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The electronic structures and thermal properties of hexagonal XO ($\mathrm{\text{X}}=\mathrm{\text{Be}}$, Mg and Sr) nanosheets are studied within the density functional theory. The thermal properties are computed using the specified structural parameters of the electronic properties. Thermal properties including entropy, enthalpy, free energy and heat capacity for XO nanosheets are reported. It is found that BeO is an insulator, whereas MgO and SrO are semiconductors based on the energy gap value within GGA and HSE06. The electronegativity and bonding nature of XO nanosheets differ, resulting in considerable variations in thermodynamic parameters that follow a similar pattern as a function of temperature. Enthalpy and entropy increase with temperature whereas free energy falls, owing to a change in the binary oxide internal energy of the system and the electron density distribution. Thermal energy absorbed by the lattices grows with increasing temperature to the point at which all of their modes are activated and the systems start to display unharmonicity deviating from a linear dependence. Variable parameter ranges for XO nanosheets are useful in the development of thermoelectric nanodevices.

Due to their great physical and mechanical behaviors, polymers have become essential in various industries. Polymers have been produced using chemical monomer synthesis, potentially dangerous non-biodegradable waste in the environment. Therefore, biopolymers are introduced, and organic compounds are found in natural sources as monomeric units. Also, biopolymers were discovered to be biodegradable and biocompatible, and these biopolymers are beneficial in numerous applications. Natural plant fibers have drawn more attention recently as potential reinforcing materials. The composites made with natural fibers have excellent mechanical and thermal characteristics. Materials made of natural fibers are inexpensive, recyclable, and environmentally beneficial. These natural fibers are excellent candidates to replace conventional fibers due to their biodegradability and eco-friendliness. The adhesion between the fibers and matrix has the most impact on the mechanical characteristics of composites. The mechanical characteristics of the composites were improved by combining chemical and physical modification techniques to increase fiber–matrix adhesion. The main objective of this study is to provide a thorough understanding of common types of biopolymers, various natural fibers, fillers, chemical treatments, and the performance of biopolymers and their composites-reinforced natural fibers. Moreover, the characterization and application of various biopolymers and composites were reviewed.

Lattice vibrations or phonons play an important role in determining material properties, including thermal conductivity. To model the phenomenon accurately and efficiently, the most important factors governing phonon physics need to be identified, for example, polarization branches. Research continues into many aspects of the fundamental physical processes involved in phonons and into possible applications of these processes in modern physics. One of the most interesting controversies in the thermal properties of graphene involves the importance of out-of-plane acoustic phonons. The need for clarity in understanding this importance dictates that the thermal conductivity of graphene should be evaluated in various circumstances. The nanoscale heat conduction properties of graphene are studied by iteratively solving the Boltzmann transport equation and rigorously treating the normal and Umklapp collisions in the frame of three-phonon interactions. This captures the mechanistic aspects of thermal conductivity by revealing what phonon branches are present. The thermal conductivity is evaluated in different crystallite sizes and at different frequencies and temperatures. The results indicated that out-of-plane acoustic phonons become increasingly important in the frame of three-phonon interactions. The out-of-plane acoustic branch dominates thermal transport whereas the other acoustic branches make small contributions. The importance of this branch is generally attributed to the high density of states and restrictions governing anharmonic effects. The three-phonon normal and Umklapp processes must be clearly accounted for and the contribution from optical branches is not negligible at higher temperatures. The results have implications in the quest for predictive and quantitative calculations of thermal conductivity.

The embedded element (EE) technique has been developed in mechanical analysis to overcome the difficulties, such as poor mesh quality or high computational cost, of conventional direct mesh (DM) in finite element modeling of complex geometry. In this paper, the application of EE technique was expanded to thermal conduction analysis, and two new simplified EE modes (EE-Surf and EE-Sgl) were presented for comparison. Meanwhile, the EE technique was combined with the representative volume element, and the issues due to the combination were well addressed. Unidirectional and plain woven composites were selected as the test models for verification of the EE technique. The predictions of the homogenized properties, heat flux patterns and heat flux profiles by the DM and EE methods were compared. The results show that the EE technique is in good agreement with the DM model. Furthermore, the proposed EE-Surf mode, which only constrains the surface nodes of reinforcement domains with the matrix nodes, produces comparable high accuracy and can save computational cost due to the much reduction of constraint equations, compared with the standard EE mode. In addition, the mesh sensitivity analysis was performed to investigate the convergence of the results.

In this study, we investigate the Pauli oscillator in a noncommutative space. In other words, we derive wave function and energy spectrum of a spin half non-relativistic charged particle that is moving under a constant magnetic field with an oscillator potential in noncommutative space. We obtain critical values of the deformation parameter and the magnetic field, which they counteract the normal and anomalous Zeeman effects. Moreover, we find that the deformation parameter has to be smaller than $2.57\times 10^{-26}{\mathrm{\text{m}}}^2$. Then, we derive the Helmholtz free energy, internal energy, specific heat and entropy functions of the Pauli oscillator in the non commutative space. With graphical methods, at first, we compare these functions with the ordinary ones, and then, we demonstrate the effects of magnetic field on these thermodynamic functions in the commutative and noncommutative space, respectively.

In this study, we examine the thermal properties of the medium formed in ultra-relativistic heavy-ion collisions at chemical freeze-out using a thermal model. We utilize experimental data on various hadron species from 0% to 5% most central Au+Au collisions at $\sqrt{s_{\mathrm{\text{NN}}}}=7.7$GeV from the STAR BES program to analyze the thermal properties, namely, chemical freeze-out temperature, baryon chemical potential, and strangeness chemical potential. We employ a ${\chi }^2$ minimization technique to obtain these thermal properties. Furthermore, we also obtain thermal properties with strangeness conservation condition and at zero potentials ${\mu }_B∕T={\mu }_S∕T=0$. We compare particle ratios from the thermal model with the experimental data. The thermal model describes particle ratios within $\pm$2.5 standard deviations and ${\chi }^2∕\mathrm{\text{NDF}}$ between 1–2. We also discuss the collision energy dependence of thermodynamic properties of the medium at freeze-out and compare results with the published STAR results and other thermal model calculations.

We have produced bulk amorphous materials by quenching arc melted melts in water cooled copper die. Alloys of the composition Zr₅₇Cu₂₀Al₁₀Ni₈Ti₅ and Zr₅₅Cu₁₉Al₈Ni₈Ti₅Si₅ were produced in the form of small cylinders with a diameter of 3 mm and a length of 25 mm. The alloys were investigated by X-ray diffraction and thermal analysis to determine the structure and thermal properties. Complete amorphous X-ray patterns were observed for both alloys. The glass transition temperature is 362°C for the Zr₅₇Cu₂₀Al₁₀Ni₈Ti₅ alloy and 363°C for the Zr₅₅Cu₁₉Al₈Ni₈Ti₅Si₅ alloy. The crystallization temperature of the Zr₅₇Cu₂₀Al₁₀Ni₈Ti₅ alloy was measured to be 414.6°C. The Zr₅₅Cu₁₉Al₈Ni₈Ti₅Si₅ alloy has a higher crystallization temperature of 425.5°C.

We present characteristic functions, thermal equation of state and heat capacity at constant volume for nondegenerate relativistic quantum gases without and with generation and annihilation of particle-antiparticle pairs. For some physical quantities, nonrelativistic and ultrarelativistic expressions are analysed.

Novel distributed Bragg reflectors (DBRs) with 6-pair-GaAs/AlAs short period superlattice for the oxide-confined vertical-cavity surface-emitting lasers (VCSEL) are designed. They are for the VCSEL that emits at 840 nm and is grown with 34-period n-type mirrors, three-quantum-well active region, and 22-period p-type mirrors. In addition, a 35-nm-layer of Al_0.98Ga_0.02As was inserted in the top mirrors for being selectively oxidized. The maximum output power is more than 2 mW with low threshold current of about 2 mA. The fact that the device's threshold current in both CW and pulsed operation depends slightly on the operation temperature shows its higher characteristic temperature (T₀).

ZnO nano wire synthesized by microemulsion mediated hydrothermal process is characterized by X-ray diffraction, scanning electron microscope, UV–VIS and photoluminescence. The optical and thermal properties are then studied by photoacoustics. These studies reveal that the ZnO nano wires exhibit a strong ultra violet absorption and a relatively weak defect emission.

An effective interionic interaction potential is developed to study the pressure-induced phase transitions from zinc blende (B3) to rock salt (B1) structure in diluted magnetic semiconductors Zn_1-xMn_xSe (x=0.08 and 0.15). As a first step, the elastic constants, including the long-range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction up to second-neighbor ions within the Hafemeister and Flygare approach, are derived. Assuming that both the ions are polarizable, the Slater–Kirkwood variational method is employed to estimate the vdW coefficients. The estimated values of the phase transition pressure (P_t) increase with Mn concentration. The vast volume discontinuity in the pressure volume phase diagram identifies the structural phase transition from zinc blende to rock salt structure. The variation of second-order elastic constants with pressure resembles that observed in some binary semiconductors. It is noticed that the vdW interaction is effective in obtaining the thermodynamical parameters such as Debye temperature, Gruneisen parameter, and thermal expansion coefficient. However, the inconsistency in the value of pressure derivative of the theoretical and experimental value of C₄₄ is attributed to the fact that we have derived the expressions by assuming that the overlap repulsion is significant only up to nearest neighbors, as well as neglecting thermal effects.

Polycrystalline garnet ferrites Dy_3-xNi_x Fe₅O₁₂, where (x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) have been prepared by the standard ceramic technique and their crystalline structure were identified by X-ray diffraction and IR spectroscopy. The differential thermal analysis (DTA) reveals two peaks. It is observed that an endothermic peak between 587 and 498 K for all samples which is due to the magnetic phase change from ferrimagnetic to paramagnetic state. The exothermic peak at about 700 K may be attributed to the crystallization of Dy_3-x Ni_xFe₅O₁₂ with garnet structure. DC electrical resistivity, thermoelectric power, charge carrier concentration and charge carrier mobility have been studied at different temperatures: It was found that the DC electrical conductivity increases linearly with increasing temperature ensuring the semiconducting nature of samples. The values of the thermoelectric power were negative for samples of 0.0 < x < 0.4 indicating that the majority of the charge carrier are electrons in these samples while it was positive for sample of x = 0.5 at room temperature, and negative at high temperature. Using the values of the DC electrical conductivity and thermoelectric power, the values of the charge carrier concentration and the charge carrier mobility were calculated. Finally thermal properties have been studied.

The crystal structure at room temperature (RT), thermal expansion from RT to 1000°C and electrical conductivity, from RT to 600°C, of the perovskite-type oxides in the system Pr_1-xSr_xFeO₃(x = 0, 0.2, 0.4, 0.6) were studied. All the compounds have the orthorhombic perovskite GdFeO₃-type structure with space group Pbnm. The lattice parameters were determined by X-ray powder diffraction. The Pseudo cubic lattice parameter decreases with an increase in x, while the coefficient of linear thermal expansion increases. The thermal expansion is almost linear for x = 0 and 0.2. The electrical conductivity increases with increasing x while the activation energy decreases. The electrical conductivity can be described by the small polaron hopping conductivity model.

We have investigated the elastic, cohesive and thermal properties of (Lu, Sc) VO₃ and Sc_1-xLu_xVO₃(0.6 ≤ x ≤ 0.9) perovskites by means of a modified rigid ion model (MRIM). The variation of specific heat is determined following the temperature driven structural phase transitions. Also, the effect of lattice distortions on the elastic and thermal properties of the present pure and doped vanadates has been studied by an atomistic approach. The calculated bulk modulus (B_T), reststrahlen frequency (ν₀), cohesive energy (ϕ), Debye temperature (θ_D) and Gruneisen parameter (γ) reproduce well with the corresponding experimental data. The specific heat results can further be improved by including the magnetic ordering contributions to the specific heat.

Bonding nature as well as structural, optoelectronic and thermal properties of the cubic XMg₂O₄(X = Si, Ge) spinel compounds have been calculated using a full-potential augmented plane-wave plus local orbitals (FP-APW+lo) method within the density functional theory. The exchange-correlation potential was treated with the PBE-GGA approximation to calculate the total energy. Moreover, the modified Becke–Johnson potential (TB-mBJ) was also applied to improve the electronic band structure calculations. The computed ground-state parameters (a, B, B′ and u) are in excellent agreements with the available theoretical data. Calculations of the electronic band structure and bonding properties show that these compounds have a direct energy band gap (Γ-Γ) with a dominated ionic character and the TB-mBJ approximation yields larger fundamental band gaps compared to those obtained using the PBE-GGA. Optical properties such as the complex dielectric function ε(ω), reflectivity R(ω) and energy loss function L(ω), for incident photon energy up to 40 eV, have been predicted. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the effects of pressure P and temperature T on the thermal expansion coefficient, Debye temperature and heat capacity for the considered compounds are investigated for the first time.

Ca_2.9Ce_0.1Co₄O_9+δ/x wt% Cu₂O nanocomposites have been studied as the thermoelectric materials for energy harvesting purpose. We evaluate the thermoelectric properties of the composites through temperature dependent thermopower, thermal conductivity and resistivity measurements. It is found that the introduction of Cu₂O nanoparticles serves as phonon scattering centers, which reduces the thermal conductivity. The nanoinclusions contribute to a remarkable increase in electrical resistivity due to enhanced carrier scattering. As a result, Cu₂O nanoinclusions do not succeed in improving ZT of Ca_2.9Ce_0.1Co₄O_9+δ material.

The structural, electronic thermodynamic and thermal properties of Ba_xSr_1-xTe ternary mixed crystals have been studied using the ab initio full-potential linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT). In this approach, the Perdew–Burke–Ernzerhof-generalized gradient approximation (PBE-GGA) was used for the exchange-correlation potential. Moreover, the recently proposed modified Becke Johnson (mBJ) potential approximation, which successfully corrects the band-gap problem was also used for band structure calculations. The ground-state properties are determined for the cubic bulk materials BaTe, SrTe and their mixed crystals at various concentrations (x = 0.25, 0.5 and 0.75). The effect of composition on lattice constant, bulk modulus and band gap was analyzed. Deviation of the lattice constant from Vegard's law and the bulk modulus from linear concentration dependence (LCD) were observed for the ternary Ba_xSr_1-xTe alloys. The microscopic origins of the gap bowing were explained by using the approach of Zunger and co-workers. On the other hand, the thermodynamic stability of these alloys was investigated by calculating the excess enthalpy of mixing, ΔH_m as well as the phase diagram. It was shown that these alloys are stable at high temperature. Thermal effects on some macroscopic properties of Ba_xSr_1-xTe alloys were investigated using the quasi-harmonic Debye model, in which the phononic effects are considered.

The thermal properties of TiN-based nitrides are studied using first-principles calculations. Bulk modulus, thermal expansion, heat capacity, vibrational entropy and melting point for TiN–X compounds are computed, considering all possible transition-metal solute species X. The calculated properties show clear trends as a function of d-band filling. The results indicate that the largest increase of melting point of TiN is caused by alloying element W. Computed thermal properties for pure TiN are in good agreement with the available experimental and theoretical data.

The phase stability and electronic properties in Al₃Ta compound are studied using the FP-LAPW method. In this approach, the generalized gradient approximation (GGA) is used for the exchange-correlation potential calculation. The total energy calculations show that the D0₂₂ structure is more stable than that of D0₂₃ and L1₂. The densities of states exhibit a pseudo gap near the Fermi level for all considered structures. By analyzing the electronic charge density we find a build-up of electrons in the interstitial region, and the bonds are directed from the Ta atoms to the Al atoms, which is the characteristic of covalent bonding. The temperature and pressure effects on the structural parameters, Debye temperature, Grüneisen parameter, heat capacities (C_v, C_p) and thermal expansion are predicted through the quasi-harmonic Debye model.

A theoretical study of TiX₂ (X = Cr, Mn) with C14 Laves phase compounds has been performed by using the first-principles pseudopotential plane-wave method within the generalized gradient approximation (GGA). The electronic properties (Fermi surface and charge density) have been calculated and analyzed. The optical characteristics (dielectric functions, absorption spectrum, conductivity, energy-loss spectrum and reflectivity) are calculated and discussed. The calculated large positive static dielectric constant indicates good dielectric properties. The reflectivity of TiX₂ (X = Cr, Mn) is high in the IR–Visible–UV region up to $\sim$13 eV showing promise as a good solar heating barrier material. The temperature and pressure dependence of bulk modulus, Debye temperature, specific heats and thermal expansion coefficient are obtained for T = 1200 K and P = 50 GPa through quasi-harmonic Debye model with phononic effects. Fermi surface, optical and thermodynamic properties are very important for practical applications of the materials in optical and other devices.