A novel route to phase formation of cobalt oxyhydrates using KMnO4 as an oxidizing agent

We have first succeefully synthesized the sodium cobalt oxyhydrate superconductors using KMnO4 as a de-intercalating and oxidizing agent. It is a novel route to form the superconductive phase of NaxCoO2.yH2O without resorting to the commonly used Br2/CH3CN solution. The role of the KMnO4 is to de-intercalate the Na+ from the parent compound Na0.7CoO2 and oxidize the Co ion as a result. The higher molar ratio of KMnO4 relative to the sodium content tends to remove more Na+ from the parent compound and results in a slight expansion of the c-axis in the unit cell. The superconducting transition temperature is 4.6-3.8 K for samples treated by the aqueous KMnO4 solution with the molar ratio of KMnO4 relative to the sodium content in the range of 0.3 and 2.29.Comment: 10 pages, 3 figure

Size Dependent Properties of CdSe Quantum Dots

[[abstract]]Temperature dependences of the magnetic susceptibility χ and heat capacity Cp of CdSe quantum dots with size d=2.8, 4.1, and 5.6 nm are compared to those of bulk CdSe to determine the size-dependent effects. With decreasing size d, the following effects are observed: (i) room temperature optical absorption shows a blueshift of the band gap; (ii) room temperature x-ray diffraction show wurtzite structure but with smaller lattice constants; (iii) magnetic susceptibility changes from negative (diamagnetic) for the bulk to positive χ with magnitude increasing with decreasing d; and (iv) the Sommerfeld constant γ determined from the Cp/T vs T2 data increases. Possible explanations for these size-dependent properties are presented.

Size dependence properties of CdSe quantum dots

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Synthetization and Characterization of Mo-doped Mn4Si7 by High Energy Ball Mill

759-761Mn4Si7 is a non-degenerating semiconductor with an indirect band gap of 0.77eV having multi-domain applications. The Mn4Si7 and Mo-doped Mn4Si7 were synthesized by high-energy ball milling at 600 RPM for 50H. From the X-ray diffraction (XRD), the tetragonal phase was observed. The average crystalline size was estimated by the Debye-Scherrer equation which lies below ~25 nm. The morphology studies reveal different shapes and sizes were observed by scanning electron microscopy (SEM)

Synthetization and Characterization of Mg-doped SnSe with Mg Substitution at the Sn Site by High Energy Ball Milling Technique

762-764Tin selenide (SnSe) is a semiconductor with an orthorhombic crystal structure having an indirect and direct band gap of 0.9 eV and 1.3 eV respectively. The SnSe and Mg-doped SnSe was synthesized by high energy ball milling technique at 300 RPM for 22 hrs. The formation of pure orthorhombic phases of SnSe and Mg-doped SnSe were confirmed by X-ray diffraction (XRD). From the XRD pattern, the crystalline size was estimated which lies below ~10 nm. The morphology of particle size distribution was carried out by scanning electron microscopy (SEM)

The effect of carbon nanotubes (CNT) on thermoelectric properties of lead telluride (PbTe) nanocubes

We report the thermoelectric properties of different weight percentage of carbon nano tubes (CNT) dispersed (0.025, 0.05 and 0.1%) in PbTe nanocubes matrix. The sample with 0.05% CNT distribution in the PbTe matrix significantly enhanced the electrical conductivity, and Seebeck coefficient above 450 K. In this system CNT's acting as a low energy filter at potential barrier and good passage for high energy electron which may cause enhance the electrical conductivity. Mixing of CNT into PbTe nanocubes created numerous additional interfaces which are acted as scattering centers for phonons and thus resulted in ultra low thermal conductivity of 0.24 and 032 W/m K at 525 K for 0.025 and 0.05% CNT dispersed PbTe matrix, respectively. An optimum quantity of CNT addition to PbTe enhanced the zT similar to 0.11 at 525 K for both 0.025 and 0.05% CNT dispersed PbTe matrix, respectively, which is 90% higher in comparison to PbTe nanocubes. Finally, CNT's dispersed PbTe nanocomposite exhibited good thermoelectric compatibility factor and these materials are good candidate materials for segmentation to get maximum power output during power generation applications

Superiority of ion irradiation over annealing for enhancing the thermopower of PbTe thin films

International audiencePresent study reveals that swift heavy ion (SHI) irradiation enhances thermoelectric properties and the annealing deteriorates thermoelectric performance of PbTe thin film. X-ray diffraction (XRD), Atomic force microscopy (AFM) and Rutherford backscattering spectrometry (RBS) measurements are performed for phase formation, surface morphology and elemental composition of all the samples, respectively. Electrical conductivity (sigma) and thermo power (S) measurement of all the samples have also been measured using four probe method. The increase in thermo power (S) is similar to 40% upto high temperature (similar to 520 K) after irradiation whereas it decreases on annealing treatment. These findings are discussed on the basis of density of states enhancement or carrier scattering due to the point defects after SHI irradiation