Papers by Keyword: Phonon

Abstract: Understanding and controlling the phonon, the dominant heat carrier of semiconductor materials, is essential to developing a wide variety of applications. This article studies the theoretical and computational approach of the calculation of lattice thermal conductivity of semiconducting materials. Despite having different methods to calculate the lattice thermal conductivity, first-principle estimates predict more accurately in most applications. This motivates to present the descriptive explanation on first-principle calculation with the combination of lattice dynamics and Boltzmann transport equation. Finally, we summarized an overview of the recent achievements and opportunities.

Abstract: The study on the Ti-based materials and its application has been the interest of many research industries. These alloys are known to have an ordered B2 phase at high temperatures and transform to a stable low B19 martensitic phase. First principle approach has been used to study L1₀, B32, B2 and B19 Ti₅₀Al₅₀ alloys and the results compared well with the available experimental data. The equilibrium lattice constants are in good agreement with the experimental values (within 3% agreement). Furthermore, the elastic constants of these alloys are calculated, and revealed stability for L1₀ and B19 structures, while B2 and B32 gave C′<0 (condition of instability).

Abstract: To study the physical origin of the periodic arrangement of the quadrople solute-enriched layers in Mg-based LPSO structures, we carry out first-principles calculations of the formation energy of the L1₂ cluster and investigate effects of phonon on the inter-planer ordering of the solute-enriched layers using the 1-dimensional chain model with mass change. The formation energy of the L1₂ cluster increases as the period of the LPSO structure decreases. Thus, it is found that the electron-mediated interaction is short-range repulsive. On the other hand, in the case of considerably heavy mass change, the ordering of the mass changes is stabilized by phonons and the energy gain increases with the concentration of the mass changes, i.e., the short LPSO period is favorable. A promising mechanism of the inter-planer ordering of the LPSO structures is the phonon-mediated interaction of the quadrople layers where heavy solute atoms are enriched as the L1₂ clusters at SFs.

Abstract: The structural, electronic, dynamical and thermodynamical properties of binary Zr-Al alloy (Zr₃Al) with its end members are studied using the first principles calculations based on density functional theory. We have employed the Perdew-Zunger local density approximation as the exchange correlational functional in these calculations. There is a good agreement between present and available and experimental and other theoretical data. The calculated electronic band structure and density of states suggest that the Zr-Al alloy and its end members are metallic in nature consistent with earlier studies. Full phonon dispersion curves and phonon density of states are also calculated which show the dynamical stability of these compounds at zero pressure. The temperature dependence of the thermodynamical functions are also presented.

Abstract: In the present paper, we have reported the results of our computational study of phonon frequencies in binary metallic glass CuZr₂. Model potential formalism is used here along with two different approaches namely due to Hubbard and Beeby (HB) as well as due to Takeno and Goda (TG). The results are compared with the recent experimental results and the possible ways of improvements in the results are also discussed. Further, sound velocities are also reported.

Abstract: The structural, electronic, phonon and thermodynamic properties of rocksalt (RS) structure LiF are studied using a plane-wave pseudopotential method within the local density approximation (LDA). The values of lattice constants, elastic constants, and bulk modulus and its pressure derivatives are in well agreement with the available experimental data and other theoretical results. The LiF crystal exhibits a wide band gap of about 8.727 eV. The linear response method is applied to determine the phonon dispersion, phonon density of states and Born effective charge. The phonon frequencies at the Γ, X, L points are analyzed using group theory. We also calculate the thermodynamic functions such as free energy, enthalpy, entropy, specific heat using the phonon density of states. We compare the present calculation results satisfactorily to experimental and previous theoretical results.

Abstract: Phonon properties of cobalt doped rutile TiO₂ single crystal was investigated using a Raman Spectrometer with laser wavelength at 532 nm in the temperature range from 140 K to 750 K. The phonons modes of B_1g, E_g, and A_1g with the energy of 140 cm^-1, 450 cm^-1 and 600 cm^-1 are clearly observed. The second order phonon process is also observed at the energy of 250 cm^-1_. The temperature dependence of the A_1g, E_g modes become stiffen as lowering the temperature, while the B_1g mode becomes soften. The temperature dependence of the B_1g is found to be a signature as the effect of doping. Based on the harmonic model, this is explained due to the change the Ti-O coupling strengths of TiO₆ octahedral. A larger change is found for the longer distance of the Ti-O bond.

Abstract: The lattice vibrational properties of wurtzite ternary mixed crystal aluminium indium nitride (Al_xIn_1-xN) are investigated thoroughly using modified random element iso-displacement (MREI) model and Born-Huang procedure. MREI model, which considers the nearest neighbour interactions, is used to predict the composition dependence of longitudinal and transverse optical phonon frequencies. For Al_xIn_1-xN alloy, oscillator strength of its weak mode is sufficiently significant for composition range of 0 < x < 0.4. As a result, Al_xIn_1-xN alloy is deduced to exhibit mixed-mode behaviour. Finally, the calculated dielectric functions for the entire composition range (0 < x < 1) are used to simulate the surface phonon polariton characteristics of the Al_xIn_1-xN alloy.

Abstract: The structure model of silicon nanograins was built. And then based the modification of the mean free path of phonons according to the size of nanograins, the expression of thermal conductivity in nanograins was obtained according to the phonon kinetic theory. The dependence of the thermal conductivity of silicon nanograins on size was investigated. The results showed that thermal conductivity of nanograins decrease with the reduction of characteristic sizes when the characteristic sizes of nanograins are comparable to or smaller than the phonon mean free path.

Abstract: Phonon is undoubtedly one of the most important concepts in the physics of materials. Phonon is the result when we quantize vibrational field. Whereas Schrodinger’s wave function method is the most popular and intuitive method in doing the first quantization, one usually uses Heisenberg’s operator method in the second quantization. We feel that there is a methodological and pedagogical discontinuity here. So in this paper we will use Schrodinger’s wave functional method to quantize the lattice vibration to produce phonons. Wave functional is difficult due to the nondenumerably infinite number of dimensions of its domain. In this paper we will approximate this infinity through the discrete nature of crystalline lattice so that phonon can be represented by wave function with many variables