Calculation Of Elastic Constants Research Articles

A Newly Predicted Magnetic TMB6 Monolayer for Efficient Nitrogen Fixation.

Developing electrocatalysts for the N2 reduction reaction (NRR) with high activity, high selectivity, and low cost is urgently required to enhance the NH3 yield rate. Based on first-principles calculations, we predict a series of new transition metal boride TMB6 (TM = Ti, V, Cr, Mn, Fe, and Co) monolayers and investigate their magnetoelectronic and electrocatalytic properties. The results reveal that VB6 and CoB6 favor ferromagnetic coupling, while TiB6, CrB6, MnB6, and FeB6 display antiferromagnetic ordering. Furthermore, TiB6 exhibits a high Néel temperature of 344 K and a large magnetic anisotropy energy of 614 μeV per Ti atom. Most interestingly, TiB6 and VB6 exhibit superior NRR catalytic activity with a limiting potential of -0.50 and -0.19 V, respectively, and favorable NRR selectivity over the HER. Finally, the structural stability of TMB6 monolayers has been confirmed by a set of phonon dispersion, molecular dynamics, and elastic constant calculations. Our results highlight the use of the newly designed two-dimensional (2D) TM borides as promising candidates for spintronic devices and nitrogen fixation applications.

The first-principles prediction of mechanical, electronic, elastic and thermodynamic properties of Mo2XB2 (X=Nb, Os, Ta)

The mechanical, electronic and elastic properties of Mo2XB2 (X = Nb, Os, Ta) at different pressures (0–50 GPa) were predicted using first-principles calculations. The enthalpy of formation and the elastic constant calculations show that the three transition metal borides are thermodynamically and mechanically stable. The analysis of density of state and band structure reveals that Mo2XB2 (X = Nb, Os, Ta) have metallic and covalent properties. The increase of pressure will increase the elastic modulus of Mo2XB2 (X = Nb, Os, Ta). The elastic modulus of Mo2XB2 (X = Nb, Os, Ta) are anisotropic. Furthermore, the quasi-harmonic Debye model is used to predict thermodynamic parameters at various temperatures (0–1200K) and pressures (0–50 GPa), such as heat capacity at constant pressure, heat capacity at constant volume, coefficient of thermal expansion, Debye temperature, and the Grüneisen parameter.

Stability and properties of six new Ru3Al structures: A first-principles study of mechanical, electronic, and superconducting properties

Ruthenium–aluminium (Ru–Al) alloys demonstrate excellent properties; however, the Ru3Al structure has a higher formation energy than those of other Ru–Al structures. Herein, to identify more stable Ru3Al structures, we employed the CALYPSO code and discovered six stable structures: one hexagonal structure, two monoclinic structures and three orthorhombic structures. First-principles calculations and the density functional theory were used to assess their mechanical, electrical and superconducting properties. The formation energies of these newly discovered Ru3Al structures were lower than those of previously proposed structures, confirming their thermodynamic stability. Elastic constant calculations indicated that all the structures were mechanically stable and ductile. Moreover, electronic structure analyses revealed that the structures were metallic, primarily owing to the contribution of Ru d orbitals. Phonon dispersion and density of states analyses also confirmed the dynamic stability of the structures, with low-frequency phonons contributing considerably to electron–phonon coupling. The superconducting transition temperatures (Tc) of the structures were calculated using the Allen–Dynes-modified McMillan equation. The Cmcm structure showed the highest Tc of 3.99 K, and the P2/c structure showed the lowest Tc of 1.56 K. Overall, this study identified six novel and stable Ru3Al structures with good mechanical and superconducting properties, potentially advancing the development of Ru–Al-based superconductors.

Theoretical insights into the structures and fundamental properties of pnictogen nitrides

Abstract Recent experimental advancements reported a chemical reaction between antimony and nitrogen under high temperature and high pressure, yielding crystalline antimony nitride (Sb3N5) with an orthorhombic structure. Motivated by this statement, we calculate the stability, elastic properties, electronic properties and energy density of the Cmc21 structure for pnictogen nitrides X 3N5 (X = P, As, Sb, and Bi) using first-principles calculations combined with particle swarm optimization algorithms. Calculations of formation enthalpies, elastic constants and phonon spectra show that P3N5, As3N5 and Sb3N5 are thermodynamically, mechanically and kinetically stable at 35 GPa, whereas Bi3N5 is mechanically and kinetically stable but thermodynamically unstable. The computed electronic density of states shows strong covalent bonding between the N atoms and the phosphorus group atoms in the four compounds, confirmed by the calculated electronic localization function. We also calculate the energy densities for Sb3N5 and find it to be a potentially high-energy-density material.

Material Design and Discovery in Full-Heusler Compounds: A Comprehensive First-Principles Analysis of XMg2Hg, XMgHg2, and X2MgHg (X = Sc, Li)

This study conducts a comprehensive first-principles analysis of the structural, mechanical, phonon dispersion, and electronic properties of XMg2Hg, XMgHg2, and X2MgHg (X = Sc and Li) compounds. Using energy-volume curves, cohesive and formation energy, and phonon dispersion analyses, we confirm the stability of these compounds. Our calculations reveal that Li2MgHg and ScMg2Hg are more stable in the cubic structure with space group F4¯3m (216), whereas other compounds are stable in the Fm3¯m (225) structure. Phonon dispersion calculations indicate dynamical stability for all compounds except Li2MgHg in the Fm3¯m structure and Sc2MgHg and LiMg2Hg in the cubic structure with space group F4¯3m (216). Mechanical stability is confirmed through the calculation of elastic constants, with Sc-based compounds showing higher bulk modulus, shear modulus, and Young's modulus compared to Li-based compounds. Electronic properties, analyzed through density of states and band structure calculations, confirm the metallic nature of these compounds, with significant contributions from Mg atoms at the Fermi energy. The study also identifies distinct electronic features such as flat electron bands and a Dirac point at the Gamma point for ScMgHg2​. Pressure-dependent studies indicate these materials are normal metals without topological phase transitions.

Ab Initio Studies of Mechanical, Dynamical, and Thermodynamic Properties of Fe-Pt Alloys.

The density functional theory (DFT) framework in the generalized gradient approximation (GGA) was employed to study the mechanical, dynamical, and thermodynamic properties of the ordered bimetallic Fe-Pt alloys with stoichiometric structures Fe3Pt, FePt, and FePt3. These alloys exhibit remarkable magnetic properties, high coercivity, excellent chemical stability, high magnetization, and corrosion resistance, making them potential candidates for application in high-density magnetic storage devices, magnetic recording media, and spintronic devices. The calculations of elastic constants showed that all the considered Fe-Pt alloys satisfy the Born necessary conditions for mechanical stability. Calculations on macroscopic elastic moduli showed that Fe-Pt alloys are ductile and characterized by greater resistance to deformation and volume change under external shearing forces. Furthermore, Fe-Pt alloys exhibit significant anisotropy due to variations in elastic constants and deviation of the universal anisotropy index value from zero. The equiatomic FePt showed dynamical stability, while the others showed softening of soft modes along high symmetry lines in the Brillouin zone. Moreover, from the phonon densities of states, we observed that Fe atomic vibrations are dominant at higher frequencies in Fe-rich compositions, while Pt vibrations are prevalent in Pt-rich.

Control of spin on structural stability, mechanical, magneto-optoelectronic and thermodynamic properties of RbTaX (X =P and As) materials: Emerging candidates for opto-spintronics and spin filter applications

In the present work, the density functional theory has been utilised in inspecting the ground state-structural, electronic, magnetic, optical, elastic and thermodynamic properties of new semiconductor RbTaX (X = P and As) half-Heuslers. Out of the possible three structures (α, β, γ) studied in ferromagnetic (FM) as well as non-magnetic (NM) phases, α – FM phase is found to be the most stable configuration. Both studied materials have estimated a net magnetic moment of 3μB, following the Slater-Pauling rule (Mtot=Ztot−8). With the use of modified Becke Johnson potential (mBJ) potential, the band profile reveals non-zero band gap in the spins and henceforth display spin filter property in the compounds. The predicted energy band gaps for RbTaP and RbTaAs are 3.04 and 2.87 eV for minority spin channels and 0.137 and 0.26 eV for majority spin channels, respectively. This unique feature of the Heusler compound may be advantageous for quantum information processing and spin-transport in electronic and magnetic devices. Also, a moderate exchange splitting and a Curie temperature well above the room temperature are noted. The stability of the materials under investigation was further confirmed by calculations of cohesive energy, formation energy, and second order elastic constants. The optoelectronic as well as thermodynamic properties of the studied compounds are also investigated. The estimated high value of refractive index (>4) is making them suitable for optical lenses. Moreover, photon energy absorption in the visible and ultraviolet spectrums renders them valuable for UV-VIS absorbers.

An in-depth look at the stability, electronic structure, mechanical properties, and thermodynamics characteristic of Ir3TM (TM: Sc, Ti, V) compounds

In this paper, the structural, mechanical, electronic, and thermodynamic properties of Ir3TM (TM = Sc, Ti, and V) intermetallic compounds in the cubic (L12) and hexagonal (D019 and D024) phases are presented. The outcomes of the simulation rely on density functional theory (DFT) within the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) based on the full-potential linearized augmented plane wave (FP-LAPW) approach. The existing study was performed on the L12 cubic phase. in addition to hexagonal D024 and D019 phases, which may be relative but differ in the way that the atomic layers are stacked. The calculated total, cohesive energy, and heat formation suggest that the Ir3Sc compound can be stable in the D024 phase because of an overlap between the L12 and D024 phases with a total energy difference of around 0.026 eV/atom. Ir3Ti and Ir3V are more stable in L12 and D019, respectively. From elastic constants calculations, it reveals that the studied compounds are mechanically stable and harder in the cubic phase than hexagonal phase. However, Ir3Sc has the lowest hardness due to its relative ductility. Inversely, Ir3V has the maximum hardness with a lack of ductility. It was observed that these compounds have an elastic anisotropy based on the three-dimensional Young's modulus surface, and Ir3Sc has the strongest anisotropy, while Ir3V has the weakest in the L12 phase. The total density of state (TDOS) calculations shows that Ir3Ti and Ir3V are stable in the L12 and D019 phases, respectively, except for the Ir3Sc compound which might undergo a martensitic transition. Also, the pseudogap for Ir3V moves quite close to the Fermi level, indicating that the covalent bonding in this compound is sharper than the other compounds. Moreover, via the quasi-harmonic Debye model within the Gibbs computational code, thermodynamic properties are calculated and analyzed with temperature and pressure.

Tailoring structural and optical properties of ZnO system through elemental Mn Doping through First-principles calculations

In this study, band structure and optical properties of Manganese (Mn) doped ZnO are investigated adopting first-principles study calculations. It is observed that, by addition of Mn in ZnO crystal, the electrical properties like conductivity and dielectric function of material have been improved. The elastic constants for the elements are also calculated which shows that the element is stable after addition of dopant. The computational study is done on CASTEP and Material Studio. The ZnO system is simulated and atoms of Mn has been added replacing Zn atoms. The properties that studied are band structure and optics including conductivity, reflectivity, dielectric function, absorption and refractive index. Furthermore, this study also includes calculation of Elastic constants, XRD Spectra, Phonon dispersion and Temperature profile of doped ZnO systems. The computational study produced promising results and experimental approach can be adopted to reinforce the outcomes of this study.

First‐Principles Investigation on the Structural, Mechanical, and Bonding Properties of ZrB2 Under Different Pressures

The crystal structures of zirconium diboride have been thoroughly explored up to 200 GPa by applying the particle‐swarm optimization technique in company with first‐principles calculations. The hexagonal ZrB2 with space group of P6/mmm is always stable in the pressure region of 0–200 GPa. Structurally, this structure consists of the intriguing regular ZrB12 hexagonal column and the planar hexagonal B ring unit. In addition, the stable AlB2–ZrB2 configuration is mechanically and dynamically stable as confirmed by the respective calculations of elastic constants and phonon dispersion curves. The hardness values exhibit a shrinking variation upon further compression, which mainly originates from the decreasing brittleness and degree of the directionality of the covalent bonds with the growing pressure. Interestingly, the analyses of the Poisson's ratio, density of states, electron location function and Bader charge substantiate that a combination of covalent and ionic characters exists in the AlB2–ZrB2 crystalline with the formidable covalent interaction in the BB bonds, and partially covalent and partially ionic interactions in the ZrB bonds. The hardness value for this phase unexpectedly reaches 45.41 GPa under ambient pressure, higher than the lower limit of superhard materials.

Remarkable Optoelectronic Characteristics of Synthesizable Square‐Octagon Haeckelite Structures: Machine Learning Materials Discovery

AbstractThe research explores new compounds with structures similar to square‐octagonal beryllium oxide, commonly known as Haeckelites. The goal is to identify semiconducting variations compounds that can be synthesized and show promising potential in optoelectronic devices. Start with 1083 binary Haeckelite structures, and to test the synthesis potential of these materials quickly, develop new descriptors and use machine learning techniques. As a result, it identifies a subset of 350 materials with suitable properties in terms of phase stability and electronic perspective. These materials are further investigated to analyze their electronic structure and phase stability, which are determined through density functional theory calculations. The phase stabilities of the predicted semiconducting Haeckelites are also compared to other binary compounds using an evolutionary structure search algorithm. The comprehensive methodology also includes examining the dynamic stabilities through phonon calculations and mechanical properties through elastic constant calculations. Eventually, 13 new Haeckelite compounds are discovered, demonstrating exceptional stability and performance in electronic tests. Among these compounds, eight have shown remarkable absorption coefficients and are considered promising candidates with high reflectivity. Additionally, they have exhibited high electron mobility. These findings strongly suggest the potential of these compounds for synthesis and their application in optoelectronic devices.

First-principle simulations of inorganic halides Li2TlBiY6 (Y = Cl, Br, I) for optoelectronic applications

In this emerging technological era, lead-free (Li-based) inorganic halides have drawn a lot of researchers’ consideration due to their optoelectronic applications. Based on this, we explored theoretically mechanical, optical, and thermoelectric features of halides Li2TlBiY6 (Y = Cl, Br, I) by employing first-principle simulations (Wien2k code). Our finding of optoelectronic parameters using appropriate mBJ approach is in favorable alignment to previously reported data, and PBEsol is employed to scrutinize structural as well as mechanical features of these materials. The Born stability and formation energy are examined concerning the structural stability associated with all halides. The distinction between brittle and ductile nature is investigated concerning the calculation of elastic constants of the cubic symmetry. Being based on the mBJ potential, the bandgasps for Li2TlBiCl6, Li2TlBiBr6, and Li2TlBiI6 are 2.8 eV, 2.3 eV, and 1.9 eV, correspondingly. To confirm their optimal absorbability in the electromagnetic domain (visible), all halides were further analyzed concerning dielectric parameters. Additionally, thermoelectric properties are explained in detail within the temperature range of 300-800K using classical Boltzmann theory, making them promising materials for thermoelectric applications.

First-principles study of binary and ternary phases in Mg-Gd-Ni alloys

Given the high demand for magnesium alloys across industries, it's crucial to enhance their performance by developing alloys with superior characteristics. The performance of magnesium alloys is closely related to the properties of the precipitated phase. However, there has been insufficient exploration of the mechanical properties of precipitated phases in Mg-Gd-Ni alloys. Hence, this paper calculates the formation energy, electronic structure, elastic modulus, and elastic anisotropy of the precipitated phase in Mg-Gd-Ni alloys using first principles. Calculations of formation energies and elastic constants demonstrate that MgGdNi4, Mg2Ni, 18R-LPSO, Mg2Gd, and 14H-LPSO possess commendable thermodynamic and mechanical stability. Elastic modulus calculations reveal a significant increase in the elastic modulus of magnesium, especially the bulk modulus, upon the addition of Gd and Ni elements, increasing from 34.5 GPa to a peak of 84.9 GPa. Furthermore, the strength increments of the corresponding precipitated alloys, calculated based on the elastic modulus, underscore MgGdNi4 as exhibiting the most significant strength increment. The elastic anisotropy of each second phase is evaluated using the elastic anisotropy factor, the three-dimensional surface, and the projection onto each two-dimensional plane. The order of elastic modulus anisotropy for shear and Young's modulus is MgGdNi4 > Mg2Ni > 18R-LPSO > Mg2Gd > 14H-LPSO. This study provides valuable data for regulating properties in magnesium alloys.

Regarding the structural, thermodynamic, mechanical, thermoelectric, and optoelectronic properties of anti-perovskite Mg3XN (X = As, Sb, and Bi) through a DFT approach

In this work, we comprehensively analyzed the structure, thermodynamics, mechanical, thermoelectric, and photoelectric properties of antiperovskite Mg3XN (X = As, Sb, and Bi) using first-principles calculations and semi-classical Boltzmann transport theory. Our calculations of phonon spectra and elastic constants suggest that Mg3XN (X = As, Sb, and Bi) exhibit excellent dynamic and mechanical stability, characterized as brittle materials with Vickers hardness (HV) values exceeding 10 GPa. Electronic structure analysis reveals that Mg3AsN is a direct bandgap semiconductor with a 2.25 eV gap, whereas Mg3SbN and Mg3BiN are indirect bandgap semiconductors with gaps of 1.58 eV and 1.41 eV, respectively. At room temperature, the lattice thermal conductivities (κL) for Mg3AsN, Mg3SbN, and Mg3BiN are 13.63, 9.93, and 7.26 Wm−1K−1, respectively, with ZT values of 0.32, 0.08, and 0.10 at optimal doping concentrations. At 1000 K, κL values decrease to 3.19, 2.29, and 1.65 Wm−1K−1, respectively, with ZT values reaching 2.12, 0.98, and 0.92. Our analysis of optical properties demonstrates that these materials exhibit absorbance in the visible and ultraviolet spectra, with negligible energy loss in the respective energy ranges, thereby rendering them suitable for photovoltaic applications.

DFT-based first-principles calculations of new NaXH[formula omitted] (X = Ti, Cu) hydride compounds for hydrogen storage applications

Density functional theory (DFT) was employed to perform an ab-initio study of new hydrogen storage materials NaXH3 (X = Ti, Cu) using the Generalized Gradient Approximation (GGA) and CASTEP package. The structural, electronic, elastic, optical, and hydrogen storage properties of NaTiH3 and NaCuH3 were calculated within the Pm3̄m cubic-perovskite phase. The thermodynamic stability of both structures was ensured by their negative formation energy. The dynamic stability has been investigated through phonon dispersion, and it has been proven that these compounds are stable. The calculations of elastic constants confirm the mechanical stability of these materials. Furthermore, bulk modulus, shear modulus, and Poisson’s ratio have been derived by employing the obtained elastic constants. NaXH3 hydrides were found to be elastically anisotropic and brittle. The electronic band structures turn out metallic behavior in NaXH3 perovskites. The optical characteristics demonstrate that both compounds exhibit their highest absorption and conductivity levels within the ultraviolet wavelength range. The calculation of gravimetric hydrogen storage capacities for NaTiH3 and NaCuH3 was performed and found to be ≈3.932 and 3.266 wt%, respectively. The hydrogen desorption temperature was identified as 637 and 563 K for NaTiH3 and NaCuH3, respectively. The current DFT results highlight that NaXH3 (X = Ti, Cu) hydrides have considerable potential as candidates for H2 storage purposes.

The coexistence of high piezoelectricity and superior optical absorption in Janus Bi2X2Y (X = Te, Se; Y = Te, Se, S) monolayers.

Bismuth chalcogenide and its derivatives have been attracting attention in various fields as semiconductors or topological insulators. Inspired by the high piezoelectric properties of Janus Bi2TeSeS monolayer and the excellent optical absorption properties of the Bi2X3 (X = Te, Se, S) monolayers, we theoretically predicted four new-type two-dimensional (2D) monolayers Janus Bi2X2Y (X = Te, Se; Y = Te, Se, S) using the first principles combined with density functional theory (DFT). The thermal, dynamic, and mechanical stabilities of Janus Bi2X2Y monolayers were confirmed based on ab initio molecular dynamics (AIMD) simulations, phonon dispersion, and elastic constants calculations. Their elastic properties, band structures, piezoelectric, and optical properties were systematically investigated. It was found that Janus Bi2X2Y monolayers have a typical Mexican hat-shaped valence band edge structure and, therefore, have a ring-shaped flat band edge, which results in their indirect band gaps. The results show that Janus Bi2X2Y monolayers are semiconductors with moderate band gaps (0.62-0.98 eV at the HSE + SOC level). After considering the electron-phonon renormalization (EPR), the band gaps are reduced by less than 5% at 0 K under the zero-point renormalization (ZPR) and further reduced by approximately 10% at 300 K. Besides, Janus Bi2X2Y monolayers also exhibit excellent optical absorption properties in the blue-UV light region, with the peak values at the order of 8 × 105 cm-1. Particularly, the Janus Bi2Te2S monolayer was found to exhibit a piezoelectric strain coefficient d11 of up to 20.30 pm V-1, which is higher than that of most of the 2D materials. Our results indicate that Janus Bi2X2Y monolayers could be promising candidates in solar cells, optical absorption, and optoelectronic devices; especially, a Janus Bi2Te2S monolayer can also be an excellent piezoelectric material with great prospects in the fields of mechanical and electrical energy conversion.

Characterization of soil stiffness anisotropy at small strains based on phase velocities of shear waves measured by novel testing apparatus

For the characterization of soil stiffness anisotropy at small strains and the calculation of soil elastic constants derived from the cross-anisotropic model, it is important to obtain stress wave phase velocities of soils in both principal and oblique directions. This study developed an original eight-prismatic shape apparatus equipped with disk-shaped shear plates to measure shear (S-) wave phase velocities (Vphase) in multiple directions, and four granular materials of various shapes were tested by this apparatus under isotropic confinement. Experimental results confirm the capability of the new apparatus and reveal that both S-wave propagation and oscillation directions are sensitive to soil inner fabric, i.e., Vs changes with the variation of either S-wave propagation or oscillation direction. Based on the experimental observations, it is suggested to keep the same S-wave oscillation direction when measuring Vs in multiple propagation directions so that the corresponding shape of the S-wave surface (polar plots of Vs in arbitrary propagation directions) is more precise to reflect the small-strain stiffness anisotropy of soils.

Calculation of elastic constants of bulk metallic glasses from indentation tests

One of the challenges in the applications of instrumented indentation is to simultaneously measure elastic modulus and Poisson's ratio of homogeneous, isotropic materials. This work proposes empirical equations for simultaneous calculation of elastic modulus and Poisson's ratio of bulk metallic glasses (BMGs) from the ratio of the short diagonal length to the long diagonal length and the area of the Knoop imprint. The parameters presented in the empirical equations are determined first by Knoop microhardness tests of 24 BMGs, whose elastic moduli and Poisson's ratios are measured by resonant ultrasound spectroscopy. These empirical equations are further validated by the Knoop microhardness tests of other 3 BMGs, which yield elastic moduli and Poisson's ratios in good accordance with the corresponding ones available in the literature and with the results from nanoindentation tests. This work opens a new venue of Knoop microhardness test as an economical and efficient method to measure both elastic modulus and Poisson's ratio of BMGs.

First-principles calculations to investigate Structural, mechanical, electronic, magnetic and thermoelectric properties of MRh2O4 (M = Mg, Mn, Cd) spinel oxides

Structural, mechanical, magnetic, electronic and thermoelectric properties of MRh2O4 (M = Mg, Mn, Cd) spinel oxides are studied through first-principles calculations. Calculations of structural and elastic stiffness constants (Cij’s) show that the MRh2O4 oxides are stable structurally and mechanically. Elastomechanical results show that the CdRh2O4 is ductile, MnRh2O4 is brittle, while MgRh2O4 lies on the borderline differentiating the ductile and brittle character. MnRh2O4 has high bulk modulus and high Young’s modulus which indicate its ability to resist plastic deformation. MnRh2O4 spinel oxide bears the highest values of Debye temperature (TD = 634.4 K) and melting temperature (Tm = 3530.4 K) among the MRh2O4 (M = Mg, Mn, Cd) oxides. Band structure calculations and density of states spectra indicate the p-type semiconducting nature of MRh2O4 (M = Mg, Mn, Cd) oxides. Spin-polarized electronic structure of CdRh2O4 show 100 % spin-polarized behavior, while MgRh2O4 and MnRh2O4 oxides show 0.12 % and 0.29 % spin-polarization, respectively. MnRh2O4 exhibits saturation magnetization Ms = 172 emu/g and total magnetic moment mtot = 9.99 µB/f.u. Temperature dependent thermoelectric properties (thermal conductivity, electrical conductivity, Seebeck coefficient, Hall coefficient, power factor and figure of merit) are also studied for MRh2O4 oxides. Calculated thermoelectric properties of MRh2O4 (M = Mg, Mn, Cd) oxides show that these oxides are promising for applications as novel thermoelectric materials.

First-principles calculation of Si–C–N structures with metallicity and high hardness

Stable hard and conductive ceramics under ambient conditions are vital for many industrial applications. However, maintaining high hardness while achieving semiconducting-metallic transition in Si3N4 materials is greatly challenging both experimentally and theoretically. Herein, two hexagonal Si–C–N structures, denoted SiC6N7-1 and SiC6N7-2, were constructed using α-Si3N4 as a matrix model. Calculations of elastic constants and phonon spectra showed stable structures under ambient pressure. Both SiC6N7-1 and SiC6N7-2 can possibly be synthesized at the pressures attainable by large-volume press technology. Compared to a-Si3N4, both Si–C–N ternary compounds achieved a semiconductive-metallic transition owing to the elemental substitution. Property calculations showed conductive Si–C–N compounds with high hardness values of 52 GPa for SiC6N7-1 and 31 GPa for SiC6N7-2. Therefore, the introduction of C atoms tuned the intrinsic properties of both structures, achieving high hardness along with good electrical conductivity. Overall, these findings look promising for future design and synthesis paths of novel conductive ceramics with prospective applications.