G. A. Pankova

Piezoelectric properties of crystals of some protein aminoacids and their related compounds

Growth of single crystals of some protein aminoacids and synthesis and growth of single crystals of their related compounds are reported. The temperature dependence of the integrated piezoelectric response of the single crystals grown was studied in the temperature range 120–320 K. The specific features in the temperature dependence are shown to be due to the enhanced damping of elastic vibrations in the crystals, which originates from the elastic vibrations being coupled to thermally activated rotation of the CH3 and NH3 molecular groups.

Protein Amino Acid Crystals: Structure, Symmetry, Physical Properties

Data on the growth of single crystals of protein amino acids and their compounds are presented. The structure and symmetry of the crystals are discussed. The piezoelectric response was studied at temperatures between 120 K and 320 K. The results of studies of optical second harmonic generation and optical activity from the literature are presented.

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.

Piezoelectricity in protein amino acids

The piezoelectric activity of protein amino acids and their compounds has been measured using the pulse method at a frequency of 10 MHz. It has been established that, at room temperature, the piezoelectric effect is not observed in α-glycine (achiral amino acid) and protein amino acids of the L modification, namely, methionine, phenylalanine, and tryptophan. An assumption has been made that this phenomenon is associated with the enhanced damping of elastic vibrations excited in samples due to the piezoelectric effect.

Dielectric properties of betaine phosphite and deuterated betaine phosphite films

Polycrystalline films of betaine phosphite (BPI) and deuterated BPI have been grown by evaporation on LiNbO3, α-SiO2, α-Al2O3, and NdGaO3 substrates. These films consist of large single-crystal blocks in which the polar axis (b) lies in the substrate plane. The results of studying the dielectric properties of the films using interdigital electrodes, X-ray diffraction, and block images in a polarized-light microscope in reflection are reported. The film transition into the ferroelectric state at T = Tc is accompanied by strong anomalies of the capacitance of the film/interdigital structure/substrate structure. The deuteration of BPI films leads to an increase in their temperature Tc: from Tc = 200 K for BPI-based structures to Tc = 280 K for structures with a high degree of deuteration (d ∼ 90%).

Acoustic properties of glycine phosphite crystals with an admixture of glycine phosphate

Acoustic and dielectric anomalies in the region of the ferroelectric phase transition in crystals of glycine phosphite (GPI) with a 2 mol % admixture of glycine phosphate (GP) are studied. The acoustic anomalies were found to differ strongly from those observed in nominally pure glycine phosphite crystals. A theoretical analysis of the acoustic and dielectric properties of the crystals was carried out within the model of a pseudoproper ferroelectric phase transition. It is shown that the acoustic anomalies, as well as the temperature dependences of the dielectric constant (for various external electric fields) and pyroelectric current observed in the vicinity of the phase transition in GPI-GP crystals, can be adequately described when the macroscopic polarization present in these crystals above the phase transition temperature is taken into account. The thermodynamic-potential parameters describing electrostriction and the biquadratic relation between the polarization and strain turned out to be close to those characterizing a nominally pure GPI crystal. An irreversible phase transition was observed to occur in GPI-GP crystals at T = 240 K, i.e., above the ferroelectric phase transition temperature.

Pyroelectric, piezoelectric, and polarization responses of glycine phosphite crystals with an admixture of glycine phosphate

Temperature dependences of the pyroelectric, piezoelectric, and polarization responses of glycine phosphite crystals containing different amounts of glycine phosphate were studied in the range 120–320 K. The experimental data obtained suggest the presence of a built-in bias field oriented along the twofold symmetry axis in these crystals. This field was found to be 5 kV/cm. It is suggested that the built-in bias plays a decisive role in the formation of the pyroelectric and piezoelectric crystal responses in the temperature interval 225–280 K, which is significantly higher than the ferroelectric phase transition point in nominally pure glycine phosphite crystals (224 K).

Acoustic and dielectric anomalies in the temperature range of a ferroelectric phase transition in glycine phosphite crystals

The acoustical and dielectric properties of glycine phosphite crystals are investigated in the temperature range of a ferroelectric phase transition. The acoustic anomalies for longitudinal waves along the X, Y, and Z crystallographic axes (where Y is the spontaneous polarization axis) are analyzed in the framework of the Landau theory. It is shown that pronounced acoustic anomalies of the velocity can be quantitatively described within the pseudoproper ferroelectric phase transition model with due regard for the long-range dipole-dipole interaction. For longitudinal acoustic waves propagating along the polar crystal axis, the striction anomaly of the velocity is only partly suppressed by the long-range dipole-dipole forces and an abrupt jump in the velocity is observed in the vicinity of the phase transition. The temperature coefficients of the velocity in the paraphase are determined. The striction contribution and the contributions biquadratic in the order parameter and in the strain to the velocity anomaly are separated.

Pyroelectric properties of some compounds based on protein aminoacids

Protein aminoacid-based compounds were synthesized, and their single crystals were grown. The dielectric and pyroelectric properties of the crystals were studied in the temperature ranges 80–340 and 140–340 K, respectively. It was established that three of the compounds studied (L-His(H3PO4)2, L-TyrHCl, L-Ala2H3PO3 · H2O) are linear pyroelectrics, with their room-temperature pyroelectric figures of merit being close to those of ferroelectric triglycine sulfate crystals.

Crystal Structure of di-(L-alanine)Monophosphite Monohydrate [{\rm C}_3{\rm O}_2{\rm NH}_7 ]_2 \cdot {\rm H}_3 {\rm PO}_3 \cdot {\rm H}_2{\rm O}

An X-ray analysis of the crystal structure of di-(L-alanine)monophosphite monohydrate was carried out. The symmetrically nonequivalent L-alanine molecules were found to be present in the structure in two different forms coupled by a strong hydrogen bond: monoprotonated positively charged [CH3CH(NH3)COOH] molecule and CH3CH(NH3)COO zwitterion. Two layers are distinguished in the structure: one is a positively charged layer formed by L-alanine molecules and the other is a negatively charged layer composed of phosphite ions and water molecules. These layers, alternating along the a axis, are connected to each other by a network of hydrogen bonds.