H. W. Zandbergen

Structures and thermoelectric properties of the infinitely adaptive series "Bi2…m"Bi2Te3…n

The structures and thermoelectric properties of the Bi2mBi2Te3n homologous series, derived from stacking hexagonal Bi2 and Bi2Te3 blocks, are reported. The end members of this series are metallic Bi and semiconducting Bi2Te3; nine members of the series have been studied. The structures form an infinitely adaptive series and a unified structural description based on a modulated structure approach is presented. The as-synthesized samples have thermopowers S that vary from n type for Bi2Te3 to p type for phases rich in Bi2 blocks but with some Bi2Te3 blocks present, to n type again for Bi metal. The thermoelectric power factor S 2 / is highest for Bi metal 43 W/K 2 cm at 130 K, followed by Bi2Te3 20 W/K 2 cm at 270 K, while Bi2Te m:n=5:2 and Bi7Te3 m:n=15:6 have 9 W/K 2 cm at 240 K and 11 W/K 2 cm at 270 K, respectively. The results of doping studies with Sb and Se into Bi2Te are reported.

Crystal structure and elementary properties of NaxCoO2 ( x=0.32 , 0.51, 0.6, 0.75, and 0.92) in the three-layer NaCoO2 family

The crystal structures of NaxCoO2 phases based on three-layer NaCoO2, with x=0.32, 0.51, 0.60, 0.75, and 0.92, determined by powder neutron diffraction, are reported. The structures have triangular CoO2 layers interleaved by sodium ions, and evolve with variation in Na content in a more complex way than has been observed in the two-layer NaxCoO2 system. The phases with highest and lowest Na content studied x=0.92 and 0.32 are trigonal, with three CoO2 layers per cell and octahedral Na ion coordination. The intermediate compositions have monoclinic structures. The x=0.75 compound has one CoO2 layer per cell, with Na in octahedral coordination and an incommensurate superlattice. The x=0.6 and 0.51 phases are also single layer, but the Na is found in trigonal prismatic coordination. The magnetic behavior of the phases is similar to that observed in the two-layer system. Both the susceptibility and the electronic contribution to the specific heat are largest for x=0.6.

Ferromagnetism below 10 K in Mn-doped BiTe

Ferromagnetism is observed below 10 K in [Bi0.75Te0.125Mn0.125]Te. This material has the BiTe structure, which is made from the stacking of two Te-Bi-Te-Bi-Te blocks and one Bi-Bi block per unit cell. Crystal structure analysis shows that Mn is localized in the Bi2 blocks, and is accompanied by an equal amount of TeBi antisite occupancy in the Bi2Te3 blocks. These TeBi antisite defects greatly enhance the Mn solubility. This is demonstrated by comparison of the [Bi1?xMnx]Te and [Bi1?2xTexMnx]Te series; in the former, the solubility is limited to x=0.067, while the latter has xmax=0.125. The magnetism in [Bi1?xMnx]Te changes little with x, while that for [Bi1?2xTexMnx]Te shows a clear variation, leading to ferromagnetism for x>0.067. Magnetic hysteresis and the anomalous Hall effect are observed for the ferromagnetic samples.

Superconductivity in noncentrosymmetric Mg10Ir19B16

Mg10Ir19B16, a previously unreported compound in the Mg-Ir-B chemical system, is found to be superconducting at temperatures near 5 K. The fact that the compound exhibits a range of superconducting temperatures between 4 and 5 K suggests that a range of stoichiometries is allowed, though no structural evidence for this is observed. The compound has a large, noncentrosymmetric, body centered cubic unit cell with a = 10.568 Angstrom, displaying a structure type for which no previous superconductors have been reported.

Superconductivity in noncentrosymmetricMg10Ir19B16

Mg10Ir19B16, a previously unreported compound in the Mg-Ir-B chemical system, is found to be superconducting at temperatures near 5 K. The fact that the compound exhibits a range of superconducting temperatures between 4 and 5 K suggests that a range of stoichiometries is allowed, though no structural evidence for this is observed. The compound has a large, noncentrosymmetric, body centered cubic unit cell with a = 10.568 Angstrom, displaying a structure type for which no previous superconductors have been reported.

Superconductivity in Mg10Ir19B16

Mg10Ir19B16, a previously unreported compound in the Mg-Ir-B chemical system, is found to be superconducting at temperatures near 5 K. The fact that the compound exhibits a range of superconducting temperatures between 4 and 5 K suggests that a range of stoichiometries is allowed, though no structural evidence for this is observed. The compound has a large, noncentrosymmetric, body centered cubic unit cell with a = 10.568 Angstrom, displaying a structure type for which no previous superconductors have been reported.