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In this paper, a first-principles study of the newly known MAX phase borides Zr2AB2 (A = In, Tl) has been carried out. The stiffness constants, elastic moduli, mechanical anisotropy, thermal and optical properties are investigated for the first time. The structural lattice parameters are found to be consistent with previous study. The dynamical and mechanical stability of the titled compounds have been checked. Fundamental insights into the stiffness constants, elastic moduli, hardness parameters, brittleness and anisotropy indices are presented. The variation of these mechanical properties is explained based on the Mulliken population analysis and charge density mapping (CDM). The metallic nature and anisotropy in conductivity has been confirmed from the electronic band structure. The analysis of DOS revealed the dominant contribution from Zr-d orbitals to the conductivity. The higher values of ΘD and Tm, and lower value of Kmin for Zr2AB2 (A = In, Tl) compared to those of Zr2AC (A = In, Tl) suggest enhanced thermal properties of the compounds under study for practical applications. Besides, the specific heat capacities (Cv, Cp), thermal expansion coefficient, and different thermodynamic potential functions have been calculated. The technologically important optical constants have been studied with an intention to reveal their possible relevance for application purposes. The reflectivity spectra revealed the applicability of Zr2AB2 (A = In, Tl) as cover materials to diminish the solar heating. The studied physical properties of Zr2AB2 (A = In, Tl) are compared with those of other relevant 212 and 211 MAX phase nanolaminates.

Density functional theory (DFT) based first-principles calculations using GGA+U method have been performed for the first time to investigate elastic, electronic, optical, thermodynamic properties including charge density, Fermi surface, Mulliken population analysis, and theoretical Vickers hardness of the newly synthesized LiCuBiO4 (LCBO) compound. The calculated structural parameters are in good agreement with available experimental results, which assessed the reliability of our calculations. The analysis of elastic constants indicates mechanical stability of the LCBO. The values of Poisson's and Pugh's ratios confirm the ductile nature of the LCBO. The mechanically anisotropy is found by the different anisotropy factors. The overlapping of valence and conduction bands near the Fermi level (EF) and the several bands crossing the EF reveal the metallic behaviour of the LCBO. The electronic charge density mapping and Mulliken population analysis exhibits a combination of covalent, ionic, and metallic bonding of the LCBO. The calculated Fermi surface comprised of two-dimensional topology due to the low-dispersion of O-2p and Cu-3d states, which implies the possible multi-band nature of LCBO. The analysis of thermodynamic and various optical properties suggest that LCBO can be a potential candidate for optoelectronic devices in the visible and ultraviolet energy regions and as a thermal barrier coating (TBC) material. Keywords: DFT calculations, Mechanical properties, Electronic properties, Optical properties, Thermodynamic properties

In this article, we report the elastic, electronic, optical and thermoelectric properties of recently synthesized K2Cu2GeS4 chalcogenide. The structural parameters are found to be in good agreement with experimental results. The calculated single crystal elastic constants (Cij) show that K2Cu2GeS4 is mechanically stable. The investigated electronic band structures reveal semiconducting characteristics and are consistent with experiment. Important optical constants such as dielectric constants, refractive index, absorption coefficient, photoconductivity, reflectivity and loss function are calculated and discussed in detail. Optical conductivity is found to be in good qualitative agreement with the results of band structure calculations. The Seebeck coefficients for TB-mBJ potential within the studied temperature range vary from ∼450 to ∼200 μV/K. The anisotropic electrical conductivity and electronic thermal conductivity are observed in the layered structured K2Cu2GeS4. The power factor and electronic thermal conductivity at 800 K along xx-axis using TB-mBJ potential are found to be ∼6 μWcm−1K−2 and 0.578 Wm−1K−1, respectively and the corresponding thermoelectric figure of merit is 0.81. The obtained results predict that K2Cu2GeS4 is a promising material in thermoelectric device applications.

The effects of M atomic species mixing on the structural, elastic, electronic, and thermodynamic properties of newly synthesized MAX phase (Zr1-xTix)2AlC (0 ≤ x ≤ 1) solid solutions have been studied for the first time by means of density functional theory (DFT) based first principles calculations. The lattice constants are in good accord with the experimental results and found to decrease with Ti contents. The elastic constants, Cij, and the other polycrystalline elastic moduli have been calculated. The elastic constants satisfy the mechanical stability conditions of these solid solutions. The constants, C11, C33 and C44, are found to increase with Ti contents up to x = 0.67, thereafter they decrease slightly. A reverse trend is roughly followed by C12 and C13. The elastic moduli are also found to increase up to x = 0.67, beyond which these moduli go down slightly. Pugh's ratio and Poisson's ratio both confirm the brittleness of (Zr1-xTix)2AlC. Different anisotropy factors revealed the mechanically anisotropic character of these solid solutions. A non-vanishing value of the electronic energy density of states (EDOS) at the Fermi level suggests that (Zr1-xTix)2AlC are metallic in nature. A mixture of covalent, ionic and metallic bonding has been found from the electronic structure with dominant covalent bonding due to hybridization of Zr-4d states and C-2p states. This is also supported by the charge density distribution. The variation of elastic stiffness and elastic parameters with x is seen to be correlated with the partial DOS (PDOS) and charge density distribution. The calculated Debye temperature and minimum thermal conductivity are found to increase with Ti contents, while melting temperature is the highest for x = 0.67. The solid solution with x = 0.67 shows improved mechanical and thermal properties compared to that of the two end members Zr2AlC and Ti2AlC.

The structural, elastic, and electronic properties of newly synthesized Zr2(Al0.58Bi0.42)C, Zr2(Al0.2Sn0.8)C, and Zr2(Al0.3Sb0.7)C MAX nanolaminates have been studied using first-principles density functional theory (DFT) calculations for the first time. Theoretical Vickers hardness has also been estimated for these compounds. All the calculated results have been compared with experimental data and also with that of recently discovered Zr2AlC phase, where available. Zr2(Al0.58Bi0.42)C and Zr2(Al0.2Sn0.8)C are the two first Bi and Sn containing MAX compounds. The optimized structural parameters are found to be in good agreement with the experimental results. The single crystal elastic constants Cij and the other polycrystalline elastic coefficients have been calculated and the mechanical stabilities of these compounds have been theoretically confirmed. The bulk modulus increases and the shear modulus decreases due to partial Bi/Sn/Sb substitution for Al in Zr2AlC. The calculated elastic moduli show that these Bi/Sn/Sb containing MAX phases are more anisotropic than Zr2AlC, and have a tendency towards increasing ductility. The Vickers hardness decreases in the Bi/Sn/Sb containing compounds. The charge density mapping reveals mixed chemical bonding characteristics of the nanolaminates under study. Further, the electronic band structures and electronic density of states (EDOS) are calculated and the effects of different elemental substitution on these properties are investigated. The electronic band structures show metallic characteristics with contribution predominantly from the Zr 4d orbitals. Partial presence of Bi/Sn/Sb atoms increases the EDOS at the Fermi level to some extent. Possible implications of the theoretical results for these recently discovered MAX nanolaminates are discussed in detail in this paper.

The effects of rotation rate, filament size, mirror shape, and crystal diameter on the shape of the silicon molten zones prepared using the infrared convergent-heating floating zone method were examined. The crystal rotation rate did not significantly affect the shape of the feed-melt or crystal-melt interfaces, gap between the crystal and feed, zone length, or lamp power required to form the molten zone. More efficient heating was achieved using lamps with smaller filaments and ellipsoidal mirrors with higher eccentricity. The convexity of both the feed and the crystal sides of the molten zone decreased with increasing crystal diameter. However, the required lamp power, gap, and zone length increased with increasing crystal diameter. The stability of the molten zone seemed to reduce with increasing crystal diameter. The minimum melt width divided by the crystal diameter was found to be a good parameter to describe the stability of the molten zone.

212 MAX phase borides are new additions to the MAX phase family with enhanced thermo-mechanical properties. In this article, first-principles calculations have been carried out to explore the mechanical properties, Vickers hardness, elastic anisotropy, thermal properties, and optical properties of predicted thermodynamically stable MAX compounds Hf2AB2 (A = In, Sn). The structural properties are compared with the available data to assess the validity of calculations. The mechanical stability of Hf2AB2 (A = In, Sn) compounds is established with the help of the computed stiffness constants (Cij). The possible reason for enhanced mechanical properties and Vickers hardness of Hf2SnB2 is explained based on the analysis of bonding strength, followed by the electronic density of states. Higher mechanical strength and Vickers hardness of Hf2AB2 (A = In, Sn) compared to Hf2AC (A = In, Sn) are also indicated in the light of charge density mapping. The values of Pugh ratio, Poisson’s ratio and Cauchy pressure predict brittle character of the studied compounds. Besides, the anisotropic nature of the titled borides is investigated by 2D and 3D plots of elastic moduli along with some well established anisotropy indices. Thermal properties were investigated by calculating the Debye temperature, minimum thermal conductivity, Gruneisen parameter, and melting temperature. The thermal properties of Hf2AB2 (A = In, Sn) are also superior to Hf2AC (A = In, Sn). The optical constants such as real and imaginary parts of the dielectric function, refractive index, extinction coefficient, absorption coefficient, photoconductivity, reflectivity, and loss function are investigated.

We have carried out a first-principles investigation of mechanical, electronic, thermodynamic and optical properties of the recently predicted thermodynamically stable MAX phase boride Hf3PB4 for the first time. The calculated lattice constants of the optimized cell volume are consistent with those found earlier. Mechanical properties characterized by parameters such as C44, B (bulk modulus), G (shear modulus), Y (Young’s modulus), Hmacro (macro-hardness) and Hmicro (micro-hardness) of Hf3PB4 boride are compared with those of existing 211, 312 and 413 MAX phases. None of the MAX compounds synthesized so far has higher Hmacro and/or Hmicro than that of the predicted Hf3PB4 nanolaminate. Calculations of stiffness constants (Cij) indicate that Hf3PB4 is mechanically stable. The extraordinarily high values of elastic moduli and hardness parameters are explained with the use of density of states (DOS) and charge density mapping (CDM). The high stiffness of Hf3PB4 arises because of the additional B atoms which results in the strong B–B covalent bonds in the crystal. The band structure and DOS calculations are used to confirm the metallic properties with dominant contribution from the Hf-5d states around the Fermi level. The technologically important thermal parameters such Debye temperature, minimum thermal conductivity, Gruneisen parameter and melting temperature of Hf3PB4 are calculated. The important optical constants are calculated and analyzed in detail and their relevance to possible applications in the optoelectronic sectors is discussed. Our study reveals that Hf3PB4 has the potential to be the hardest known MAX phase based on the values of C44, Hmacro and Hmicro.

In the present work, the structural and hitherto unexplored thermal and mechanical properties of NaInS2-xSex (x = 0, 0.5, 1.0, 1.5 and 2.0) compounds have been studied using the density functional theory. Besides, the elastic anisotropy indices and hardnesses of NaInS2-xSex have been investigated as Se content is varied. The mechanical stability of all the compounds under study has been confirmed. The ratio of shear to bulk modulus (G/B) is low suggesting that the NaInS2-xSex (x = 0.5 and 1.5) compounds exhibit damage tolerant (ductility) properties while rest of the compositions are brittle in nature. The predicted hardness (H) values are also influenced with the Se content in the following order: H (NaInSSe) > H (NaInS2) > H (NaInSe2) > H (NaInS1.5Se0.5) > H (NaInS0.5Se1.5). All the anisotropic indices under study indicate that NaInS2-xSex compounds are anisotropic in nature. The Mulliken bond population analysis suggests that the degree of covalency of In-S/Se bonds decreases when S is substituted by Se. The origin of low Debye temperature ({\Theta}D) and low minimum thermal conductivity (Kmin) have been successfully explained by considering the mean atomic weight (M/n) and average bond strength of the compounds. Temperature dependence of heat capacities (Cv, Cp) and linear thermal expansion coefficient ({\alpha} ) are also estimated using the quasi-harmonic Debye model and discussed. The low values of Kmin, {\Theta}D and {\alpha} and damage tolerant behavior clearly indicate that the NaInS2-xSex (x = 0.5 and 1.5) compounds can be used as promising thermal barrier coating materials for high temperature applications., Comment: 23 pages, 11 figures, 7 Tables

The tilt effects of the mirror–lamp (M–L) system on the shape of the interface of the silicon molten zone formed during growth using the infrared convergent heating floating zone method were studied at various positions of the M–L system. The stability and the interfaces of the molten zone formed in the tilted condition were compared with those in the no tilt condition. The molten zone appeared to be more stabilized in the tilted condition than in the no tilt condition. However, the conventional parameters characterizing the interface shape such as convexities ( h / r ), gap and zone length ( L ) were almost independent of the tilt angle ( θ ) of the M–L system and insufficient to discuss the tilting effects on the molten zone shape. The curvature of the solid–liquid interface was affected by the θ . New characterizing parameters such as the growth interface and triple point angles ( δ and TPA, respectively) were effective to quantitatively describe the tilting effects on the interface shape. With increase of the θ , the δ was decreased and the TPA was increased in both the feed and crystal sides. A silicon crystal of 45 mm in diameter was grown successfully in the tilted condition.

An investigation of U2Ti, a potentially safe and heavy metal-based storage material for radioactive tritium for fusion reactor, has been performed using pseudopotential density functional theory. The analysis of the elastic constants and other moduli calculated for the first time shows large anisotropy on elasticity and brittle behavior. A quasi-harmonic Debye model, which considers the vibrational contribution to the total free energy of the system, has been used to investigate the finite-temperature and finite-pressure thermodynamic properties of U2Ti. The electronic band structure reveals metallic conductivity and the major contribution comes from U-5f states. By analyzing the optical spectra, the origin of the various structures is also explained in terms of the calculated electronic structure. Further the reflectivity spectrum shows that the material is a perfect reflector within the energy range 8–12.5 eV.