Realization of high thermoelectric performance in p-type unfilled ternary skutterudites FeSb2+xTe1−x via band structure modification and significant point defect scattering

FeSb₂Te, a ternary derivative of binary CoSb₃, displays anomalous electrical and thermal transport properties because of considerable modifications in the band structure induced by Fe and significant mixed valence state (namely Fe²⁺ and Fe³⁺) scattering of phonons. The substitution of Te for Sb generates more holes without notably affecting the band structure, while markedly improving the electrical conductivity and retaining a high Seebeck coefficient due to the enhanced density of states, thereby leading to dramatically increased power factors. Furthermore, the heat carrying phonons are strongly scattered with increasing x value because of the formation of solid solutions between two end members: □FeSb₂Te and □FeSb₃ (where □ can be viewed as a vacancy). Consequently, high thermoelectric figures of merit were achieved in the FeSb_2+xTe_1?x compounds, with the largest ZT value reaching ～0.65 for the sample with x = 0.2. This is the highest value among all p-type unfilled skutterudites and is comparable with some filled compositions. Prospects for further improving the performance of p-type FeSb₂Te-based skutterudites are discussed.     

Thermoelectric Performance of Sb- and La-Doped Mg2Si0.5Ge0.5

La _x Mg_2?x Si_0.49Ge_0.5Sb_0.01 compounds (x?=?0, 0.005, 0.01, 0.02) were synthesized by solid-state reaction followed by spark plasma sintering. The thermoelectric properties, such as the Seebeck coefficient, the electrical and thermal conductivities, and ZT, of these compounds have been studied in the temperature range of 300?K to 823?K. The figure of merit of this n-type compound has been raised above unity at 823?K for the sample with x?=?0.01, a value 60% higher than that of Mg₂Si_0.49Ge_0.5Sb_0.01. The reduction of the thermal conductivity via increasing phonon scattering is considered as the main reason for the enhanced ZT. These observations demonstrate an opportunity to improve the thermoelectric performance of Mg₂Si_1?x Ge _x solid solutions.     

Heat conduction in Ba1−xKxBiO3

We have investigated heat conduction of single crystal Ba_1?xK_xBiO₃ in the temperature range of 2–300 K and in a magnetic field of up to 6 Tesla. Temperature dependence of thermal conductivityκ(T) reveals the participation of both electrons and phonons with their relative contributions that depend critically on the potassium doping concentration. Crystals underdoped with potassium (samples with higherT _c) exhibit a strong suppression ofκ and a glass-like temperature dependence. In contrast, those with a higher potassium content (lowerT _c) show an increase as temperature decreases with a peak near 23 K. Field dependence ofκ(H) is also very sensitive to the level of potassium doping. Crystals exhibiting a large phonon contribution show an initial drop inκ(H) at low fields followed by a minimum and then a slow rise to saturation as the field increases. The initial drop is due to the additional phonon scattering by magnetic vortices as the sample enters a mixed state. The high field behavior ofκ(H), arising from a continuous break-up of Cooper pairs, exhibits scaling which suggests the presence of an unconventional superconducting gap structure in this material.     

Electronic transport in tungsten and iron-doped tungsten below 1 K

The electrical resistivity and the thermoelectric ratio G have been measured for zone-refined single crystals of both tungsten and iron-doped tungsten from 5 K down to 40 mK. The samples had residual resistance ratios RRR ranging from 1750 to 90,000. The observed behavior is conveniently divided into two classes, normal and anomalous. Completely normal behavior was displayed by only three W samples with high RRRs. The Fe-doped W and the remaining W samples contained one or more anomalies. Normal behavior is that which would be expected for W containing impurities with no internal degrees of freedom. In normal behavior decreased monotonically with decreasing temperature and was consistent with the equation = _o + AT ² below about 1.5 K. This form for is taken as evidence that electron-electron scattering dominates electron-phonon scattering in for W at such low temperatures. For the range of sample purities studied, A increased slightly with increasing ₀, but did not vary systematically with either the sample diameter d or with the ratio (273 K)/d(T). In normal behavior, G was positive and constant below about 0.5 K, increased in magnitude as T rose to 4 or 5 K, and then began to decrease, becoming negative above about 7 K. An explanation is provided for this behavior. Those samples that fell into the anomalous class displayed at least one of three anomalies: (1) a minimum in the electrical resistivity, with an approximately logarithmic variation with T at temperatures below the minimum; (2) a positive contribution to G which increased in magnitude with decreasing temperature approximately as T ^–1/2from about 4 K down to at least 0.5 K; and (3) a negative contribution to G which set in at about 0.5 K, varied approximately as log T, and dominated G at the lowest temperatures. These anomalies are presumably due to one or more impurities dissolved in the W, possibily including Fe. However, chemical and spectroscopic analyses of pieces from several samples, including the Fe-doped W, failed to establish a clear link between any specific impurities and the observed anomalies. At the moment we neither know the source nor understand the nature of these anomalies.Supported in part by NSF Grants DMR-77-04680 and DMR-78-07892.Part of this work was done while the author was at the Physics Department, University of Lancaster, Lancaster, England, during a sabbatical.Part of this work was done while the author was at the Physics Department, Catholic University, Nijmegen, The Netherlands, during a sabbatical.     

Thermoelectric properties of Bi2O2Se

Bi₂O₂Se was synthesized from Bi₂Se₃ and Bi₂O₃ by solid state reaction in an evacuated quartz ampoule. The product crystallizes in the tetragonal type lattice and X-ray pattern displays lines of the Bi₂O₂Se only. Samples for thermoelectric property measurements were prepared using hot pressing in rectangular graphite dies. The samples were characterized by the measurements of Seebeck coefficient, electrical conductivity and thermal conductivity as a function of temperature. From the experimental data we calculate the dimensionless figure of merit ZT that for a non-optimized material approaches the value 0.2 at 800 K.     

Evaluating the sources and fate of anthropogenic dissolved inorganic nitrogen (DIN) in two contrasting North Sea estuaries

Nitrogen isotope ratios (delta(15)N) were used to help elucidate the sources and fate of ammonium (NH(4)(+)) and nitrate (NO(3)(-)) in two northeastern English estuaries. The dominant feature of NH(4)(+) in the heavily urbanised Tyne estuary was a plume arising from a single point source; a large sewage works. Although NH(4)(+) concentrations (ranging from 30-150 microM) near the sewage outfall varied considerably between surveys, the sewage-derived delta(15)N-NH(4)(+) signature was remarkably constant (+10.6+/-0.5 per thousand) and could be tracked across the estuary. As indirectly supported by (15)N-depleted delta(15)N-NO(3)(-) values observed close to the mouth of the Tyne, this sewage-derived NH(4)(+) was thought to initiate lower estuarine and coastal zone nitrification. In the more rural Tweed, NH(4)(+) concentrations were low (<7 microM) compared to those in the Tyne and delta(15)N-NH(4)(+) values were consistent with mixing between riverine and marine sources. The dominant form of dissolved inorganic nitrogen (DIN) in the Tweed was agricultural soil-derived NO(3)(-). A decrease in riverine NO(3)(-) flux during the summer coinciding with an increase in delta(15)N-NO(3)(-) values was mainly attributed to enhanced watershed nutrient processing. In the Tyne, where agricultural inputs are less important compared to the Tweed, light delta(15)N-NO(3)(-) (ca. 0 per thousand) detected in the estuary during one winter survey pointed to a larger contribution from precipitation-derived NO(3)(-) during high river discharge. Regardless of the dominant sources, in both estuaries most of the variability in DIN concentrations and delta(15)N values was explained by simple end-member mixing models, implying very little estuarine processing.     

How the great apes (Pan troglodytes, Pongo pygmaeus, Pan paniscus, Gorilla gorilla) perform on the reversed reward contingency task II: Transfer to new quantities, long-term retention, and the impact of quantity ratios.

We tested 6 chimpanzees (Pan troglodytes), 3 orangutans (Pongo pygmaeus), 4 bonobos (Pan paniscus), and 2 gorillas (Gorilla gorilla) in the reversed reward contingency task. Individuals were presented with pairs of quantities ranging between 0 and 6 food items. Prior to testing, some experienced apes had solved this task using 2 quantities while others were totally na?ve. Experienced apes transferred their ability to multiple-novel pairs after 6 to 19 months had elapsed since their initial testing. Two out of 6 na?ve apes (1 chimpanzee, 1 bonobo) solved the task--a proportion comparable to that of a previous study using 2 pairs of quantities. Their acquisition speed was also comparable to the successful subjects from that study. The ratio between quantities explained a large portion of the variance but affected na?ve and experienced individuals differently. For smaller ratios, na?ve individuals were well below 50% correct and experienced ones were well above 50%, yet both groups tended to converge toward 50% for larger ratios. Thus, some apes require no procedural modifications to overcome their strong bias for selecting the larger of 2 quantities. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sacral reflexes: physiology and clinical application

Sacral reflexes consist of motor responses in the pelvic floor and sphincter muscles evoked by stimulation of sensory receptors in pelvic skin, anus, rectum, or pelvic viscera. These responses may be elicited by physical or electrical stimuli. They have been used in research studies of the pathophysiology of pelvic floor and anorectal disorders and many have been recommended for diagnostic use. These reflexes are described and discussed in this review. More rigorous evaluation of their value in the clinical assessment and care of patients with pelvic floor and sphincter disorders is required. Currently direct comparisons of the value of particular responses are generally not available, and few of these reflexes have proven validity for use in clinical diagnosis.     

Magnetically tunable rectangular waveguide E-plane integratedcircuit filters

A rigorous field theory method is described for the computer-aided design (CAD) of magnetically tunable E-plane metal-insert filters, where the waveguide sections are symmetrically loaded with ferrite slabs, and for large-gap finlines filters on a ferrite substrate. The design method is based on field expansion in suitably normalized eigenmodes which yields directly the modal scattering matrix of all discontinuities. The theory includes both higher-order mode interaction and the finite thickness of the metal inserts. Optimized data are given for magnetically tunable Ku-band metal insert and finline filter examples. The metal-insert type achieves a tuning range of its operating midband from about 14.1 to 15.7 GHz. The theory is verified by measurements