All inorganic CsPbI3 perovskites have emerged as a potential candidate for next-generation photovoltaics (PVs) and optoelectronics. In this article, the influence of hydrostatic pressure on the structural, electronic, and optical properties of CsPbI3 perovskites was investigated using first-principles calculations within the framework of density functional theory (DFT). At 0 GPa, the orthorhombic delta-phase was found to be the most stable phase, while the alpha-phase is the most unstable phase. Within the applied pressure range of 0-2 GPa, delta-CsPbI3 was found to be thermodynamically stable; however, beta- and gamma-CsPbI3 exhibited thermodynamic stability up to 0.8 and 1.6 GPa. On the contrary, the cubic phase was thermodynamically stable only at 0 GPa. Phonon dispersion relations revealed that alpha- and beta-phases are dynamically unstable, whereas gamma-CsPbI3 is dynamically stable within the applied pressure range. Electronic structure results revealed that the band gap of alpha- and beta-CsPbI3 decreases with increasing pressure, whereas gamma-CsPbI3 showed a non-monotonic band gap variation as a function of pressure. In addition, all the three phases exhibited strong optical absorption in the visible region, and the absorption peak was radically red-shifted with applied pressure. These findings would be beneficial for experimental study and imply that pressure plays an important role in determining the properties of the CsPbI3 perovskite.

New 2D layered materials WX2N4(X & esdot;Si, Ge)(1) are suitable for thermoelectric applications for a pretty good value of the figure of merit (ZT). Here, the thermoelectric properties of the 2D monolayer of WX2N4(X & esdot;Si, Ge) using Density Functional Theory (DFT) is investigated combined with Boltzmann Transport Equation (BTE) along with spin-orbit coupling (SOC). An excellent thermoelectric ZT of 0.91 (0.92 with SOC) is obtained at 900 K for p-type WGe2N4, and a ZT of 0.81 (0.86 with SOC) is observed for n-type at the same temperature. Furthermore, the WGe2N4 showed a ZT of more than 0.7 (0.79 with SOC) at room temperature for p-type. On the other hand, the WSi2N4 showed a comparatively lower ZT at room temperature. However, the ZT value increases significantly at higher temperatures, reaching 0.72 (0.79 with SOC) and 0.71 (0.62 with SOC) for p and n-type at 900 K, respectively. The electronic band structure is examined and discovered that WSi2N4 and WGe2N4 possess indirect bandgaps (BG) of 2.68 eV (2.57 eV with SOC) and 1.53 eV (1.46 eV with SOC), respectively, according to Heyd-Scuseria-Ernzerhof (HSE) approximation. These materials may also be useful in UV and visible range optoelectronic devices because of their strong absorption in the respective regions.

Recently, researchers have focused on developing more stable, Pb-free perovskites with improved processing efficiency and notable light harvesting ability. In this regard, Sn-based (Sn-b) perovskites have gained considerable interest in developing eco-friendly perovskite solar cells (PSCs). However, the oxidation of Sn(2+)to Sn(4+)deteriorates the performance of Sn-b PSCs. Nevertheless, this issue could be mitigated by doping alkaline earth (AE) metal. Herein, we have studied the significance of AE doping on CsSnX3(X = Br, I) perovskites using density functional theory based calculations. The structural, electronic, and optical properties of CsAE(y)Sn(1-y)X(3)(y= 0, 0.25; AE = Be, Mg, Ca, Sr) compounds were systematically investigated to explore potential candidate materials for photovoltaic applications. Formation energy calculations suggested that the synthesis of other AE-doped compounds is energetically favorable except for the Be-doped compounds. The band gaps of the materials were calculated to be in the range of 0.12-1.02 eV using the generalized gradient approximation. Furthermore, the AE doping considerably lowers the exciton binding energy while remarkably enhancing the optical absorption of CsSnX3, which is beneficial for solar cells. However, in the case of Be and Mg doping, an indirect band gap is predicted. Our theoretical findings demonstrate the potential of executing AE-doped perovskites as absorber material in PSCs, which could deliver better performance than pristine CsSnX3PSCs.

Fe2O3 is one of the most common anode materials beyond carbons but suffers from unsatisfactory capacity and poor stability, which are associated with the insufficient utilization of active material and the structural instability caused by the phase transformation. In this work, we report an effective strategy to overcome the above issues through electronic structure optimization by constructing delicately designed Fe2O3@VN core-shell structure. The Fe2O3@VN/CC exhibits a much higher areal capacity of 254.8 mC cm-2 at 5 mA cm-2 (corresponding to 318.5 mF cm-2, or 265.4 F g-1) than the individual VN (48 mC cm-2, or 60 mF cm-2) or Fe2O3/CC (93.36 mC cm-2, or 116.7 mF cm-2), along with enhanced stability. Moreover, the assembled asymmetric supercapacitor devices based on Fe2O3@VN/CC anode and RuO2/CC cathode show a high stack energy density of 0.5 mWh cm-3 at a power density of 12.28 mW cm-3 along with good stability (80% capacitance retention after 14000 cycles at 10 mA cm-2). This work not only establishes the Fe2O3@VN as a high-performance anode material but also suggests a general strategy to enhance the electrochemical performance of traditional anodes that suffer from low capacity (capacitance) and poor stability.

Optoelectronic and thermoelectric properties of two-dimensional (2D) transition metal dinitride (HfN2) have been studied using first-principles calculations. Monolayer and bilayer HfN2 transport properties were calculated by solving the transport equations for electrons and phonons. The highest calculated ZT value for the bilayer HfN2 was 0.85 at 900 K in the negative chemical potential region. This high value of figure of merit suggests that the material would be an excellent choice for thermoelectric energy harvesting devices. The optical property of the material suggests that it is a very good absorber in the ultraviolet (UV) region; thus, it can also be used as a UV-photodetector and as an absorber layer in photovoltaic devices.

Lower-dimensional TMDC materials are suitable for thermoelectric applications for their specific quantum confinement and being distinct in the density of states (DOS). Here we investigated thermoelectric parameters of the 2D TMDC monolayer of ZrXY ((X=O, S,) (Y=S, Se)) by using Density Functional Theory (DFT) combined with Boltzmann Transport Equation (BTE)

Temperature dependence of structural, mechanical, and thermodynamic properties of γ -TiAl is modeled using an extended quasi-harmonic approximation and first-principles calculations. In the first step, the volumes are estimated as a function of temperature following the quasi-harmonic approximation. The lattice parameters are further optimized at fixed volumes in the second step. Modeled mechanical properties (bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, and hardness) agree with the experimentally reported mechanical properties. Similarly, the modeled thermodynamic properties (entropy, heat capacity at constant pressure, Gibbs free energy) are in good agreement with the thermodynamic properties reported from experiments and CALculation of PHAse Diagrams approaches. This study suggests that further optimization of the degree of freedom in the unit cell improves the model accuracy of properties estimated following the quasi-harmonic approximation.

Perovskite solar cells (PSCs) have received intensive attention and demonstrated power conversion efficiency (PCE) as high as 25.8%. Concerning Pb toxicity and the instability of organic elements, all inorganic lead‐free perovskites (ILPs) have been extensively studied to achieve comparable or greater photovoltaic performance. To develop ILPs as an alternative for solar cell (SC) applications, first‐principles calculations of ABBr 3 perovskites (A = Cs, Rb, K, and Na, and B = Sn, and Ge) is performed. Structural, electronic, and optical properties are systematically studied to probe the potential for photovoltaic applications. These ILPs exhibit a direct bandgap in the range of 1.10–1.97 eV, which is highly beneficial for absorbing solar energy. Furthermore, these ILPs demonstrated significant optical absorption (over 10 5 cm −1 ) in the UV–Vis spectrum. These results will help design high‐performance lead‐free PSCs.

The strain- and electric field-dependent electronic and optical properties of monolayer GaInS 2  have been calculated using density functional theory (DFT) and time-dependent DFT (TD-DFT) GaInS 2 monolayer shows an indirect band gap of 1.79 eV where valence band maxima (VBM) and conduction band maxima (CBM) rest between the K and Γ point and at the Γ point, respectively, while at 4% compressive strain, the material changes from indirect to direct band gap of 2.22 eV having the VBM and CBM at the Γ point. With a further increase in compressive strain, the CBM shifts, from the Γ to the M point, which leads to an indirect band gap again. The electric field also affects the band structure of monolayer GaInS 2 and shifts the transition from direct to indirect band gap at a positive electric field of 4 V/nm, which acts normal to the surface. The strain-dependent optical properties are also calculated, which suggests that the absorption coefficient increases with compressive strain. Our work demonstrates a wide range of band gap variation and optical properties improvement upon application of biaxial strain and electric field on the monolayer of GaInS 2 .

In this work lead free perovskite ferroelectric ceramics, K0.5Na0.5NbO3 (KNN), has been synthesized by two different methods, conventional solid state (SS) and co-precipitation (CPP), from the same starting materials, Nb2O5, Na2CO3 and K2CO3 and their properties have been compared. Double calcination, 700 degrees C for 7h followed by 850 degrees C for 6h, of the co-precipitation precursor resulted in single phase perovskite structure (JCPDS card No. 01-077-0038), whereas for solid state precursor a triple calcination, 850 degrees C for 5h, 1000 degrees C for 5h followed by 1050 degrees C for 5h, ended up with producing the cubic perovskite KNN phase. Both samples were sintered at 1120 degrees C for 2h under atmospheric condition in a muffle furnace. FESEM is used to find the microstructural features. Energy dispersive X-ray spectroscopy is used to confirm the chemical composition of the samples. Evolution of the phase structure and variation in Curie temperature, dielectric constant, piezoelectric voltage coefficient (g(33)), piezoelectric charge coefficient (d(33)) as well as mechanical properties such as hardness, stiffnesshave been studied and compared for the KNN samples prepared by two different synthesis methods.

In this work, a simple eco-friendly, one-step, green synthesis method was employed to prepare reduced graphene oxide-Cu nanocomposite. The structural, morphological, elemental characterization was done by XRD, SEM, and FTIR. The surface morphologies of Cu NPs were in spherical particles decorated with an average size of 10 nm. The Cu nanoparticles were uniformly distributed on RGO sheets. The electrochemical performance of as synthesized Cu and RGO-Cu nanocomposite fabricated on Ni foam studied and compared the obtained data from using the techniques such as cyclic voltammetry, chrono potentiometry, and electrochemical impedance spectroscopy in presence of 3 M NaOH a three electrode aqueous method. A highest specific capacitance of 245 +/- 2 F/g was noted at a current density of 0.5 A/g and with excellent capacity retention at 8 A/g even after 2000 cycles. The outstanding electrochemical performance of RGO-Cu nanocomposite can be using as electrode material for future electrochemical energy storage in particular high performance supercapacitor applications.

Lead-free Sodium bismuth titanate (Na0.5Bi0.5TiO3, NBT) ferroelectric ceramic was prepared by conventional solid state reaction method. Microstructural, dielectric and mechanical properties were explored. Single perovskite phase is revealed by XRD. Homogeneously compacted microstructure with square shape grain morphology is observed in FESEM. The depolarization temperature and Curie temperature have been found as 160 degrees C and 265 degrees C respectively. The transition of phases from ferroelectric to relaxor ferroelectric occurs at 220 degrees C. Piezoelectric charge coefficient (d(33)) of the sintered sample is 75 pC/N. The hardness value of 706 HV was measured by Vickers Hardness Tester. Nanoindentation test shows the stiffness and hardness of the sintered sample as 922 mu N/nm and 2.59 GPa respectively.

Novel lead-free BFO–STO, BFO–CTO, and BFO–BZO ceramics were fabricated by the conventional method and their structural, microstructural, and dielectric properties were characterized. Dielectric measurements were carried out at room temperature in a large frequency range, from 20 Hz to 1.8 GHz. XRD analysis has demonstrated differences in the crystalline structure of the samples. BFO–STO exhibits a very different behavior compared to BFO–CTO and BFO–BZO ceramics because its XRD pattern contains peaks from diffracting planes of BFO and STO simultaneously. In comparison, the diffraction patterns of BFO–BZO and BFO–CTO are dominated by the peaks from diffracting planes of BZO and CTO, respectively. SEM observation has also revealed important differences in their microstructure. BFO–BZO and BFO–CTO have presented similar values of dielectric constant at low and high frequencies, ε′ ~ 85 from 1 to 100 MHz. The lowest value of the loss tangent was measured on BFO–CTO with tan δ = 5 × 10–3 at f = 50 MHz. The BFO–STO ceramic has given higher values of the dielectric constant, closer to those reported for the bulk STO. Nearly frequency-independent high dielectric constant with very low loss over a broad frequency range (20 Hz to 1.8 GHz) of BFO–STO ceramic makes this material a potential candidate for high-temperature and high-frequency application with superior energy performance.