2-methylbenzimidazole single crystals and films are obtained by evaporation from an ethanol solution. The films have a texture with a predominant orientation of the pseudotetragonal axis in the film plane. The blocks are split crystals of the spherulite type, in which the pseudotetragonal axis rotates around the block center. Dielectric hysteresis loops are investigated in the crystals and films in the temperature range of 290–350 K. In the films, loops are observed for both in-plane and out-of-plane electric-field orientation. The maximum value of polarization in the films is close to that observed in single crystals P s ~ 5 μC/cm 2 . The difference in the temperature behavior of the hysteresis loops in the crystals and films is associated with the specific structure of the blocks.

The polarization switching was studied in single crystals and thin films of 2- methylbenzimidazole (MBI) obtained by evaporation method from an MBI ethanol solution. Dielectric hysteresis loops were measured in the temperature interval 290-390 K and frequency range 20-1000 Hz for different amplitudes of the electric field. The Kolmogorov β-model with account of Mertz law is used for simulation of hysteresis loops. The temperature dependence of domain wall motion activation field Ea has been obtained. Mechanisms of polarization switching in single crystals and films of MBI are discussed. In MBI films, a comparison of polarization switching for in-plane and out-of-plane electric field orientation is presented.

Thin films of partially deuterated betaine phosphate have been grown by the evaporation on Al 2 O 3 (110) and NdGaO 3 (001) substrates with a preliminarily deposited structure of interdigitated electrodes. The grown films have a polycrystalline block structure with characteristic dimensions of blocks of the order of 0.1–1.5 mm. The degree of deuteration of the films D varies in the range of 20–50%. It has been found that, at the antiferroelectric phase transition temperature T c afe = 100–114 K, the fabricated structures exhibit an anomaly of the electrical capacitance C , which is not accompanied by a change in the dielectric loss tangent tanδ. The strong-signal dielectric response is characterized by the appearance of a ferroelectric nonlinearity at temperatures T > T c afe , which is transformed into an antiferroelectric nonlinearity at T < T c afe . With a further decrease in the temperature, double dielectric hysteresis loops appear in the antiferroelectric phase. The dielectric properties of the films have been described within the framework of the Landau-type thermodynamic model taking into account the biquadratic coupling ξ P 2 η 2 between the polar order parameter P and the nonpolar order parameter η with a positive coefficient ξ. The E–T phase diagram has been constructed.

Subject of Research.We present results of structural and dielectric study of organic ferroelectric 2-methylbenzimidazole (MBI) thin films. Method. The films have been grown on substrates of leuco-sapphire, fused and crystalline silica, neodymium gallate, bismuth germanate, gold, aluminium, platinum. The films have been grown by two different methods: substrate covering by ethanol solution of MBI and subsequent ethanol evaporation; sublimation at the temperature near 375 K under atmospheric pressure. Crystallographic orientation studies have been performed by means of «DRON-3» X-ray diffractometer, block structure of the films has been determined by «LaboPol-3» polarizing microscope. Small-signal dielectric response has been received with the use of «MIT 9216A» digital LCR-meter, while strong-signal dielectric response has been studied by Sawyer-Tower circuit. Main Resuts. We have shown that the films obtained by evaporation are continuous and textured. Obtained film structure depends on the concentration of the solution. Films may consist of blocks that are splitted crystals like spherulite. Spontaneous polarization components in such films may be directed both perpendicularly and in the film plane. We have also obtained structures consisting of single-crystal blocks with spontaneous polarization components being allocated in the film plane. Block sizes vary from a few to hundreds of microns. Films obtained by sublimation are amorphous or dendritic. The dielectric properties of the films obtained by evaporation have been studied. We have shown that the dielectric constant and dielectric loss tangent increase under heating. The dielectric hysteresis loops are observed at the temperature equal to 291-379 K. The remnant polarization increases with temperature for constant amplitude of the external electric field, and achieves 4.5mC/cm2, while the coercive field remains constant. We propose that such behavior is explained by increase of the number of crystallites with switchable polarization due to decrease in the coercive field under heating. The remnant polarization decreases with frequency increase. Practical Relevance. Proposed method of ferroelectric films manufacture is characterized by low cost and convenience. Unlike many other ferroelectrics, the films contain no lead and rare metals. MBI films demonstrate the low value of the coercive fields. This paper may be useful for electronic components developers.

Ferroelectric thin films of partially deuterated betaine arsenate have been grown by evaporation method on NdGaO3 and -Al2O3 substrates. The films consist of small single-crystal blocks, in which ferroelastic domains have been visualized by polarizing microscope. X-ray diffraction shows that the blocks form a polycrystalline structure of film. Ferroelectric phase transition in DBA films is followed by dielectric anomaly and appearance of dielectric hysteresis loops. The magnitude of dielectric anomaly is small as compared with DBA single crystals. Small value of anomaly is associated with polycrystalline structure of DBA films. The deuteration degree of betaine arsenate films is smaller than that of crystals used for film preparation due to substitution of deuterium by hydrogen ions during the crystallization process.

The dielectric properties of deuterated betaine phosphite crystals with a high degree of deuteration in the region of the antiferrodistorsive (at T = T c 1 ) and ferroelectric (at T = T c 2 ) phase transitions have been investigated. The temperature behavior of the dielectric permittivity of betaine phosphite and deuterated betaine phosphite has been described within the framework of the Landau thermodynamic model taking into account the biquadratic coupling between the polar order parameter of the ferroelectric transition and the nonpolar order parameter of the antiferrodistorsive phase transition. It has been shown that an increase in the degree of deuteration leads to a decrease in the coupling between the order parameters. An increase in the temperature of the ferroelectric phase transition due to the deuteration of betaine phosphite is caused by an increase in the dielectric permittivity in the symmetric phase above the temperature of the antiferrodistorsive phase transition.

Thin ferroelectric films of deuterated glycine phosphite are grown by evaporation in a nitrogen atmosphere on NdGaO3 and α-Al2O3 substrates. The strong- and small-signal dielectric response of the resulting structures is studied using an interdigitated electrode system predeposited on the substrate. Crystallization of the films in a nitrogen atmosphere makes it possible to significantly (up to 291 K) increase the temperature of the occurrence of dielectric hysteresis loops, which characterize the transition of the film in the ferroelectric state. Unlike films grown in a normal atmosphere, the small-signal dielectric anomaly is heavily smeared with respect to temperature, which is attributed to an inhomogeneous distribution of deuterium over the film.

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 T c depends on the degree of deuteration D of the glycine phosphite. The maximum value T c = 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.