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Register a new userNewly synthesized 3D boron-rich chalcogenides B12X (X = S, Se): Theoretical characterization of physical properties for optoelectronic and mechanical applications
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Added by
Md. Mukter Hossain PhD
Publication date
2021
fields
Physics
and research's language is
English
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Boron rich chalcogenides have been predicted to have excellent properties for optical and mechanical applications in recent times. In this regard, we report the electronic, optical and mechanical properties of recently synthesized boron rich chalcogenide compounds, B12X (X = S and Se) using density functional theory for the first time. The effects of exchange and correlation functional on these properties are also investigated. The consistency of the obtained crystal structure with the reported experimental results has been checked in terms of lattice parameters. The considered materials are mechanically stable, brittle and elastically anisotropic. Furthermore, the elastic moduli and hardness parameters are calculated, which show that B12S is likely to be a prominent member of hard materials family compared to B12Se. The origin of different in hardness is explained on the basis of density of states near the Fermi level. Reasonably good values of fracture toughness and machinability index for B12X (X= S and Se) are reported. The melting point, Tm for the B12S and B12Se compounds suggests that both solids are stable, at least up to 4208 and 3577 K, respectively. Indirect band gap of B12S (2.27 eV) and B12Se (1.30 eV) are obtained using the HSE06 functional.The electrons of B12Se compound show lighter average effective mass compared to that of B12S compound, which signifies higher mobility of charge carriers in B12Se. The optical properties are characterized using GGA-PBE and HSE06 method and discussed in detail. These compounds possess bulk optical anisotropy and excellent absorption coefficients in visible light region along with very low static value of reflectivity spectra (range: 7.42-14.0% using both functionals) are noted. Such useful features of the compounds under investigation show promise for applications in optoelectronic and mechanical sectors.
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New boron-rich sulfide B6S and selenide B6Se have been discovered from high pressure - high temperature synthesis combined with ab initio evolutionary crystal structure prediction, and studied by synchrotron X-ray diffraction and Raman spectroscopy at ambient conditions. As it follows from Rietveld refinement of powder X-ray diffraction data, both chalcogenides have orthorhombic symmetry and belongs to Pmna space group. All experimentally observed Raman bands have been attributed to the theoretically calculated phonon modes, and the mode assignment has been performed. Prediction of mechanical properties (hardness and elastic moduli) of new boron-rich chalcogenides have been made using ab initio routines, and both compounds were found to be members of a family of hard phases (Hv ~ 31 GPa).
In the present study, the structural and hitherto uninvestigated mechanical (elastic stiffness constants, machinability index, Cauchy pressure, anisotropy indices, brittleness/ductility, Poissons ratio), electronic, optical, and thermodynamic properties of novel boron-rich compounds B6X (X = S, Se) have been explored using density functional theory. The estimated structural lattice parameters were consistent with the prior report. The mechanical and dynamical stability of these compounds have been established theoretically. The materials are brittle in nature and elastically anisotropic. The value of fracture toughness, KIC for the B6S and B6Se are ~ 2.07 MPam0.5, evaluating the resistance to limit the crack propagation inside the materials. Both B6S and B6Se compounds possess high hardness values in the range 31-35 GPa, and have the potential to be prominent members of the class of hard compounds. Strong covalent bonding and sharp peak at low energy below the Fermi level confirmed by partial density of states (PDOS) resulted in the high hardness. The profile of band structure, as well as DOS, assesses the indirect semiconducting nature of the titled compounds. The comparatively high value of Debye temperature ({Theta}D), minimum thermal conductivity (Kmin), lattice thermal conductivity (kph), low thermal expansion coefficient, and low density suggest that both boron-rich chalcogenides might be used as thermal management materials. Large absorption capacities in the mid ultraviolet region (3.2-15 eV) of the studied materials and low reflectivity (~16 %) are significantly noted. Such favorable features give promise to the compounds under investigation to be used in UV surface-disinfection devices as well as medical sterilizer equipment applications. Excellent correlations are found among all the studied physical properties of these compounds.
In the present study, the structural, electronic, optical and thermoelectric properties of two isostructural chalcogenide materials, NaInS2 and NaInSe2 with hexagonal symmetry (R-3m) have been studied using the first principles method. A very good agreement has been found between our results with the available experimental and theoretical ones. The studied materials are semiconducting in nature as confirmed from the electronic band structure and optical properties.The strong hybridizations among s orbitals of Na, In and Se atoms push the bottom of the conduction band downward resulting in a narrower band gap of NaInSe2 compared to that of NaInS2 compound. Different optical (dielectric function, photoconductivity, absorption coefficient, reflectivity, refractive index and loss function) and thermoelectric (Seebeck coefficient, electrical conductivity, power factor and thermal conductivity) properties of NaInX2 (X = S, Se) have been studied in detail for the first time. It is found that all these properties are significantly anisotropic due to the strongly layered structure of NaInX2 (X = S, Se). Strong optical absorption with sharp peaks is found in the far visible to mid ultraviolet (UV) regions while the reflectivity is low in the UV region for both the compounds. Such features indicate feasibility of applications in optoelectronic sector.The calculated thermoelectric power factors at 1000 K for NaInS2 and NaInSe2 along a-axis are found to be 151.5 micro Watt /cmK2 and 154 micro Watt/cmK2, respectively and the corresponding ZT values are ~0.70. The obtained thermal conductivity along a-axis for both compounds is high (~22 W/mK).This suggests that the reduction of such high thermal conductivity is important to achieve higher ZT values of the NaInX2(X = S, Se) compounds.
A DFT study of the synthesized MAX phase Zr2SeC has been carried out for the first time to explore its physical properties for possible applications in many sectors. The studied properties are compared with prior known MAX phase Zr2SC. The structural parameters (lattice constants, volume, and atomic positions) are observed to be consistent with earlier results. The band structure and density of states (DOS) are used to explore the metallic conductivity, anisotropic electrical conductivity, and the dominant role of Zr-d states to the electrical conductivity. Analysis of the peaks in the DOS and charge density mapping (CDM) of Zr2SeC and Zr2SC revealed the possible variation of the mechanical properties and hardness among them. The mechanical stability has been checked using elastic constants. The values of the elastic constants, elastic moduli and hardness parameters of Zr2SeC are found to be lowered than those of Zr2SC. The anisotropic behavior of the mechanical properties has been studied and analyzed. Technologically important thermodynamic properties such as the thermal expansion coefficient, Debye temperature, entropy, heat capacity at constant volume, Gruneisen parameter along with volume and Gibbs free energy are investigated as a function of both temperature (0 to 1600 K) and pressure (0 to 50 GPa). Besides, the {Theta}D, minimum thermal conductivity (Kmin), melting point (Tm), and {gamma} have also been calculated at room temperature and found to be lowered for Zr2SeC compared to Zr2SC owing to their close relationship with the mechanical parameters. The value of the {Theta}D, Kmin, Tm, and TEC suggest Zr2SeC as a thermal barrier coating material. The dielectric constant (real and imaginary part), refractive index, extinction coefficient, absorption coefficient, photoconductivity, reflectivity, and loss function of Zr2SeC are computed and analyzed.
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.
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