Speed of ultrasound and internal pressure of 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, and 1,3-butanediol at the temperatures ranging from 293.15 to 318.15 K and pressures up to 101 MPa are analyzed and discussed in terms of molecular structure and ability to form inter- and intramolecular hydrogen bonds.
We present some preliminary results of the first hydrostatic-pressure study of the electronic level related to the Sb-heteroantisite defect in GaAs. We studied two kinds of n-type GaAs samples doped with antimony: bulk samples grown by liquid encapsulated Czochralski method and thin layers grown by metalorganic chemical vapour deposition technique. We found strongly nonlinear pressure dependence of the activation energy of the emission rate for the level. Moreover, the results obtained for the bulk material were fairly different from those obtained for thin metalorganic chemical vapour deposition layers. The possible explanation of this difference is presented.
By means of density-functional theory with the generalized gradient approximation and using the virtual-crystal approximation, we report first-principles calculation results on the structural and elastic properties of Ti_{1-x}Zr_{x}N alloy. In order to gain some further information on the mechanical properties of Ti_{0.5}Zr_{0.5}N compound, we also calculated the Young modulus, Poisson ratio, and anisotropy factor. The variation of calculated unit cell parameter for Ti_{1-x}Zr_{x}N structure increases with Zr content x. A linear dependence of the elastic constants and the bulk modulus over a range of composition x is found. All the C_{ij} of Ti_{0.5}Zr_{0.5}N increase linearly with increasing pressure. The same behaviour is observed for the other compounds with Zr compositions x.
We have carried out high pressure theoretical structural studies of yttrium nitride to examine the phase transition phenomena from the NaCl structure to CsCl structure by using a three-body potential model. The phase transition pressure (140 GPa) predicted by this approach is close to the phase transition pressure, predicted by others (138 GPa). Yttrium nitride is a novel and less explored material. Under high pressure yttrium nitride goes through a sudden collapse in volume showing the first order phase transition. To understand the effect of pressure we studied bulk properties, elastic constants and their combination. The pressure volume equation of state provides meaningful signatures of physical and chemical phenomena under high pressure. Moreover we have successfully checked the stability criterion for this compound.
The structural phase transition and elastic properties of CoN are investigated by ab initio plane-wave pseudopotential density function theory method. The equilibrium lattice parameters a₀, elastic constants C_{ij}, bulk modulus B₀ and its derivative B'₀ are calculated. From the usual condition of equal enthalpy, the phase transition of CoN from zinc-blende to rocksalt structure occurs at 35.4 GPa with a volume collapse of about 15.6%, consistent with the calculated result 36 GPa (FP-LDA), but an uncertainty is about 4.4 GPa compared with the 31 GPa (ASA-GGA). All three independent elastic constants, C₁₁, C₁₂, and C₄₄ for CoN are calculated from direct computation of stresses generated by small strains. Both C₁₂ and C₄₄ are less sensitive to pressure as compared with C₁₁. The calculated conclusions offer theoretical data for the further research of the mechanical properties for CoN.
Magnetoresistivity measurements on a superconducting system of YB_{6} (T_c ≈7.5 K) down to 60 mK at hydrostatic pressures up to 47 kbar are presented. The superconducting transition temperature, as well as the third critical field H_{c3} reveal a linear decrease with increasing pressure with slopes of d ln H_{c3}/dp=-1.1 %/kbar, and d ln T_c/dp=-0.59 %/kbar. From the latter a critical pressure, p_c ≈ 170 kbar, at which T_c vanishes, is determined.
We present first experimental results of ^{11}B-NMR of SmB_6 under applied pressure. From measurement of nuclear spin-lattice relaxation time (T_1) we find that with applied pressure the value of activation gap E_{g} is decreasing. This decrease is larger than in case of other experimental techniques. We suppose that the enhancement of 1/T_1 in temperature range 20-100 K with applied pressure reflects not only a suppression of hybridization gap, but also changes in spin correlations.
Our finding of the current spike effect highlighted for the first time in 2009 offers an enhanced understanding of the link between nanoscale mechanical deformation and electrical behavior, and ultimately suggests key advances in unique phase-change applications in future electronics. Certainly, crystal imperfections affect the properties of the nanoparticles themselves, e.g., their biocompatibility and biodegradability. The potential role of dislocations having a profound impact on the use of Si nanoparticles was largely overlooked, since plastic deformation of bulk Si is dominated by amorphization and phase transformations. Here we show an effect of bulk → nanoparticle transition (deconfinement) on incipient plasticity of Si-nanovolume. Our results provide a fresh insight into the dilemma concerning dislocation or phase transformation origin of nanoscale plastic deformation of semiconductor nanoobjects.
Results of compressibility measurements of AgI-Ag_{2}MoO_{4} materials for different concentrations of AgI were presented. The obtained results were compared with phase diagram and internal structure of material. It was found that observed values of compressibility coefficient can be related to internal structure of investigated material.
Raman piezospectroscopy of high quality 6H-SiC crystals is presented. The crystals used in experiments were grown by the seeded physical vapor transport method. Uniaxial stress up to 0.9 MPa, obtained using a spring apparatus, was applied along [11-20] and [10-10] directions. It was found that the application of uniaxial stress led to different energy shifts of the observed phonon excitations in the investigated 6H-SiC crystals. The obtained pressure coefficients vary in the range 0.98-5.5 cm^{-1} GPa^{-1} for different transverse optical phonon modes. For longitudinal optic phonon modes pressure coefficients in the range 1.6-3.6 cm^{-1} GPa^{-1} were found. The data obtained could be useful in evaluation of local strain fields in SiC based structures and devices including epitaxial graphene.
There was employed the density functional theory plane-wave pseudopotential method with local density approximation and generalized gradient approximation to investigate the structural, elastic and mechanical properties of the intermetallic compound Ni_3Ga. The calculated equilibrium lattice constant and bulk modulus are in good agreement with the experimental values. The elastic constants were determined from a linear fit of the calculated stress-strain function according to Hooke's law. From the elastic constants, the bulk modulus B, anisotropy factor A, shear modulus G, Young's modulus E and Poisson's ratio υ for Ni_3Ga compound are obtained. Our results for the bulk modulus B, anisotropy factor A, shear modulus G, Young's modulus E and Poisson's ratio υ are consistent with the experimental values. The sound velocities and the Debye temperature are also predicted from elastic constants. The dependences of the elastic and mechanical properties of Ni_3Ga compound on pressure were investigated for the first time. It was found that the cubic Ni_3Ga compound is mechanically stable according to the elastic stability criteria and it is not elastically isotropic. By analyzing the ratio B/G, it was concluded that Ni_3Ga compound is ductile in nature.
TmB_{4} is a Shastry-Sutherland frustrated system which exhibits very complex magnetic properties. In this contribution the phase diagram of magnetic field vs. temperature of TmB_{4} under hydrostatic pressure up to 26.5 kbar is investigated using sensitive ac-resistance measurements. Temperature and magnetic field dependences of resistance at various pressures were carried out in a piston cylinder pressure cell between 1.7 and 14 K and in magnetic fields up to 6 T. The obtained results exhibit shifts of ordering temperatures T_{N} as well as shifts of boundaries between different magnetic phases. The observed pressure dependences of T_{N} can be described by the relation d lnT_{N}/dp=+(0.16÷0.18) %/kbar. The effect of pressure on various interactions between magnetic ions in this compound is discussed.
We have employed the density functional theory plane-wave pseudopotential method with local density approximation and generalized gradient approximation to investigate the structural, elastic and mechanical properties of the intermetallic compound NiGa. The calculated equilibrium lattice constant and bulk modulus are in good agreement with the experimental and other calculated values. According to our best knowledge, from the elastic constants, the bulk modulus B, anisotropy factor A, shear modulus G, the Young modulus E and the Poisson ratio σ for NiGa compound are obtained for the first time. By comparison, our results for the elastic constants C_{ij}, bulk modulus B, shear modulus G and the Young modulus E are as good as those of NiAl compound. The dependences of the elastic and mechanical parameters of NiGa compound on pressure were also investigated. It was found that the cubic NiGa compound is mechanically stable under pressure according to the elastic stability criteria up to 13 GPa, and it is not elastically isotropic. By analyzing the ratio (B/G), it was concluded that NiGa compound is ductile in nature.
The structural phase transition from tetragonal to triclinic structure in CePd₂Ga₂ compound was studied by means of electrical resistivity measurement under hydrostatic pressure. The shift of the transition to the higher temperature with increasing pressure was revealed: 195 K in 3 GPa compared to 125 K in ambient pressure.
Isobaric heat capacities and internal pressures of cyclopentanol at pressures up to 100 MPa and temperatures ranging from 293 to 318 K were determined by the acoustic method. The obtained results were compared with those of pentan-1-ol in order to study the influence of the molecular configurations comprising cyclic and normal-chain structures on pressure and temperature dependence of the thermodynamic properties. It was found that the temperature and pressure coefficients of internal pressure were sensitive to the structural organization of the liquid and reflected the character of the interactions.
In this paper, the structural, elastic and thermodynamic properties of CdO under different pressure range have been reported. An extended interaction potential model (including the zero point energy effect) has been used for this study. Phase transition pressures are associated with a sudden collapse in volume. At compressed volume, the present oxide is found in cesium chloride (CsCl) phase. The calculated second order elastic constants and their various combinations have been reported in different pressure range. The calculated values have been compared with available results. Our values have been found in good agreement with existing findings.
In this research paper we have discovered the structural phase transition and elastic properties of transition metal carbides (TaC and HfC). Phase transition pressures are associated with a sudden collapse in volume showing the incidence of first order phase transition. At ambient condition the present compounds exhibit rock salt (NaCl) structure, they transform into cesium chloride (CsCl) structure under high pressure. The phase transition pressures and associated volume collapses obtained from present potential model show a generally good agreement with the available literature. The elastic constants and bulk modulus are also reported for the present compounds.
We study theoretically the influence of external hydrostatic pressure on the valence band structure in [0001]-oriented Al_{x}Ga_{1-x}N/AlN quantum wells used in deep-ultraviolet light emitting devices. The calculations performed using the multi-band k·p method with excitonic effects show that for Al_{x}Ga_{1-x}N/AlN quantum wells with x = 0.7 and quantum well width of 1.5 nm, reordering of the topmost valence subbands having different symmetries occurs with increasing pressure. In these structures, at low pressure values the topmost valence level is of Γp_9 symmetry whereas it changes to the Γp_7 state for pressures about 2.5 GPa. We also find that the excitonic effects increase the critical value of pressure at which the change in the polarization of the emitted light occurs to 7 GPa. This behavior is opposite to the pressure-dependent reordering of the topmost valence band states in thin GaN/AlGaN quantum wells which occurs from Γp_7 to Γp_9 states.
This work focuses on the high pressure Raman study of carbon nanostuctures comprising of single- or double-wall carbon nanotubes. The detailed examination of the Raman peaks, especially those attributed to the radial breathing modes of the carbon nanotubes, as a function of pressure provides a wealth of information concerning the pressure response of individual nanotubes as well as the internal-external tube (intratube) interactions. The radial breathing modes of both the internal and the external tubes in double-wall carbon nanotubes show reduced pressure slope values as compared to the corresponding in single-wall carbon nanotubes. The reduced slopes for the internal tubes reflect the pressure screening effect inside the external tubes, while those for the external tubes their structural reinforcement due to the encapsulation of smaller diameter tubes in their interior. Moreover, the magnitude of the pressure screening effect depends strongly on the intratube spacing and thus on the intratube interaction. All the experimental observations are well reproduced qualitatively by means of theoretical calculations based on a simple phenomenological model.
We refer to our recent calculations Eur. Phys. J. B 86, 252 (2013) of metallization pressure of the three-dimensional simple-cubic crystal of atomic hydrogen and study the effect on the crucial results concocting from approximating the 1s Slater-type orbital function with a series of p Gaussians. As a result, we find the critical metallization pressure p_{C} = 102 GPa. The latter part is a discussion of the influence of zero-point motion on the stabilizing pressure. We show that in our model the estimate magnitude of zero-point motion carries a little effect on the critical metallization pressure at zero temperature.
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