S. G. Shul’man

Resistive switching in Au/TiO2/Pt thin film structures on silicon

The conditions and mechanisms of preliminary treatment in strong electric fields (forming) and subsequent resistive switching in Au/TiO2/Pt thin-film structures on silicon were investigated. The thin TiO2 films in these structures were prepared by different methods, namely, vacuum evaporation of metallic titanium followed by thermal oxidation in air and radio-frequency cathode sputtering of titanium dioxide from a powder target. The current-voltage and voltage-capacitance characteristics of the structures, as well as the dependences of their conductivity on the time of exposure to a dc voltage of different polarities and on the temperature were measured. The data obtained permitted the conclusion that the physical mechanism underlying the forming process consists in a sharp increase in the density of surface states in TiO2 films due to the electric breakdown of the Schottky barrier at the contact with the platinum electrode, whereas the resistive switching of the structures is governed by the variation in the population of surface states in the TiO2 band gap and/or in the defect concentration in the barrier region of the structures acted upon by voltage pulses of different polarities.

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).

Is there ferroelectricity in DNA

This paper reports on a study of the dielectric properties of DNA (sodium salt from calf thymus, SIGMA) under heating and cooling of a sample within the temperature interval 20–60°C, which was conducted in air, in a humid environment, and in vacuum. It is shown that the data obtained can be accounted for by the sample conductivity increasing as a result of DNA releasing water into a separate phase with increasing temperature and the formation of a double electric layer at the DNA interface with metallic electrodes, without invoking the idea of ferroelectricity present in DNA.

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.

Phase transition in thin epitaxial ferroelectric films as derived from thermal measurements

The temperature dependence of the heat capacity of thin epitaxial films BaTiO3/MgO is studied by the dynamic 3ω method in the thickness range 50–500 nm. It is revealed that the heat capacity exhibits diffuse anomalies due to phase transitions. The temperature of the ferroelectric phase transition TC increases with decreasing film thickness. The reasons for the strong diffuseness of the transition and the nonlinear dependence of the transition temperature on the film thickness are discussed.

Phase transition in diserine sulfate monohydrate crystals

The temperature dependences of the real and imaginary parts of the complex permittivity of diserine sulfate monohydrate crystals and of their electrical response in different crystallographic directions to a change in temperature are investigated. It is confirmed that these crystals undergo a first-order phase transition in the temperature range 260–270 K. This phase transition is assumed to originate from the freezing of the orientational degrees of freedom of the crystallization water molecules involved in these crystals.

On the effect of spontaneous polarization on the height of the Schottky barrier at the metal-ferroelectric contact

A comparison of the available concepts on the effect of spontaneous polarization on the height of the Schottky barrier at the metal-ferroelectric contact with the corresponding experimental data has been used as a basis for setting up an alternative model of this phenomenon, which draws on the dependence of the electron work function of a ferroelectric on the magnitude and orientation of the spontaneous polarization vector.

Electric field induced ferroelectricity in PbBO3 perovskites with complex substitution in the B position

Processes of the polarization switching in ceramic relaxors Pb(Mg1/3Ti1/3W1/3)O3, Pb(Mg1/4Sc1/4Nb1/4W1/4)O3, Pb(Mg1/5Sc1/5Ti1/5Nb1/5W1/5)O3, and Pb(Mg1/6Sc1/6Ti1/6Sn1/6Ta1/6W1/6)O3 have been investigated at frequencies from 50 Hz to 2 kHz in the temperature range 90–300 K for measuring field amplitudes up to 20 kV/cm. It has been demonstrated that, under specific conditions, these materials are characterized by saturated dielectric hysteresis loops, which indicate the appearance of the ferroelectric state induced by the electric field. The dependences of the spontaneous polarization and the coercive field of the relaxors under investigation on their chemical composition, temperature, and frequency of the measuring voltage have been determined.

Experimental studies of the thermal properties of thin films by a probe technique with periodic heating

The thermal properties of SrTiO3 thin films are investigated experimentally by recording the amplitude and phase of the temperature oscillations of a flat probe with the heat flux perpendicular to the plane of the film. Results are given from measurements of the specific heat and thermal conductivity of a leucosapphire substrate and the thermal conductivity of a SrTiO3 film of thickness 2 µm.

Study of the thermal properties of Ba1−xSrxTiO3 thin films by the ac hot-probe method

The heat capacity and heat conductivity of Ba1−xSrxTiO3 (x=0.2, 0.5, 0.8) polycrystalline films 1.5–2.0 µm thick on a massive substrate have been studied by the ac hot-probe method for three-layer systems (conducting probe-dielectric film-substrate) at temperatures ranging from 100 to 400 K. It is found that the thermal properties exhibit anomalies in the phase transition range.