Advanced Materials Research Vol. 665

Abstract: FeSb₂ was recently found to be a narrow-gap semiconductor with strong electronelectron correlation and a large thermopower at low temperatures. We report measurements of the electrical resistivity, Seebeck coefficient and thermal conductivity between 5 K to 300 K on polycrystalline samples of FeSb₂ and FeSb_1.9. We found that the deficiency of Sb in the parent compound leads to a giant anomalous peak in thermopower (S) at low temperatures, reaching ~ 426 μV/K at 20 K, resulting in a high thermoelectric power factor at low temperatures, achieving 10 μW/K²m at 27 K._. Consequently, a significantly enhanced thermoelectric figure of merit ZT ~ 0.0015 is achieved near room temperature. At low temperatures there is no improvement in ZT values due to the high thermal conductivity (phonon dominant region). Keywords: Seebeck coefficient, thermal conductivity, resistivity, thermoelectric figure of merit. PACS: 72.20.Pa, 71.27.+a, 71.28.+d

Abstract: The development of highly sensitive, selective, reliable, low power and compact sensing devices to detect gas is of major importance for terrestrial and space applications. The gas response to different gases and chemicals is related to a great extent to the surface state and morphology of the materials. Zinc oxide (ZnO) is a direct wide band gap semiconductor with an energy gap of ~3.37 eV and a large exciton binding energy of ~60 meV at room temperature (RT) is a promising candidate for functional component for devices and materials in chemical and gas sensors and so on. ZnO nanostructures with various interesting structures and properties have been synthesized, such as nanoparticles, nanorods, nanobelts, nanocombs, nanowires, tetrapod nanostructures. Mn-doped hexagonal (ZnO) semiconductor micro and nanostructures have been synthesized by a simple one-step aqueous solution method at relatively low temperature. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and photoluminescence spectroscopy (PL) have been used to characterize the samples in detail. The XRD studies revealed that Mn doped ZnO micro and nanostructures had wurtzite structure (hexagonal). The as-synthesized ZnO micro and nanostructures consist of very uniform and no secondary phase is observed. X-ray diffraction and EDX results provide the evidence that Mn is incorporated into the ZnO crystals. A strong and wide ultraviolet emission has been observed for the Mn doped ZnO micro and nanocrystals as evidenced by the photoluminescence spectra at room temperature.PL spectra reveals that as synthesized samples are highly pure and crystalline. Magnetism in these samples was also studied by using vibrating sample magnetometer.

Abstract: Spin momentum density in Ni₂Mn_1.4Sn_0.6 shape memory alloy has been measured using magnetic Compton scattering technique. The experiment has been performed using 182 keV circularly polarized synchrotron radiation at temperature 10 K at SPring-8, Japan. Experimental magnetic Compton profile has been decomposed to determine the site specific magnetic moments, where the magnetic moment at Mn site was found to be dominating. It is seen that the total spin moment in present non-stoichiometric alloy is smaller than that of stoichiometric Ni₂MnSn.

Abstract: The complex relative dielectric function ε^*(ω) = ε-jε of binary mixture of anisole (AN) with methanol (MeOH) ,1-propanol (1-PrOH), 1-butanol (1-BuOH), 1-heptanol (1-HeOH) of varying concentration have been measured using Precision LCR meter in the frequency range 20 Hz to 2 MHz at 303 K. The electrical/dielectric properties of the liquid samples are represented in terms of intensive quantities namely, complex relative dielectric function ε^*(ω), electrical modulus M^*(ω), and extensive quantities, i.e. complex admittance Y^*(ω) and complex impedance Z^*(ω). All of these presentations are used to explore various processes contributed in the electrical/dielectric properties of the mixtures of polar-polar liquids.

Abstract: Physical vapour technique (PVT) is a versatile method to grow IIVI semiconductors. In present investigations, CdS crystals have been grown by this method using dual zone micro processor controlled horizontal furnace. CdS crystals grown in present case have been characterized by EDAX for stoichiometric conformation. The roughness of surface of grown CdS crystals has been studied in detail using optical microscopy, SEM and AFM. The surface topography study of as grown crystals has been carried out to understand the growth mechanism which was necessary for its application in electronic devices.

Abstract: W-type hexagonal ferrite with composition BaCa₂Fe₁₆O₂₇ was prepared using a stearic acid gel method. The precipitate of barium calcium hexaferrite was calcinated at 650°C, 750°C, 850°C and 950°C in a furnace for 4 hours and then slowly cooled to room temperature. The dielectric constants (real Є and imaginary Є), conductivity (σ) and dielectric loss (tan δ) have been measured at room temperature as a function of frequency (10²-10⁶ Hz). The dielectric behavior of prepared hexaferrite samples can be explained by the mechanism of polarization and the electrical conduction mechanism is explained by using the electronic hopping model of Heike Johnson.

Abstract: The effects of argon ion implantation on the structure and refractive index of CR-39 polymer has been investigated. CR-39 specimens were implanted with 130 keV argon ions in the fluence range of 5×10¹⁴-1×10¹⁶ ions cm^-2. The structural changes produced as an effect of implantation has been studied using specular reflectance Fourier transform infrared spectroscopic technique. The absorption and specular reflectance spectra in the visible region of these specimens has been recorded by using UV-Visible spectroscopic technique. The extinction coefficient has been measured using the absorption coefficient values calculated from absorption spectra. Utilizing the values of extinction coefficient and reflectance, the refractive index of virgin and implanted specimens has been calculated. Significant enhancement in the refractive indices of implanted specimens has been observed. These changes in the values of refractive index have been further correlated with the hydrogen depleted graphitelike structures formed on the surface of implanted specimens as evidenced from specular reflectance FTIR technique. The potential of forming planar waveguides using these implanted specimens has been explored.

Abstract: In the present work, our aim is to reveal the effect of Ar⁺ implantation on the structural behaviour of Polyethylene terephthalate (PET) using Fourier Transform Infrared and UV-Visible Spectroscopic techniques. PET specimens were implanted with 200 keV Ar⁺ ions in the fluence range of 1x10¹⁵ to 1x10¹⁷ ions cm^-2. The structural changes have been observed due to change in the position and intensity of the bands in the FTIR spectra of both implanted and unimplanted specimens. A continuous decrease in optical energy gap (from 3.63 eV to 1.48 eV) and enhancement in Urbach energy (from 0.29 eV to 3.70 eV) with increasing ion dose have been observed. The structural changes have been correlated with the optical parameters observed in PET specimens as a result of implantation.

Abstract: The present study deals with the investigation of conduction behavior of filler free and filler based blend electrolyte system. The polymer blend films consisting of PVA and PEO doped with silver salt and PEG plasticizer, are prepared using solution cast technique. The filler free system is prepared for varying ratios of host polymers (PVA: PEO); whereas the filler based system is prepared with various Al₂O₃ concentrations in the blend films. The conductivity studies of prepared samples are carried out using impedance spectroscopic analysis. The conductivity for the filler free blend system is found to increase with increasing amount of PEO in all the blend specimens. On the other hand, the filler based system shows the conductivity enhancement upto 6wt% which mitigates with further addition of filler into the electrolytes. The DSC scans are found to support the conductivity results.

Abstract: Electrical and optical character of nanostructured Cr_1-xV_xS₂ is studied here. This sulphide based nanoClusters (NC) was developed through chemical sol-gel route using (NH₄)₂Cr₂O₇ and NH₄VO₃ as active reagent and biopolymer gum acacia is used as capping agent. Core-shell NC has developed with sequential addition of active reagents in sulphation process. It is also possible to develop another type of core shell NC by reversal of the sequence of added reagents, i.e. interchanging the core and shell part. Experimental investigation including UV-VIS spectroscopy, dc current-voltage characteristics (CVC) have carried on. The results of CVC at room temperature (RT) show the distinctive features of localized energy levels. UV-VIS spectroscopic analysis shows absorption peak is blue shifted due to quantum confinement of nanoparticles. Overall appearance of optical absorption curve is completely different for two NCs. Peak positions are different for two types of core shell NC which confirms that the constituent materials of core and shell of two NC s has interchanged.