A high temperature apparatus for measurement of the Seebeck coefficient

A high temperature Seebeck coefficient measurement apparatus with various features to minimize typical sources of error is designed and built. Common sources of temperature and voltage measurement error are described and principles to overcome these are proposed. With these guiding principles, a high temperature Seebeck measurement apparatus with a uniaxial 4-point contact geometry is designed to operate from room temperature to over 1200 K. This instrument design is simple to operate, and suitable for bulk samples with a broad range of physical types and shapes

High thermoelectric figure of merit in heavy hole dominated PbTe

Thermoelectric transport properties of p-type PbTe:Na, with high hole concentrations of approximately 10^(20) cm^(−3), are reinvestigated from room temperature to 750 K. The greatly enhanced Seebeck coefficient at these doping levels can be understood by the presence of a sharp increase in the density of states around the Fermi level. As a result, the thermoelectric figure of merit, zT, reaches ~1.4 at 750 K. The influence of these heavy hole carriers may contribute to a similarly high zT observed in related p-type PbTe-based systems such as Tl-doped PbTe and nanostructured composite materials

A combinatorial approach to microstructure and thermopower of bulk thermoelectric materials: the pseudo-ternary PbTe–Ag_2Te–Sb_2Te_3 system

The microstructures and Seebeck coefficients of thermoelectric alloys in the pseudo-ternary PbTe–Ag_2Te–Sb_2Te_3 system were examined using samples that were compositionally graded by unidirectional solidification by the Bridgman method and diffusion couples. At compositions near the middle of the pseudo-binary PbTe–AgSbTe_2 line, a compositionally modulated microstructure has been found. From diffusion couple experiments, it is found that the PbTe–AgSbTe_2 system exhibits a miscibility gap at low temperatures while it forms a complete solid solution at high temperatures; the critical temperature is between 400 °C and 450 °C. The modulated microstructure originates from the decomposition of the high-temperature solid solution during cooling. Scanning Seebeck coefficient measurement on these samples covers a wide compositional space of the pseudo-ternary system. The Seebeck coefficient transitions from positive values at AgSbTe_2-rich compositions to negative values at PbTe-rich compositions on the pseudo-binary PbTe–AgSbTe_2 line. Composition-graded samples prepared by the Bridgman method are thus useful to investigate thermoelectric materials in multi-component systems

Scanning Seebeck Coefficient Measurement System for Homogeneity Characterization of Bulk and Thin-Film Thermoelectric Materials

Larger-scale production of thermoelectric materials is necessary when mass-producing thermoelectric devices at industrial level. Certain fabrication techniques can create inhomogeneity in the material through composition and doping fluctuations throughout the sample, causing local variations in thermoelectric properties. Some variations are in the range of sub-millimeter scale or larger but may be difficult to detect by traditional materials characterization techniques such as x-ray diffraction or scanning electron microscopy when the chemical variation is small but the doping variation, which strongly affects thermoelectric performance, is large. In this paper, a scanning apparatus to directly detect local variations of Seebeck coefficient on both bulk and thin-film samples is used. Results have shown that this technique can be utilized for detection of defective regions, as well as phase separation in the 100-μm range or larger

Limulus factor D, a 43-kDa protein isolated from horseshoe crab hemocytes, is a serine protease homologue with antimicrobial activity

AbstractA glycoprotein (Mr = 43 000) from horseshoe crab hemocytes with antimicrobial activity against Gram-negative bacteria was purified. The internal peptide sequences coincided exactly with the deduced amino acid sequence of a cDNA clone, designated limulus factor D, which was isolated by screening a hemocyte cDNA library with an anti-human plasminogen antibody. The open reading frame codes for a precursor of factor D of 394 amino acid residues, including an NH2-terminal signal sequence. The COOH-terminal domain of factor D has significant sequence homology with the catalytic domain of mammalian serine proteases, in particular with human tissue plasminogen activator (32% identity), except for the substitution of Ser of the active site triad to Gly. Factor D has a unique NH2-terminal domain with weak sequence homology with part of the mammalian interleukin-6 receptor α-chain. Factor D is likely to have an important role in host defense mechanisms