystal blocks of several tens of microns in size. X-ray diffraction analysis proves that the non-polar c* axis in blocks coincides with the normal to the surface, and the polar axis b is oriented in the film plane. Temperature dependences of capacitance of GPI/NdGaO3 structures measured using interdigital structure of electrodes exhibit strong anomaly at ferroelectric phase transition temperature of glycine phosphite single crystals. Dielectric hysteresis loops in glycine phosphite films were measured by Sawyer-Tower method. The difference in frequency dependence of coercive field and remnant polarization in structures with GPI and previously studied betaine phosphite films is analyzed and attributed to considerable difference in dimensions of blocks in these structures.

Dielectric properties of betaine phosphite films

Polycrystalline films of betaine phosphite are grown on single-crystal quartz and lithium niobate substrates atop interdigitated transducers. It is revealed using a light-polarizing microscope in the reflection mode that the films are made up of large (up to 1 mm in size) single-crystal blocks. The temperature dependences of the film capacitance measured at frequencies from 120 Hz to 1 MHz pass through a strong maximum at the ferroelectric phase transition point. The effect of a bias on the permittivity of the films is investigated. It is shown that the differences in the temperature dependences of the permittivity of single crystals and films originate from the influence of dynamic strains in the substrate on the film and from the presence of an effective depolarizing field.

Ferroelectric films of deuterated glycine phosphite: Structure and dielectric properties

Polycrystalline textured films of deuterated glycine phosphite consisting of single-crystal blocks with lateral dimensions ∼(50–100) μm and a thickness d ∼ (1–5) μm have been grown by evaporation on NdGaO3(100) and α-Al2O3 substrates with preliminarily deposited interdigitated electrodes, as well as on Al substrates. The c* (Z) crystallographic axis in the blocks is normal to the film plane, and the a (X) axis and the polar axis b (Y) are oriented in the film plane. The temperature dependences of the capacitance of the structures measured with the interdigitated electrode system reveal a strong dielectric anomaly at the film transition to the ferroelectric state. The phase transition temperature Tc depends on the degree of deuteration D of the glycine phosphite. The maximum value Tc = 275 K obtained in the structures studied corresponds to a degree of deuteration of the glycine phosphite D ∼ 50%. The frequency behavior of the dielectric hysteresis loops in glycine phosphite films differs radically from that of the previously studied films of deuterated betaine phosphite, which evidences that polarization switching in these structures proceeds by different mechanisms. It has been that application of a dc bias to the electrodes changes the shape of the dielectric hysteresis loops and shifts them along the electric field axis. The shift of the loops depends on the sign, magnitude, and time of application of the bias. Possible mechanisms underlying the induced unipolarity are discussed.

Effect of electric field on the dielectric permittivity of betaine phosphite crystals in the paraelectric phase

Temperature dependences of the dielectric permittivity of betaine phosphite crystals are studied both without and under application of an electric bias. It is shown that, in view of the fact that the high-temperature improper ferroelastic (antiferrodistorsive) phase transition at Tc1=355 K is nearly tricritical, the nonlinear temperature dependence of inverse dielectric permittivity in the paraelectric phase and the effect of the field on the dielectric permittivity can be described within a phenomenological model containing two coupled (polar and nonpolar) order parameters with a negative coupling coefficient. An analysis of the model revealed that, in the case where two phase transitions, a nonpolar and a ferroelectric one, can occur in the crystal, all of its dielectric properties, including the polarization response in a field, can be described by one dimensionless parameter a. For the crystal under study, we have a=−2.5. This value of the parameter corresponds to a second-order ferroelectric transition far from the tricritical point, at which a=−1. It is shown that the polarization response in the paraelectric phase in an electric field calculated within this model differs radically from that in the ferroelectric phase-transition model for which the Curie-Weiss law holds in the paraelectric phase.

Ultrasonic study of betaine compounds

Abstract Acoustic properties of deuterated betaine phosphate (DBP), deuterated betaine arsenate (DBA) and betaine phosphite (BPI) were studied in the vicinity of antiferrodistortive, antiferroelectric and ferroelectric phase transitions. Anomalies of the velocity and the attenuation of acoustic waves and some features of phase diagrams for these solid solutions are described in the framework of the Landau theory. Some coefficients of the thermodynamic potential and the relaxation time of the order parameters are determined. Rather large values of the relaxation time allow to relate the phase transitions to the order-disorder type.

Small- and strong-signal dielectric response in a single-crystal film of partially deuterated betaine phosphite

Poly- and single-crystal films of betaine phosphite deuterated to ∼20% have been grown by evaporation on NdGaO3 (001) substrates with a preliminarily deposited planar interdigital structure of electrodes. The small-signal dielectric response in the 0.1–100.0-kHz frequency range has revealed a strong anomaly in capacitance upon the transition of the films to the ferroelectric state. Application of a bias field brings about suppression and a slight shift of the dielectric anomaly toward higher temperatures. The strong-signal dielectric response has been studied by the Sawyer-Tower method over the frequency range 0.06–3.00 kHz both in the para- and ferroelectric phases. In contrast to the case of a plane-parallel capacitor, in the planar structure studied, the dielectric hysteresis loops exhibit a very small coercivity at low frequencies, which grows with increasing frequency. This difference should be assigned to different domain structures formed in a planeparallel capacitor and in a planar structure in a saturating field. The growth of hysteresis with increasing frequency in a planar structure is considered to be associated with the domain wall motion.