Cu-based chalcopyrite semiconductors (I–III–VI₂) are leading candidates for thin-film photovoltaics, thermoelectrics, and nonlinear optics due to their tunable optoelectronic properties and radiation hardness. This work presents a combined first-principles and empirical investigation of the structural stability, cohesive energy, elastic constants, and thermal behavior of four key compounds: CuInSe₂, CuGaSe₂, CuInS₂, and CuGaS₂. Using density functional theory (DFT) within the generalized gradient approximation (GGA-PBE), we calculate equilibrium lattice parameters, cohesive energies, elastic constants, and bulk moduli. The Born-Huang stability criteria confirm mechanical stability for all compounds. Our results show negative cohesive energies (ranging from –3.82 eV/atom for CuInSe₂ to –4.56 eV/atom for CuGaS₂), indicating strong thermodynamic stability. Elastic constants systematically increase when replacing Se with S and In with Ga, with CuGaS₂ exhibiting the highest stiffness (C₁₁ = 115 GPa, B = 84 GPa). Empirical models estimate Debye temperatures (265–372 K), thermal conductivity, and elastic anisotropy. The anisotropy factors near unity (1.16–1.30) suggest nearly isotropic mechanical behavior. Sulfur-containing compounds display higher Debye temperatures and thermal conductivity due to enhanced covalent bonding. These results agree well with available experimental and theoretical data, providing a quantitative basis for designing mechanically robust chalcopyrite-based d
Abstract Although covalent and ionic inorganic semiconductors have traditionally been excluded from exhibiting superelastic behavior, recent atomic-scale high-resolution transmission electron microscopy has revealed superelasticity in bulk group-IV monochalcogenides (e.g., GeSe). In this study, we extend the concept of superelasticity to the two-dimensional (2D) atomic limit using ab initio simulations, with GeSe serving as a paradigmatic example. Under uniaxial tensile strain under zigzag direction, resonant-bonding-induced transverse phonon softening is activated, triggering a reversible structural transition mediated by metastable twin boundary—an essential characteristic that distinguishes superelasticity from ferroelasticity. Through systematic analysis, we identify GeSe, SnS, and GeS as promising superelastic candidates, while SnSe, Bi, and Sb exhibit ferroelastic behavior under similar zigzag tensile strain. Additionally, we demonstrate that uniaxial compressive strain along the armchair direction universally induces ferroelasticity in Bi, Sb, GeSe, SnS, and SnSe. These findings not only confirm the existence of superelasticity in 2D materials but also establish a clear criterion for differentiating superelasticity from ferroleasticity. This work provides a transformative framework for understanding and designing flexible electronic devices based on superelastic monolayer group-IV monochalcogenides.
Covalent semiconductors play an important role in key technological advancements in areas such as communications, consumer electronics, automotive, energy, and more. However, the low ductility of covalent semiconductors, originating from the strong chemical bonding, prevents them from a wide range of engineering applications. In this work, we demonstrate that the bond strength of covalent materials is very sensitive to the electron distribution, able to be effectively modified via the electron-hole pairs (EHPs) induced by photoexcitation. The photomechanical effects in the III-V covalent semiconductors GaP, GaAs, and InP have been examined by a combination of advanced quantum mechanics (QM) simulations, nanoindentation experiments, and state-of-the-art transmission electron microscopy measurements. The QM results indicate that the energy barrier for deformation slip in GaP is reduced by more than $50%$ by generating high-concentration EHPs $(\ensuremath{\sim}{10}^{21}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}3})$, exhibiting metal-like ductility. Theoretical prediction agrees very well with the experimental measured performance where more dislocations are activated under light-illumination conditions.
There are few known semiconductors exhibiting both strong optical response and large dielectric polarizability. Inorganic materials with large dielectric polarizability tend to be wide-band gap complex oxides. Semiconductors with a strong photoresponse to visible and infrared light tend to be weakly polarizable. Interesting exceptions to these trends are halide perovskites and phase-change chalcogenides. Here we introduce complex chalcogenides in the Ba-Zr-S system in perovskite and Ruddlesden-Popper structures as a family of highly polarizable semiconductors. We report the results of impedance spectroscopy on single crystals that establish BaZr S 3 and Ba 3 Zr 2 S 7 as semiconductors with a low-frequency relative dielectric constant ɛ 0 in the range 50–100 and band gap in the range 1.3–1.8 eV. Our electronic structure calculations indicate that the enhanced dielectric response in perovskite BaZr S 3 versus Ruddlesden-Popper Ba 3 Zr 2 S 7 is primarily due to enhanced IR mode-effective charges and variations in phonon frequencies along 〈001〉; differences in the Born effective charges and the lattice stiffness are of secondary importance. This combination of covalent bonding in crystal structures more common to complex oxides, but comprising sulfur, results in a sizable Fröhlich coupling constant, which suggests that charge carriers are large polarons.
The outermost layers of many single crystal materials undergo reconstruction, i.e., the geometry at the surface differs from that expected for an ideal termination of the bulk. Most of these reconstructions result in a change in the size of the repeating surface unit cell and therefore can immediately be identified by the simple observation of the diffraction spot pattern in a low-energy electron diffraction (LEEP) apparatus. In particular the common semiconductors, which are primarily covalent materials with strong directional bonding, all undergo surface reconstruction with some faces exhibiting one or more metastable surface structures. These may be considered to be driven by the high potential energy of the half-filled orbitals generated when the bulk bonds are broken to make surface atoms. The resulting periodicities of these surfaces in many cases have been known from LEED for over twenty years. Despite numerous experimental and theoretical studies, the geometrical configurations of almost all these surfaces are still to be resolved. In Table 1 are listed a selection of the reconstructions observed for some low index faces of common semiconductors. Out of this list, the geometries of GaAs(110) and Si(111)2×1 are the only ones generally accepted as well determined.
The outermost layers of many single-crystal materials undergo reconstruction, i.e., the geometry at the surface differs from that expected for an ideal termination of the bulk. Most of these reconstructions result in a change in the size of the repeating surface unit cell and therefore can be identified by the simple observation of the diffraction spot pattern in a low-energy electron diffraction (LEED) apparatus. In particular, the common semiconductors, which are primarily covalent materials with strong directional bonding, all undergo surface reconstruction with some faces exhibiting one or more metastable surface structures. These may be considered to be driven by the high potential energy of the half-filled orbitals generated when the bulk bonds are broken to make surface atoms. The resulting periodicities of these surfaces have in many cases been known from LEED for over twenty years. Despite numerous experimental and theoretical studies the geometrical configurations of almost all these surfaces are still to be resolved. In Table 7.1 are listed a selection of the reconstructions observed for some low-index faces of common semiconductors. At the present time the geometries of GaAs {110} and Si{111} 2 × 1 are the only ones generally accepted as well determined. In both cases the structures are close to the ideal bulk termination geometry.
Continuum-buried defect states in semiconductors are generally expected to be optically inactive because of their strong coupling to continuum bands. Here, we show that such defects can instead host radiative electronic bound states in the continuum (BICs) using the silicon G center as a prototypical example. Hybrid functional first-principles calculations with a Hubbard U correction reveal that a localized defect state, initially buried below the valence band maximum (VBM) in the ground state, undergoes exchange-driven energy-level reordering under optical excitation and shifts above the VBM. This exchange-induced transition suppresses nonradiative decay and enables a robust radiative emission. By computing temperature-dependent nonradiative lifetimes and comparing them to experimental photoluminescence (PL) lifetimes, we quantitatively reproduce the observed temperature dependence of the emission. These results uncover a stabilization mechanism for continuum-embedded defect states and establish electronic BICs as a general paradigm for designing defect-based optical systems, including quantum emitters and qubits.
Metal silicon phosphides composed of earth-abundant Si and P tend to exhibit semiconducting properties and adopt diverse crystal structures with relatively small additions of structure-directing elements. The potential of silicon phosphide materials in nonlinear optical applications has been hindered by the inability to systematically produce noncentrosymmetric structures with such a flexible framework. Here, in this work, two isostructural compounds with a novel noncentrosymmetric structure were made possible by the inclusion of elements with stereochemically active lone pairs (Sn 2+ and Pb 2+ ). The structures were determined through single-crystal and synchrotron powder X-ray diffraction. Analysis of chemical bonding in real space through the electron localization function revealed stereochemically active Pb 2+ and Sn 2+ species in a trigonal pyramidal coordination with {Pb/Sn}–P bonds. Such covalent bonding between Pb and P is quite uncommon in extended solids and has been reported in a few rare instances. Band structure calculations and linear optical measurements confirm the semiconducting nature of Cs X Si 15 P 21 ( X = Sn or Pb). The synthesis was optimized to yield high-purity polycrystalline samples. The nonlinear optical properties show promising second-harmonic generation (SHG) coefficients from the Kurtz–Perry method. First-principles calculations of the nonlinear optical properties support the experimentally determined SHG values and provide moderate values of b
Tracking the structural evolution of colloidal nanocrystals (NCs) facilitates the mechanistic studies of their materials chemistry. NC engineering via phase transformation reveals the chemical and physical determinants that drive lattice-scale dynamic processes such as cation exchange. Here, in this study, we employed NCs to demonstrate the cation exchange process from Cu 3 As to InAs and GaAs within nanocubes. The symmetry conversion in unit cells from cubic Cu 3 As to hexagonal InAs and GaAs can be described using a schematic cellular automaton model, which suggests a simplified cube-to-sphere transition. The strong covalent characteristics of III–V materials highlight the kinetic control that navigates the tailorable transformation through either an isotropic trajectory, leading to hollow structures, or a topotaxial trajectory, with abundant stacking faults. The reconstruction of complex covalent bonds is envisioned as the foundation for the synthesis of NCs.
Chalcogenides-rich transition metal compounds host a rich landscape of emergent quantum phenomena that are intimately governed by their quasi-onedimensional chemical-bonding frameworks and their response to external perturbations such as pressure. Here, we report a pressure-induced iso-symmetric structural transition in the quasi-one-dimensional compound CrNbSe 5 , in which the electronic ground state is controlled not by symmetry breaking but by a continuous reorganization of local bonding interactions. Applied pressure reversibly tunes CrNbSe 5 between semiconducting and semimetallic states, enabling access to low- and high-carrier electronic regimes through direct modulation of metal−chalcogen bonding. High-pressure singlecrystal X-ray diffraction directly resolves the evolution of Cr−Se and Nb−Se bond distances, coordination polyhedra, and connectivity, revealing a fully reversible semimetal−semiconductor−semimetal transition driven by gradual yet cooperative bond rearrangements within a preserved crystallographic symmetry. In contrast to chemical substitution, which irreversibly alters composition and introduces disorder, pressure acts as a clean, continuous control parameter that reshapes the bonding landscape without disrupting structural symmetry. These results establish CrNbSe 5 as a model system for electronically driven phase switching via tunable chemical bonding, highlighting iso-symmetric bond reorganization as a powerful design principle for pressure-controlled
Everything we examined (10)
This check searched the claim as stated. It did not run a separate search for evidence against it.