Ashok Rao

Thermal transport in (Y,Gd)Ba2(Cu1−xMnx)3O7−δ for x≤0.02

Thermal conductivity ?(T) and thermoelectric power S(T) studies on (Y,Gd)Ba2(Cu1?xMnx)3O7?? (x?0.02) superconductors are presented here. Thermal conductivity for all the samples exhibits a hump below the superconducting transition temperature Tc. The peak height of the hump decreases with the Mn content in both the Y-?and Gd-based systems, barring GdBa2(Cu0.99Mn0.01)3O7??. The peak height reduction in the Gd-based cuprates is much faster (~one?fourth) compared to the Y-based samples. The thermoelectric power (TEP) of the Y-based samples for x?0.0075 is electron-like (up to ~140?K) whereas it turns to hole-like even at x = 0.005 for the Gd-based system. On the basis of the structure of the thermal conductivity hump, and of the electron-?or hole-like nature of the thermopower, it has been argued that, in the Y-based system up to x = 0.0075, Mn produces qualitatively the same effect as Gd in the Gd-based system. An analysis of the thermal conductivity data in terms of lattice theory, and the TEP data in terms of a narrow-band picture, has been made to invoke the role of Mn in these systems. Boundary scattering, point defects and sheet-like faults (from ?(T) data analysis) and chemical potential (from S(T) data analysis) support different roles of Mn for x?0.0075 and x>0.0075.

Impact of Average, Local, and Electronic Structure on Visible Light Photocatalysis in Novel BiREWO6 (RE = Eu and Tb) Nanomaterials

Crystal structures of hydrothermally synthesized BiEuWO6 and BiTbWO6 nanomaterials are deduced for the first time by combined Rietveld refinement of neutron and synchrotron data using the ordered and disordered models available in literature. The ordered model is validated for the average structure of these nanomaterials, and it is further supported by the local structure analysis using neutron pair distribution function. Nanomaterials are characterized by field-emission scanning electron microscopy, transmission electron microscopy, Brunauer-Emmett-Teller surface area, diffused reflectance spectroscopy, and Raman Spectroscopy. Rare-earth-substituted nanomaterials are found to be efficient photocatalysts over the parent Bi2WO6 under visible light irradiation for Congo-red dye degradation. Particularly, BiTbWO6 shows an enhanced photocatalytic (PC) activity compared to BiEuWO6, as evidenced from the photoelectrochemical and time-resolved fluorescence studies. The difference in the observed PC activity of these nanomaterials is also explored through a detailed comparison of crystal structure and electronic structure calculated through the density functional theory method.