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Influence of sintering temperature on the electrical and thermal properties of bulk samples of Pr2/3Sr1/3MnO3-delta
No full textWe present temperature-dependent studies on electrical and thermal properties of bulk samples of Pr2/3Sr1/3MnO3-delta synthesized at different sintering temperatures (T-S). It is established that these properties intensely influenced by the sintering temperatures. Analysis of electrical resistivity data rho(T) by means of standard models, demonstrated that electron-electron scattering processes play a key role in the conduction process in the low-temperature region. At high temperatures, the rho(T) follows the small polaron hopping (SPH) model. Analyses of the Seebeck coefficient data S(T) in the low temperature regime illustrates that electron-magnon scattering governs the thermoelectric transport, on contrary, the high-temperature S(T) follows the SPH model. The low-temperature phonon peak in thermal conductivity kappa(T) increases with increasing T-S, demonstrating that a better crystallinity of Pr2/3Sr1/3MnO3 samples was obtained at higher sintering temperatures. Magnetic transitions are observed to increase with a higher T-S, and the entropy change associated with the transition also increases with T-S
Realization of 2.4mm coaxial microcalorimeter system as national standard of microwave power from 1 MHz to 50 GHz
No full textA 2.4mm coaxial microcalorimeter system based on thermoelectric principle has been realized as a national standard of microwave power at National Physical Laboratory India (NPLI). The design is based on two symmetrical and thermally isolated transmission lines, one connected to power standard and the other connected to an identical power standard used as a thermal reference. The main function of the system is to determine the temperature variation between the two power standards, which is of the order of few milli-Kelvin, using a specially designed thermopile. The coaxial microcalorimeter along with the thermocouple power sensor will provide traceable measurements from 1 MHz to 50 GHz. An interlaboratory measurement comparison of microwave power for the validation of the 2.4mm coaxial microcalorimeter system has been carried out between NPLI and Laboratoire National de Metrologie et d'Essais (LNE) France. The difference between the effective efficiency evaluated by the two laboratories was less than 0.5% at all frequency points. The normalized error value of NPLI for effective efficiency varies between -0.23 and +0.09 with respect to LNE. The result shows good agreement in assigning the effective efficiency to power sensor among the two labs within their claimed expanded uncertainty. It proves the degree of equivalence in measurements between two national metrology institutes (NMIs)
Significant enhancement in thermoelectric performance of nanostructured higher manganese silicides synthesized employing a melt spinning technique
No full textThe limited thermoelectric performance of p-type Higher Manganese Silicides (HMS) in terms of their low figure-of-merit (ZT), which is far below unity, is the main bottle-neck for realising an efficient HMS based thermoelectric generator, which has been recognized as the most promising material for harnessing waste-heat in the mid-temperature range, owing to its thermal stability, earth-abundant and environmentally friendly nature of its constituent elements. We report a significant enhancement in the thermoelectric performance of nanostructured HMS synthesized using rapid solidification by optimizing the cooling rates during melt-spinning followed by spark plasma sintering of the resulting melt-spun ribbons. By employing this experimental strategy, an unprecedented ZT similar to 0.82 at 800 K was realized in spark plasma sintered 5 at% Al-doped MnSi1.73 HMS, melt spun at an optimized high cooling rate of similar to 2 x 10(7) K s(-1). This enhancement in ZT represents a similar to 25% increase over the best reported values thus far for HMS and primarily originates from a nano-crystalline microstructure consisting of a HMS matrix (20-40 nm) with excess Si (3-9 nm) uniformly distributed in it. This nanostructure, resulting from the high cooling rates employed during the melt-spinning of HMS, introduces a high density of nano-crystallite boundaries in a wide spectrum of nano-scale dimensions, which scatter the low-to-mid-wavelength heat-carrying phonons. This abundant phonon scattering results in a significantly reduced thermal conductivity of similar to 1.5 W m(-1) K-1 at 800 K, which primarily contributes to the enhancement in ZT
Significant role of antiferromagnetic GdFeO3 on multiferroism of bilayer thin films
Get PDFInversion of BaTiO3 and GdFeO3 thin films in bilayer configuration has been deposited by pulsed laser deposition technique. A significant effect of strain on thin film has been observed by X-ray diffraction analysis. Tensile strain of 1.04% and 0.23% has been calculated by X-ray diffraction results. Higher polarization value 70.4 mu C cm(-2) has been observed by strained BaTiO3 film in GdFeO3/BaTiO3 bilayer film. Strained GdFeO3 film in BaTiO3/GdFeO3 bilayer configuration exhibited ferromagnetic behaviour showed maximum magnetization value of 50 emu gm(-1). Magnetoelectric coupling coefficient of bilayer films have been carried out by dynamic method. Room temperature magnetoelectric coupling 2500mV cm(-1)-Oe has been obtained for BaTiO3/GdFeO3 bilayer film. The high ME coupling of the BaTiO3/GdFeO3 bilayer film reveals strong interfacial coupling between ferroelectric and ferromagnetic dipoles. On magnetoelectric coupling coefficient effect of ferromagnetic GdFeO3 layer has a significant role. Such high value of ME coupling may be useful in realization of magnetoelectric RAM(MeRAM) application
Highly selective and reversible NO2 gas sensor using vertically aligned MoS2 flake networks
No full textWe demonstrate a highly selective and reversible NO2 resistive gas sensor using vertically aligned MoS2 (VA-MoS2) flake networks. We synthesized horizontally and vertically aligned MoS2 flakes on SiO2/Si substrate using a kinetically controlled rapid growth CVD process. Uniformly interconnected MoS2 flakes and their orientation were confirmed by scanning electron microscopy, x-ray diffraction, Raman spectroscopy and x-ray photoelectron spectroscopy. The VA-MoS2 gas sensor showed two times higher response to NO2 compared to horizontally aligned MoS2 at room temperature. Moreover, the sensors exhibited a dramatically improved complete recovery upon NO2 exposure at its low optimum operating temperatures (100 degrees C). In addition, the sensing performance of the sensors was investigated with exposure to various gases such as NH3, CO2, H-2, CH4 and H2S. It was observed that high response to gas directly correlates with the strong interaction of gas molecules on edge sites of the VA-MoS2. The VA-MoS2 gas sensor exhibited high response with good reversibility and selectivity towards NO2 as a result of the high aspect ratio as well as high adsorption energy on exposed edge sites
Key optoelectronic properties of Diiodo-bis(carbamide)-zinc(II): An experimental and computational investigation
No full textLarge size single crystals of Diiodo-bis(carbamide)-zinc(II) [ZnI2. 2[CO(NH2)(2)] were grown successfully for the first time by slow evaporation techniques at room temperature within the evaporation time of two weeks. The single phase and high crystalline nature of the grown crystals was confirmed by X-ray diffraction analysis. Quantum chemically the geometrical parameters were found in good correlation with experimental values calculated at B3LYP/6-31G* (LANL2DZ), B2LYPD/6-31G* (LANL2DZ), M062X/6-31G* (LANL2DZ) and MP2/6-31G* (LANL2DZ) level of theories. Additionally, the experimental vibrational modes also have shown a good agreement with calculated ones. The optical transparency and band gap were calculated and found to be similar to 80% and 4.706 eV, respectively. The calculated value of HOMO-LUMO gap was found in correlation with experimental energy gap. The electronic properties were investigated by shedding light on the frontier molecular orbitals, partial density of states (PDOS), and total density of states (TDOS). The mechanical and dielectric studies show that the grown crystals possess quite good mechanical strength and dielectric constant. The dielectric loss revealed that the grown crystal contains low defects. The total ac electrical conductivity was increased with frequency and the frequency components confirm the sudden hoping mechanism in the grown crystal
Design and Development of Strain Gauge Pressure Transducer Working in High Pressure Range of 500 MPa Using Autofrettage and Finite Element Method
No full textDevelopment of strain gauge based pressure transducers is very common but its development in high pressure range without sacrificing cost effectiveness and design simplicity is a challenge. While keeping this perspective, we have discussed the development of strain gauge based hydraulic pressure transducer working up to pressure of 500 MPa. The present paper describes the different design stages bearing own challenges and feasible solutions. For design considerations, stress analysis has been performed by using finite element method (FEM). A mathematical modeling is developed for determining the sensitivity of the transducer and is validated with the experimental results. We have also introduced the concept of using autofrettage technique first time in pressure transducer design and its validity for effectiveness in the proposed design is performed with the help of the finite element analysis which reveals that the autofrettage of sensing element, not only increase the pressure bearing capacity of the transducer but also improve the sensitivity. Finally, we have performed the calibration and performance testing experiments on this newly manufactured transducer which shows good linearity (R-2=0.999), minimal hysteresis (0.18% of full scale), minimal short term repeatability (0.32% of full scale) and an overall accuracy better than 1% of full scale
Determination of band alignment at two-dimensional MoS2/Si van der Waals heterojunction
No full textTo understand the different mechanism occurring at the MoS2-silicon interface, we have fabricated a MoS2/Si heterojunction by exfoliating MoS2 on top of the silicon substrate. Raman spectroscopy and atomic force microscopy (AFM) measurement expose the signature of few-layers in the deposited MoS2 flake. Herein, the temperature dependence of the energy barrier and carrier density at the MoS2/Si heterojunction has been extensively investigated. Furthermore, to study band alignment at the MoS2/Si interface, we have calculated a valence band offset of 0.6660.17 eV and a conduction band offset of 0.4260.17 eV using X-ray and Ultraviolet photoelectron spectroscopy. We determined a type-II band alignment at the interface which is very conducive for the transport of photoexcited carriers. As a proof-of-concept application, we extend our analysis of the photovoltaic behavior of the MoS2/Si heterojunction. This work provides not only a comparative study between MoS2/p-Si and MoS2/n-Si heterojunctions but also paves the way to engineer the properties of the interface for the future integration of MoS2 with silicon
Development and Realization of Iron-Carbon Eutectic Fixed Point at NPLI
No full textThe concept of metal-carbon eutectic temperature fixed point has been introduced in 1999 and is extensively being investigated by thermometry researchers to cover the high-temperature range above copper fixed point. Metal-carbon eutectic fixed points also helped to provide direct traceability with reduced associated uncertainty in the high temperature range for thermometry and radiometry applications. In view of this, CSIR-National Physical Laboratory, India (NPLI) has developed iron-carbon (Fe-C, 1153 A degrees C) eutectic fixed point cell in the graphite crucible and realized by using the noble metal thermocouples. The preparation parameters such as design and fabrication of a graphite crucible, Fe:C eutectic composition and filling procedure, furnace profile, melting and freezing plateau measurements, heat flux immersion, inhomogeneity, etc. have been optimized and presented in this paper. The measurement uncertainty of the Fe-C eutectic cell realized with Type-S thermocouple was estimated to be 3.04 mu V (0.25 A degrees C) at coverage factor k = 2
Effect of temperature on magnetic and impedance properties of Fe3BO6 of nanotubular structure with a bonded B2O3 surface layer
No full textIn this investigation, we explore a facile synthesis of Fe3BO6 in the form of small crystallites in the specific shape of nanotubes crystallized from a supercooled liquid Fe2O3-B2O3 precursor. This study includes high resolution transmission electron microscopy (HRTEM) images, magnetic, optical, and impedance properties of the sample. HRTEM images reveal small tubes of Fe3BO6 of 20 nm diameter. A well resolved hysteresis loop appears at 5K in which the magnetization does not saturate even up to as high field as 50 kOe. It means that the Fe3BO6 nanotubes behave as highly antiferromagnetic in nature in which the surface spins do not align along the field so easily. The temperature dependent impedance describes an ionic Fe3BO6 conductor with a reasonably small activation energy E-a similar to 0.33 eV. Impedance formalism in terms of a Cole-Cole plot shows a deviation from an ideal Debye-like behavior. We have also reported that electronic absorption spectra are over a spectral range 200-800 nm of wavelengths in order to find out how a bonded surface layer present on the Fe3BO6 crystallites tunes the 3d -> 3d electronic transitions in Fe3+ ions