Papers by Keyword: Lattice Vibration

Abstract: In this paper we discuss the role of anharmonicity of lattice waves in electronic specific heat of metals and insulators at very low temperatures. Previous researchers have revealed the anharmonicity of the lattice waves to cause deviation in specific heat from Debye T³ law. Different researchers have given different concepts of anharmonicity in electronic specific heat of metals at very low temperatures. The energy spectrum of phonons can not be fully described by the Debye law. On the whole all reports dilute the contention of the electronic contribution to be responsible for linear temperature dependent component of specific heat of metals at very low temperatures. For anharmonicity of lattice waves this contribution must be expected for metals and insulators also.

Abstract: Molecular dynamics (MD) simulations were performed to investigate unique crystalline states of typical ionic crystal at condition of a strong gravitational field (one million G). The simulation results showed that lattice vibration spectra of anion and cation along the gravity direction were different from the spectra along normal directions of the gravity. It is also shown that the shapes of spectra along the gravity are obviously different from the others along normal directions of the gravity. In addition, the peaks of spectra along the gravity were shifted. The simulation results showed that anisotropic lattice vibration spectra were induced by strong gravitational field, and it is insisted that the unique crystalline states and physical properties are induced by strong gravitational field.

Abstract: Abstract. The phonon spectrum of zigzag h-BN nanoribbons with the edges passivated by hydrogen atoms under tensile strain along the axis direction were calculated by first-principle calculations. It is found that the uniaxial strain can lead to a narrow frequency range of lattice vibration modes. But it hardly affects the two highest frequency modes due to the vibration of B-H or N-H bonds. In particular, the strain usually promotes the softening of phonon modes. It means that more phonons should be activated at a given temperature. This may result in the changes of thermal properties, such as, heat capacity and vibration entropy.

Abstract: The phase stability and site preference of transition metal carbides Cr in Fe7-xCrxC3 are studied based on the pair potentials obtained by the lattice inversion method. The lattice constants and cohesive energy of Fe7-xCrxC3 with the content x are calculated. The results show that Cr atoms substitute for Fe with a strong preference for the 6c1 sites and the order of site preference is 6c1, 6c2 and 2b. Calculated lattice parameters are in good agreement with the experimental data. Moreover, the total and partial phonon densities of states are first evaluated for the Fe7-xCrxC3 compounds with the hexagonal structure. We also provide some information on the vibrational properties of transition metal carbides, such as the specific heat and Debye temperature were also evaluated.

Abstract: In the present work, the microstructure and microwave dielectric properties of BaTi₄O₉ ceramics derived from a sol-gel precursor were presented. Density measuring results demonstrated that the largest densities of ceramic sample about 96.7% could be reached by virtue of a cool iso-static press and a sintering process at at 1300 °C for 6 hours. The dielectric constant (ε_r), quality factor (Q×f) and the temperature coefficients (τ_f) of the BaTi₄O₉ ceramic samples were 36.65, 28000 GHz, +20.2 ppm/°C, respectively. XRD, SEM and XPS were used to characterize the microstructure of the ceramics samples. Substantial Ti³⁺ was proposed to be the cause of dielectric loss.

Abstract: An atomistic study is presented on the phase stability, interatomic distances and lattice parameters of the new actinide intermetallic compounds AFe₂Al₁₀ (A = Th, U). Calculations are based on a series of interatomic pair potentials related to the actinides and transition metals, which are obtained by lattice inversion method. The cohesive energy of AFe₂Al₁₀ with two possible structures of YbFe₂Al₁₀-type and ThMn₁₂-type are calculated and compared with each other. Calculated lattice parameters of AFe₂Al₁₀ are found to agree with reports in the literatures. In particular, the phonon densities of states, vibrational entropy and Debye temperature related to dynamic phenomena are evaluated for the first time.