Polymer creep in a static magnetic field

By noting changes in the color of samples in a polarization microscope with varying degree of birefringence, the effect of a weak static magnetic fields (2 and 4 kOe) on molecules of glassy polymers has been observed. Variations in the nonmonotonicity of the rate of discontinuous creep at +18° were studied interferometrically. It is shown that the abruptness of the deformation jumps varies in a magnetic field, where this abruptness is assumed to be due to the existence of strong physical junctions between the kinetic units of deformation. The reactivity of the polymers to the magnetic field stands in satisfactory correspondence with their magnetic susceptibilities. Results show that such nonmagnetic materials as glassy polymers can noticeably alter their deformational properties in response to the action of magnetic fields. Fiz. Tverd. Tela (St. Petersburg) 39, 1690–1692 (September 1997)     

Modeling creep in L12-superstructure single crystals

Creep curves for compression and extension under constant loads and constant external stress are calculated using a model of the creep of L1₂-superstructure single crystals. It is shown that features of the creep in alloys with L1₂ superstructure can be explained via the superpositioning of normal and anomalous deformation mechanisms. It is established that during creep, the localization of deformation, which can lead to inverse creep, is important.     

Effect of a pulsed magnetic field on the microhardness of C60 single crystals

Magnetic-field pulses with induction greater than 10 T were observed to influence the microhardness of C₆₀ single crystals. It was established that the magnetic field reversibly alters the bulk properties of the material. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 2, 110–113 (25 January 1999)     

Interstitial oxygen in zinc oxide single crystals

Irradiation of zinc oxide single crystals with 2.5 MeV electrons produces both interstitial ions and vacancies. By means of ESR measurements oxygen ions on interstitial sites with tetrahedral and octahedral symmetry have been identified. Furthermore the behaviour of the oxygen vacancyV _o ⁺ is discussed.     

Effect of a magnetic field on the flow stress of Co and Fe single crystals

In a range of plastic deformation, the flow stress drop and the stress relaxation of Co and Fe single crystals are observed under an a.c. magnetic field. The magnitude of these drops is discussed on the basis of different deformation modes due to the crystal structure.     

Effect of a magnetic field on the plasticity and photo-and electroluminescence of ZnS single crystals

It is found that a ∼10 T magnetic field influences the microhardness and the photo-and electroluminescence of ZnS single crystals containing microtwins. It is established that a magnetic field irreversibly changes the properties of the crystal, leading to relaxation of the metastable states of structural defects. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 2, 114–118 (25 January 1999)     

Oscillations of a bubble separated from an air cavity under compression caused by magnetic field in a magnetic fluid

Based on the concept of mapping the free surface geometry of a weakly magnetic medium by the topography of isolines of the magnetic field strength magnitude, the shape of the free surface of a magnetic fluid is studied in the static state at two stages: the initial stage, where an annular magnet is moving toward the surface of the magnetic fluid column in a tube, and at the stage where the air cavity is pressed to the bottom. It is shown that the separation of bubbles from the air cavity occurs at the magnet axis in the immediate vicinity of the magnet symmetry plane. A method and an experimental setup are proposed to investigate possible electromagnetic indication of the size of air bubbles formed in the magnetic fluid. The results of an experimental study of bubble separation from an air cavity held in the magnetic fluid and compressed by the pondermotive forces of the magnetic field are discussed. The results may be of importance for designing a new technique for metering small gas shots to a reactor.     

Dislocation structure of copper single crystals in high-temperature creep test

It has been shown that in the high-temperature creep test at 0·85 kp mm^?2 and 0·7T _m (T _m is the melting temperature in °K) the dislocation substructure of copper single-slip oriented crystals is formed practically at the early stage of the test. The subsequent changes of substructure consist in the growth of subgrain misorientation and in the transformation of tangled subgrain boundaries into regular dislocation networks. There is a pronounced tendency to the formation of subboundaries in the {111} and {110} planes.     

Internal friction of deformed zinc single crystals

Zinc single crystals with the side in a (0001) basal plane were elongated and the internal friction measurements were carried out as a function of temperature in the mode of a flexural vibration. Two relaxation peaks were observed to appear: one at around 500°K and the other at about 570°K. Each activation energy was obtained 0.70±0.08eV and 1.01±0.06eV, respectively, by the peak shift method. The experimental results were discussed in terms of dislocations in pyramidal slip system {$\text{11}$22} 〈11$\text{2}$3〉 and twinning dislocations in the planes {$\text{1}$012} 〈10$\text{1}$1〉, respectively.     

Infrared radiation of zinc selenide single crystals

Long-wave photoluminescence (PL) spectra of both as-grown and Au-doped n-ZnSe single crystals are studied in the temperature range from 81 to 300 K. A narrow band of infrared (IR) radiation centered at 878 nm (1.411 eV) manifests itself in the low-temperature PL spectrum. It is established that this band intensity first increases and then decreases with increasing concentration of doping impurity. With increasing excitation radiation intensity, spectral position of the IR PL band is unchanged and its intensity increases under the linear law. With increasing excitation radiation wavelength, the IR PL band intensity increases, it becomes narrower and shifts towards long wavelengths. It is shown that the observed IR radiation is caused by recombination of free electrons with holes localized on associative acceptors in the ZnSe:Zn:Au crystals or in the undoped crystals.     

Transient creep of Cd single crystals at room temperature

Czechoslovak Journal of Physics -     

Destruction of SmS single crystals during the semiconductor-metal phase transition under hydrostatic compression

The behavior of internal microstresses, the size of the X-ray coherent scattering region, and the residual amount of the metal phase during the cyclic loading of SmS single crystals at hydrostatic pressure above the critical pressure of the semiconductor-metal phase transition has been investigated. It has been shown that the samples are destroyed as the microstresses reach the values corresponding to the ultimate stress of SmS single crystals. As the number of loading cycles increases, the coherent scattering region gradually decreases, which is accompanied by a decrease in the amount of the metal phase in the samples.     

Effect of constant magnetic field on the microhardness of LiIO3 single crystals

The microhardness of LiIO₃ crystals is found to decrease after action of a constant magnetic field B. The maximum change in the microhardness is observed within an hour after the magnetic treatment. Then, the microhardness demonstrates a gradual relaxation return to the initial value. The change in the microhardness is dependent on the orientation of magnetic inductance vector with respect to the polar axis. The effect is pronounced at B ⊥ [0001] and is absent at B ‖ [0001]. The sensitivity of the microhardness of LiIO₃ to a constant magnetic field has a threshold character: the effect appears at the magnetic induction higher than 1 T, increases quickly, and reaches the saturation even at 1.3 T. The reversibility of the magnetically induced decrease in the microhardness has been justified: the effect is exactly reproduced during repeated tests after two weeks. The study of the crystals doped with chromium shows that the increase in the Cr concentration enhances the magnetoplastic effect in LiIO₃, i.e., favors the softening of the material after the magnetic treatment.     

The influence of a weak magnetic field on the radiation-induced conductivity of C60 single crystals

The radiation-induced conductivity of C₆₀ single crystals is found to increase under the influence of a weak magnetic field (B < 1 T). It is shown that the observed effect is not related to the known galvanomagnetic phenomena. The results obtained are explained in terms of the proposed mechanisms of the influence of a weak magnetic field on the spin-dependent processes involving intermediate electron-hole pairs generated under radiation excitation of the fullerite single crystals.