Search

We have synthesized a series of Sm 0.55 Sr 0.45−x Ag x MnO 3 (x = 0 & 0.15) by conventional solid state reaction method to scrutinize the effect of monovalent Ag + as a replacement of Sr 2+ ion on structural, electrical, magnetotransport and thermoelectric properties. The structural parameters obtained using Rietveld refinement of X-ray diffraction data which showed perovskite structure having orthorhombic ( Pnma ) symmetry without any detectable impurity phase. It is observed that M ZFC and M FC curves become more manifested as Ag + content is increased which indicates an increase in magnetic frustration arising due to bending of Mn-O-Mn bond. The M-H plots show the narrow hysteresis loops which indicate the soft ferromagnetic nature. Magnetic studies also show that the Curie temperature T C is found to decrease with Ag + content. The metal–insulator transition temperature (T MI ) is observed which decreases with the increase of Ag + content when magnetic field is applied. The resistivity data in high temperature region are explained within the framework of variable range hopping (VRH) and small polaron hopping (SPH) models. The thermoelectric power (S) of the reported samples exhibits a crossover from positive to negative value and value of S increases in doped samples. The analysis of thermoelectric power data confirms that the small polaron hopping model in high temperature region and at low temperature electron–magnon scattering is the dominating in the FM region. With increasing the Ag + content the samples showed very high magneto-resistance (MR%) and temperature coefficient of resistance (TCR%) which make the compound more promising for scientific and technological applications.

We have synthesized the single phase polycrystalline sample of silver doped disordered Sm0.55Sr0.45−xAgxMnO3 using the conventional solid state method. They have been investigated by X-ray diffraction for phase evolution and their Rietveld refined X-ray diffraction pattern indicates an increase in lattice parameters and unit cell volume with Ag doping. The magnetization analysis shows the presence of a first order paramagnetic to ferromagnetic transition; the transition temperature and amount of thermal hysteresis decreases on Ag doping. The transport, magneto-transport results indicates decrease in metal to insulator transition, drastic increase in resistance and temperature coefficient of resistance (TCR %) with nearly unaffected colossal magnetoresistance effect which indicates that at least a part of silver is incorporated in the lattice. Scanning electron micrographs indicate that silver has also increased the grain growth sharpness and thus decrease the effect of grain boundary scattering. The significant value of TCR of ∼43% of our samples indicates their applied nature for bolometric application.

Herein, we propose a quantum dots (QDs) based spectroscopic sensor for determination of ascorbic acid, gallic acid and oxalic acid. These aqueous stable AgInS2 (AIS) and AIS@ZnS QDs having average sizes of 2.5 ± 0.5 and 3.4 ± 0.5 nm, respectively, were surface coated with Glutathione (GSH), which provided enhanced stability against the aggregation/oxidation. These glutathione (GSH) capped AIS and AIS@ZnS core-shell nanostructures were systematically studied as a luminescence probe for the sensing of routinely used analytes. AIS QDs exhibit better specificity and selectivity for ascorbic acid and gallic acid detection, whereas, core-shell QDs show higher binding affinity and sensing ability for oxalic acid. It was noticed that AIS QDs exhibited 80% quenching efficiency towards gallic acid, compared to 55% of AIS@ZnS QDs. In addition, AIS QDs shows threefold increment in binding affinity towards gallic acid compared to AIS@ZnS nanostructures. As the consequence, AIS and AIS@ZnS QDs show concentration dependent red-shifted after binding with analytes. Based on this, AIS@ZnS QDs was found highly sensitive for the detection of oxalic acid with excellent detection limit as 35 nM. Interestingly, AIS QDs shows the specific and selective binding towards gallic acid where fluorescence quenching was noted and ascorbic acid for which fluorescence enhancement was observed. It was noted that these QDs shows the detection limit as 20 nM for GA and 45 nM for AA. Based on this, AIS and AIS@ZnS QDs can be used as fluorescence tool for multimode sensing of gallic acid ascorbic acid and oxalic acid with high selectivity and sensitivity.