Tailoring the mechanical properties of thermoelectric lead telluride by alloying with non-doping calcium

Thermoelectric generators have a great potential in waste heat recovery and energy harvesting due to their principle of directly converting thermal into electrical energy. Despite a long history in space travel and a broad range of potential applications, TEGs are rarely found in terrestrial applications. Reasons are manufacturing problems and limited durability in dynamic operation conditions due to deficient mechanical properties of the thermoelectric materials, which often suffer from low strength and high brittleness. We present a concept for the basically independent tailoring of mechanical and thermoelectric properties. This can be achieved by the alloying of TE materials with additional elements having preferably no or only little influence on the TE properties. We demonstrate a route of improving the mechanical properties of PbTe by alloying with calcium. It is shown that calcium has minor effects on the thermoelectric properties of PbTe while significantly increasing hardness and fracture strength. As proof of concept, mechanically more stable sodium and calcium co-doped Pb0.966Ca0.02Na0.014Te with ZT exceeding 1.2 above 650 K is demonstrated

Current assisted sintering of PbTe—Effects on thermoelectric and mechanical properties

Lead telluride is among the best performing thermoelectric materials in an intermediate temperature range up to 750 K. It has thus been widely used for technology development and is still a candidate material for high efficiency thermoelectric generators for space applications. However, its mechanical properties present major difficulties for processing and successful application. Material preparation such as milling and sintering has a great influence on the resulting material properties and can be utilized to optimize material properties. Within this work the influence of powder preparation and sintering temperature on the resulting thermoelectric and mechanical properties of undoped lead telluride (PbTe) is investigated. We find that thermoelectric properties are mainly dominated by formation and healing of lattice defects, whereas mechanical properties are dominated by grain size. Additionally the relevance of residual strain as a consequence of temperature gradients inside samples during sintering is demonstrated

Foveal Cone Spacing and Cone Photopigment Density Difference: Objective Measurements in the Same Subjects

7 pages, 6 figures.-- PMID: 9274776 [PubMed].Foveal cone spacing was measured in vivo using an objective technique: ocular speckle interferometry. Cone packing density was computed from cone spacing data. Foveal cone photopigment density difference was measured in the same subjects using retinal densitometry with a scanning laser ophthalmoscope. Both the cone packing density and cone photopigment density difference decreased sharply with increasing retinal eccentricity. From the comparison of both sets of measurements, the computed amounts of photopigment per cone increased slightly with increasing retinal eccentricity. Consistent with previous results, decreases in cone outer segment length are over-compensated by an increase in the outer segment area, at least in retinal eccentricities up to 1 deg.Supported by the Comisión Interministerial de Ciencia y Tecnología (Spain) TIC94/0849 to RN, Zr 1/6 to R-P T, and EYO7624 and the Chartrand Foundation to AEE.Peer reviewe

Oligophrenin 1 (OPHN1) gene mutation causes syndromic X-linked mental retardation with epilepsy, rostral ventricular enlargement and cerebellar hypoplasia

peer reviewedWe identified an oligophrenin 1 (OPHN1) gene mutation in a family with five brothers affected by a recognizable pattern of clinical and neuroradiological hallmarks. The distinctive phenotype comprised moderate to severe mental retardation, myoclonic-astatic epilepsy, ataxia, strabismus and hypogenitalism. Neuroimaging displayed fronto-temporal atrophy with rostral enlargement of the lateral ventricles, lower vermian agenesis and asymmetric cerebellar hypoplasia. Mutation analysis of the OPHN1 gene on Xq12 disclosed a genomic deletion of exon 19 causing a frameshift. Notably, OPHN1 mutations have been previously reported as a rare cause of non-syndromic X-linked mental retardation. Our findings, however, indicate that OPHN1 mutations result in a recognizable syndrome. In addition, identification of OPHN1 as a further gene associated with epileptic seizures will help to unravel aetiologic factors of epilepsy