Intrinsic and strain dependent ultralow thermal conductivity in novel AuX (X = Cu, Ag) monolayers for outstanding thermoelectric applications.

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.

Effect of Strain on the Electronic Structure and Phonon Stability of SrBaSn Half Heusler Alloy.

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.

Optical, electrochemical and photocatalytic properties of cobalt doped CsPbCl3 nanostructures: a one-pot synthesis approach.

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.

Lattice dynamics, mechanical stability and electronic structure of Fe-based Heusler semiconductors.

The structural and mechanical stability of Fe2TaAl and Fe2TaGa alloys along with the electronic properties are explored with the help of density functional theory. On applying different approximations, the enhancement of semiconducting gap follows the trend as GGA < mBJ < GGA + U. The maximum forbidden gaps observed by GGA + U method are Eg = 1.80 eV for Fe2TaAl and 1.30 eV for Fe2TaGa. The elastic parameters are simulated to determine the strength and ductile nature of these materials. The phonon calculations determine the dynamical stability of all these materials because of the absence of any negative frequencies. Basic understandings of structural, elastic, mechanical and phonon properties of these alloys are studied first time in this report.

Electronic structure, mechanical and thermodynamic properties of BaPaO3 under pressure.

Density functional theory (DFT)-based investigations have been put forward on the elastic, mechanical, and thermo-dynamical properties of BaPaO3. The pressure dependence of electronic band structure and other physical properties has been carefully analyzed. The increase in Bulk modulus and decrease in lattice constant is seen on going from 0 to 30 GPa. The predicted lattice constants describe this material as anisotropic and ductile in nature at ambient conditions. Post-DFT calculations using quasi-harmonic Debye model are employed to envisage the pressure-dependent thermodynamic properties like Debye temperature, specific heat capacity, Grüneisen parameter, thermal expansion, etc. Also, the computed Debye temperature and melting temperature of BaPaO3 at 0 K are 523 K and 1764.75 K, respectively.

A case study of Fe2TaZ (Z = Al, Ga, In) Heusler alloys: hunt for half-metallic behavior and thermoelectricity.

We have computed the electronic structure and transport properties of Fe2TaZ (Z = Al, Ga, In) alloys by the full-potential linearized augmented plane wave (FPLAPW) method. The magnetic conduct in accordance with the Slater-Pauling rule classifies them as non-magnetic alloys with total zero magnetic moment. The semiconducting band profile and the density of states in the post DFT treatment are used to estimate the relations among various transport parameters such as Seebeck coefficient, electrical conductivity, thermal conductivity, and figure of merit. The Seebeck coefficient variation and band profiles describe the p-type behavior of charge carriers. The electrical and thermal conductivity plots follow the semiconducting nature of bands along the Fermi level. The overall measurements show that semi-classical Boltzmann transport theory has well-behaved potential in predicting the transport properties of such functional materials, which may find the possibility of their experimental synthesis for future applications in thermoelectric technologies.