Effect Of Uniform Pressure Research Articles

Novel half-metallicity in Y-type equiatomic quaternary Heusler alloys XFeCrAl (X = Rh, Pd, and Pt)

In the present study, we performed theoretical investigations to understand the origin of the half-metallic properties of new types of equiatomic quaternary Heusler compounds XFeCrAl (X = Rh, Pd, and Pt) and their possible applications in spintronics. These compounds crystallize in the Y-type structure with the F-43m space group, where the constitutive atoms are located in their non-equivalent positions in Type-I. Furthermore, we verified the thermodynamic, chemical, mechanical, and dynamical stabilities of these alloys. The results showed that they are stable in the magnetic phase where the optimized lattice constants are X-dependent. Among the three sample alloys, PdFeCrAl was shown to be the hardest with a brittle nature, whereas the others were found to be ductile. Analyses of the energy bands and magnetic profiles indicated the 100% spin-polarized, half-metallic, ferromagnetic natures of PdFeCrAl and PtFeCrAl, with EHM values of 0.09 eV and 0.03 eV, respectively, whereas RhFeCrAl is a nearly half-metallic ferrimagnet with 91% spin-polarization and it tends to act as a half-metal under the effect of uniform pressure. Their half-metallic nature can be expected because of the wide range of uniform strain due to their high bulk moduli. Thus, they have novel characteristics with lattice constants in the ranges of 5.55–5.64 Å, 5.53–6.04 Å, and 5.55–5.99 Å for RhFeCrAl, PdFeCrAl, and PtFeCrAl, respectively. The total magnetic moments of 1.98 μB, 2.99 μB, and 3.0 μB per formula unit obtained for RhFeCrAl, PdFeCrAl, and PtFeCrAl follow the Slater–Pauling rule. The highest Curie temperature (1113 K) obtained for PtFeCrAl demonstrates its feasible applications in spintronics with a high temperature limit.

Energy Condition of Plasticity

A strength condition is obtained that takes into account the deformation anisotropy and the effect of uniform pressure on the mechanical properties of materials.

Effect of pressure on the lifetime and the creep of metals and the kinetic equation parameters

The effect of uniform pressure on the activation parameters of the kinetic equation that describes the exponential dependence of the steady-state creep rate and the lifetime of polycrystalline metals on stress and temperature is estimated. It is shown that, under pressure, the parameters that determine the behavior of a metal under load are the activation energy and the internal stresses. The dependence of these parameters on the applied pressure is revealed.

Initial Stage of Void and Crack Healing in Polycrystalline Metals under Uniform Compression

The effect of uniform pressure and temperature on voids and cracks located at grain boundaries in polycrystalline metals is studied. A high-sensitivity method for measuring density, scanning electron microscopy, and optical microscopy were used to analyze the healing of cavities. The results obtained are discussed on the basis of the existing notion of the kinetics of healing under pressure at various temperatures.

Electron Metal-Dielectric Phase Transitions in Semiconductors under Pressure

The effect of uniform pressure on the character of metal-dielectric transitions in compensated weakly- and highly doped semiconductors (WHDCS) is considered. The influence of hybridization of resonance quasilocalized impurity states with band continuum states on the transition is shown. Minimum metallic conductivities in p-CdSnAs2 are determined for Mott and Anderson transitions. Special features of the metal-dielectric transformation in weakly-doped narrow- and high energy-gap semiconductors are discussed for the case of hydrogen-like impurities. Anderson localization in WHDCS is also considered. Phase diagrams are presented.

Generation of exact stiffness matrix for a spherical shell element

This paper deals with a method of generating stiffness coefficients and fixed edge forces for a spherical shell frustrum element. The formulation is based upon an approximate analytical solution of the differential equations governing elastic behaviour of the frustrum. Effect of uniform pressure p n, self weight, uniform temperature rise and edge loads have been considered. The paper also presents results of application of the proposed method to some selected problems.

Foundation Uniform Pressure and Soil‐Structure Interaction

Practicing foundation engineers tend to consider the foundation load as the point load when they want to consider its influence on the adjacent foundations. They believe that it will yield conservative results when a Boussinesq equation is considered. This derivation shows that such an assumption is groundless. The effect of uniform pressure on the adjacent foundations could be as high as 25% more than its effect when the pressure is lumped as a concentrated load at the center of the footing. The derivation converts the square footing into a shape that fits the polar coordinates. Such conversion facilitates the integration of the uniform pressure effect of one footing on the adjacent footings. Parameters and limits of integration are derived, then used in a practical example.

Uniform Pressure Effect on Magnetic Phase Transitions and Magnetization of Single Crystals of TbxY1−x Alloys

The effect of uniform pressure up to 109 Pa on the magnetization of single crystals of TbxY1−x (x = 0.91 and 0.835) in the temperature range 78 to 300 K and magnetic fields up to 1.2 × 106 A/m in the base-plane of the single crystals is investigated. The effect of the uniform pressure on the magnetic phase diagram (H, T) and temperatures of the magnetic phase transitions is discussed. It is revealed that the temperature dependence of the specific magnetization on pressure (δσ-effect) is caused by the pressure effect on: (1) spontaneous magnetization at H > Hcr; (2) magnetic anisotropy constants; (3) critical magnetic field. In magnetic fields less than the critical field the temperature dependence of δσ-effect becomes more complicated and acquires both negative and positive values. A large value of δσ-effect ((∂σ/∂P ≈︁ −10−6 emu g−1 Pa−1) is obtained for the Tb0.835Y0.165 alloy. The temperature dependence of the volume magnetostriction and change of the hexagonal lattice basis area which reach large values ((ω ≈︁ 400 × 10−6, ΔSB/SB ≈︁ −700 × 10−6) are calculated. Der Einfluß von hydrostatischem Druck bis zu 109 Pa auf die Magnetisierung von TbxY1−x-Einkristallen (x = 0.91 und 0,835) wird im Temperaturbereich 78 bis 300 K und in Magnetfeldern bis zu 1,2 × 106 A/m in der Basisebene der Einkristalle untersucht. Der Einfluß von hydrostatischem Druck auf das magnetische Phasendiagramm (H, T) und Temperaturen der magnetischen Phasenübergänge wird diskutiert. Es wird gefunden, daß die Temperaturabhängigkeit der spezifischen Magnetisierung vom Druck (δσ-Effekt) durch den Druckeinfluß (1) der spontanen Magnetisierung bei H > Hcr; (2) der magnetischen Anisotropiekonstanten; (3) des kritischen Magnetfeldes verursacht wird. In Magnetfeldern kleiner als das kritische Feld wird die Temperaturabhängigkeit des δσ-Effekts komplizierter und nimmt sowohl negative als auch positive Werte an. Ein größerer Wert für den δσ-Effekt (∂σ/∂P ≈︁ −10−6 emu g−1 Pa−1) wird für die Tb0,835Y0,165-Legierung erhalten. Die Temperaturabhängigkeit der Volumen-Magnetostriktion und änderung der Basisfläche des hexagonalen Gitters, die große Werte erreichen (ω ≈︁ 400 × 10−6, δSB/SB ≈︁ −700 × 10−6) werden berechnet.

Effect of uniform pressure on magnetization and magnetic phase diagram of terbium single crystal

The effect of uniform pressure on magnetization of a terbium single crystal (Δσ-effect) in the temperature range 80–330 K in magnetic fields up to 14 kOe has been studied. Terbium volume magnetostriction which in the vicinity of the Néel temperature in the magnetic field H = 13 kOe acquires enormous values of ω = 650 × 10 −6, was concluded on the basis of experimental data for Δσ-effect. It has been shown that in terbium the dependence of the magnetic anisotropy constant on pressure in the base-plane is well described by the magnetic anisotropy single-ion theory. The terbium magnetic phase diagram exhibits an anomaly in the vicinity of T≈223 K caused by helicoid angle passage of 18° value. The effect of pressure on temperatures of magnetic phase transitions, critical fields of helicoidal antiferromagnetic ordering destruction, paramagnetic Curie temperature and efficient magnetic moment has been studied.

Phenomenological theory of the superconductivity phase diagram of U1-xThx

Possible phenomenological theories to describe the phase diagram of ${\mathrm{U}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Th}}_{\mathrm{x}}$${\mathrm{Be}}_{13}$ based on a crossing of two different types of anisotropic superconductivity at x\ensuremath{\approxeq}0.018 are examined. In this description the second transition for xg0.018 is interpreted as a further superconducting transition. It is shown that measurements of the critical magnetic field support this assumption. The effects of uniform pressure and the specific-heat measurements are qualitatively in a good agreement with these theories. The large peak in the ultrasonic attenuation in the low-temperature phase in the region xg0.018 is explained by a dissipative domain-wall motion, induced by the sound wave, which in this case couples in both [001] and [111] directions. The theory predicts nonunitary superconducting states below the second phase transition. Such states have a finite local spin polarization in each unit cell, which leads to an explanation of zero-field relaxation rate data in muon-spin-rotation experiments.

Effect of uniform pressure on the energy spectrum of electrons and the kinetic properties of II-IV-V2 semiconductors

The data surveyed above for IV semiconductors and III–V groups indicate the effectiveness of applying uniform pressure in investigating the electron energy spectrum, transport effects, optical and other properties of II-IV-V2 semiconductors. Similar studies have only started, and their continuation is, obviously, recommended. However, the results obtained, mostly complex studies on the model object CdSnAs2 for the II-IV-V2 group, allow us to diagnose with some degree of probability the nature of the action of uniform pressure on electron energy spectra and their scattering mechanisms. Experiments under high pressure conditions play a particularly important role in investigating the behavior of impurities and various kinds of defects.

Quasistatic crack growth under the effect of uniform pressure

Quasistatic crack growth under the effect of uniform pressure