Effect Of External Hydrostatic Pressure Research Articles

First‐Principles Calculations of Pressure Effects on the Structural, Electronic, Elastic, and Thermodynamic Properties of Rb2MF6 (M = Si, Ni, Pd) Crystals

Three double perovskite crystals Rb2MF6 (M = Si, Ni, Pd) are studied using the first‐principles methods. Their structural, electronic, elastic, and thermodynamic properties are calculated; effects of external hydrostatic pressure in the range from 0 to 10 GPa are analyzed. A remarkable feature of all studied compounds is the complicated structure of the valence bands, which consist of several sub‐bands separated by gaps that may produce intraband luminescence. Dependencies of the band gaps, unit cell volumes, and chemical bond lengths on pressure are calculated. It is observed that the Rb–F bonds are about 20 times more compressible than the M–F bonds. The influence of partially filled 3d orbitals of Ni in Rb2NiF6 and 4d orbitals of Pd in Rb2PdF6 on the electronic properties of these materials is analyzed by calculating the crystal field strength parameter 10Dq at varying hydrostatic pressure. Estimations of the Debye temperature from the calculated elastic constants yield the values of 198 K (Rb2SiF6), 199 K (Rb2NiF6), and 180 K (Rb2PdF6). The results of this investigation highlight the importance of systematic first‐principles calculations of physical properties for isostructural compounds and expands the existing databases of physical properties of double perovskite crystals.

Sn-doping induced modification of the magnetic and magnetocaloric properties in MnNiGe alloy

Sn-doped MnNiGe alloy of nominal composition MnNiGe0.915Sn0.085 has been examined through structural and magnetic investigations. Sn-doping stabilizes the hexagonal structure (with P63/mmc space group) at room temperature. On cooling from room temperature, it first orders antiferromagnetically (with commensurate structure) around 185 K. Further cooling results in a structural change of martensitic type around 145 K. The observed structural transition is also found to be associated with a simultaneous magnetic transition from high temperature commensurate antiferromagnetic state to low temperature incommensurate antiferromagnetic state. Both conventional and inverse magnetocaloric effect (MCE), with peak values of −6.01 J/kg-K and 6.56 J/kg-K for 0 to 5 tesla of changing magnetic field, have been visible around the magnetic and structural transitions, respectively. A significant effect of external hydrostatic pressure on the magnetic and MCE behaviors has also been observed.

Exploring Hydrothermal Synthesis of SAPO-18 under High Hydrostatic Pressure.

The effect of external hydrostatic pressure on the hydrothermal synthesis of the microporous silicoaluminophosphate SAPO-18 has been explored. The crystallization of the SAPO-18 phase is inhibited at 150 °C under high pressures (200 MPa) when using relatively diluted synthesis mixtures. On the contrary, the use of concentrated synthesis mixtures allowed SAPO-18 to be obtained in all the studied conditions. The obtained solids were characterized with XRD, SEM, ICP-AES, TG and 27Al and 31P MAS NMR spectroscopy. The results highlight the importance of the external pressure effect on the hydrothermal synthesis of molecular sieves and its influence on the interaction between the organic molecule and the silicoaluminophosphate network.

Buckling Mechanism of Offshore Pipelines: A State of the Art

The buckling analysis of an offshore pipeline refers to the analysis of temperature-induced uplift and lateral buckling of pipelines by analytical, numerical, and experimental means. Thus, the current study discusses different research performed on thermal pipe-buckling and the different factors affecting the pipeline’s buckling behaviour. The current study consists of the dependency of the pipe-buckling direction on the seabed features and burial condition; the pre-buckling and post-buckling load-displacement behaviour of the pipeline; the effect of soil weight, burial depth, axial resistance, imperfection amplitude, temperature difference, interface tensile capacity, and diameter-to-thickness ratio on the uplift and lateral resistance; and the failure mechanism of the pipeline. Moreover, the effect of external hydrostatic pressure, bending moment, initial imperfection, sectional rigidity, and diameter-to-thickness ratio of the pipeline on collapse load of the pipeline during buckling were also included in the study. This work highlights the existing knowledge on the topic along with the main findings performed up to recent research. In addition, the reference literature on the topic is given and analysed to contribute to a broad perspective on buckling analysis of offshore pipelines. This work provides a starting point to identify further innovation and development guidelines for professionals and researchers dealing with offshore pipelines, which are key infrastructures for numerous maritime applications.

Effect of External Hydrostatic Pressure and Temperature on the Impurity States and Diamagnetic Susceptibility in Strongly Oblate Ellipsoidal Quantum Dot

In this work, the hydrogen-like impurity states in a strongly oblate ellipsoidal quantum dot have been investigated in the presence of the external hydrostatic pressure and temperature. Numerical computations were performed within the framework of the variational method. The dependences of the binding energy on the location of the donor impurity were obtained for various values of external pressure and temperature. At various values of external pressure, the dependence of the diamagnetic susceptibility on the impurity coordinate has been revealed. The dependence of the oscillator strength for the first two transitions from the impurity ground state to the conduction band has been computed. The three-dimensional dependence of the photoionization cross section on the frequency of the incident light and hydrostatic pressure is given.

Simple analytical model of the effect of high pressure on the critical temperature and other thermodynamic properties of superconductors

Within the general conformal transformation method a simplified analytical model is proposed to study the effect of external hydrostatic pressure on low- and high-temperature superconducting systems. A single fluctuation in the density of states, placed away from the Fermi level, as well as external pressure are included in the model to derive equations for the superconducting gap, free energy difference, and specific heat difference. The zero- and sub-critical temperature limits are discussed by the method of successive approximations. The critical temperature is found as a function of high external pressure. It is shown that there are four universal types of the response of the system, in terms of dependence of the critical temperature on increasing external pressure. Some effects, which should be possible to be observed experimentally in s-wave superconductors, the cuprates (i.e. high-Tc superconductors) and other superconducting materials of the new generation such as two-gap superconductors, are revealed and discussed. An equation for the ratio {{boldsymbol{ {mathcal R} }}}_{{bf{1}}} ≡ 2Δ(0)/Tc, as a function of the introduced parameters, is derived and solved numerically. Analysis of other thermodynamic quantities and the characteristic ratio {{boldsymbol{ {mathcal R} }}}_{{bf{2}}} ≡ ΔC(Tc)/CN(Tc) is performed numerically, and mutual relations between the discussed quantities are investigated. The simple analytical model presented in the paper may turn out to be helpful in searching for novel superconducting components with higher critical temperatures induced by pressure effects.

Pressure-induced itinerant electron metamagnetism in UCo0.995Os0.005Al ferromagnet

The effect of external hydrostatic pressure on magnetic properties is studied for the UCo0.995Os0.005Al single crystal. At ambient pressure, the ground state is ferromagnetic. Even lowest applied pressure 0.11GPa is sufficient to suppress ferromagnetism. A sharp metamagnetic transition is observed only in magnetic fields along the c axis of the crystal, similar to previously studied itinerant electron metamagnet UCoAl. Temperature dependence of the susceptibility for various pressures shows a broad maximum at Tmax ~ 20K. The experimental data are analyzed with the theory of itinerant electron metamagnetism, which considers anisotropic thermal fluctuations of the uranium magnetic moment. The observed pressure dependence of the susceptibility at Tmax and the temperature for the disappearance of the first-order metamagnetic transition are explained with the theory.

Diffusion coalescence in НоBa2Cu3O7−x single crystals under the application of hydrostatic pressure

Experimental results on the effect of external hydrostatic pressure up to 5 kbar on the ρ(T) dependence in the ab plane of HoBa2Cu3O7−x single crystals (x ≈ 0.35) in the temperature range from 300 K to the superconducting transition temperature Tc are presented and discussed. It was established that the application of external hydrostatic pressure P = 5 kbar significantly intensified the process of diffusion coalescence of oxygen clusters, causing the growth of their average size. This leads to an increase in the number of negative U-centers, the presence of which results to the appearance of a phase capable of generating paired carriers of electric charge and, correspondingly, characterized by a higher transition temperature Tc. Employing this hypothesis that concerns the mechanism of the diffusion coalescence of oxygen clusters, the change in the form of the temperature and time dependences of the electrical resistivity under the application of external hydrostatic pressure is discussed.

Effect of hydrostatic pressure on the conductivity of YBa2Cu3O7-δsingle crystals in a broad range of temperature and oxygen content

The effect of external hydrostatic pressure on the electrical resistance of optimally doped and underdoped YBa2Cu3O7-δ single crystals is investigated in a broad temperature range, which includes the normal state and the region of superconducting fluctuations. The temperature dependences of the resistivity in the normal state are determined by scattering of charge carriers by phonons and defects. The application of pressure leads to significant changes in the electronic structure of the sample and reduces the degree of their defectiveness. This is accompanied by changeû in the lattice characteristics as the sample volume decreases. The fluctuation conductivity only exists within the range of ∼0.1Tc. With increasing δ the superconducting characteristics are close to the values typical for conventional low-temperature superconductors.

Pressure induced insulator–metal transition and giant negative piezoresistance in Pr0.6Ca0.4Mn0.96Al0.04O3 polycrystal

The effect of external hydrostatic pressure (P) on the magnetization (M) and resistivity (ρ) properties of charge-orbital (CO) ordered-insulating phase-separated manganite Pr0.6Ca0.4Mn0.96Al0.04O3 system is reported here. At ambient P, CO ordering transition and spin-canting in the AFM are observed at 223K and 55K respectively in M(T) and ρ(T) measurements. Application of P increases simultaneously the magnitude of magnetization (M) and transition temperature, and weakens the CO ordering in M(T) measurements up to 0.98GPa. During ρ(T) measurements, P induces an insulator–metallic transition (TIM) at 1.02GPa, and further increase of P up to 2.84GPa leads to increase of TIM (dTIM/dP =21.6K/GPa). ρ at TIM is reduced about three orders of magnitude at 2.84GPa, and leads to the giant negative piezoresistance (~98%). These results are analyzed separately in two temperature regions i.e., below and above TIM by power function equation and small polaronic hopping model respectively. It is understood from these analyses that the application of P suppresses the Jahn–Teller distortions, electron–electron and electron–magnon scattering factors, and induces the insulator–metal transition in Pr0.6Ca0.4Mn0.96Al0.04O3 system.

Development of methods and equipment for bellows assemblies testing under hydrostatic pressure

The paper presents a newbellows assemblies test method for stop and safety valves. To create the real conditions it is suggested testing under external hydrostatic pressure, which is available in the piping system.A designed test apparatus allows testing of the bellows under the effect of external hydrostatic pressure. The paper describes the design of the apparatus, its specifications and the test procedures.

Effects of External Hydrostatic Pressure on Orthogonal Cutting Characteristics

In this paper, effects of external hydrostatic pressure on the cutting characteristics are investigated. Orthogonal cutting experiments are conducted in a high pressure chamber using four kinds of materials; two of them are brittle materials and the others are ductile materials. Chip formation processes of soda glass specimen are studied by in-situ observation. It is confirmed that chip formation style changes from the crack type to the segmented chip type, then to the continuous chip type with the increase of hydrostatic pressure. Furthermore, cutting forces under various hydrostatic pressures are measured, and effects of hydrostatic pressure on the cutting forces are studied. It is found that hydrostatic pressure increases the cutting force in the brittle mode cutting of glasses, but does not affect the cutting force in ductile mode cutting. In case of ductile materials, hydrostatic pressure increases the cutting force of polycarbonate too, but does not affect the cutting force of pure aluminum. Based on those experimental results, mechanism of hydrostatic pressure effects on cutting characteristics is discussed.

Effects of External Hydrostatic Pressure on Finished Surface in Silicon Cutting

In this paper, machining tests of silicon wafer under high hydrostatic pressure are reported. A lathe type machining tester was developed, and machining tests were conducted on the upper surface of silicon wafers whose crystal orientation was (001). Roughness of the finished surface was measured by using AFM, and the effect of hydrostatic pressure on roughness was studied. It was found that roughness decreases with increase of hydrostatic pressure. It was also found that the roughness depends on the cutting direction. The roughness is large when the cutting direction is parallel to the <100> direction, but it is small when the cutting direction is parallel to the <110> direction. Mechanism of effects of hydrostatic pressure and crystal orientation are discussed.

Pressure effect and electron diffraction on the anomalous transition in ternary superconductor Bi2Rh3Se2

The effect of external hydrostatic pressure up to 22.23kbar on the temperature-dependent transport properties of the ternary compound Bi2Rh3Se2 is investigated. Interestingly, the resistive anomaly at Ts~250K, previously proposed as a charge-density-wave (CDW) transition, is shifted to higher temperature with increasing pressure, in distinct contrast to an established knowledge for CDW. Using temperature-dependent electron-diffraction characterizations, we have unraveled that this transition is, in effect, of a structural phase-transformation nature, experiencing the symmetry reduction from a high-symmetry C-centered monoclinic lattice to a low-symmetry primitive one below Ts. A more elaborately determined room-temperature C-centered lattice was also proposed.

Effect of chemical substitution and pressure on YbRh2Si2

AbstractWe carried out electrical resistivity experiments on (Yb,La)Rh2Si2 and on Yb(Rh,Ir)2Si2 under pressure and in magnetic fields. YbRh2Si2 exhibits a weak antiferromagnetic transition at atmospheric pressure with a Néel temperature of only $T_N \approx 70$ mK. By applying a small magnetic field TN can be continuously suppressed to $T = 0$ at $B_c = 60$ mT ($B \bot c$) driving the system to a quantum critical point (QCP). On applying external pressure the magnetic phase is stabilized and TN (p) is increasing as usually observed in Yb‐based heavy‐fermion metals. Substituting Yb by La or Rh by Ir allows to create a negative chemical pressure, La (Ir) being smaller than Yb (Rh), and eventually to drive YbRh2Si2 to a pressure controlled QCP. In this paper we compare the effect of external hydrostatic pressure and chemical substitution on the ground‐state properties of YbRh2Si2.

On the effect of hydrostatic pressure on the auxetic character of NAT-type silicates

Abstract Materials with negative Poisson’s ratios (auxetics) exhibit the property of expanding laterally when uniaxially stretched and becoming narrower when compressed. A system which exhibits this unexpected property is natrolite (NAT), a zeolite which is auxetic in its (0 0 1) plane. Here, we examine the effect of external hydrostatic pressure on the crystal structure of hypothetical silicates equivalent to frameworks in the NAT group. We show that the crystal structure and mechanical properties of the SiO 2 equivalents of the NAT, THO (thomsonite) and EDI (edingtonite) frameworks are highly pressure dependent and that these systems are most auxetic at non-ambient conditions, in particular at positive external hydrostatic pressures which are predicted to be approximately 2–8% of the bulk modulus. An attempt is made to explain this pressure dependency of the Poisson’s ratio in terms of the framework geometry and the deformation mechanism.

Phase transitions and pressure effects in simple pyridinium salts

Structural phase transitions in the pyridinium iodide [C5NH6]+.I−and bromide [C5NH6]+.Br−crystals were studied by calorimetry, volumetric dilatometry and dielectric methods.The pressure dependences of the transition temperatures were determined bydielectric constant and differential thermal analysis measurements under hydrostaticpressures of up to 1 GPa. Analysis of the experimental data indicated that thep–Tphase diagrams of simple pyridinium salts could include tri-critical points in thepressure range above 1 GPa. The effect of external hydrostatic pressure iscorrelated with the chemical pressure that appears due to the change in theanionic radius. A new model of the phase transition is proposed that includesantiferroelectric order and six-fold disorder of the pyridinium cations, respectively,in the low- and high-temperature phases.

Interplay between non-magnetic dilution and pressure effects in magnetism of UCoAl

Effects of external hydrostatic pressure and Y(Lu) substitutions for U on magnetism in U 1− x Y(Lu) x CoAl compounds were studied. Y and Lu doping of UCoAl leads to a gradual development of ferromagnetism in a limited concentration range. Reentrant metamagnetism of the UcoAl type is observed in the ferromagnetic U 1− x Y(Lu) x CoAl compounds after application of a sufficient external pressure.

Alloying and pressure-induced transitions between5f-band metamagnetism and ferromagnetism

Effects of external hydrostatic pressure up to 1.2 GPa and the Al-Ga alloying on the magnetism in ${\mathrm{UCoAl}}_{1\ensuremath{-}x}{\mathrm{Ga}}_{x}$ compounds have been studied. Ga substitutions for Al in UCoAl lead to gradual transformation of a $5f$-band metamagnetism towards ferromagnetism (for $x>~0.2$). The application of pressure yields reverse effects clearly seen in compounds with $x<~0.4.$ The spontaneous magnetization ${\ensuremath{\mu}}_{s}$ and the Curie temperature ${T}_{C}$ of ferromagnetic compounds are gradually suppressed with increasing pressure. The values of $d\mathrm{ln}{T}_{C}/dp$ and $d\mathrm{ln}{\ensuremath{\mu}}_{s}/dp$ slowly increase with x decreasing down to 0.4, whereas for $x<0.4$ an abrupt growth of pressure parameters is observed with further lowering Ga content. This is a fingerprint of a pressure-induced collapse of ferromagnetism and a simultaneous reentrance of the ``UCoAl-type'' metamagnetism in compounds with lower Ga content $(x<~0.3).$ The observed evolution of magnetism is discussed in terms of pressure and alloying-induced variation of the $5f$-ligand hybridization that determines both the stability of the U magnetic moment and the strength of U-U exchange interactions.

Effect of high hydrostatic pressure on phase composition and microstructure in Au-28 at. % Ge alloy/GaAs contacts

Effects of external hydrostatic pressure up to 7 kbar on the Au-Ge binary phase diagram and on the arsenic sublimation are evaluated by thermodynamic calculations. Experimental observations in the eutectic Au-28 at. % Ge/GaAs contacts which were annealed at vacuum and in a 7 kbar argon gas, respectively, are taken as illustrative examples for the comparison with the calculated results. It is concluded that pressures up to 7 kbar shift only slightly the phase boundaries in the Au-Ge phase diagram that were obtained in standard conditions (1 atm) and a pure argon gas with a pressure of 7 kbar acts as a good capsulation to prevent species As from sublimation. The measurements indicate that the film/GaAs interface and the film surface in the contacts annealed at 7 kbar are rich in Ge and are morphologically smooth.