Thermoelectric and Photovoltaic Properties of Mn-Doped Kesterite Cu2Zn1-xMnxSnSe4.

The semiconductor Cu2ZnSnSe4 (CZTSe) is a promising candidate for both thermoelectric and photovoltaic energy harvesting applications due to a combination of features such as direct band gap, high absorption coefficient, and low thermal conductivity. We report the solid-state synthesis and characterization of Mn-doped Cu2Zn1-xMnxSnSe4 (x = 0, 0.05, 0.10, and 0.15) in an attempt to explore the effect of isovalent substitution at the Zn site. X-ray diffraction and Raman spectroscopy of all specimens confirmed the formation of a single-phase tetragonal kesterite structure (space group I4̅). The band gap obtained by UV-visible diffuse reflectance measurements was 1.42 eV for all compositions. Thermoelectric properties were measured in the range 300-785 K. Electrical resistivity was metallic and reduced on Mn doping, while the Seebeck coefficient exhibited a p-type semiconducting behavior that enhanced on Mn doping, with associated enhancement of the power factor. Lattice thermal conductivity showed a 1/T behavior, falling from about 1.9-2.7 W m-1 K-1 at 300 K to 0.51-0.9 W m-1 K-1 above 750 K. The combined effect of enhanced power factor and reduced lattice thermal conductivity resulted in a figure of merit ZT in the range of 0.19-0.42 above 750 K. Thin-film photovoltaic devices with a CZTSe absorber and an SnSe electron transport layer gave 3.2% efficiency.

Synthesis and characterization of reduced graphene oxide supported gold nanoparticles-poly(pyrrole-co-pyrrolepropylic acid) nanocomposite-based electrochemical biosensor.

A conducting poly(pyrrole-co-pyrrolepropylic acid) copolymer nanocomposite film (AuNP-PPy-PPa) incorporating gold nanoparticles (AuNP) was electrochemically grown using a single step procedure over electrochemically reduced graphene oxide (RGO) flakes deposited on a silane-modified indium-tin-oxide (ITO) glass plate. The RGO support base provided excellent mechanical and chemical stability to the polymer nanocomposite matrix. The porous nanostructure of AuNP-PPy-PPa/RGO provided a huge accessible area to disperse AuNP, and it avoided metallic agglomeration within the polymer matrix. The AuNP-PPy-PPa/RGO was characterized by high-resolution transmission electron microscopy (HRTEM), contact angle measurements, Fourier transform infrared spectroscopy (FTIR), and electrochemical techniques. The pendant carboxyl group of AuNP-PPy-PPa/RGO was covalently bonded with myoglobin protein antibody, Ab-Mb, for the construction of a bioelectrode. Electrochemical impedance spectroscopy technique was used for the characterization of the bioelectrode and as an impedimetric biosensor for the detection of human cardiac biomarker, Ag-cMb. The bioelectrode exhibited a linear impedimetric response to Ag-cMb in the range of 10 ng mL(-1) to 1 µg mL(-1), in phosphate-buffered solution (PBS) (pH 7.4, 0.1 M KCl) with a sensitivity of 92.13 Ω cm(2) per decade.

Inhomogeneous magnetism in single crystalline Sr(3)CuIrO(6+delta): implications to phase-separation concepts.

The single crystalline form of an insulator, Sr(3)CuIrO(6+delta), is shown to exhibit unexpectedly more than one magnetic transition (at 5 and 19 K) with spin-glass-like magnetic susceptibility behavior. On the basis of this finding, viz., inhomogeneous magnetism in a chemically homogeneous material, we propose that the idea of "phase separation" described for manganites is more widespread in different ways. The observed experimental features enable us to make a comparison with the predictions of a recent toy model on magnetic phase separation in an insulating environment.