Search

Glasses and vitroceramics in the xMoO 3 ·(100 − x)[4PbO 2 ·Pb] system with x = 5-50 mol% MoO 3 were prepared by melt quenching method. The influence of MoO 3 content on optical properties and structure of the 4PbO 2 ·Pb host network was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman, photofluorescence and X-ray photoelectron (XPS) spectroscopies. The X-ray patterns show the presence of a small amount of Pb 2 MoO 5 crystalline phase in the sample with x = 40 mol% MoO 3 . By increasing of MoO 3 content up to 50 mol% MoO 3 , Pb 2 MoO 5 and tetragonal PbO crystalline phases were detected. Raman data show the bending modes of the O Pb O linkages which allow the intercalation of [PbO 4 ] structural units, isolated [MoO 4 ] and deformed [MoO 6 ] structural units as basic structural units formed by lead and molybdenum atoms. The photofluorescence spectroscopy data shows the transitions of Mo + 5 and Pb 2 + ions. According to the XPS data, the vitroceramic network contains mainly [MoO 4 ] tetrahedral units and small amounts of [MoO 6 ] octahedral units.

Lithium–lead–germanate glasses in the xLi 2 O·(100-x)[7GeO 2 ·3PbO] system, where 0 ≤ x ≤ 40 mol% Li 2 CO 3 exhibit a “germanate anomaly”, which is a maximum in their density profiles with the addition of Li 2 CO 3 up to 20 mol%. The structural characterization of the samples was performed by investigations of Raman spectroscopy and X-ray scattering analysis. An EXAFS analysis of the spectra collected at the germanium K-edge for series of lithium–lead–germanate glasses is also presented. With the EXAFS-extracted structural parameters were reconstructed to the local neighborhood of Ge atoms and were verified current opinions on the germanate anomaly in the considered glasses. The formation of higher-coordinated Ge species in the glassy network can be correlated with the density anomaly. Several structural mechanisms can be summarized by increasing of lithium carbonate in the lead–germanate glassy: i) depolymerization of germanate network; ii) conversion of 3- to 4-membered [GeO 4 ] rings; iii) transformation of connected [GeO 6 ] structural units into isolated [GeO 6 ] structural units and a conversion part of higher to lower coordination number of germanium atoms.

The influence of DC current on the resistivity and phase transition of polycrystalline La 0.7 Ca 0.3 MnO 3 has been investigated. The specific heat measurement found that charge carriers and ferromagnetic spin-wave contributions were changed after applied DC current. Applying high electric fields leads to the formation of ferromagnetic regions. The resistivity drops abruptly once the percolating current path is established. As current through the sample disappears, the larger ferromagnetic (FM) clusters, however, remain and are frozen in giving a measurable contribution to the specific heat of the system. The larger clusters should give rise to the value of spin-wave stiffness constant ( D ), as it is expected to increase the strength of the ferromagnetic coupling. The metallic ferromagnetic regions would make the charge carrier delocalization and attribute to specific heat linear term γ .

A new high-temperature thermal sensor based on large-grain polysilicon film formed by metal-induced lateral crystallization (MILC) is proposed. The sensor demonstrates a positive temperature coefficient (PTC) characteristic from 130 °C to high temperatures above 600 °C. Its fabrication process is more cost-effective than its silicon on insulator (SOI) counterpart, and its performance is better than the sensor based on small-grain polysilicon formed by solid-phase crystallization (SPC). Therefore, the proposed sensor is more suitable to be integrated into single-chip CMOS-MEMS gas-sensor system for monitoring the high temperature of sensing membranes.

La0.67Ca0.33MnO3 (LCMO)/YBa2Cu3Oy (YBCO)/Ni trilayers were fabricated with varying thickness of the mid-superconducting YBCO layer. Two different deposition systems were used to avoid oxidation of the magnetic metal Ni and contamination of the deposition systems. Transport properties show that the temperature dependence of resistance goes from a metallic-to-metal-insulator transition (manganite-like behavior) to a superconducting behavior (M-M-S) with increase of the thickness of the YBCO layer. The magnetoresistance (MR) ratio is very small in comparison with LCMO/YBCO bilayers at low temperature. Such phenomenon may depend on the charge transfer and the magnetic spin interaction between the bottom and cap magnetic layers. (c) 2005 Elsevier B.V. All rights reserved.

An analytical two-dimensional model is developed to explain the minority-carrier exclusion effect in circular spreading-resistance temperature (SRT) sensor fabricated on thin silicon film. The model can be used to show the relation between minority-carrier exclusion length and maximum operating temperature of the sensor under different bias currents and different doping levels. Comparison is made between the proposed model and the conventional one-dimensional model used for similar sensors with rectangular shape. Experimental results show that the new model is more accurate than the one-dimensional model for predicting the characteristics of the circular SRT sensor.

A thermal sensor built from a silicon resistor with a simple rectangular layout structure on thin-film (0.1 μm) silicon-on-insulator (SOI) substrate is studied and compared with those on thick-film (10 μm) SOI and bulk (450 μm) Si. Besides supporting the theory of minority-carrier exclusion effect through one-dimensional highly confined carrier transport in the ultra-thin rectangular silicon film, the thin-film SOI device demonstrates the effect of silicon-film thickness on the maximum operating temperature ( T max ) of the sensor: thinner Si film results in higher T max due to higher current density and hence stronger exclusion effect. Measurements and simulations both show that the SOI structure can indeed have the silicon-film thickness as an additional degree of freedom for increasing T max . More importantly, the thin-film SOI thermal resistor can achieve a T max beyond 400 °C even under a very low operating current of 0.1 μA, which is about 1000 times smaller than that of the thick-film SOI counterpart with the same T max . In conclusion, silicon resistor on SOI is a promising low-cost thermal sensor for a broad scope of low-power high-temperature applications.

Substitution of Pb for Hg was performed in the Hg based 1223 phase HgBa2Ca2Cu3O8+delta a (T-c similar to 135 K), resulting in an increase of the superconducting transition temperature to T-c(dia) = 143 K for samples with a nominal composition of Hg0.7Pb0.3Ba2Ca2Cu3O8+delta. The crystal structure of this solid solution has been investigated by neutron powder diffraction (NPD) and synchrotron X-ray diffraction (SXRD) techniques at room temperature (RT). The compound has the same crystal structure as Hg-1223 with the space group P4/mmm and lattice parameters a = 3.8457(1) Angstrom and c = 15.8252(7) Angstrom. Rietveld analysis results indicate that Hg is partially replaced by Pb, and the oxygen content, delta, is 0.450(2). The lattice parameter changes resulting from the Pb substitution are too small to account for the T-c change mimicking the effect of pressure.