We systematically investigate the structural, electronic, phononic, and thermoelectric properties of the ABSO (A = Ca, Ba, Sr, Mg; B = Cd, Co) monolayer using first-principles DFT and Boltzmann transport theory. The Ca2Cd2S2 monolayer exhibits exceptional dynamic and thermal stability, as confirmed by phonon dispersion and AIMD simulations. Electronic structure calculations reveal a direct band gap of 0.75 eV at Γ and highly dispersive bands near the Fermi level, facilitating efficient charge transport. Deformation potential theory predicts remarkable carrier mobilities of 2840 cm2 V-1 s-1 for electrons and 306 cm2 V-1 s-1 for holes. Phonon transport analysis indicates low lattice thermal conductance (2.64 W m-1 K-1 at 300 K) due to strong anharmonic scattering, particularly in flexural acoustic modes. A maximum thermoelectric figure of merit (ZT) of 1.15 is achieved at 500 K for p-type doping, with an average ZT of 1.04 and energy conversion efficiency of ∼51%, comparable to conventional heat engines. Additionally, the coefficient of performance reaches 23.45% of the Carnot limit at 400 K, highlighting potential for refrigeration. This work establishes CaCdSO as a promising 2D thermoelectric material and introduces Zintl-like design principles for mixed-anion systems for future energy applications.
Nonhydrostatic stress can influence pressure-dependent optical measurements of GaN, whereas conventional pressure-gap relations usually describe only hydrostatic loading. Here a symmetry-adapted reduced-order thermo-optoelastic framework is formulated for zinc-blende GaN over 0-12 GPa by separating volumetric compression from signed tetragonal distortion. The framework uses published inputs only: digitized hydrostatic and biaxial modified-HSE06 curves, a Murnaghan equation of state, cubic elasticity and a Varshni temperature correction. The digitized calibration curves are reproduced with root-mean-square residuals of 1.1 meV (hydrostatic) and 7.8 meV (biaxial); these values quantify reproduction of the source curves and are not independent validation. At 12 GPa and 300 K, the EOS-based hydrostatic gap is 3.698 eV. Within the adopted ambient-elasticity approximation, an axisymmetric state with τ/P = 0.10 suggests a gap reduction of about 35 meV, while reversing the tetragonal-strain sign at τ/P = 0.05 gives an increase of about 18 meV. These mixed-stress shifts change by less than 1.5 meV when an alternative elastic dataset is used, but direct nonhydrostatic experiment or dedicated first-principles mixed-loading calculations are still required for validation. The principal contribution is therefore a traceable reduced-order bridge between EOS compression, symmetry-adapted strain and optical-gap response rather than a replacement for a microscopic Bir-Pikus treatment.
Boron-rich compounds are promising platforms for phonon-mediated superconductivity because light B atoms and covalent B–B bonding provide high-frequency phonon modes. In this work, we investigate a manually constructed MgB6 polymorph that is dynamically unstable at ambient pressure but becomes stabilized under compression, with imaginary phonon modes disappearing from 7 GPa onward. The fully relaxed structures exhibit a pressure induced symmetry evolution from triclinic P1̄ through monoclinic C2/m to trigonal R3̄m, accompanied by significant changes in the lattice dynamics, elastic properties, and electronic structure, and satisfy the pressure-corrected Born stability criteria. The structures remain metallic throughout the dynamically stable range, with states near the Fermi level dominated by B-p orbitals. The calculated superconducting transition temperature is nonmonotonic: Tc=21.73 K at 7 GPa, decreases to 16.13 K at 10 GPa, effectively vanishes at 25 and 50 GPa within the Allen–Dynes formalism, and reappears with Tc=18.92, 17.55, and 18.30 K at 60, 70, and 80 GPa for μ∗=0.10. Pressure-dependent convex-hull calculations show that the polymorph remains metastable throughout the studied pressure range. The suppression and reappearance of superconductivity correlate with the pressure evolution of the B–B bond-length distortion index, identifying local bond-network heterogeneity as a structural descriptor for pressure-induced reentrant superconductivity.
This study examines the concentration-dependent influence of dilute A-site Tm substitution on the structural, electronic, optical, thermoelectric, elastic, thermodynamic, and magnetic properties of SrTiO3 using first-principles calculations. Pristine SrTiO3 and Sr1-xTmxTiO3 with x = 2.5% and 5.0% were studied using the all-electron FP-LAPW + lo method within the GGA + U framework. Structural optimization shows that the perovskite framework remains intact after Tm incorporation. The equilibrium volume increases from 2533.4554 a.u.3 for pristine SrTiO3 to 2755.1025 and 3155.7362 a.u.3 for the 2.5% and 5.0% Tm-substituted systems, respectively, whereas the bulk modulus decreases from 215.3005 GPa to 167.1973 and 163.9482 GPa. These changes reveal a systematic expansion and softening of the lattice with increasing Tm content. Negative formation energies of −3.62, −3.57, and −3.51 eV atom−1, together with phonon spectra without imaginary modes, support the thermodynamic and dynamical stability of the investigated structures. Electronic-structure calculations show that pristine SrTiO3 is a spin-symmetric indirect-gap semiconductor with Eg ≈ 2.7–2.9 eV, whereas Tm substitution introduces localized Tm-4f-derived states near the Fermi level and reduces the spin-up/spin-down gaps to approximately 1.2–1.3/1.0–1.2 eV for x = 2.5% and 0.7–0.9/0.0–0.1 eV for x = 5.0%. Charge-density and density-of-states analyses reveal dopant-induced redistribution of electronic charge and modified Tm–O and Ti–O orbital interactions. The optical spectra retain strong ultraviolet activity, while Tm substitution introduces additional low-energy, spin-sensitive optical features. Thermoelectric calculations show that pristine SrTiO3 retains the highest electrical conductivity normalized by relaxation time, reaching approximately 1.5 × 1019 (Ω cm s)−1 at 800 K, whereas Tm substitution suppresses conductivity but modifies the Seebeck polarity and carrier-transport response. Pristine SrTiO3 yields the highest calculated electronic-only figure of merit, with ZTe ≈ 0.019 near 50 K.Elastic constants decrease from C11/C12/C44 = 340/153/126 GPa in pristine SrTiO3 to 286/108/98 GPa and 279/106/92 GPa for x = 2.5% and 5.0%, respectively, demonstrating concentration-dependent elastic softening while preserving the adopted mechanical-stability conditions. Within the adopted spin-polarized GGA + U treatment, Tm substitution produces total cell moments of 1.00402 and 1.99550 μB for x = 2.5% and 5.0%, respectively, compared with Mcell = 0.00131 μB for pristine SrTiO3. Spin-density analysis shows that the magnetic response is predominantly localized around the Tm-4f centres, with weak induced polarization in the neighbouring Ti–O framework. The results establish a direct relationship between Tm concentration and the band-edge structure, optical activity, carrier polarity, lattice compliance, and localized magnetism of SrTiO3. This coupled response highlights the potential of Tm-substituted SrTiO3 for spin-sensitive oxide electronics, ultraviolet/near-visible optoelectronics, resistive sensing, and multifunctional perovskite platforms.
An analytical index is proposed for predicting miscibility in binary systems of transition metals and lanthanides: the Mendeleev Analytical Miscibility Index (MAMI), based on two classical physical principles: (i) the incompatibility between rare earths and early transition metals, and (ii) the incompatibility between platinum group metals and the IB/IIB blocks, both encoded via the modified Pettifor scale (Mendeleev number). The index comprises two sigmoid components and ten optimisable parameters. Applied to 813 binary systems, MAMI achieves an accuracy of 92.00% (95% CI: [90.0%, 93.9%]), an MCC of 0.815 and an AUC-ROC of 0.918, demonstrating that miscibility classification is captured by classical physical principles without machine learning. The explicit formula immediately identifies the dominant physical mechanism for any binary pair, an advantage unattainable in black-box neural networks.To quantify the limits of the Hume-Rothery rules within their natural domain, a second index (HRMI) with three descriptors and eight parameters is calibrated on 351 transition metal pairs. Despite its domain advantage, HRMI does not outperform MAMI: accuracy 81.48% versus 87.46%, MCC 0.503 versus 0.678, AUC-ROC 0.741 versus 0.918. The Mendeleev number thus carries more discriminatory signal than atomic radius, crystal structure and valence combined, even within the natural domain of the latter.Comparison with a 770-neuron network achieving near-perfect in-sample classification illustrates the trade-off between memorisation and interpretability: MAMI, with a compression ratio of 81:1, sacrifices approximately 8 percentage points of accuracy in exchange for a physically transparent formula applicable across the full RE–TM–I/II chemical space.
Perovskite materials occupy a central position in modern materials science due to their structural versatility and wide range of functional applications, including solid-state hydrogen storage. Hydrogen storage, in particular, has emerged as a key technological pathway for meeting growing global energy demands cleanly and sustainably. In this study, we systematically investigate the structural, mechanical, electronic, and hydrogen-storage properties of LiKA2H6 (A = Mg, Ca, Sr, and Ba) double perovskite hydrides to evaluate their potential as solid-state hydrogen carriers. Structural optimization of phonon dispersion and elastic properties confirms chemical, thermodynamic, and mechanical stability, indicating promise for hydrogen storage applications. Electronic structure calculations show that all compounds exhibit semiconducting character, with indirect Γ–X band gaps of 4.13 eV, 3.67 eV, 2.74 eV, and 1.73 eV for LiKMg2H6, LiKCa2H6, LiKSr2H6, and LiKBa2H6, respectively, as obtained using the HSE06 functional. The corresponding gravimetric hydrogen storage capacities are The LiKA2H6 (A= Mg, Ca, Sr, and Ba) double perovskite hydrides exhibit gravimetric hydrogen storage capacities ranging from 2.09 to 6.01 wt%, reaction enthalpies of 40.44–54.78 kJmol−1 H2, and desorption temperatures of 309.4–419.2 K. Overall, the present findings identify LiKA2H6 hydrides as promising candidates for next-generation solid-state hydrogen-storage applications. However, that the reported hydrogen-storage properties are theoretical predictions based on first-principles DFT calculations and require future experimental validation to confirm their practical performance.
High-temperature oxygen diffusion in indium oxide (In2O3) is critical for advanced devices, but standard Buckingham potentials fail under extreme conditions due to unphysical atomic overlaps. We developed a Morse-type interatomic potential for bixbyite In2O3 to ensure robust numerical stability up to the melting point. Molecular dynamics simulations confirm that the potential accurately reproduces experimental lattice constants, macroscopic elastic properties, and vacancy-induced microscopic softening. Oxygen diffusion dynamics investigated up to 2400 K revealed a distinct mechanistic transition near 1200 K. While the high-temperature activation energy aligns with density functional theory predictions, the estimated trial frequency is anomalously low, being two to three orders of magnitude below the lattice Debye frequency. This deviation stems from a correlated “gated hopping” mechanism, where oxygen migration is statistically constrained by the thermal expansion of adjacent indium cation gates. These findings underscore the critical role of entropic constraints and lattice anharmonicity in complex oxides, providing a robust computational framework for predicting high-temperature ionic transport in next-generation materials.
The identification of lead-free, stable piezoelectric materials remains a key challenge for sustainable technologies. Although first-principles calculations based on density functional theory (DFT) provide reliable property predictions, their high computational cost prevents their direct use in large-scale screening. Here we present a systematic machine learning (ML) benchmark for the prediction of the maximum piezoelectric modulus em of inorganic crystalline materials, trained on >3,000 DFT-computed compounds from the Materials Project. We evaluate thirteen predictive architectures spanning gradient-boosted tree ensembles, deep neural networks, and seven graph neural network (GNN) models. The three top-performing models are then used to screen promising piezoelectric materials among >10,000 unlabelled Materials Project compounds. After filtering for thermodynamic near-stability (Ehull<0.1 eV/atom), insulating behaviour (Eg>0.1 eV), and non-centrosymmetric crystal structures, eight promising lead-free candidates are identified. Independent DFT calculations of the full piezoelectric tensor for twenty selected compounds confirm the screening results. Among the identified materials, SrTaNO2, YWN3, and SrTa2Bi2O9 emerge as the most promising targets for experimental synthesis as they exhibit large piezoelectric moduli in the range of 3–103 C/m2.
TBT-graphene is a structural derivative of T-graphene, characterized by the integration of additional four-membered carbon rings into the buckled T-graphene framework. This study investigates the mechanical response of TBT-graphene under varying temperatures, strain rates, and nanohole defects, utilizing molecular dynamics simulations. Quantitatively, TBT-graphene possesses a competitive Young's modulus of 148.9 N/m at 300 K, which noticeably outperforms monolayer MoS2 and InSe yet remains highly competitive among representative four-membered ring carbon allotropes, demonstrating a well-balanced combination of moderate stiffness and flexibility. Temperature is found to exert a profound influence on the failure modes: the material exhibits brittle fracture within the 10 K-350 K range, whereas a significant brittle-to-plastic transition occurs at higher temperatures (400 K-600 K), maintaining structural integrity even at 50% tensile strain (e.g., 600 K). The mechanical response demonstrates a relative insensitivity to the strain rate at low-to-moderate levels; however, this dependency intensifies under high-strain conditions, characterized by a non-monotonic behavioral trend. Furthermore, the effects of circular, square, and diamond nanohole defects have been investigated. While these defects generally degrade mechanical properties, an anomalous enhancement in fracture strain is observed for square and diamond defects at concentrations of 6%. This phenomenon is driven by a “blunt crack” effect, where local atomic reconstruction at defect edges passivates crack tips and homogenizes stress distribution. These findings provide valuable insights into the deformation physics of TBT-graphene and highlight its potential for resilient nanomechanical systems and flexible electronics.
The development of materials with outstanding thermoelectric properties is crucial for advancing thermoelectric device applications. The structural, mechanical, dynamical, and thermodynamic properties of novel Zintl-phase materials SrAg2X2 (X = S, Se, and Te) have been investigated using first-principles density functional theory (DFT) calculations. The calculated lattice constants and bulk moduli agree with previous theoretical data. Analysis of elastic constants revealed that SrAg2S2 and SrAg2Se2 are mechanically stable, whereas SrAg2Te2 is mechanically unstable. The bulk modulus, Young's modulus, shear modulus, Pugh ratio (B/G), Poisson's ratio (ν), and Vickers hardness (HV) were determined for the mechanically stable SrAg2S2 and SrAg2Se2. The mechanical anisotropy of SrAg2S2 and SrAg2Se2 was further investigated using three-dimensional (3D) and two-dimensional (2D) visualizations of the elastic moduli along with several anisotropy indices. Dynamical stability was assessed through phonon dispersion curves and phonon density of states (PHDOS). Furthermore, thermodynamic properties such as Debye temperature, bulk modulus, heat capacity and thermal expansion coefficient were evaluated. These insights can guide future experimental work on synthesizing and optimizing Zintl-phase materials with mechanical stability and potential thermoelectric applications.
Halide perovskite compounds have gained considerable attention due to their potential application in optoelectronics and photovoltaics; however, the physical properties of Cs2InAgCl6 under pressure remain unclear. This study seeks to systematically explore the electrical, mechanical, and optical properties of Cs2InAgCl6 under hydrostatic pressures of 0 to 160 GPa. First principles calculations through DFT have been performed using generalized gradient approximation with the use of GGA-PBE, GGA-RPBE, and HSE06 exchange-correlation functionals, as done by CASTEP, in order to study the structural, electronic, mechanical, and optical properties of Cs2InAgCl6. The hydrostatic pressure significantly reduces the direct band gap at Γ point from 1.039 eV to 0.434 eV (GGA-RPBE), 0.970 eV to 0.437 eV (GGA-PBE), and 3.031 eV to 0.754 eV (HSE06), mainly owing to the downward shift of conduction band minimum. The mechanical properties show that the material remains stable and ductile over the entire range of pressures. Optical parameters like refractive index, loss function, absorption coefficient, and reflectivity were analyzed between 0 and 160 GPa. The effect of pressure on the physical properties of Cs2InAgCl6 is significant, which reveals the good potential of this compound for the latest optoelectronic devices.
First-principles calculations were carried out to investigate random boron-rich high-entropy 81-atom MB2-xNx (M = Ti0.1852Zr0.1852Hf0.1852Nb0.2222Ta0.2222, x = 0, 1/3, 2/3, 1) boronitride samples. The stability, structural, electronic, thermodynamic and mechanical properties were studied. All the boronitrides are thermodynamically stable due to the negative formation enthalpies. It is also assumed that MB2-xNx can be synthesized at low temperatures using individual diborides and dinitrides, or boronitrides as precursors. The electronic density of states (EDOS) at the Fermi level (EF) changes extremely with increasing N content due to a shift of EF towards low energies and an increase of metal states near the EDOS minimum. The main peaks of the phonon spectra of the boronitrides shift towards low frequencies with increasing N content. The elastic moduli, Vickers hardness, fracture toughness and Debye temperature decrease according to a parabolic law, and the B/G ratio and Poisson ratio increase parabolically with positive curvature with nitrogen concentration. The three-dimensional surface anisotropy of the Young's modulus and the linear compressibility of MB2-xNx increases significantly with increasing x.
The pursuit of sustainable and high-performance optoelectronic applications has brought increasing attention to lead-free II–VI-based double perovskites. In this work, ab-initio calculations within density functional theory are employed to investigate the structural, electronic, and optical properties of A2CaB'O6 (A = Sr, Ba and B′ = Cr, W) compounds. The modified Becke–Johnson potential is used to improve the accuracy of the electronic band gaps, while spin–orbit coupling is included to account for relativistic effects in the tungsten-containing systems. Formation energies, elastic constants, phonon spectra, and geometrical factors are analyzed to assess the energetic, mechanical, and dynamical characteristics of the cubic phase. The phonon calculations indicate that Ba2CaCrO6 is dynamically stable in the cubic structure, whereas Sr2CaCrO6, Sr2CaWO6, and Ba2CaWO6 exhibit imaginary phonon modes, suggesting a tendency toward lower-symmetry distortions at 0 K. Despite their indirect band gaps (∼0.98–3.88 eV), the investigated compounds display significant optical absorption across the visible and ultraviolet regions (0–8 eV), highlighting their potential as light-harvesting materials. Application-oriented analysis further identifies Ba2CaCrO6 as a promising absorber layer for perovskite solar cells, supported by favorable photovoltaic parameters obtained from SCAPS simulations. Overall, these results provide insight into the structure–property relationships of II–VI double perovskites and support their potential for environmentally friendly optoelectronic applications.
The structural, mechanical, electronic, optical, and thermoelectric properties of quaternary diamond-like chalcogenides K2VCuX4 (X = S, Se, Te) were systematically investigated using density functional theory calculations based on the Pseudopotential Plane-Wave (PP-PW) method. The calculated equilibrium structural parameters exhibit excellent agreement with available experimental data. Mechanical stability analysis derived from single-crystal elastic constants demonstrates that while the K2VCuS4 and K2VCuTe4 phases are mechanically stable by satisfying the Born-Huang criteria, the K2VCuSe4 phase exhibits mechanical instability and was thus excluded from further transport evaluations. Electronic band structure calculations reveal that both stable compounds are indirect band-gap semiconductors. Furthermore, the temperature-dependent thermoelectric transport properties including electronic thermal conductivity (κe/τ), Seebeck coefficient (S), and electrical conductivity (σ/τ) were evaluated using semi-classical Boltzmann transport theory. At an ambient temperature of 300 K, the stable compounds yield exceptional dimensionless figure of merit (ZT) values approaching or exceeding unity (0.978 for K2VCuS4 and 1.033 for K2VCuTe4), underscoring their remarkable efficiency for solid-state waste heat recovery. The comprehensive analysis of the electronic and optical spectra conclusively demonstrates that these stable quaternary configurations hold substantial promise for deployment in advanced optoelectronic devices and high-performance thermoelectric systems.
