Papers by Keyword: Transport Property

Abstract: Sn-doped CoSb3 skutterudites were prepared by encapsulated induction melting and their electronic transport properties were examined. The Sn dopant generated excess charge carriers, which increased in concentration with increasing Sn doping content. However, the carrier mobility decreased with increasing doping content, indicating a decrease in the hole mean free path by impurity scattering. The Seebeck coefficient decreased and the electrical resistivity decreased slightly with increasing the carrier concentration due to the reduced carrier mobility by impurity scattering. The lattice thermal conductivity was dominant in the Sn-doped CoSb3 skutterudites.

Abstract: In-filled CoSb3 skutterudites (InzCo4Sb12) were prepared and the filling effects on the thermoelectric and transport properties were examined. Seebeck coefficient and Hall coefficient confirmed that all the samples showed n-type conductivity. Temperature dependence of the electrical resistivity suggested that InzCo4Sb12 is a highly degenerate semiconducting material. The thermal conductivity was considerably reduced by In filling and the lattice contribution was dominant.

Abstract: Molecularly imprinted composite membranes for selective binding and permeation of roxithromycin were prepared by means of thermal initiated co-polymerization method using polysulfone ultra-filtration membranes as porous supports. Scanning electron microscope was utilized to visualize surface and cross-sections of the membranes to gain more better understanding in the analysis of imprinted layers deposited on PSF support membranes and differential scanning calorimetric was used for determining the thermal stability of the membranes. Static equilibrium binding and recognition properties of the imprinted and non-imprinted membranes to roxithromycin and its analogues in ethanol solution system were tested. The results showed that saturated binding capacity of imprinted membrane to roxithromycin was about 2.24μmol/g, higher than those of its analogues, and the selectivity factors of αRM/EM, αRM/AM and αRM/EE were 1.75, 2.46 and 2.67, respectively. The transport performances of the membranes were evaluated through kinetic filtration experiments. The separation mechanism of the roxithromycin imprinted membrane could be defined as facilitated permeation mechanism.

Abstract: The all oxide magnetic multilayer system [LaNiO3/SmFeO3]n (for n = 1 and 2), grown on single crystal SrTiO3(100) substrates, has been produced using the laser MBE (Molecular Beam Epitaxy) technique. We have made a systematic study of the electrical transport properties in the temperature range from 15–300K. As part of this work, we have made a detailed study of the metallic properties of the LaNiO3 layer as a function of the oxygen partial pressure (pO2) and substrate temperature (TS). We have measured magnetic layers of SmFeO3 with LaNiO3 electrodes as a function of the magnetic layer thickness (10 – 470 nm). A non-metallic behaviour is observed with evidence of a “hopping” mechanism at low temperatures. For the n = 2 multilayers, we have measured the temperature dependence of resistance for the sample series with varying LaNiO3 interlayer thickness (t = 2 – 30 nm). We observe an appreciable increase of the low temperature resistance for the interlayer thicknesses between 3.75 – 7.5 nm. This could indicate a change in coupling from ferromagnetic to antiferromagnetic between the magnetic layers.

Abstract: Ge1-xMnx (x=0.05, 0.07, 0.11, 0.15, 0.19, 0.23, 0.26, 0.29) thin films were prepared by magnetron sputtering. All the films had a Ge cubic structure, and no indication of a secondary phase was found in any sample using X-ray diffraction (XRD). The crystal lattice constant increases with the Mn concentration, in accordance with Vegard's law. No films show clear magnetic domain structure under a magnetic force microscope (MFM). Atom force microscope (AFM) measurements show that all films have a uniform particle size distribution, and a columnar growth pattern. X-ray photoelectron spectroscopy (XPS) measurements indicate that the Mn atoms are not singlely in the bivalent. Electrical transport properties show that the resistance of the films increases with increasing Mn concentration, suggesting that the Mn ions are in deep-level acceptor states, while resistance decreases with increasing temperature, which is a typical semiconductor property.

Abstract: Statistical continuum approach is used to predict effective conductivity of anisotropic random porous heterogeneous media using two-point correlation functions. Probability functions play a critical role in describing the statistical distribution of different constituents in a heterogeneous media. In this study a 3-dimensional two-point correlation function is utilized to characterize the anisotropic porous media of a Cathode materials to incorporate all the details of the microstructure. These correlation functions are then linked to the effective properties using homogenization relations. An anisotropioc Green’s function solution is used to solve the set of field equations. Examples in this study demonstrated how the model captured the anisotropy in effective conductivity of the random heterogeneous media. Predicted results showed the influence of microstructure on the effective conductivity tensor.

Abstract: Carrier transport properties of AlGaN/GaN heterostructures have been analyzed with the quantitative mobility spectrum analysis (QMSA) technique. The nominally-undoped Al0.15Ga0.85N/GaN sample was grown by metal-organic vapor phase epitaxy. Variable-magneticfield Hall measurements were carried out in the temperature range of 4-160 K and magnetic field range of 0-6.6 T. QMSA was applied to the experimental variable-field data to extract the concentrations and mobilities associated with the high-mobility 2DEG and the relatively lowmobility bulk electrons for the temperature range investigated. For temperatures below 100 K the calculated mobility and carrier density values were close to the experimental results. No bulk conduction was observed in this temperature range. At 160 K, QMSA results show that parallel conduction in 3 mm thick GaN layer started to affect the average electron mobility.

Abstract: This work was directed at a comprehensive study of the role of the nanostructure and nanochemistry on the transport properties of yttria-stabilized zirconia. Alumina additions lead to a decrease of sgb when the samples have clean grain boundaries, while sgb goes through a maximum in samples having glassy grain boundaries. The differences were attributed to the strong interaction between Al2O3 and SiO2 impurities leading to a glassy phase depletion at the grain-boundaries, due to a change in wettability. Moreover, XPS analyses show that Si and Y segregate near these interfaces according to a kinetic demixing process, explaining why a faster cooling rate after sintering has a beneficial effect on sgb.

Abstract: The La1-xSrxCo0.2Fe0.6Ni0.2O3-d, La1-xSrxCo0.4Fe0.4Ni0.2O3-d and La1-xSrxCo0.2Fe0.4Ni0.4O3-d perovskites were synthesized with Sr contents 0.1 ≤ x ≤ 0.3 using precursors obtained by citric acid method and their structural and transport properties were measured. All obtained samples crystallize in hexagonal R-3c perovskite structure. The thermal stability was found to decrease with increasing Ni and Sr amounts, what leads to appearance of La2NiO4 like secondary phases with spinel structure and even NiO for higher Ni concentration. The DC electrical conductivity and thermoelectric power measurements at low temperatures (77 – 300K) suggest an appearance of variable hopping mechanism in this temperature range. The transport properties were found to improve with both Sr and Ni concentration increases. The moessbauer spectroscopy studies of La1-xSrxCo0.2Fe0.6Ni0.2O3-d samples revealed presence of two valence states of iron (Fe2+, Fe3+). The measured high temperature (870 – 1070K) DC electrical conductivity is relatively high for samples with high Sr and Ni amounts, what makes them good candidates for a possible application as cathode materials for Intermediate Temperature Solid Oxide Fuel Cells and points to further studies of perovskites from the (La, Sr)(Co, Fe, Ni)O3 system.