arXiv subjects

Enamul Haque

Publications and source records attributed to Enamul Haque.

22 records · Page 2Linked to original sources

arXiv2018

Enhanced thermoelectric performance in Ca substituted Sr3SnO

We report 45% enhancement in the thermoelectric figure of merit, ZT of Sr3SnO via Ca substitution. First-principles calculations have been performed to study the electronic and thermoelectric transport properties of Ca substituted Sr3SnO (Sr3-xCaxSnO). The effects of Ca subtitution on bandgap are studied and detailed mechanisms are proposed to explain the obtained results. We have found that effective mass and thermopower of Sr3SnO redueces with the increase of hole concentration. The optimum hole concentration has been obtained for Sr2CaSnO and the corresponding Seebeck coefficient is 219 μV/K. The electrical conductivity of Sr3SnO and its alloys exhibits semiconducting nature which contradicts with experimental results in Ca3SnO. We have found that due to the Ca-deficiency, the Ca3SnO shows the metallic conductivity and removes this contradiction with our results. The lattice thermal conductivities (\kl) of Sr3SnO and Ca3SnO have been calculated by using both PBE and GW functionals. The lattice thermal conductivity obtained by PBE functional largely underestimates the experimental value for Ca3SnO. The total thermal conductivity (with kl obtained by GW) at 300K is 2.33 and 1.897 W/mK for Sr3SnO and Ca3SnO, respectively, with excellent agreement with experimental value 1.707 W/mK for Ca3SnO. The dimensionless figure of merit (ZT) for Sr2CaSnO at 500 K is 0.6 and making it promising for thermoelectric applications.

cond-mat.mtrl-sci↗

arXiv2018

Ultra-low lattice thermal conductivity in Cs2BiAgX6 (X=Cl, Br): Potential thermoelectric materials

We have explored electronic and thermoelectric properties of bismuth-based double-perovskite halides Cs2BiAgX6 by using first principles calculations. The calculated indirect bandgaps 2.85 eV and 1.99 eV for Cs2BiAgCl6 and Cs2BiAgBr6, respectively well agree with the measured value (2.77 eV of Cs2BiAgCl6 and 2.19 eV of Cs2BiAgBr6). We have calculated the relaxation time and lattice thermal conductivity by using relaxation time approximation (RTA) within supercell approach. The lattice thermal conductivities for both compounds are remarkably low and the obtained values at 300K for Cs2BiAgCl6 and Cs2BiAgBr6 are 0.078 and 0.065 Wm-1K-1, respectively. Such quite low lattice thermal conductivity arises due to low phonon group velocity in the large weighted phase space and large phonon scattering. The large Seebeck coefficient obtained for both halides at 400K. We have obtained the maximum power factors at 700K and the corresponding thermoelectric figure of merit for Cs2BiAgCl6 and Cs2BiAgBr6 are 0.775 and 0.774, respectively. The calculated results reveal that both halides are potential thermoelectric materials.

cond-mat.mtrl-sci↗

arXiv2018

Structural, elastic, electronic, magnetic and thermoelectric properties of new quaternary Heusler compounds CoZrMnX (X=Al, Ga, Ge, In)

We have performed a comprehensive set of first principles calculations to study the structural, elastic, electronic, magnetic and transport properties of new quaternary Heusler compounds CoZrMnX (X =Al, Ga, Ge, In). The results showed that all the quaternary Heusler compounds were stable in Type(I) structure. CoZrMnX are elastically stable and relatively hard materials. CoZrMnAl, CoZrMnGa, and CoZrMnIn are found to be ductile and CoZrMnGe is brittle in nature. The calculated Debye temperatures of all compounds are relatively high. The electronic structure calculations reveal that CoZrMnAl is nearly half metallic, CoZrMnGa and CoZrMnIn are metallic, and CoZrMnGe is a narrow indirect bandgap semiconductor. The calculated magnetic properties implies that CoZrMnAl, CoZrMnGa, and CoZrMnIn are ferromagnetic while CoZrMnGe is non-magnetic material. The CoZrMnAl is highly spin-polarized (96%) and CoZrMnGe is non-spin-polarized. Seebeck coefficent (S) in CoZrMnGe is relatively high (-106 μV/K at 650K) due to its semiconducting nature. The calculated thermoelectric figure of merit CoZrMnGe is 0.1 at 600K and for CoZrMnIn it is also 0.1 at 900 K. We hope our interesting results will inspire experimentalist to synthesis the new quaternary Heusler compounds CoZrMnX (X =Al, Ga, Ge, In).

cond-mat.mtrl-sci↗

arXiv2017

Elastic, electronic, thermodynamic and transport properties of XOsSi (X=Nb, Ta) superconductors: A first-principles exploration

A first-principles calculation has been performed to study elastic, electronic, thermodynamic, transport and superconducting properties of recently reported osmium based two superconductors, XOsSi (X=Nb, Ta). We have calculated elastic constants and elastic moduli of XOsSi for the first time. The calculated values of bulk, Youngs, shear moduli are reasonably larger than the average value obtained from the rule of mixtures of the constituents. NbOsSi and TaOsSi both compounds are found to be relatively hard material, elastically stable and ductile in nature. The obtained directional bulk modulus and shear anisotropic factors indicate that both compounds have high elastic anisotropy. The shear anisotropic factors show higher elastic anisotropy than the percentage anisotropy in these compounds. The Debye temperature and bulk modulus increases with pressure but decreases with temperature as usual for metals. The magnetic susceptibility of TaOsSi follow the Curie law but NaOsSi do not follow due to its delocalized magnetic moment and electronic specific heat slightly deviates from the linear relationship with temperature. The calculated band structures of XOsSi compounds show metallic nature. In both cases d-orbitals have the dominating contribution to the total density of states. The smaller electron-phonon coupling constant implies that XOsSi (X=Nb, Ta) are weakly coupled superconductors.

cond-mat.mtrl-sci↗