Effect of silver content on the mechanical and electrical properties of the YBaCuO/Ag ceramic

Doping the YBaCuO superconducting ceramic with 3–5 wt % silver is shown to substantially increase its microplasticity and strength. Temperature spectra of microplastic strain rates for YBaCuO/Ag ceramics with 0, 1.6, 2.9, 4.2, and 7.6 wt % silver were obtained. The structure of the spectra and the relation of one of the peaks to the superconducting transition are discussed. The specific features of the I–V characteristics of samples cooled in a magnetic field are considered. It is shown that the position of the rising branch of a I–V characteristic depends on its origin; this observation can be used to fix two or more stable states of an HTSC-based memory cell.     

Effect of magnetic field on the microplastic strain rate for C60 single crystals

Microplastic deformation in a magnetic field and in a zero field, as well as after preliminary action of a magnetic field on C₆₀ crystals, is studied with the help of a laser interferometer, which makes it possible to measure the strain rate on the basis of linear displacements of 0.15 µm. It is shown that the introduction of a sample into the field and its removal from a field of 0.2 T directly during sample deformation lead to a change in the strain rate, the decrease in the rate being accompanied by a brief interruption of deformation. The sign of the effect depends on temperature: the magnetic field accelerates deformation at room temperature and slows it down at 100 K. Preliminary holding of a sample in a field of 0.2 or 2 T produces a similar effect on the strain rate. Possible reasons for the observed manifestations of the magnetoplastic effect in C₆₀ and the relation between the sign of the effect and the phase transition at 260 K are considered.     

Inelastic deformation of C60 single crystals in the temperature range 80–300 K

The rate spectrum of small inelastic strains of the C₆₀ single crystal in the temperature range 80–300 K has been obtained with a precision laser interferometer. It is revealed that the spectrum exhibits two large peaks in the glass formation (90–100 K) and phase transition (250–260 K) ranges. A small strain acceleration is also observed at ～220 and 240 K. The first two maxima are attributed to the changes in strain resistance upon transitions, and the strain acceleration at 220 and 240 K is associated with the annealing of the defects formed upon rapid cooling of the crystal. It is demonstrated that the peak at 250–260 K broadens with an increase in the stress. The spectrum of strain rates is compared with the calorimetric curve for the same single crystal.     

Small-inelastic-strain rate spectrum of C60 single crystals near the phase transition at 250–260 K

The temperature spectrum of small-inelastic-strain rates in a vapor-phase-grown C₆₀ single crystal has been measured within the 200–290 K interval with a high-precision strain-rate meter based on a laser interferometer. The spectrum exhibits a strong peak in the region of the phase transition at 250–260 K and a slight strain acceleration at ∼240 K, which correlates well with the calorimetric curve. The first maximum is associated with strain that developes more easily in an fcc than in a primitive cubic lattice, and the second, to the effect on the strain rate of annealing of the defects created with fast crystal heating. Fiz. Tverd. Tela (St. Petersburg) 41, 1115–1118 (June 1999)     

Serrated creep of zinc single crystals under compression in a magnetic field

The compressive creep rate of zinc single crystals was measured for sample deformation increments of 150 nm, which permits the measurement of deformation jumps larger than 300 nm. A weak magnetic field B = 0.2 T is shown to increase the average creep rate and decrease the height and sharpness of submicron-sized deformation jumps. Preliminary holding of a sample in a magnetic field also influences the creep rate and the characteristics of deformation jumps. The data are explained in terms of a model relating the effect of a magnetic field to the destruction of barriers to dislocation motion.     

Deformation of solid polymers in a constant magnetic field

The effect of a constant magnetic field on the creep rate is investigated for poly(vinyl butyral), styrene-methacrylic acid copolymer [poly(styrene) + 16 wt % methacrylic acid], poly(methylene oxide), and other polymers. It is demonstrated that the constant magnetic field can variously affect different polymers and that the effect of the magnetic field is enhanced in a particular range of strain rates.     

Activation parameters of stepped deformation of polymers

Creep rates on short deformation base lines before and after a change in temperature and stresses were measured by interferometry to determine the activation energies and activation volumes of the process. It is shown that the activation parameters of polymer creep vary not only at a macroscopic level but also within the micron-size deformation steps. The largest potential barrier corresponds to the lowest rate in a step and plays the role of a “physical node.” The results confirm the supposition that micron-size jumps (steps) of polymer deformation are caused by the nonmonotonic nature of intermolecular interactions in microvolumes of this level. Fiz. Tverd. Tela (St. Petersburg) 40, 1635–1638 (September 1998)     

Evolution of nanoscale nonuniformities under deformation of irradiated Plexiglas

The example of Plexiglas irradiated with γ radiation to the dose of D = 330 kGy is used to demonstrate the presence of minor deformation jumps. Deformation levels are determined by deformation jumps values measured by the interferometric technique. These results support the position on the existence of domains from nanometers to tens of nanometers in size within amorphous polymers and allow one to study multilevel organization of the deformation process and determine the influence of external factors on various structures on the nanoscale and above.     

Jumplike deformation of polymer materials on the micrometer and submicrometer structural levels

Jumplike creep is considered as a reflection of the structural heterogeneity of amorphous polymers on the mesoscopic and nanoscopic levels. The D-450 epoxy resin, poly(vinyl chloride), poly(vinyl butyral), and a composite consisting of the D-450 epoxy resin and diabase microparticles are studied at a temperature of 290 K. The creep rate of the specimens under compression is measured with a laser interferometer in submicrometer-scale deformation increments. Periodic variations of the creep rate with time or under deformation correspond to a jumplike (stepwise) behavior of the creep. It is shown that diabase particles (5–10 μm in size) are responsible for the appearance of micrometer-scale jumps in the creep of the composite and that the deformation jumps on the nanometer level are comparable to the sizes of the globules. The role of the resolution of the method employed in the evaluation of the scale of deformation jumps and structural units is considered.     

Creep of linear unoriented polymers in tension,compression, and torsion

The creep of polymethyl methacrylate, polystyrene, and polyethylene in tension, compression, and torsion has been investigated over a broad interval of temperature below the glass transition point. It is shown that the creep criterion changes depending on the temperature. This is associated with changes in molecular mobility.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 24–28, January–February, 1970.