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The structure and transport properties of single crystal whiskers of the TiS3 quasi-one-dimensional semiconductor have been investigated. The anisotropy of the conductivity in the plane of layers (ab) has been measured as a function of the temperature. The anisotropy at 300 K is 5 and increases with a decrease in the temperature. Features on the temperature dependences of the conductivity along and across the chains are observed at 59 and 17 K. Near the same temperatures the form of the current-voltage characteristics measured along the chains is qualitatively changed. The current-voltage characteristics below 60 K exhibit nonlinearity and have a threshold form below 10 K. The results indicate possible phase transitions and the collective conduction mechanism at low temperatures.

We report the effects of electric field induced deformations of quasi one-dimensional conductors with charge-density wave (CDW). The most pronounced sort of deformation is torsional strain (TS). The TS is found to comprise two contributions. The features of the 1st—the larger one—are threshold hysteretic dependence on electric field and high relaxation time τ : For o-TaS 3 τ ∼10 −2 s at T =80 K and falls as exp(900 K/ T ) with increasing T . The 2nd contribution is linear in electric field and does not drop with frequency increase. The amplitude of this contribution falls abruptly with T approaching the Peierls transition temperature T P from below. Similar features of TS are demonstrated for other CDW compounds: (TaSe 4 ) 2 I, K 0.3 MoO 3 and NbS 3 type II, for which T P ≈360 K. We attribute the 1st and the 2nd contributions to large (hysteretic) and small (near-equilibrium) CDW deformations, respectively, likely—shear at the surface. The TS is observed also above T P : For TaS 3 and (TaSe 4 ) 2 I typical torsional amplitude is 10 −1 °/V in the resonance regimes, corresponding to the piezomodulus ∼10 −9 m/V. A separate study of TS was performed at room temperature with AFM technique. Apart from this (‘intrinsic’) effect, we observe electrostatic contribution to the TS. In contrast to the intrinsic response, the electrostatic one is proportional to the potential either over the sample, or over an additional electrode (‘gate’) placed nearby, but not to the difference of potentials between the sample ends. It is typically 2 orders of magnitude less. The intrinsic TS reveals a new electromechanical effect at room temperature, presumably associated with the excitations of the pinned mode of the CDW fluctuations. Its observation opens prospects for application of quasi one-dimensional conductors as micro- and nano-actuators. Basing on the electrostatic-induced TS we propose prototypes of electrometers and a technique for measurements of work function changes. Using a cryogenic transmission electronic microscope we observe also flexural deformation of TaS 3 in the double-clamped mode, visible both in resonant and static modes.

Texture and microstructure formation during equal channel angular pressing (ECAP) of Mg-0.49%Al-0.47%Ca alloy were studied. The selected ECAP condition (route BC, N=6 passes, true strain ε ≈ 6.8, T=300°C) ensures an ultrafine-grained structure of the alloy and basal texture, inclined at an angle of 45-55º relative to the direction of extrusion. The expectation that such a change of the texture, together with the refinement of microstructure, should improve the low temperature ductility of this material was confirmed by tensile testing.

Severe plastic deformation of a Mg-Al-Ca alloy resulted in different types of grain structure. High pressure torsion (HPT) was shown to lead to the formation of a nanocrystalline structure with a grain size of 100-200 nm, while equal channel angular pressing (ECAP) produced ultrafine grained (UFG) or submicrocrystalline (SMC) structures, depending on the ECAP temperature. An UFG structure with a grain size of 2-5 -m was formed at 300°C, as distinct from a finer SMC structure with a grain size of 300-800 nm formed at a lower temperature (220°C). The possibility of increasing the strength of the alloy in the UFG condition by a factor of 1.5-2, combined with a reasonable level of ductility and enhanced functional properties was thus demonstrated. ECAP of annealed Mg-Al-Ca with the formation of UFG structure was shown to lead to increased yield strength (by a factor of 2) and enhanced tensile ductility (by a factor of 3).

The influence of magnetic field and microwave irradiation on dynamical phase separation in submicron Bi2Sr2CaCu2O8+x bridges has been studied. Strong effect on the shape and metastable character of the step-like I-V characteristics are found. Under a weak field H < 2 Oe and low level microwave irradiation the step-like structure of the I-V characteristics smears out and disappears completely. The average frequency of switching between metastable states grows by 5 orders under increase of magnetic field by only 1 Oe. This behavior is explained in terms of the model of dynamical vortex lines.

The resistive state above the Larkin-Ovchinnikov (LO) instability current has been experimentally studied. Analysis of the stepwise I–V curves of thin superconducting bridges ≤1 μm wide, etched from the Bi2Sr2Ca1Cu2Oy (Bi2212) whiskers, reveals the following scenario of vortex dynamics: first, a pair of current-induced Abrikosov vortices enter the bridge, then they are accelerated by the current above the critical velocity of the LO instability and approach the limiting velocity of the normal phase propagation, of the order of 107 cm/s. Each vortex leaves a tail of normal phase behind itself, which is equivalent to a phase slip line. At low temperatures the tails cover the whole width of the bridge—the I–V curves between the steps become Ohmic.

The defect structure of superconducting single crystal whiskers BSCCO (2212) was studied by high voltage transmission electron microscopy. Dislocations, twins, growth steps, antiphase domains associated with a commensurate modulation and antiphase boundaries of incommensurate modulation were found. The latter are inherent to all whiskers in contrast to any other defects. The defect structures of the whiskers and BSCCO (2212) plate-like single crystals are compared. The influence of some defects on superconducting properties of the material is discussed.

The temperature dependence of the resistance and the current-voltage characteristics are measured for Bi2Sr2CaCu2Ox whiskers of different width, including whiskers possessing a width step. As the width decreases, the resistivity of the whiskers below the Berezinski\(\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\smile}$}}{l} \)-Kosterlitz-Thouless transition temperature increases, while above the transition it decreases. This effect is explained by two-dimensional vortices leaving the sample through its edge and confirms the existence of vortex pairs in layered high-Tc superconductors.

The decomposition at 250 °C of the Mg supersaturated solid solution in the ternary Mg–Nd–Y system and in binary Mg–Nd and Mg–Y alloys was studied. The kinetics of precipitation in ternary Mg–Nd–Y alloys differs from the kinetics of precipitation in binary Mg–Nd and Mg–Y alloys. Precipitates with the same crystal structure form in a shorter ageing time in ternary Mg–Nd–Y alloys than in binary Mg–Y alloys. The change of volume and the kinetics of solid solution decomposition in the ternary Mg–Nd–Y alloys as compared with the binary ones suggest that there is a certain solubility of Y in the Nd-rich precipitates and of Nd in the Y-rich precipitates.

The results of a combined study of the structural and conductive properties of BSCCO (2212) whiskers are reported. After electrical measurements the samples are examined by transmission electron microscopy, without preliminary thinning. The whiskers with transverse dimensions as small as 1 × 0.1 μ m 2 are single crystals of high quality. Some of the samples are free of dislocations. It is found that the quasi-one-dimensional behavior of the paraconductivity is independent of the presence of dislocations. However, the excess conductivity is suppressed in the twinned whiskers. The existence of a superstructure along the b -direction in a BSCCO crystal could be a possible reason for the a - b -plane paraconductivity anisotropy, resulting in the one-dimensional conducting fluctuations.

The growth of perfect single-phase (2212) superconducting BSCCO whiskers with cross-sectional area S as small as 0.1 μm 2 is described. Submicron cross section whiskers are shown to have perfect crystalline structure, some of them being free of dislocations. The critical current density of the whiskers J c , is shown to increase as S decreases 2 achieving 5 × 10 5 A/cm 2 for S = 0.15 μm 2 . The temperature dependence of resistivity ϱ( T ) of submicron whiskers in contrast to bulk-like single crystals exhibits a prominent deviation Δϱ down from linear temperature dependence ϱ N up to T ≈ 200 K. Δϱ is shown to be proportional to s −1 Δϱ / ϱ N S −1 exp(− T / T 0 ), T 0 =40 K K. The origin of Δϱ due to one-dimensional (1D) superconducting fluctuations is discussed.

High-T c superconductors are known to have a layered structure: the high conductivity Cu-O planes are separated by low conductivity layers in c direction. Moreover, there are some one-dimensional (1D) crystal structure entities: Cu-0 chains in YBCO compounds and superstructure in BSCCO and TBCCO materials. Because of this structure one might expect 1D behavior of fluctuations besides the 3D [1] and 2D [2–4]. Then, crossovers of the dimensionality due to temperature dependence of coherence length in a high-T c superconductor can be observed.

Temperature dependences of the resistance and current}voltage (I}

Temperature and electric-field dependencies of the conductivity for perfect BSCCO (2212) whiskers were measured. The two-dimensional (2D) behavior of linear and nonlinear fluctuation conductivity and 3D-2D and 2D-1D crossovers of dimensionality were observed.

The defect structure of BSCCO (2212) single crystal whiskers was studied by HV TEM. Dislocations, twins, growth steps, antiphase domains associated with a commensurate modulation and incommensurate superstructure defects were observed. The latter are inherent to all whiskers in contrast to any other defects mentioned above.