Thermodynamic properties of wadsleyite with anharmonic effect

The thermodynamic properties of crystals can be routinely calculated by density functional theory calculations combining with quasi-harmonic approximation. Based on the method developed recently by Wu and Wentzcovitch （Phys Rev B 79：104304, 2009） and Wu （Phys Rev B 81：172301, 2010）, we are able to further ab initio include anharmonic effect on thermodynamic properties of crystals by one additional canonical ensemble with numbers of particle, volume and temperature fixed （NVT） molecular dynamic simulations. Our study indicates that phonon-phonon interaction causes the renormalized phonon frequencies of wadsleyite decrease with temperature. This is consistent with the Raman experimental observation. The anharmonic free energy of wadsleyite is negative and its heat capacity at constant pressure can exceed the Dulong-Petit limit at high temperature. The anharmonicity still significantly affects thermodynamic properties of wadsleyite at pressure and temperature con- ditions correspond to the transition zone.

QUANTUM MECHANICAL AND PHENOMENOLOGICAL STUDY OF THE ABNORMAL THERMAL EXPANSION OF MATERIALS

The abnormal thermal expansion of Bi based high Tc ( HTC) superconductor Bi2 Sr2 Ca2 Cu3 O10( Tc = 105 K) isstudied quantum mechanically and phenomenologically. Itisshown thatthe abnormalexpansion behaviorisof relevancetothe differentenergy ab sorption mechanismsofsuperconducting and normalstatesand pairing mechanisms.

Synthesis,Structure,Photoluminescence and Thermal Expansion of a Rare Earth Formate Oxalate Framework

A new lanthanide formate oxalate framework [Eu（C2O4）（HCOO）]n （1） has been synthesized via hydrothermal method and characterized by single-crystal X-ray diffraction （SC-XRD）. The framework crystallizes in the orthorhombic Pnma space group, with a = 7.0984（4）, b = 6.6442（3）, c = 10.6793（6） ？, V = 503.68（4） ？3, Z = 3, C3HO6Eu, Mr = 285.00 g/mol, Dc = 3.7581 g/cm3, F（000） = 520.3796, μ = 12.413 mm-1, the final R = 0.0264 and wR = 0.0628 for 797 observed reflections with I 〉 2σ（I）. The photoluminescence （PL） measurements reveal the significant red emission of the framework is dominated by the （5D0 → 7F2） electronic transition at 614 nm. Further variable-temperature powder X-ray diffraction （VT-PXRD） indicates that framework 1 shows slight negative thermal expansion （NTE） along the a-axis, and positive thermal expansion （PTE） along the b and c axes.

First-Principles Study of Orthorhombic Perovskites MgSiO3 up to 120 GPa and Its Geophysical Implications

High-pressure behaviour of orthorhombic MgSiO3 perovskite crystal is simulated by using the density functional theory and plane-wave pseudopotentials approach up to 120 GPa pressure at zero temperature. The lattice constants and mass density of the MgSiO3 crystal as functions of pressure are computed, and the corresponding bulk modulus and bulk velocity are evaluated. Our theoretical results agree well with the high-pressure experimental data. A thermodynamic method is introduced to correct the temperature effect on the O-K first-principles results of bulk wave velocity, bulk modulus and mass density in lower mantle PIT range. Taking into account the temperature corrections, the corrected mass density, bulk modulus and bulk wave velocity of MgSiO3-perovskite are estimated from the first-principles results to be 2%, 4%, and 1% lower than the preliminary reference Earth model （PREM） profile, respectively, supporting the possibility of a pure perovskite lower mantle model.

Effect of Carbon Nanotube Orientation on Mechanical Properties and Thermal Expansion Coefficient of Carbon Nanotube-Reinforced Aluminum Matrix Composites

Carbon nanotube-reinforced 2009Al （CNT/2009Al） composites with randomly oriented CNTs and aligned CNTs were fabricated by friction stir processing （FSP） and FSP-rolling, respectively. The CNT/2009A1 composites with aligned CNTs showed much better tensile properties at room temperature and elevated temperature compared with those with the randomly oriented CNTs, which is mainly attributed to larger equivalent aspect ratio of the CNTs and avoidance of preferential fracture problems. However, much finer grain size was not beneficial to obtaining high strength above 473 K. The aligned CNTs resulted in tensile anisotropy, with the best tensile properties being achieved along the direction of CNT aligning. As the off-axis angle increased, the tensile properties were reduced due to the weakening of the load transfer ability. Furthermore, aligned CNTs resulted in much lower coefficient of thermal expansion compared with randomly oriented CNTs.

Microstructure evolution and thermal physical properties of CuCr alloy after high pressure treatment

The thermal diffusion coefficient, thermal conductivity, and thermal expansion coefficient of CuCr alloy prepared by infiltration were measured by thermal constant tester and dilatometer before and after high pressure heat treatment, at the same time, the effect of high pressure treatment on the thermal physical properties of CuCr alloy was discussed by the analysis of its microstructure. The experimental results show that high pressure heat treatment can increase the thermal diffusion coefficient and thermal conductivity of CuCr alloy, but it changes slightly in the pressure range of 1-6 GPa. As for thermal expansion coefficient, when the temperature is higher than 130 °C, it is obviously higher than that of the alloy without high pressure treatment after 1 GPa pressure treatment, and the higher the temperature is, the larger their differences are.