Influence Of Uniaxial Compression Research Articles

On the low-temperature isotropic point in Rb2SO4 crystals

In this work, Rb2SO4 single crystals of good optical quality were synthesized and the spectral (300–700 nm) and temperature (300–77 K) dependencies of birefringence were experimentally investigated. It was found that with a temperature decreasing, at a temperature of T = 85 K and a light wavelength of λ = 500 nm, the birefringence value in the Y direction is zero (Δny = nz – nх = 0), which testifies to the existence of a new isotropic point. The influence of uniaxial compression on changes in Δny (Т, λ) was studied, and their significant sensitivity was revealed. The temperature-baric and spectral-baric changes of the isotropic point position were analyzed, based on which the temperature-spectral-baric diagram of the isotropic state of the crystal was constructed, which will be of practical importance for the use of crystal as an active element in a crystal-optical temperature sensor for a low-temperature region. Based on the Δny (Т, λ, σ) dependencies, the combined piezo-optic coefficients of the crystal were estimated, and it was assumed that not only thermal but also mechanical deformation of the optical indicatrix takes place in the vicinity of the isotropic point.

Влияние межслоевой механической связи в мультиферроике на мультикалорический эффект

The influence of uniaxial compression on the electrocaloric effect in a barium titanate-based bilayer was studied using the Landau-Ginzburg thermodynamic approach. Barium titanate was used as a model material. It was shown that the electrocaloric effect can be controlled by uniaxial compression. Application of compressive stress is an effective approach to enhance the electrocaloric effect in ferroelectric ceramics. The compressive stress in the considered magnetostrictive-ferroelectric bilayer is a result of mechanical coupling between ferroelectric and magnetostrictive phases.

Influence of uniaxial compression on the shape memory behavior of vitrimer composite embedded with tension‐programmed unidirectional shape memory polymer fibers

AbstractTension programmed shape memory polymer (SMP) fibers have been used as sutures for closing wide‐opened cracks per the close‐then‐heal strategy. However, the composite may be subjected to compression loading during service. These compression loads can reduce the amount of recoverable strain in these pre‐tensioned fibers, limiting their ability to close cracks. The purpose of this study is to investigate the effect of in‐service compression loading on the shape memory effect (SME) of composites consisting of SMP fiber and SMP matrix. To this end, pre‐stretched shape memory Polyethylene Terephthalate (PET) fibers were embedded into a shape memory vitrimer to obtain composite samples with different fiber volume fractions. The SME of both the PET fiber and the vitrimer was investigated. The effect of compression load on the SME of the composite was studied. It is found that, uniaxial compression on the composite along the fiber direction significantly reduced the shrinking ability of the embedded pre‐tensioned SMP fibers. Hence, this is a factor that needs to be considered when designing such types of self‐healing composites.

The influence of uniaxial compression upon pore size distribution in bi-modal soils

Transport of water, of dissolved and non-dissolved chemicals, of gas, the rooting of plants and the conditions for all soil biota are influenced by the soil porous system and by the soil pore size distribution. We have analyzed the change of the soil porous system due to the short time compression in ranges from 0 to 300 kPa in Entisols, Alfisols, and Vertisols. The procedure was based upon the evaluation of the soil water retention curves. The equation of log-normal pore size distribution in bi-modal soils was applied for the analysis. The obtained physical parameters describe the soil porous system and its change due to the compression. The minimum pressure head h A between two peaks of pore size distribution represents the boundary between the structural and matrix domains of the soil porous system. The value of h A was in broad ranges from h A = −136 up to h A = −585 cm. Pressure head corresponds to equivalent pore radius from r = 10.9 to r = 2.5 μm. The rate of change of h A due to the applied compression was not the same in all examined soils. h A decreased in some soil taxons and in other soils it slightly increased when the compression stress rose. It follows that the boundaries between the soil pore categories cannot be taken as a fixed value for all soils and for all compression stresses. The increase of the compression stress caused a decrease of the total porosity, but the decrease of the structural porosity was much more expressed. The ratio of the decrease of structural porosity due to compression was in ranges between 0.91 and 0.48. The change of the matrix porosity has not the same tendency in all soils. In majority of instances it was increasing, but in two soils it was slightly decreasing with the increase of compression stress. The characteristics of the pore size distribution did not change in a uniform way either. The pores size distribution curve is more flat and more broadly distributed due to compression in the structural domain. The tendency is opposite in the matrix domain. A generally valid rule on the change of the pore size distribution due to compression does not exist for all soil taxons. The change was great in both domains of soils with a low stability of aggregates. The change was relatively small in soils with a well-developed structure where it was more related to the structural domain. The log-normal model does not fit in all instances to pore size distribution in the structural domain. A profound study of the soil micromorphology may result in a better description of the soil porous system and its internal change during compression.

Mobility anisotropy of two-dimensional hole gases in (001)GaAs/Al0.5Ga0.5As heterostructures and the influence of uniaxial compression

Transport properties of 2D hole gases in (001)GaAs/Al0.5Ga0.5As heterostructures in the [1 = 10] and [110] directions have been investigated. In-plane uniaxial compression up to 5 kbar was applied in one or the other of the two directions, and measurements were performed in the temperature range 1.4 - 60 K and in a magnetic field up to 6 T. Without uniaxial compression the mobility is largest in the [1 = 10] direction, the [1 = 10]:[110] mobilities ratio attaining its largest values at low temperatures and high carrier densities. Interface roughness scattering together with acoustic phonon scattering is suggested to be the underlying phenomenon. Under uniaxial compression the electrical resistance decreases in the direction parallel to the compression, and it increases in the direction perpendicular to the compression. This behaviour is found to be in qualitative agreement with recent band structure calculations.

Influence of uniaxial compression on the photoconductivity of highly compensated Si〈B, Mn〉

It was observed that the photosensitivity limit and the increase in the photoresponse depend fairly strongly on uniaxial elastic deformation in compensated Si〈B, Mn〉 crystals.

Influence of uniaxial compression at 80 K on the formation of radiation defects in KCl, KBr, and KI crystals

The influence of uniaxial compression at 80 K on the efficiency of formation of stable radiation defects in KCl, KBr and KI crystals is investigated by absorption spectroscopy. It is found that compression along the 〈100〉 directions does not alter the efficiency of radiation defect formation in KCl and KBr crystals, but in KI the efficiency drops by more than an order of magnitude. It is concluded from a semiquantitative analysis that the observed difference is attributable to the impossibility of H centers fitting into the compression-reduced interstitial voids in KI, whereas several multiples of ten-percent compression is required to produce the analogous effect in KCl and KBr.

On the anomalous phonon mode behavior in HgSe

From the recent information on the neutron scattering data of phonon dispersions, we have established an eleven parameter rigid-ion model to understand the vibrational properties of both perfect and imperfect HgSe. Model calculations for the lattice dynamics, frequency spectrum, and the temperature dependence of the specific heat are shown to be in very good agreement with the recent experimental measurements. Our Green’s function calculations suggests that the possibility of a gap mode (due to Hg in HgSe) for the observed anomalous structure in infrared reflectivity experiments near ∼110 cm−1 cannot be completely ruled out. More optical (infrared and Raman) experiments regarding the influence of uniaxial compression are very much needed to help at least in assigning the symmetry of the defect center involved in the observed behavior.

Some Magnetic Properties of Two Basalts Under Uniaxial Compression Measured at Different Temperatures

Two basalt samples with homogeneous titanomagnetites as the only ferrimagnetic component, have been investigated, to find out about the influence of uniaxial compression on coercive force and saturation remanence at different temperatures and on thermoremanent magnetization. The samples have been investigated in natural state and after a heat treatment of 30h at 700°C in air. Caused by this heat treatment the original homogeneous titanomagnetites are transformed into an inhomogeneous mineral aggregate. The natural samples show a strong dependence of all measured values on uniaxial compression: At room temperature and a compression of 1kbar for example, the coercive force increases by about 100% and the saturation remanence decreases by about 50%. These variations are reversible. The behaviour of thermoremanence is distinctly different depending upon whether uniaxial compression and applied magnetic field are parallel or perpendicular to each other. In the first case a decrease of about 50%, in the second case an increase of about 50% is observed.In contrast to these results the heat treated samples show only a very slight dependence of their magnetic parameters on uniaxial compression.