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We present the promising selective conversion capabilities of group IV (Ti2X and Zr2X; X = C, N or B) MXenes with O-termination for catalyzing the carbon dioxide reduction reaction to methane.

The breathtaking success of MXenes arising from a library of unique and fascinating properties has triggered world-wide research interest and opened up several new directions in understanding the science and technology of two-dimensional materials.

The capture, activation, and dissociation of carbon dioxide (CO2) is of fundamental interest to overcome the ramifications of the greenhouse effect. In this regard, high-throughput screening of two-dimensional MXenes has been examined using well-resolved first-principles simulations through DFT-D3 dispersion correction. We systematically investigated different types of structural defects to understand their influence on the performance of M2X-type MXenes. Defect calculations demonstrate that the formation of M2C(VMC) and M2N(VMN) vacancies require higher energy, while M2C(VC) and M2N(VN) vacancies are favorable to form during the synthesis of M2X-type MXenes. The M2X-type MXenes from group III to VII series show remarkable behavior for active capturing of CO2, especially group IV (Ti2X and Zr2X) MXenes exhibit unprecedentedly high adsorption energies and charge transfer (>2e) from M2X to CO2. The potential CO2 capture, activation, and dissociation abilities of MXenes are emanated from Dewar interactions involving hybridization between π orbitals of CO2 and metal d-orbitals. Our high-throughput screening demonstrates chemisorption of CO2 on pure and defective MXenes, followed by dissociation into CO and O species.

Carbon allotropes are known to be promising materials as chemical gas sensors. Proper modification in the electronic structure is required using suitable heteroatom doping to acquire better sensing property. We present the homonuclear B2 (B B) and B3 (B B B) doped carbon allotropes for the detection of toxic gases such as NO2, CO2, NH3, H2S and CO using the density functional theory. The sensitivity and selectivity of pure and boron doped C60 surfaces towards toxic gas molecules are estimated. With a new perception, the gas sensitivity has been correlated with π electron occupancy of the host materials. The adsorption behaviour of toxic gases on the host surface during the presence of H2O, O2 and O molecule/atom is estimated. The concept of homonuclear B sites is extended to 585 divacancy graphene and 585 divacancy carbon nanotube (CNT) system and verified that the phenomena are general for sp2 hybridized carbon allotrope. We also tested the CO oxidation and CO2 hydrogenation on B2 and B3 doped: C60 cage, 585 DV graphene and 585 DV CNT. The CO oxidation occurs via Langmuir–Hinshelwood (LH) mechanism. Overall we have found that the presence of homonuclear bond can change the inert carbon allotropes into highly active sensor material.

First successful ab initio calculations on electronic structure, magnetic, elasto-mechanical and thermodynamic properties of cubic double perovskite oxide Ba2ZnOsO6 has been effectively calculated within density functional theory via full potential linearized augmented plane wave (FP-LAPW) method. The structural investigation exposes the ferromagnetic phase stability of the compound. The spin polarized electronic and magnetic properties were calculated within generalized gradient approximation (GGA), Hubbard approximation (GGA + U), mBJ (modified Becke-Johnson approximation). The electronic profile establishes half-metallic nature for the compound. The calculated total spin magnetic moment was found equal to 2 µB. The elastic constants have been calculated and used to predict mechanical stuffs like Shear modulus (G) Poisson ratio (ν) and anisotropic factor (A). The calculated B/G and Cauchy pressure (C12-C44) both characterize the material as brittle. The thermodynamic parameters like heat capacity and Debye temperature have also been predicted in the temperature range of 0 K–1000 K.

The structural, electronic, elasto-mechanical and thermodynamic properties of cubic ABO3 perovskites BaCmO3 has been successfully calculated within density functional theory via full potential linearized augmented plane wave. The structural study divulges ferromagnetic stability for the compound. For the precise calculation of electronic and magnetic properties a generalized gradient approximation (GGA), and a Hubbard approximation (GGA + U), (modified Becke Johnson approximation) mBJ have been incorporated. The electronic study portrays the half-metallic nature for the compound in all the approximations. The calculated magnetic moment with different approximations was found to be large and with an integer value of 6 μb, this integer value of magnetic moment also proves the half-metallic nature for BaCmO3. The calculated elastic constants have been used to predict mechanical properties like the Young modulus (Y), the Shear modulus (G) and the Poisson ratio (ν). The calculated B/G and Cauchy pressure (C12-C44) present the brittle nature for BaCmO3. The thermodynamic parameters like heat capacity, thermal expansion, and Debye temperature have been calculated and examined in the temperature range of 0 K to 700 K and pressure between 0 GPa and 40 GPa. The melting temperature was also calculated and was found to be 1847 ± 300 K.

A hierarchical NiO-[CdO]2 nanocomposite has been synthesized by a sol–gel auto-combustion route and characterized with a view to studying the electric field emission and conduction mechanism therein. The structural features, surface morphologies, and elemental compositions of the as-prepared samples have been characterized by XRD, Raman, FESEM, and TEM techniques. A low turn-on field (4.50 V/μm) and threshold field (5.04 V/μm) were found to be sufficient to draw emission current densities of 1 μA/cm2 and 10 μA/cm2 from NiO-[CdO]2-modified cathodes. A maximum emission current density of 121 μA/cm2 at a low applied electric field of 6.5 V/μm and long emission current stability were achieved at a preset value of 5 μA. The field enhancement factor (β) was determined as 1854 in the high-field region by computing the local work function (φ) through density functional theory (DFT), and the entire field emission (FE) performances have been compared with those of various pristine compounds. The temperature-dependent electrical conduction mechanism has been further explained with the help of impedance analysis over the temperature range 323–623 K and a wide frequency range from 5 Hz to 1 MHz. The grain and grain boundary contributions were well distinguished by impedance and a modulus formalism, with respective activation energies of Eg = 0.25–0.26 eV and Egb = 0.31–0.32 eV. The temperature-dependent frequency exponents for grains (n1) and grain boundaries (n2) demonstrate two different conduction mechanisms, namely quantum mechanical tunneling for grains, and correlated barrier hopping for grain boundaries. Maxwell–Wagner-type dielectric polarizations are explained by our experimental results, and the highest real dielectric constant (er) 1893 was calculated at 623 K.

The electronic structure, the magnetic, elasto-mechanical and thermodynamic belongings of cubic double oxide perovskites Ba2MgOsO6 have been successfully investigated within the full potential linearized augmented plane wave method (FP-LAPW), based upon the density functional theory (DFT). The structural examination reveals ferromagnetic stability and the spin polarized electronic band structure and density of states display half-metallic nature of the compound. The calculated magnetic moment was found to have an integer value of 2μ_B. From the knowledge of obtained elastic constants mechanical properties like Young’s modulus (E), shear modulus (G), Poisson ratio ( $\nu$ ) and the anisotropic factor have been predicted. The calculated B/G and Cauchy pressure ( $ C_{12}-C_{44}$ ) both portray the ductile nature of the compound. For a complete understanding of the thermo-physical behavior of vital parameters like heat capacity, thermal expansion, Gruneisen parameter and Debye temperature were predicted using quasi harmonic Debye approximation.

We have investigated the bulk modulus and thermal properties of proton conducting perovskite RCeO 3 ( R = Ba, Sr) for the first time by incorporating the effect of lattice distortion in modified rigid ion models (MRIM). The computed bulk modulus, specific heat, thermal expansion coefficient and other thermal properties of BaCeO 3 and SrCeO 3 reproduce well with the available experimental data. In addition the cohesive energy ( ϕ ), molecular force constant ( f ), reststrahlen frequency ( ν ), Debye temperature ( θ D ) and Gruneisen parameter ( γ ) are also reported and discussed. The specific heat results can further be improved by taking into account the spin and the orbital ordering contribution in the specific heat formulae.

Microstructural NiO–SnO2 nano-ceramic matrix was synthesized via a solgel auto-combustion technique with a perspective to investigate its noteworthy electric field emission and temperature-induced conduction anomaly. Exceptional field emission performance of nickel-tin oxide composites was discovered with a low turn-on field of 3.9 V/μm and a threshold field of 5.30 V/μm with a good field emission current density of 110.44 μA/cm2 and current stability. Density functional theory was employed to estimate its local work function (Φ) 3.365 eV, and the field enhancement factor (β) was obtained as 1570 by Fowler–Nordheim plot. The anomalies in conductivity spectra at 523 K were detected by a number of physical properties measurement including impedance, conductivity, dielectric, and differential scanning calorimetry with thermal expansion. These phenomena can be rationalized in terms strain-dependent thermal hysteresis effects and localized/delocalized e g electron with a transition from inferior conductive linkage [Ni2+–O2−–Ni2+] and [Sn2+/Sn4+–O2−–Sn2+/Sn4+] to higher conductive linkage [Ni2+–Ni3+] and [Sn2+–Sn4+] of coupled NiO–SnO2 matrix. The temperature dependence frequency exponent (n), ln τ, Rg, Rgb, Cg, and Cgb support additionally the conduction anomaly behavior, and the variation of dielectric constant (ɛr) and loss (tan δ) with temperature around 523 K has been explained in terms of the reduction of space charge layers due to reversal movement of delocalized e g electrons from the grain boundary limit. The frequency dispersing impedance, conductivity, and dielectric spectra with elevated temperature were also demonstrated to comprehend its conduction mechanism with theoretical correlation.

Effects on temperature on thermal properties of proton conducting perovskite material CaZrO3 is studied using Modified Rigid Ion Model (MRIM). The computed bulk modulus, specific heat, thermal expansion coefficient and other thermal properties of CaZrO3 reproduce well with the available experimental data. In addition the cohesive energy (ϕ), molecular force constant (f), reststrahlen frequency (v), Debye temperature (θD) and Gruneisen parameter (γ) are also reported and discussed. To our knowledge, some of the properties are being reported for the first report on this material.

We have investigated the elastic and thermal properties of proton conducting Ba0.8Ca0.2ZrO3 at temperature 20K ≤ T ≤ 700K by using the Modified Rigid Ion Model (MRIM). We have computed the Second Order Elastic Constants (SOECs) C11, C12, C44 in the cubic phase. The cohesive energy (ϕ), molecular force constant (f), reststrahlen frequency (v), Debye temperature (θD) and Gruneisen parameter (γ) are also discussed. In addition, the variation of specific heat and volume thermal expansion coefficient with temperature are reported below and above room temperature.

Metal halide perovskites are optoelectronic materials that have attracted enormous attention as solar cells with power conversion efficiencies reaching 20%. The benefit of using hybrid compounds resides in their ability to combine the advantage of these two classes of compounds: the high mobility of inorganic materials and the ease of processing of organic materials. In spite of the growing attention of this new material, very little is known about the electronic and phonon properties of the inorganic part of this compounds. A theoretical study of structural, electronic and phonon properties of metal-halide cubic perovskite, CsPbI3 is presented, using first-principles calculations with planewave pseudopotential method as personified in PWSCF code. In this approach local density approximation (LDA) is used for exchange-correlation potential.

The effect of Yttrium doping (0.01 ≤ x ≤ 0.5) on elastic and thermal properties of multiferroic BiCrO3 has been investigated using the Modified Rigid Ion Model (MRIM). We have computed the specific heat and volume thermal expansion coefficient for pure and doped BiCrO3 as a function of temperature (1K ≤ T ≤ 300K). The specific heat results are in good agreement with the available experimental data. A check on thermal stability of the pure and doped compounds is made by computing other properties like Debye temperature, cohesive energy and bulk modulus.

The effect of temperature on elastic, cohesive and thermal properties of LaCrO3 in orthorhombic, rhombohedral and cubic phases has been investigated using Modified Rigid Ion Model (MRIM). We present the elastic constants (C11, C12, C44) and other elastic properties like bulk modulus (BT), Young’s modulus (E) and shear modulus (G). We have computed the specific heat and volume thermal expansion coefficient as a function of temperature (0K ≤ T ≤ 2000K). The specific heat results are in reasonable agreement with the available experimental data. A check on thermal stability of this compound is made by computing other properties like Debye temperature (θD), cohesive energy (ϕ), Reststrahlen frequency (υ) and Gruneisen parameter (γ). The computed properties reproduce well with the available experimental results. To our knowledge some of the properties are reported for the first time.

We present the thermal properties of the proton conducting orthorhombic BaCeO3 by the means of a Rigid Ion Model (RIM). We report the cohesive energy (φ), Reststrahlen frequency (υ), Debye temperature (θD) and Gruneisen parameter (γ). The value of Gruneisen parameter (γ), which supports the earlier, reported values. Besides, the specific heat values presented in this work by using RIM are in reasonable agreement with the available experimental data for BaCeO3 at low temperature (2K ≤ T ≤ 300K).