V. V. Lemanov

Ferroelectric properties of SrTiO3-PbTiO3 solid solutions

Dielectric properties of ceramic samples of Sr1−xPbxTiO3 solid solutions for x varying from 0 to 0.3 have been studied. The ferroelectric phase transition in this system has been established to persist down to x=0.005. Within the x values of 0.002 to 0.05, the ferroelectric transition temperature is shown to follow the relation Tc=A(x−xc)1/2, with A=440 K and xc=0.002.

Phase transitions in SrTiO3-based solid solutions

Phase transitions in solid solutions of strontium titanate with titanates of the divalent metals Pb, Ba, and Ca are considered. It is shown that the critical concentration xc in the well-known expression relating the transition temperature to the polar state in SrTiO3 with the concentration x of divalent metals, Tc=A(x−xc)1/2, is practically the same for all impurities. For large values of x, the ferroelectric transition temperature Tc depends linearly on x. The volume and impurity contributions to the Tc(x) relation are determined for this concentration range.

An experimental study of submerged jets at low reynolds numbers

Results of an experimental study of submerged subsonic air jets exiting from axially symmetric and plane channels in the Reynolds number range of 100–6000 are presented. Data on visualizing the flow picture and zone of the laminar-turbulent transition have been obtained. The measurement results are compared with well-known experimental data for gas macro- and microjets. The coordinate of the transition to the turbulence for microjets is shown to be able to reach high values, and a generalization of the experimental data is presented.

Refractometric study of polar ordering in Sr1−xBaxTiO3 single crystals

Abstract The temperature variations of the index of refraction were studied in nominally pure SrTiO3, Sr1−xBaxTiO3 single crystals (x = 0.02, 0.05, 0.07 and 0.14) and in Sr1−x CaxTiO3 (x = 0.014). Contributions of the spontaneous electrooptical effect to the temperature variations of the refractive index allowed us to obtain the concentration and temperature variations of the spontaneous polarization. It is shown, that the concentration dependence of the spontaneous polarization in Sr1−xBa.TiO3 has no significant peculiarities near the critical concentration xc = 0.035 and belowxX = 0.07 the polarization is proportional to (X — Xg)1/2, where xg = 0.0027. Contrary to that the precursor polarization increases, when x goes down to xc .

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.

Optical study of Sr1−xBaxTiO3 single crystals

Abstract The temperature variations of the index of refraction and of the birefringence were studied in nominally pure SrTiO3 and Sr1−xBaxTiO3 single crystals (x=0.025, 0.07 and 0.15). In Sr1−xBaxTiO3 (x=0.15 and 0.07) phase transitions from the paraelectric phase to a ferroelectric one were detected. A contribution of the spontaneous electrooptical effect to the temperature variation of the refractive index was obtained. This allowed us to evaluate the spontaneous polarisation and its temperature variation. For x=0.025 the transition at T≈28 K was explained by a polar state with glass-like behavior

Structure and properties of Sol-Gel PbZrTiO3 thin films

Abstract Crystal structure and electrical properties of PZT thin 200 nm films deposited on Si substrates with a 100/20 nm Pt/Ti sublayer were investigated by varying conditions of thermal treatment during gel drying and using different metals as the top electrode. Under definite conditions of gel drying a strong / textured films were obtained as a result of artificial epitaxy caused by stresses in the films due to their non-uniform shrinkage after drying and high temperature treatment. The electrical measurements indicate an essential role of near-electrode ionic processes and surface barriers in forming of metal-ferroelectric-metal thin film structures properties.

Measurement of thermal properties of thin dielectric films and anisotropic solids by ac hot-strip method

Abstract The present work deals with the foundations of the theory of the method of measuring the thermal properties of anisotropic solids and thin dielectric films deposited onto them. The experimental setup is briefly described. The authors demonstrate the possibility of measuring a set of thermal properties of solids by means of recording the amplitude and phase of temperature oscillations of a strip, which has a width comparable with the attenuation length of a temperature wave in the sample. The paper offers the results of measurements of the heat capacity, thermal conductivity, thermal diffusivity and thermal activity of leucosapphire. The thermal conductivity of an SrTiO3 film about 2 μm thick sputtered onto a single crystal of leucosapphire was determined by measuring the temperature oscillation amplitude at various frequencies.

An experimental study of the flow of subsonic flat mini and micro air jets

We have experimentally studied subsonic submerged air jets emitted from flat mini and micro nozzles with characteristic dimensions from 22 to 600 μm in a range of Reynolds numbers 70–2600. The point of laminar-turbulent transition (jet penetration range) was determined using the flow visualization technique. It is established that the penetration range of micro jets can reach 100–300 nozzle calibers. The Reynolds number for the transition to turbulence in flat mini and micro jets reaches high values (1000–2600), which are two to three orders of magnitude greater than the Reynolds numbers for the loss of stability (3–10). Available experimental data are summarized and generalized based on the Reynolds number determined for the jet penetration range.

Depolarization field as a driving force of fatigue in PZT ferroelectric thin films

Abstract A study has been made of the dependence of switched charge in ferroelectric lead-zirconate-titanate films on the number of polarization reversal cycles produced by bipolar voltage pulses of fixed amplitude and duration under variation of their repetition rate. The film fatigue in the polarization switching frequency range studied (100 Hz - 100 kHz) has been shown to be dominated by the depolarization field caused by the presence in the near-electrode film regions of a pyrochlorestructure nonferroelectric phase.