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The polymeric compounds M(pyrazine)2Br2 [M = Fe (1), Co (2), and Ni (3)] have been synthesized by the addition of a solution of pyrazine in methanol to a methanolic solution of the anhydrous metal bromide. The crystal structures of (1)-(3) were determined using powder synchrotron and neutron diffraction data and were found to be isostructural. The structures consist of pseudo-octahedral units, doubly linked by pyrazine ligands to form two-dimensional sheets. Magnetic susceptibility data were recorded for each complex down to 5 K and reveal paramagnetic behaviour at high temperatures and antiferromagnetic interactions at low temperatures. Comparison of the structures and magnetism of these and other M(pz)2X2 compounds highlight the relative importance of the canting of the pyrazine ligands on the strength of the magnetic exchange.

The thermoelectric properties from 300 – 1275 K of calcium-doped La3-xTe4 are reported. La3-xTe4 is a high temperature n-type thermoelectric material with a previously reported zTmax ~ 1.1 at 1273 K and x = 0.23. Computational modeling suggests the La atoms define the density of states of the conduction band for La3-xTe4. Doping with Ca2+ on the La3+ site is explored as a means of modifying the density of states to improve the power factor and to achieve a finer control over the carrier concentration. High purity, oxide-free samples are produced by ball milling of the elements and consolidation by spark plasma sintering. Calcium substitution upon the lanthanum site was confirmed by a combination of Rietveld refinements of powder X-ray diffraction data and wave dispersive spectroscopy. A zTmax ~ 1.2 is reached at 1273 K for the composition La2.2Ca0.78Te4 and the relative increase compared to La3-xTe4 is attributed to the finer carrier concentration.

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The purpose of this work was to investigate the influence of different technological treatments of silver sheathed Bi-2223 tapes on the critical current density and the AC transport losses. The tapes were produced using the 'tube-in-tube' technique, by including a silver rod in the centre of the superconducting powder during packing of the silver tube. The aim of the process is to increase the silver to superconductor surface area and thus also the alignment at the centre of the conductor ceramic core. AC transport losses were measured by means of an electrical method using sinusoidally varying currents in the frequency range 30-180 Hz. In this range the power losses are hysteretic. The measured variation in losses from those predicted by a critical state model is attributed to the complex geometry of superconducting regions existing in these tapes.

Absiract-High quality reproducible junctions are mandatory in the construction of high-?', RF and DC SQUIDs using YBazCu307-, thin films. In this paper, we describe two methods used to produce step-edge junctions on MgO substrates suitable for SQUID devices. In both processes a titanium mask has been used to produce a straight, well defined step which assists, in minimizing the occurrence of multiple junctions. We describe two ionmilling processes which produce differently connected stepedge junctions as indicated by SEM micrographs, I-V and I,-B characteristics. Predictable relationships between the ratio of the film thickness t o step height and the junction critical-current density are demonstrated; these enable the creation of step-edge junctions with appropriate values of I, for particular SQUID designs.

An investigation of the Yb,-,SrxNi04-d system has shown that no phases crystallise with a K,Ni F, structure for reaction temperatures up to 11 00 "c at 1 atm oxygen pressure, but a new phase of ideal composition YbSr3Ni06 is formed.Rietveld refinement using powder X-ray diffraction data shows that YbSr3Ni06 adopts a rhombohedra1 KdPtCI6 type structure [ R k , 2 = 6, a = 9.6851 (2) A, c = 11.0960(2) A, R,, = 2.8%], with a deficiency of scattering from the Yb site due to 11 */o Yb vacancies or possibly cation substitutions. lodometric titrations suggest an average Ni oxidation state of 3.0 + . Magnetic susceptibility data for YbSr3Ni06 between 5 and 300 K show Curie-Weiss behaviour at higher temperatures, characteristic of Yb3+ and low-spin Ni3+ with overall peff=4.63(1) pB and &, , = -29.0(1) K. A broad susceptibility maximum at 12 K may be due to one-dimensional antiferromagnetic order.

La 3-x Te 4 is a state-of-the-art high temperature n-type thermoelectric material with a previously reported maximum zT~1.1 at 1273 K. Computational modeling suggests the La atoms play a crucial role in defining the density of states for La 3-x Te 4 in the conduction band. In addition to controlling charge carrier concentration, substitution with Ca 2+ atoms on the La 3+ site is explored as a potential means to tune the density of states and result in larger Seebeck coefficients. High purity, oxide-free samples are produced by ball milling of the elements and consolidated by spark plasma sintering. Powder XRD and electron microprobe analysis are used to characterize the material. High temperature thermoelectric properties are reported and compared with La 3-x Te 4 compositions. A maximum zT of 1.3 is reached at 1273 K for the composition La 2.22 Ca 0.775 Te 4 .