An optical method is used for measurements of mechanical properties of foams. The method is based on analysis of diffraction pattern and does not require calibration. The measurements of the stiffness were performed for the conventional and auxetic foams. It was found that the stiffness of auxetic foams is several times greater than that of conventional foams.
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.
A new phase of C2/m OsN_2 is proposed in this paper. The crystal structure, elasticity and electronic properties of C2/m OsN_2 were studied by first-principles calculations. The elastic constants, the elastic moduli (B, G, and E) and Poisson's ratio v of OsN_2 have been investigated. From the first-principles calculations, we find that C2/m OsN_2 is metallic and mechanically stable. The quasi-harmonic Debye model, using a set of total energy versus molar volume obtained from the first-principles calculations, is applied to the study of the thermal and vibrational effects. The dependence of structural parameters, thermal expansions, heat capacities, Grüneisen parameters and Debye temperatures on the temperature and pressure are obtained in the whole pressure range from 0 to 80 GPa and temperature range from 0 to 800 K as well as compared with available data.
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.
A method is devised of extracting the explicit form of the coupling between the primary and secondary order parameters with the use of experimental data and respecting classical and non-classical values of the effective critical exponents. The corresponding equation of state stems from the Ising model on a compressible lattice treated within the mean field approximation supplemented with terms ascertaining scaling invariance in the vicinity of the critical point. The theory is exemplified by the molecular ferroelectric crystals (CH_{3}NH_{3})_{5}Bi_{2}Cl_{11} (MAPCB) and (CH_{3}NH_{3})_{5}Bi_{2}Br_{11} (MAPBB).
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