Mikhail D. Malinkovich

Effect of the structure of a ferroelectric vinylidene fluoride-tetrafluoroethylene copolymer on the characteristics of a local piezoelectric response

The surface topography and characteristics of a local piezoelectric-response signal in isotropic films of a ferroelectric vinylidene fluoride-tetrafluoroethylene copolymer with a composition of 94: 6 are studied via scanning probe microscopy. The X-ray diffraction and IR spectroscopy data indicate that crystallization occurs in a mixture of β and γ polymorphic modifications. The exposure of the original film to a dc field bipolar leads to the formation of polarized regions exhibiting low stability. Recrystallization is followed by structural transformations accompanied by conformational transitions. As a result, there is a decrease in the concentration of chain segments in the T3GT3G− conformation and, conversely, an increase in the concentration of isomers in the planar zigzag conformation. In addition, the characteristics of the local piezoelectric response after polarization become more stable, while the signal undergoes phase reversal. A second-harmonic piezoelectric response signal induced by the electrostriction effect is detected for the studied ferroelectric polymer samples. It is found that the original film has two types of regions that contribute to the measured signal. A change in the pattern of the second-harmonic piezoelectric-response signal in the recrystallized film is attributed to a change in the contribution of the electrostriction effect to the macroscopic piezoelectric response.

Local ferroelectric properties in polyvinylidene fluoride/barium lead zirconate titanate nanocomposites: Interface effect

The local piezoelectric properties of ferroelectric composites consisting of P(VDF-TrFE) copolymer matrix with barium lead zirconate titanate ceramic inclusions were addressed both experimentally using piezoresponse force microscopy technique and theoretically applying the Landau-Ginzburg-Devonshire formalism. A transient region with a width of approximately 40 nm has been found at the interface between the two constituents. It is shown that the piezoresponse in the vicinity of the interface is strongly affected by inhomogeneous stresses originating from an incompatibility of thermal expansion coefficients of PVDF and lead zirconate titanate.

Magnetoelectric metglas/bidomain y + 140°-cut lithium niobate composite for sensing fT magnetic fields

We investigated the magnetoelectric properties of a new laminate composite material based on y + 140°-cut congruent lithium niobate piezoelectric plates with an antiparallel polarized “head-to-head” bidomain structure and metglas used as a magnetostrictive layer. A series of bidomain lithium niobate crystals were prepared by annealing under conditions of Li2O outdiffusion from LiNbO3 with a resultant growth of an inversion domain. The measured quasi-static magnetoelectric coupling coefficient achieved |αE31| = 1.9 V·(cm Oe)−1. At a bending resonance frequency of 6862 Hz, we found a giant |αE31| value up to 1704 V·(cm Oe)−1. Furthermore, the equivalent magnetic noise spectral density of the investigated composite material was only 92 fT/Hz1/2, a record value for such a low operation frequency. The magnetic-field detection limit of the laminated composite was found to be as low as 200 fT in direct measurements without any additional shielding from external noises.

The effect of silicon-substrate orientation on the local piezoelectric characteristics of LiNbO3 films

The domain structure of lithium-niobate thin films grown on Si(111) and Si(100) substrates coated with a native oxide layer with a thickness of no less than 2 nm is investigated by X-ray diffraction, scanning electron microscopy and piezoresponse force microscopy. The films are synthesized by the rf magnetron sputtering of a single-crystal lithium-niobate target. A high degree of grain orientation in the polycrystalline films is demonstrated. The piezoelectric coefficients dzz of the lithium-niobate films on Si(111) and Si(100) substrates are calculated from the measured dependences of the amplitude of the piezoresponse signal on the ac voltage applied between the cantilever tip and the substrate. Piezoelectric hysteresis loops are obtained in the remanent piezoelectric response regime

ФОРМИРОВАНИЕ БИДОМЕННОЙ СТРУКТУРЫ В ПЛАСТИНАХ НИОБАТА ЛИТИЯ, ПРЕДНАЗНАЧЕННЫХ ДЛЯ БЕТА–ВОЛЬТАИЧЕСКИХ ГЕНЕРАТОРОВ ПЕРЕМЕННОГО ТОКА

This article discusses the possibility of increasing the efficiency of betavoltaic generators by using lithium niobate single−crystal bimorph as the piezoelectric transducer element. Existing betavoltaic alternating voltage generators consist of a piezoelectric cantilever and a  electron source, wherein the cantilever is a resilient member, for example silicon, to which a PZT ceramics piezoelectric element is connected. In this study we suggest changing the structure of the silicon cantilever with a piezoelectric element for a uniform cantilever which is a thin plate of bidomain lithium niobate single crystal. This increases the efficiency of converting mechanical vibrations to electrical power, Q of the system, and the stability of the working parameters, and furthermore significantly increases — up to several hundred degrees — the operation temperature range. We have considered in details the solution of the main task —formation of a bidomain structure in a thin lithium niobate plate. A method of the sample high−temperature annealing in a nonuniform electric field is proposed. The possibility of domain structure prediction on the basis of the developed model is shown. Samples with a domain boundary depth of 120—150 microns have been obtained, and we have shown that the clarity of the boundary depends on the voltage between the working cell strip electrodes and the external electrode. The method is effective for bidomain structure formation in plates of about 300 microns in thickness.