High Debye Temperature Research Articles

Computational study of hydrostatic pressure effect on MgSiO3 perovskite oxide for photocatalytic water splitting application

Despite the challenges of developing efficient photocatalysts for water splitting, we demonstrate that MgSiO3 perovskite oxide, under applied external stress, significantly enhances photocatalytic activity. The use of earth-abundant and low-cost photocatalysts for high-efficiency photocatalytic water splitting is extremely important. Using density functional (DFT) calculations, we present increased photocatalytic water splitting activity of MgSiO3 perovskite oxide by applying external stress. Our findings indicate that raising the concentrations of pressure can lower the lattice constants and volume of MgSiO3. An anisotropic elastic material with high stiffness that changes from brittle to ductile at high pressure (10–30 GPa). It is stable under various circumstances owing to its high Debye temperature, thermal conductivity, and melting temperature, all of which are thermodynamic properties. MgSiO₃ is an indirect bandgap (Γ →R) p-type semiconductor with a band gap energy is 2.627 eV at 0 GPa. However, the band gap energies increase as enhanced stress is confirmed by its electronic characteristics, making it appropriate for photocatalytic water-splitting applications. Strong anisotropy, effective light absorption, and reflective properties were revealed by optical investigations, which bode well for photocatalytic applications. Moreover, the optical conductivity suggests its potential for light amplification by showing a gain behavior in the visible light region. Crucially, because of its advantageous band-edge placements, MgSiO₃ shows great promise for photocatalytic water-splitting applications. This work paves the path for more investigation into effective water-splitting technologies by demonstrating the multidimensional properties and novel and inventive nature of MgSiO3 under high pressure, as well as by demonstrating its feasibility for a variety of photocatalytic applications.

Predicting potential hard materials in Nb[sbnd]B ternary boride: First-principles calculations

To identify potential superhard materials, we conducted a comprehensive theoretical investigation of the thermodynamic and kinetic stability, mechanical properties, electronic structure, Debye temperatures and melting point of sixteen ternary transition metal borides NbTMBx (x = 1, 2, 4 and TM = Ti, V, Fe, Co, Ni, Zr, Ru, Hf, W, Os) using first-principles methods. Our findings indicate that, with the exception of NbFeB, NbRuB, and NbWB, all other borides exhibit both thermodynamic and kinetic stability. Notably, NbTiB4, NbVB4, NbZrB4 and NbHfB4 demonstrate superior hardness and enhanced resistance to deformation, with NbTiB4 showing an impressive hardness value of 40.84 GPa, positioning it as a promising candidate for superhard materials. Both NbVB4 and NbTiB4 have very high Debye temperatures and melting points and can be used in high temperature environments. We further explored the mechanical properties of NbTiB4 at elevated temperatures by employing a combination of first-principles and quasi-static methods. Our analysis reveals that the elastic constants and moduli of NbTiB4 decrease with increasing temperature. Additionally, bonding analysis indicates that all NbB ternary borides exhibit hybridization involving metallic, ionic, and covalent interactions, resulting in the formation of exceptionally strong covalent bonds between boron atoms.

Room-temperature superconductivity in carbons – a mini review

The search for room-temperature superconductivity in carbons is gathering momentum because it has a long history, impressive track record, clear advancement route, and theoretical backup. The report of a suspected Josephson current in Al-C-Al sandwiches at room temperature, published in Nature 50 years ago, led to the report of a voltage in nano-graphite films believed to mark the reverse Josephson effect. The report on oxygen-doped diamonds led to full-blown superconductivity in boron-doped diamonds. The reports on highly oriented pyrolytic graphite (HOPG) and water-treated graphite powder led to the claim of a current running by itself for 50 days in a ring of HOPG soaked with alkane at room temperature. It also led to a claim of a current running for 1,000 seconds in a ring of graphene soaked in hexane. The carbons are amicable to intercalation chemistry, electrostatic carrier doping, and surface-proving techniques to promote an increase in carrier density, metallization, and applicability of the Ashcroft proposal. Consequently, the high Debye temperatures (1,670, 2,230 and 2,500 K in graphene, diamond and HOPG) may be sufficient to underwrite superconductivity at T∼300 K in carbons, provided the phonon-exchange factor, λ, is around 3 to mark strong enough interactions between electrons and phonons.

Enhanced optoelectronic and thermoelectric properties of half Heusler compounds KXSb (X = Be, Mg, Ca and Sr): A first principle study

In the present paper, structural, electronic, elastic, thermodynamic, optical, and thermoelectric properties of h-H alloys KXSb (X = Be, Mg, Ca, and Sr) are investigated for the first time. These properties were explored using quantum mechanical model – the density functional theory (DFT) with both GGA-PBE and TB-mBJ exchange-correlation functional. The Boltzmann transport equations and the Full Potential Linearized Augmented Plane wave (FP-LAPW) approach, as built into the WIEN2k code, are used to investigate these properties. The band structures and density of states (DOS) are also studied. The half-Heusler compounds show semiconductor properties with both the GGA and mBJ methods, while the KBeSb alloy exhibits metallic nature under the GGA-PBE approach. The elastic and thermo dynamical properties were also investigated, and the results revealed that the compounds are mechanically and thermally stable. The observed high Debye temperature (ϴD) implies that the alloy is harder and possesses a significant Debye sound velocity. The current paper highlights the optical and thermoelectric applications of the alloys. At 900 K, KCaSb exhibits maximum power factors of 8.83 × 1011 (W/mK2s) with the GGA-PBE method and 8.19 × 1011 (W/mK2s) with the TB-mBJ approach.

First-principles calculations of the electronic structure and thermodynamic properties of B–Co–O materials

In the present study, the structural properties, electronic, elastic, and thermodynamic properties of Co4B6O13、Co2B2O5、Co3(BO3)2、Co(BO2)2, and CoB4O7 materials were calculated by adopting first-principles calculation method based on density functional theory. The simulated lattice constant is compliant with the existing experimental data well. The formation energy, Gibbs free energy, and phonon dispersion curves show that the B–Co–O materials are thermodynamically stable. The results show that the mechanical properties of CoB4O7 material is excellent, while the mechanical properties of Co2B2O5 material is the weakest. The CoB4O7 material has higher Debye temperature and constant volume heat capacity, and the thermodynamic stability of Co3(BO3)2 is the best. By analyzing band structure and electronic density of states, Co2B2O5 and Co3(BO3)2 materials are conductors, Co4B6O13, Co(BO2)2 and CoB4O7 materials belong to P-type semiconductors. Through electronic density of states analysis and Hirshfeld analysis, they indicated that five B–Co–O materials exhibit ferromagnetic.

Unusually high thermal conductivity in suspended monolayer MoSi2N4

Two-dimensional semiconductors with high thermal conductivity and charge carrier mobility are of great importance for next-generation electronic and optoelectronic devices. However, constrained by the long-held Slack’s criteria, the reported two-dimensional semiconductors such as monolayers of MoS2, WS2, MoSe2, WSe2 and black phosphorus suffer from much lower thermal conductivity than silicon (~142 W·m–1·K–1) because of the complex crystal structure, large average atomic mass and relatively weak chemical bonds. Despite the more complex crystal structure, the recently emerging monolayer MoSi2N4 semiconductor has been predicted to have high thermal conductivity and charge carrier mobility simultaneously. In this work, using a noncontact optothermal Raman technique, we experimentally measure a high thermal conductivity of ~173 W·m–1·K–1 at room temperature for suspended monolayer MoSi2N4 grown by chemical vapor deposition. First-principles calculations reveal that such unusually high thermal conductivity benefits from the high Debye temperature and small Grüneisen parameter of MoSi2N4, both of which are strongly dependent on the high Young’s modulus induced by the outmost Si-N bilayers. Our study not only establishes monolayer MoSi2N4 as a benchmark 2D semiconductor for next-generation electronic and optoelectronic devices, but also provides an insight into the design of 2D materials for efficient heat conduction.

Computational investigation of the structural, elastic, electronic, and thermodynamic properties of chloroperovskites GaXCl3 (X = Be, Ca, or Sr) using DFT framework

In this study, we employed the pseudopotential plane wave approach to examine the influence of the X atom (X = Be, Ca, or Sr) on the physical properties of isostructural chloroperovskites GaXCl3. The GGA-PBEsol functional was employed to simulate the exchange–correlation interactions. The computed equilibrium lattice parameters exhibit a high level of concordance with the existing theoretical findings. The cohesion energy and enthalpy of formation were computed to verify the energetic stability of the materials under consideration. The determined values of the single-crystal elastic constants (Cij) indicate that GaBeCl3 remains mechanically stable up to a hydrostatic pressure of 18 GPa. Similarly, GaCaCl3 preserves its stability up to 5 GPa, while GaSrCl3 remains mechanically stable up to 1.25 GPa. The projected Cij values were used to estimate several elastic moduli and related properties, including the shear and bulk moduli, sound wave speeds, Young’s modulus, Poisson’s ratio, and Debye temperature. The energy band structures of the studied compounds, as predicted by the HSE06 functional, demonstrate their wide bandgap semiconductor nature. Specifically, GaBeCl3 demonstrates an indirect bandgap of 3.828 eV, while GaCaCl3 reveals an indirect bandgap of 4.612 eV and GaSrCl3 has an indirect bandgap of 4.405 eV. The quasiharmonic Debye approach was employed to examine various thermal parameters, including the temperature dependence of the unit cell volume, bulk modulus, expansion coefficient, Debye temperature, isochoric and isobar heat capacities, Grüneisen parameter, and entropy function. It has been shown that GaBeCl3 demonstrates a lower thermal expansion coefficient and a higher Debye temperature in comparison to GaCaCl3 and GaSrCl3.

High-entropy (Y0.2Gd0.2Dy0.2Ho0.2Er0.2)Al3C3 ceramic: A noval promising ultra-high temperature structural material

High-entropy (Y0.2Gd0.2Dy0.2Ho0.2Er0.2)Al3C3 (HE(5RE1/5)Al3C3) with high purity, high density and high compositional uniformity was prepared by in-situ hot pressing process using Y, Gd, Dy, Ho, Er, Al and C as initial materials for the first time. The results show that its crystal structure is hexagonal system (P63/mmc) with lattice constants of a = b = 3.43 Å, c = 17.35 Å. The Vickers hardness, flexural strength, Young's modulus, thermal expansion coefficient, and thermal conductivity of HE(5RE1/5)Al3C3 are 13.2 ± 0.5 GPa, 148 ± 15 MPa, 375 GPa, 8.21 × 10−6 K−1, and 10.98 W m−1 K−1, respectively. The residual Young's modulus of HE(5RE1/5)Al3C3 remained approximately 83 % of its room temperature value even at 1500 °C Additionally, compared to YAl3C3, HE(5RE1/5)Al3C3 has a high Debye temperature (921 K) and a high initial oxidation temperature (980 °C). These results indicate HE(5RE1/5)Al3C3 is a highly promising oxidation resistant ultra-high temperature structural material.

First-principles investigations of Fe-based A3BX ceramics with high stiffness and damage tolerance.

In the search for high-stiffness and damage-tolerant materials, Fe-based A3BX carbide and nitride anti-perovskites were studied using first-principles calculations. These perovskites were found to be stable in cubic structures, as substantiated by the formation energy, elastic Born stability criterion, and phonon dispersion spectrum analysis. The GGA functional was applied for geometry optimization, and the lattice constants are found to be 3.730 Å, 3.715 Å, 3.832 Å, and 3.828 Å for Fe3AlC, Fe3AlN, Fe3SnC, and Fe3SnN, respectively. Elastic property analysis reveals that all the materials have large elastic moduli, high sound velocities, and high Debye temperatures. Among them, carbides have superior stiffness and quasi-ductile properties, and they can be further improved by applying additional pressure. Preliminary analysis of electronic properties indicates that they are ferromagnetic and metallic compounds. Their high melting temperatures (>2600 K) confirm their potential in high-temperature applications. The lowest thermal conductivity of Fe3SnN suggests its potential in efficient solid-state refrigeration application. Moreover, Fe3SnC is proposed to be a viable damage-tolerant material with good prospects. Under 10 GPa external pressure, it possesses a ductile structure with a Young's modulus of 402.15 GPa and bulk modulus of 280.25 GPa.

First-principles screening of structural, electronic, optical and elastic properties of Cu-based hydrides-perovskites XCuH3 (X=Ca and Sr) for hydrogen storage applications

In the present study, density functional theory is used to conduct an in-depth investigation of the physicochemical features of the perovskite XCuH3 (X = Ca and Sr). The CaCuH3 and SrCuH3, with lattice parameters of 3.66 Å and 3.77 Å, are synthesizable and thermodynamically stable, according to structural simulations. Analysis of the electronic band structure (0 eV) and density of states (DOS) shows that XCuH3 (X = Ca and Sr) perovskites exhibit metallic behaviour. For novel polycrystalline materials, the shear and Young's moduli as well as the Poisson's ratio are computed and the findings suggested that compounds with the formula XCuH3 (X = Ca and Sr) are ductile. Hydrogen storage qualities have been analyzed and it has been shown that the CaCuH3 and SrCuH3 have gravimetric hydrogen storage capacities of 2.85 wt% and 1.97 wt%, respectively. The SrCuH3 has the highest Debye temperature (θD) 344.41 K. The findings, taken as a whole, provide a practical strategy for developing innovative, potentially useful perovskite-type hydrides for hydrogen storage.

Anisotropic mechanical behavior and thermal attributes of antiferromagnetic UX2(X=P, As, Sb) materials: A density functional and elasticity theories study

In this work, we delve into the investigation of mechanical and thermal properties of antiferromagnetic UX2 (X=P, As, Sb), which are structured in the unique anti-Cu2Sb-type tetragonal form. The study’s principal findings revolve around the revelation of distinctive compressibility patterns and an observed preference for shear deformation in these compounds. These patterns are notably marked by a lower compressibility along the [100] direction than the [001] one, and the ease of shear deformation on the (100) plane compared to the (001) one. Intriguingly, our findings identify these compounds as residing on the brink of the brittle/ductile borderline as per Pugh’s ratio and Poisson’s ratio. Furthermore, the mechanical strength in these materials is significantly influenced by shear deformation, a fact indicated by the values of bulk and Young’s modulus. Among the UX2 (X=P, As, Sb) compounds, our analysis of the Debye temperature singles out UP2 as an outstanding performer due to its higher Debye temperature. A noteworthy aspect of this study is the quicker propagation of longitudinal waves over transverse waves, as indicated by the wave velocity and anisotropy calculations. We bring forth an enriched understanding of the anisotropic behavior of these materials in terms of bulk modulus, Young’s modulus, shear modulus, and Poisson’s ratio. The predicted high melting temperatures of the UX2 (X=P, As, Sb) compounds, coupled with the computed heat capacities aligning well with existing experimental data, point towards their potential applicability in high-temperature settings. Collectively, our study not only validates the methodologies employed but also brings to light fascinating new insights into the mechanical and thermal properties of these compounds, deepening our understanding of the intricate interplay between their atomic constitution and physical properties.

First Principles Study of Negative Thermal Expansion (NTE) in Manganese Nitride materials

We report ab initio study of the electronic, mechanical and structural properties for the negative thermal expansion (NTE) application of antiperovskites manganese nitrides materials Mn3XN (X=Al, Ga, Zn). Using first principle calculations based on generalized gradient approximation (GGA), the electronic, structural, and mechanical properties of the Mn3XN (X = Al, Ga, Zn) phases were investigated. The optimized lattice parameters give the first reference to the upcoming theoretical and experimental studies. THERMO_PW as a post-processing code was used for the computation of elastic constants that were used to derive bulk modulus (B), shear modulus (G), Young's modulus (E), Poisson's ratio (õ), and hardness. The calculated elastic constants are in excellent agreement with the available data. Moreover, obtained elastic constants revealed that both the Mn3ZnN and Mn3GaN phases are brittle. The band structure and density of states analysis showed that these phases are electrical conductors, having strong directional bonding existing near the Fermi level between Mn -N atoms due to Mn-d and N-p hybridization. The Mn3GaN compound has the highest Debye temperature (452.8K), while Mn3ZnN has Debye temperature of (283.4K) indicating that they are thermodynamically and dynamically stable and can be synthesized experimentally. Mn3AlN compound has Debye temperature (0.000K) indicating the system is unstable for compressional deformation.

Structural, mechanical, electronic, optical and thermodynamic features of lead free oxide perovskites AMnO3 (A=Ca, Sr, Ba): DFT simulation based comparative study

Perovskite oxides with transition metals have been subjected to a lot of concern in the recent time having their exclusive physical and chemical property. Due to ferroelectric character these types of materials have huge technological applications in worldwide. In the existing project, the crystal structure stability, single and polycrystalline bulk properties, electron-charge density, photon and temperature related optical as well as thermal features of perovskite oxides AMnO3 (A = Ca, Sr, Ba) have been investigated through DFT simulation with CASTEP code. Very good accordance in the investigated and synthesized lattice parameters is found. Mechanical stabilities of phases AMnO3 (A = Ca, Sr, Ba) are ensured from the investigated elastic stiffness constants. Ductile nature of compounds AMnO3 (A = Ca, Sr, Ba) are ensured from the study of Pugh's and Poisson's ratios. Hardness calculations ensured that all the studied materials are hard in nature where SrMnO3 has little bit higher hardness nature compared to others. Very high machinability index of CaMnO3 confirmed its suitable industrial application compared to the rest two compounds. Anisotropic character of AMnO3 (A = Ca, Sr, Ba) is observed from the analysis of elastic anisotropy factor. Band structure calculations with up-spin and down-spin reveal the metallic and semi-metallic nature of AMnO3 (A = Ca, Sr, Ba) respectively. Ionic and covalent bonded nature of AMnO3 (A = Ca, Sr, Ba) are confirmed from the Mulliken atomic population and charge density calculations. Very high absorption and conductivity of AMnO3 (A = Ca, Sr, Ba) have been observed in the ultraviolet energy site which ensure their possible applications in optical devices operates at UV energy regions. The dielectric function make sure the metallic nature of AMnO3 (A = Ca, Sr, Ba) as the actual value approaches to zero from negative energy region. Comparatively high Debye temperature of AMnO3 (A = Ca, Sr, Ba) revealed that these compounds are thermally more conductive where CaMnO3 is more conductive than the rest two materials. Very low value of Kmin of material BaMnO3 ensured that this phase has more possibility to use in thermal barrier coating materials (TBC) than CaMnO3 and SrMnO3 materials.

Comparison of the Physical Properties and Electronic Structure of Nb2B3 and Ta2B3

Based on the first-principles method, the effects of pressure and temperature on the physical properties of Nb2B3 and Ta2B3 were discussed. The approximate linear increase in B, G, and E with pressure was observed for Nb2B3 and Ta2B3 with a minor difference for bulk modulus and similar values for shear and Young’s modulus. Nb2B3 shows higher Vickers hardness and similar fracture toughness as compared with Ta2B3. An abnormal phenomenon of the simultaneous increase in hardness and B/G (σ) with the increased pressure was observed. The strong anisotropies of bulk, Young’s, and shear modulus were observed, and the differences of anisotropy between Nb2B3 and Ta2B3 increased with pressure. At low temperatures, the α of Nb2B3 is smaller than that of Ta2B3, but is larger than that of Ta2B3 at high temperatures. The Θ of Nb2B3 are larger than those of Ta2B3 under the same conditions. The combination of relatively high Vickers hardness and fracture toughness is determined by the metallic bond and covalent bond. With the increased pressure, Nb2B3 possesses the greater strength of B–B bonds than Ta2B3, which leads to its high hardness and Debye temperature.

Superconducting properties of pt-type and bct-type YRh4B4

YRh4B4, which exhibits high- superconductivity in the RRh4B4 system, has two types of crystal structures, CeCo4B4 type (pt-type) and LuRu4B4 type (bct-type). Both types of structure have similar (pt-type; = 10.6 K, bct-type; = 9.8 K), but the of both compounds is very different, pt-type; = 2.50 T and bct-type; = 9.85 T. From our results, one can see that the difference in between pt-YRh4B4 and bct-YRh4B4 is mainly caused from the difference of the density of state at Fermi energy. The high- in pt-YRh4B4 is derived from the high Debye temperature caused by vibrations of boron. In contrast, in bct-YRh4B4 it is caused by a stronger electron–phonon coupling than in pt-YRh4B4. Regarding the symmetry of superconductivity, it is suggested that pt-YRh4B4 is a clean limit superconductor and has basically a fully gapped superconducting gap, but is slightly anisotropic from the results of ) below and . However, bct-YRh4B4 is a dirty limit superconductor and has an anisotropic superconducting gap from the results of below and .

First-principles study the mechanical, electronic, and thermodynamic properties of Mg-Al-Mn ternary compounds

In recent years, magnesium alloys have been used more and more widely due to their excellent lightweight and good plasticity. But correspondingly, the requirements for the elastic modulus (E) are more demanding. Therefore, to improve the deficiency, we are committed to find a way to increase the E. In this work, the mechanical, electronic, and thermodynamic properties of the Mg-Al-Mn ternary compounds were explored effectively based on first-principles calculations. It was found that the stabilities of these six structures were verified by the phonon spectrum, cohesive energy, and density of state, which showed that Mg3(MnAl9)2 possessed the best stability. Furthermore, Mg3(MnAl9)2 also had the largest bulk modulus, shear modulus, and E with values of 78.39, 50.94, and 125.6 GPa, respectively, due to the high bond strength of Al-Al bonds, and this was also verified by Mulliken's population analysis. Not only that, the largest hardness was reflected in Mg3(MnAl9)2 with a value of 9.04 and 9.11 GPa in Chen's and Tian's models. Similarly, the thermodynamic results showed that Mg3(MnAl9)2 had the highest Debye temperature as a value of 540.29 K and the highest limiting thermal conductivity with values of 1.216 W m−1K−1 in Clarke's model and 0.945 W m−1K−1 in Cahill's model.

DFT based comparative analysis of the physical properties of some binary transition metal carbides XC (X = Nb, Ta, Ti)

Binary metallic carbides belong to technologically prominent class of compounds. Present work theoretically explores the structural, mechanical, optoelectronic, and some thermal properties of XC (X = Nb, Ta, Ti) compounds using the density functional methodology. A number of the results obtained are novel. The computed elastic constants and moduli disclose that the compounds possess moderate elastic anisotropy and reasonably good machinability (machinability index above 1.45 for all the compounds), mixed bonding characteristics, high Vickers hardness (in the range 19–25 GPa) with very high Debye temperatures (in the range 800–925 K) and brittle characteristics. The elastic/structural stability conditions are fulfilled for all the carbides under study. The Young's modulus and bulk modulus of TiC are lower than those of NbC and TaC. All the XC (X = Nb, Ta, Ti) compounds are hard and suitable for heavy duty structural applications. The electronic band structures show finite density of states at the Fermi level revealing metallic character of the XC (X = Nb, Ta, Ti) compounds. Mixed bonding features are evident from the charge density distribution maps of the XC (X = Nb, Ta, Ti) compounds. The lattice dynamical properties, such as the phonon dispersion curves and phonon density of states for XC (X = Nb, Ta, Ti) are investigated. Absence of negative phonon modes in the Brillouin zone indicates that the carbides under study are dynamically stable. The energy dependent optical constants are nearly isotropic. The optical absorption, reflectivity spectra, and the high value of the low energy index of refraction of XC (X = Nb, Ta, Ti) compounds reveal that they hold promise to be utilized in optoelectronics. The computed melting temperature, lattice thermal conductivity, Debye temperature, and minimum phonon thermal conductivity of the XC (X = Nb, Ta, Ti) compounds exhibit conformity with the computed elastic and bonding characteristics. Extremely high melting point (4399 K) of the compound TaC suggests that it is a very good candidate for applications at high-temperatures.

Ultra-narrow-band luminescence with spectral width down to 32 nm in bismuth-activated phosphate phosphors with superior thermal stability

Bismuth-activated phosphors have become popular as a replacement for phosphors based on intensively studied lanthanide ions because of their low spectral reabsorption and sustainable utilization. However, it is of a great challenge to yield narrow-band emission from Bi3+ since its ns2-nsp electron transition lacks the shielding of outer electron orbitals. Herein, we report a new ultra-narrow band Bi3+-activated blue-violet phosphor Ca6BaP4O17 (Ca6BaP4O17:Bi3+). Impressively, its emission band width is down to ∼32 nm, which is less than that of all the reported Bi3+-activated ones. Experimental and theoretical calculation results corroborate that such unusual narrow-band emission originates from Bi3+ ions occupying two cation sites, Ca1 and Ca2, in the Ca6BaP4O17 compound. At 423 K, Ca6BaP4O17:0.5%Bi3+ shows a robust thermal quenching resistance with an integrated emission intensity loss of merely 1%. This is attributable to rare structural advantages of the host such as a high Debye temperature (Θ = 632 K) and large bandgap (∼6.1 eV), which could minimize thermally non-radiative relaxation pathways. We fabricate a blue-violet LED prototype by using the resulting phosphors and ultraviolet LED chip, and demonstrate its potential application in porrets growth. These findings provide in-depth insights the on site occupancy of Bi3+ ions and may simulate more research studies on Bi3+-activated phosphors.

First-principles calculations to investigate structural, elastic and thermodynamic properties of new M2ScSnC2 (M=V or Nb) quaternary compounds for 312 MAX phases

In this research, the approach of FP-LAPW (full potential linearized augmented plane wave) is employed within WIEN2K for the investigations of structural, thermodynamic, electronic, and mechanical properties of the V2ScSnC2 and Nb2ScSnC2 MAX-phases quaternary compounds. The V2ScSnC2 and Nb2ScSnC2 compounds exist in “α” and “β” polymorph structures. The formation energies (Eform) investigated insure that the α-polymorph is more stable than the β one. As it happens, Nb2ScSnC2 is more stable than V2ScSnC2. The Nb2ScSnC2 has an enhanced mechanical property compared to the V2ScSnC2 compound. The elastic constants (ECs) of interested materials fulfill all the conditions of mechanical stability and revealed a ductile nature. The predicted Cauchy's pressure and Poisson's ratio possess positive values signifying the ionic character of the V2ScSnC2 compound. The quaternary Nb2ScSnC2 compound exists as amalgamation of covalent and ionic bonds with a predominance of the ionic bonding character. The high melting temperature and high Debye temperature of V2ScSnC2 and Nb2ScSnC2 make them suitable for use in harsh environments. Furthermore, they exhibit potential as a promising material for thermal barrier coatings (TBCs). Electronic structure analysis confirm the metallic character of the two interested compounds. At high temperatures and pressures the thermodynamic properties including the Cv (Heat capacity) and ƟD(Debye temperature) are explored. We deem that this study of quaternary MAX-phase compounds will bring new insight for the experimentalists to employ for their future applications.

Physical and optoelectronic properties of double halide perovskites A2CuSbX6 (A = Cs, Rb, K; X = Cl, Br, I) based on first principles calculations

Double perovskites A2CuSbX6 (A = Cs, Rb, K; X = Cl, Br, I) have been investigated by first principles calculations. According to the tolerance factor, formation energy, binding energy and elastic stability criterion, the other materials except Cs2CuSbI6 can be judged to have mechanical and thermodynamic stability. All the materials are ductile and show potential in wearable devices. The perovskites possess indirect band structures with bandgaps as 1.163 eV, 0.850 eV, 0.305 eV, 1.140 eV and 1.123 eV for Cs2CuSbCl6, Cs2CuSbBr6, Cs2CuSbI6, Rb2CuSbCl6 and K2CuSbCl6, respectively. Compared with the other two Cl-based perovskites, K2CuSbCl6 exhibits better optoeletronic properties because of its smaller average effective mass(0.294 m0 for mh∗ and 0.201 m0 for me∗), longer carrier lifetime and higher light absorption coefficient (6.58 × 104 cm−1) in visible region. In addition, K2CuSbCl6 has a high Debye temperature which represents better stability. The results indicate that K2CuSbCl6 is an excellent candidate for photovoltaic and optoeletronic devices.