Two-dimensional transition metal chalcogenides (2D-TMCs) have emerged as a highly tunable class of layered materials with rich phase diversity, strong spin-orbit coupling, and exceptional electronic and optical properties. Their unique thickness-dependent behavior and defect-sensitive structure make them attractive for a range of applications in nanoelectronics, optoelectronics, and sustainable energy technologies. This review comprehensively discusses their crystallographic diversity and recent advances in understanding structural characteristics, electronic features, and optical responses, including the influence of dimensionality, defects, and heterostructuring. We examine various synthesis strategies, from exfoliation to vapor-phase and solution-based routes, highlighting their scalability and morphological control, with an emphasis on their roles in photovoltaics, photoelectrochemical water splitting, thermoelectrics, and supercapacitors. In addition, we highlight the role of density functional theory (DFT), many-body perturbation techniques, and other first-principles approaches in defining the stability, electronic structure, and optical responses of TMCs. Finally, future perspectives and key challenges for tailoring TMCs toward device-level integration are discussed.

A first-principles study of the Rb2Be2Br6-xClx (x = 0-6) series reveals systematic evolution of electronic structure driven by halide engineering. The series remains thermodynamically stable with formation energies ranging from-21.59 to-20.81 eV/f.u. as progressive Cl instead of Br substitution induces a 19.4 % lattice contraction. PBE calculations yield indirect band gaps tuneable from 1.35 eV (Rb2Be2Br6) to 2.65 eV (Rb2Be2Cl6), with HSE06 confirming this trend for the parent compound. A blue-shift is observed in the optical absorption edge from 1.41 eV to 2.81 eV accompanied with reduction of static refractive index from 2.50 to 2.19. Mechanical stability is confirmed for all compositions within the identified tetragonal symmetry. Debye temperatures increase from 206 K to 288 K and while mechanical behaviour transitions from ductile (G/B = 0.23) to brittle (G/B = 0.74). Band alignment analysis reveals the valence band maxima (+1.60 to +2.55 V vs. NHE) lie significantly above the water oxidation potential (+1.23 V), indicating strong thermodynamic favourability for oxidation-driven photocatalysis. Conversely, conduction band positions preclude overall water splitting. These computationally predicted trends establish halide engineering as an effective strategy for tuning the optoelectronic and photo-catalytic response of lead-free double perovskites.

First-principle calculations are used to analyze the electronic structure and electrochemical properties of Li/Naadsorbed ZnCo2O4 for Li-and Na-ion batteries. Li/Na adsorption increases its electrical conductivity at lower concentrations, resulting in rapid charge transfer and robust adsorption. We shaped a compact ZnCo2O4 hybrid structure in ZnCo2O4 micro/nanospheres that makes use of the multifunctional bridge provided by the hierarchical mesoporous nature. In addition to bridging the ZnCo2O4 nanoparticles, the hierarchical mesoporous structure serves as an efficient electron conduction bridge by facilitating rapid electron transportation and anchoring the micro-and nanospheres to reduce severe volume fluctuations. The rapid ion transfer during lithiation/delithiation and sodiation/desodiation processes is demonstrated by the low diffusion barriers of 0.35 eV for Li and 0.29 eV for Na in ZnCo2O4. These promising results suggest that ZnCo2O4 could serve as an effective host material for both LIBs and SIBs.

Hexagonal nanostructures of crystalline Cu(2)Sand Mn-doped Cu(2)Ssynthesized hydrothermally in this report are examined. SEM micrographs display an anisotropic nature in pristine and Mn-Cu(2)Snanostructures. Pristine Cu(2)Smaterial displays the emission at 497 nm while as the Mn-incorporation leads to a stokes shift of similar to 15 nm. The broad peak with high intensity at 511 nm in the PL is ascribed to the incorporation of 10 %-Mn into Cu(2)Snanostructures. Energy gap decrease in 10 %-Mn-Cu(2)Swas observed from the optical absorption and the electronic structure simulations, simultaneously. Where a strong spin polarization with indirect transitions is observed within the range of visible light spectrum due to spin crossover of partial Mn-d states from spin up to spin down channels. Mn induced spin interactions shift the Fermi level (EF) towards the conduction band with a gap of 1.53 eV in high spin state and 0.31 eV in low spin state. Pristine copper sulphide nanostructures and the optimal doped sample's ability to dynamically regulate their fluorescence and hole doping density could potentially result in their successful integration into optical switches and solar systems.

The present report aims at the detailed investigation of structural dynamics, ferromagnetism, and band profiles of cesium-molybdenum (Cs2MoX6) and cesium-tungsten (Cs2WX6)-based halide perovskites, where X = Cl and Br. A ferromagnetic ground state originates from the only 4d-states of Molybdenum and 5d-states of tungsten in both the cases, respectively. The relaxed lattice systems provide the precise atomic arrangements in agreement with the previous experimental data. Experimentally, Cs2MoCl6 and Cs2WCl6 exhibit cubic structures with semiconducting properties, while Cs2MoBr6 and Cs2WBr6 are assumed for comparison only. Present calculations of elastic constants predict these systems as stable, and positive phonon modes ensure the dynamic stability as well, where all the optical modes are similar to a considerable difference in low phonon manifolds having mixed optical and acoustic characteristics. Contrary to the previous theoretical studies on Cs2MoCl6, the spin-polarized HSE06 calculations decide the spin-up semiconducting nature of all these isostructural systems with a maximum gap in (Mo/W)Br compared to their Cl counterparts. Ferromagnetic exchange interactions between magnetic atoms via nonmagnetic halogen atoms constitute a total spin magnetic moment mu similar to 2.0 mu B for each material, where a transition metal atom only contributes the magnetic moment to the whole unit cell. The magnetic moment is primarily contributed by the transition metal atoms, and the compounds display high Curie temperatures (T C) ranging from 480 to 681 K. The magnetic properties confirm a second-order phase transition, with the derivative of magnetization (dM/dT) revealing sharp variations at T C. Magnetocaloric properties show a linear dependence of magnetic entropy change and relative cooling power on external magnetic fields. These findings highlight the potential of Cs2Mo/WX6 compounds for spintronic, optoelectronic, and energy-efficient magnetic refrigeration applications.

In response to the escalating global energy demand and the environmental impact of fossil fuels, oxide thermoelectric materials have emerged as promising candidates for waste heat recovery due to their stability, nontoxicity, and capacity for high-temperature applications. This comprehensive review evaluates critical advances in oxide-based thermoelectrics, focusing on p-type (Ca3Co4O9, BiCuSeO) and n-type (ZnO, SrTiO3, CaMnO3, In2O3) materials. Key challenges in achieving high thermoelectric performance, such as balancing the Seebeck coefficient, electrical conductivity, and thermal conductivity, are addressed through diverse strategies including doping, compositional tuning, nanostructuring, and interface engineering. Notable achievements include a ZT of 1.42 at 1050 K in Nb-doped SrTiO3 with graphite inclusions, a ZT of 0.9 in nonstoichiometric Ca3Co4O9, and a ZT of 0.47 at 1223 K in Ce-doped In2O3 through defect engineering. BiCuSeO stands out with a ZT of 1.5 at 923 K, achieved via three-step texturation and dual-doping, demonstrating its potential for mid-to-high-temperature applications. Innovations such as high-entropy oxide compositions, two-dimensional electron gas systems, and advanced synthesis techniques like spark plasma sintering and solvothermal synthesis have shown remarkable potential for ZT improvement across these materials. This review highlights a multi-faceted approach to improving thermoelectric efficiency and outlines strategic pathways for scalable, eco-friendly thermoelectric applications in energy harvesting and industrial heat recovery.

In the present article, facile and novel synthesis of Cu2MnSnS4/reduced-graphene (CMTS/rGO) nanocomposites is achieved. X-ray diffraction (XRD), Raman analysis, X-ray photoelectron spectroscopy (XPS) were explored to test the supposed formation. CMTS semiconductors grow within a tetragonal symmetry and rGO crystallize into hexagonal phase. CMTS particle size is very small having dimensions around 10-12 nm and corroborates with the average particle size calculated from the SEM. The TEM micrograph of rGO consists similar to 10 nm thick nanosheets. The composite materials exhibit 2D morphology with 17 nm thick rGO nanosheets holding CMTS quantum dots (9 nm). Electronic structure modulations with rGO specify the replication of energy band gaps with experimental agreements. Photocatalytic activity against malachite green (MG) enhances from 74 % (CMTS) to 95 % (CMTS/rGO). In addition, the electrochemical measurements demonstrate the specific capacitance for 10% CMTS/rGO (870 F/g) is about four times larger than that of pure CMTS (268 F/g). Our results prompt the evidence of possible applications and further research in photocatalysis via graphene reduction.

Low-dimensional materials outperform their bulk equivalents in terms of thermal and electronic charge transport phenomena. Ultralow thermal conductivity in thermoelectric (TE) semiconductors is rare and plays a crucial role in obtaining promising TE performances. Their performance can be effectively improved via strain engineering, which allows the modulation of geometrical parameters as well as electronic energy levels of a material. With this concept in mind, we systematically studied the effect of biaxial tensile strain on the structure, stability, mechanics, and thermoelectric properties of a novel La2GeI2 monolayer by using the hybrid density functional theory and solving Boltzmann transport equations. The strain-induced distortion manipulates the electronic band characteristics with an increase in the band gap, effective mass, and relaxation time of carriers. In principle, La2Ge is a metal, while the functionalized La2GeI2 structure becomes a semiconductor. Two temperature-dependent adsorption structures have been reported in experiments with the R3m phase as the most stable ground-state structure. HSE06 calculations predict an indirect gap of 0.69 eV appearing at the Gamma-M symmetry points of the Brillion zone in this monolayer. La-Ge bands being prominent around the Fermi level emerge out of p-d covalent hybridization, providing an edge to enhanced conductivities. The calculated transport coefficients and thermal conductivity (k(l)) seem to be better than those of available two-dimensional TE materials such as phosphorene, arsenene, etc. We find that a significantly low k(l) value (3.22 W/mK) at 300 K can be reduced to an ultralow value of 0.57 W/mK under strain. Owing to the strain-engineered low thermal conductivity, small band gap, significant Seebeck coefficient (similar to 1100 mu V/K), and ZT(similar to 2), we can rule out the enhanced TE conversion potentials of this monolayer in comparison to traditional TE materials.

We report the strain dependent electronic, phonon and thermoelectric properties of Li -based Half-Heusler compounds. A direct bandgap of 1.50 eV (for CuLiS) and 1.03 eV (for CuLiTe) is observed from HSE calculations. CuLiX (X = S,Te) in their conventional structure are mechanically and dynamically stable semiconductors. However, the compression beyond -15 % (for CuLiS) and -10 % (for CuLiTe) destabilizes the crystal structure due to the overlapping of atomic charge spheres. At the same time, expansion above 4 % produces instability in both systems. The maximum value of Seebeck coefficient significantly increases from -1500 mu/VK in both alloys -2400 mu/VK in CuLiS and -2000 mu/VK in CuLiTe after the application of 5 % compressive strain at 300 K. These alloys achieve maximized thermoelectric efficiency via strain engineering, and thus require further experimental research.

The present article reports the synthesis, characterization and spin-polarized electronic structure of Cu2MnSnS4 (CMTS) quantum dots. Optimization of the hydrothermal physical parameters including reaction temperature and duration has been performed. The CMTS material synthesized was characterized for its structural, morphological, chemical, compositional optical and electrochemical properties. Variation of the reaction parameters made it possible to get an idea about the process of material formation. Formation mechanism, secondary phase detection and single-phase crystallinity are achieved robustly. Single phase tetragonal CMTS was synthesized just after 8 h reaction duration. Significant reactions parameters like, prolonged reaction duration and higher temperatures influence the morphology and hence resulted in enhanced crystallinity of these nanostructures. Variable structural morphologies and shapes like polygons, cauliflower and quantum dots as small as 4–5 nm were synthesized. Optical properties indicated that the quantum dots are highly active in the visible range of the optical spectrum. Also, the electronic structure calculations for this material tracked the 1.4 eV band gap confirmed from absorption spectrum. Electrochemical properties showed the material is having pseudocapacitive nature exhibiting specific capacitance of 268 F/g revealing its charge storing ability.

A large power factor and ultralow lattice thermal conductivity in 2D-monolayers of AuX (X = Cu and Ag) are achieved via first principles calculations. Low phonon frequency, small Debye temperature and high Gruneisen parameter limit the intrinsic thermal conductivity of both the studied materials. An ultra-low lattice thermal conductivity of 0.13 (0.30) W m-1 K-1 and 0.66 (1.59) W m-1 K-1 is obtained for unstrained AuCu and AuAg monolayers, respectively, at 700 (300) K, which further reduces to 0.04 (0.09) and 0.26 (0.63) W m-1 K-1 at 6% biaxial tensile strain. Such values of thermal conductivity are lower than the critical thermal conductivity for the state-of-art thermoelectric materials (kl < 2 W m-1 K-1). The peak values of ZT for unstrained monolayers are 2.20 and 1.40, which enhances to 3.61 and 2.91 at 6% strain for AuCu and AuAg monolayers, respectively. Interestingly pudding-mold band textures are found to be responsible for this unusual thermoelectric behaviour. The stability concerns (chemical/dynamic/mechanical) of these monolayers are ensured to stimulate experimental determinations for novel synthesis and possible applications.

Researchers have looked into quaternary Heusler (QH) compounds for their potential use in futuristic gadgets like photovoltaic cells, optical fibres, thermoelectric modules and spintronic sensors. As per such motivations and research interests, here we are presenting two recently reported Li-based QH compounds LiNbCoAl and LiNbCoGa which are stabilized into face-centred cubic structure of space group F-43m with semiconducting nature. These compounds exhibit high melting temperatures, showing the p-type semiconducting nature and are found to have advantageous thermoelectric capabilities in the high-temperature range. Additionally, the dynamical stability and appropriate elastic and mechanical characteristics for the foundation of effective thermoelectric modules in the temperature range of 1600 K enhance their scientific and technical scope. The electronic band structure is discussed along with the density of states for the better understanding of the electrical properties. The thermodynamic response up to a temperature of 1600 K is also examined for understanding in terms of free energy, specific heat at constant volume and entropy. The special dependences in the two and three dimensions are applied and investigated to characterize the anisotropic nature. However all the required thermoelectric properties are calculated and presented, and the highest figure of merit value at 1600 K for both materials is 0.47 for LiNbCoAl and 0.56 for LiNbCoGa, respectively. As per their excellent practical properties, the current study asserts that both QH compounds should really be considered for energy conversion techniques in high-temperature environments. For the complete study prospectus, these materials are being disclosed for the first time here.

Metal halide perovskite materials are seamless applicants of photovoltaic and optoelectronic devices. Firstprinciples computational approach is carried out in this work to explore the structural, electronic, and optical characteristics of Tl2PtX6 (X = Cl, Br). In structural details, the formation energy (Hf) exposes the studied materials as stable and the tolerance factor along with phonon spectrum decide the stability criterion for the certainty of structural stability of these alloys. The robust p-d hybridization between cations (Pt) and anions (Cl and Br) descent the semiconducting direct band gap from 2.37 eV (Cl) to 2.12 eV(Br), respectively in response to the decreasing size of halide atom. This shrinking gap owed to replacement of Cl to Br anions swings the absorption towards visible region. Also, the possible photoreduction of CO2 by Tl2PtX6 is observed from simulated HER plots. The present materials exhibit a significant absorption coefficient alpha(omega) throughout the visible and ultraviolet spectrum (2-6eV) of light, which marks the experimental realization of photocell and optical device applications.

Present manuscript reports the hydrothermal synthesis of pristine (Zn2SnO4) and copper doped Zn2SnO4 spinals under subcritical conditions. XRD pattern identifies the cubic phase of pristine and its doped nanostructures. Tauc plot and density functional theory (DFT) studies claim the lowering of band gap values up to 2.5 eV upon the insertion of transition metal copper (Cu) into the host lattice. Blue shift occurs due to Moss-Burstein effect upon excess concentration of Copper is realized. Both pristine and Cu doped Zn2SnO4 present light green and dark blue colour upon the irradiation of different UV (252 nm and 365 nm) lamps, respectively. Besides this, Zn2SnO4 shows effectiveness in hosting Cu ions, thus could act as a prospective green/blue emitter.

This paper presents a detailed discussion of thermoelectric and electronic properties of newly designed Li-based Heusler compounds (LiScPtGe, LiYPtSn, LiYPdPb) using Boltzmann transport theory alongside the first-principles calculations. Our investigations predict that these materials exhibit band gaps 0.76 eV (for LiScPtGe), 0.67 (for LiYPtGe) and 0.21 eV (for LiYPdPb), respectively. All the reported materials are indirect band gap semi-conductors; mechanical and dynamical stability is also confirmed. At 300 K, the lowest value of lattice thermal conductivity is observed in LiYPdPb (21.64 Wm-1 K-1), which is very small as compared to the other two ma-terials. The perceived value of the figure of merit (ZT) is 0.61 (for LiScPtGe), 0.52 (for LiYPtSn) and 0.35 (for LiYPdPb) respectively, and probably ensure a considerable thermoelectric efficiency of these newly designed materials.

This paper presents the strain effects on the structural, electronic and phonon properties of a newly proposed SrBaSn half Heusler compound. Since it is stable considering chemical thermodynamics, we tested its strength against uniform strain w.r.t phonon spectrum and it produces a direct bandgap of 0.7 eV. The direct bandgap reduces to 0.19 eV at −12% strain beyond which the structure is unstable. However, an indirect gap of 0.63 eV to 0.39 eV is observed in the range of +5% to +8% strain and afterwards the strain application destabilizes the structure. From elastic parameters, the ductile nature of this material is observed.

Being a possible solution to avoid many environmental, political and economic issues, thermoelectric materials have been widely investigated for their ability to convert heat into electricity in the recent past as well as their benefit in reducing the dependence on fossil fuels. In this review we tried to highlight the challenges and possible strategies to synthesize efficient thermoelectric materials. The performance of thermoelectric power harvesting systems or thermoelectric generators (TEGs) relies on the improvement of the overall figure of merit (ZT) and the output power. Nanocomposite thermoelectrics display a vibrant augmentation of ZT and the strain engineering or band manipulation in bulk thermoelectrics prospect from the overall increase in efficiency of the TEGs. In this chapter, we will discuss the processing and feasible properties of the different nanocomposite and bulk thermoelectric systems. The physical or chemical methods of nanocomposite/bulk synthesis methods will be discussed, and the theoretical background of intrinsic transport coefficients will be highlighted in this regard. The possibilities of enhancement of the efficiency can be viewed in nanocomposites with special microstructures, which in turn scatter the phonons to minimize thermal conductivity while preserving or increasing the electrical conductivity and the Seebeck coefficient simultaneously. The benefits of these nanocomposites are to enhance ZT by 10–100% and increase the efficiency of thermoelectric devices. In the end, the future perspectives, developments, and challenges of bulk/nanocomposite thermoelectrics are put forward thoroughly.

The present manuscript aims at the synthesis of cesium based halide perovskite nanostructures and the effect of cobalt doping on the structural, optical, lumnisent, charge storage and photocatalytic properties. In a very first attempt, we report the solvothermal synthesis of Co doped CsPbCl3 nanostructures under subcritical conditions. The structural features were demonstrated by X-ray diffraction (XRD) Surface morphology determined cubic shape of the synthesized particles. Doping is an excellent way to modify the properties of host material in particular to the electronic structure or optical properties. Incorporation of Co2+ ions in the perovskite structure tunes the optical properties of the nanostructures making this perovskite a visible light active material (Eg = 1.6 eV). This modification in the optical behaviour is the result of size effect, the crystallite size of the doped nanostructures increases with cobalt doping concentration. Photolumniscance (PL) study indicated that CsPbCl3 exhibited Blue emission. Thermogravametric analysis (TGA) revealed that the nanostructures are quite stable at elavated temperatures. The electrochemical performance depicts the pseudocapacative nature of the synthesized nanostructures and can used for charge storage devices. The charge storage capability showed direct proportionality with cobalt ion concentration. And Finally the photocatalytic performance of synthesized material shows superior catalytic ability degrading 90% of methylene blue (MB) dye in 180 min under visible light conditions.

Solid state reaction synthesis of BaSn1-xMnxO3 (x = 0.0-0.3) nanostructures is presented in this article. Heavy transition metal doping in powdered BaSnO3 is accomplished to investigate the structural, morphological, chemical and dielectric properties of synthesized samples. Single phase, cubic crystal formations are revealed from the structural properties. Transmission electron micrographs (TEM) display the formation of polygonal discs with nanoscale (similar to 50 nm) dimensions. Elemental composition of the synthesized samples has been confirmed from the x-ray photoelectron spectroscopy (XPS). Optical properties demonstrate the pristine BaSnO3 as an ultraviolet active material with a band gap of 3.2 eV. The enhancement in visible light active mode is achieved via band gap tuning by proportional Mn-doping in the parent material. (C) 2021 Elsevier B.V. All rights reserved.

Here we discuss the electronic structure and optical properties of Yb based halide perovskites with keen interest on phonon and mechanical stability using the HSE06 approximated density functional theory calculations. The experimental structural parameters are exploited to calculate the semi-conducting band structures with energy gap of 4.32 eV and 3.68 eV for CsYbCl3 and CsYbXBr3 alloys, respectively. Cubic phase stability is guaranteed by the phonon dynamics and machinability of these structures. The observed relaxed structural parameters are in accord with the previous experiments. We found that the present halide perovskite compounds are semiconductors with tuneable band gaps and the f-states of Yb element play a significant role in defining the electronic structure. In addition to this, the sound velocities accompanied by the Debye temperatures (181 K for Cl and 141 K for Br) are evaluated. Furthermore, the dielectric constant optical conductivity, electron loss function, refractive index provide a fundamental basis of the feasible optical characteristics suitable for optoelectronic devices and applications. (C) 2021 Published by Elsevier B.V.