E. Bucher

Efficient dopants for ZrNiSn-based thermoelectric materials

Four efficient n-type dopants have been found for ZrNiSn-based thermoelectric materials. These are Nb or Ta at the zirconium sites, and Sb or Bi at the tin sites. No suitable dopant was found for the nickel sites. In a alloy, a power factor of and a thermal conductivity of were measured at 300 K, resulting in a dimensionless figure of merit ZT = 0.12. These values are increased to and at 700 K.

A New Class of Materials with Promising Thermoelectric Properties: MNiSn (M = Ti, Zr, Hf)

TiNiSn, ZrNiSn and HfNiSn are members of a large group of intermetallic compounds which crystallize in the cubic MgAgAs-type structure. Polycrystalline samples of these compounds have been prepared and investigated for their thermoelectric properties. With thermopowers of about –200 μV/K and resistivities of a few mΩcm, power factors S 2 /ρ as high as 38 μW/K 2 cm were obtained at 700 K. These remarkably high power factors are, however, accompanied by a thermal conductivity which is too high for applications. In order to reduce the parasitic lattice thermal conductivity, solid solutions Zr l−x Hf x NiSn, Zr l−x Ti x NiSn, and Hf l−x Ti x NiSn were formed. The figure of merit of Zr 0.5 Hf 0.5 NiSn at 700 K ( ZT = 0.41) exceeds the end members ZrNiSn ( ZT = 0.26) and HfNiSn ( ZT = 0.22).

Observation of mesoscopic vortex physics using micromechanical oscillators

It has long been known that magnetic fields penetrate type II superconductors in the form of quantized superconducting vortices. Most recent research in this area has, however, focused on the collective properties of large numbers of strongly interacting vortices,: the study of vortex physics on the mesoscopic scale (a regime in which a small number of vortices are confined in a small volume) has in general been hampered by the lack of suitable experimental probes. Here we use a silicon micromachined mechanical resonator to resolve the dynamics of single vortices in micrometre-sized samples of the superconductor 2H-NbSe2. Measurements at and slightly above the lower critical field, H c1 (the field at which magnetic flux first penetrates the superconductor), where only a few vortices are present, reveal a rich spectrum of sharp, irreversible vortex rearrangements. At higher fields, where tens of vortices are present, the sharp features become reversible, suggesting that we are resolving a new regime of vortex dynamics in which the detailed configuration of pinning sites, sample geometry and vortex interactions produce significant changes in the measurable vortex resonse. This behaviour can be described within the framework of interacting vortex linesin a ‘1 + 1’-dimensional random potential—an important (but largely untested) theoretical model for disorder-dominated systems,.

Less than 50% sublattice polarization in an insulating S = 3 2 kagomé antiferromagnet at T ≈ 0

We have found weak long-range antiferromagnetic order in the quasi-two-dimensional insulating oxide

Supercooling of the disordered vortex phase via minor hysteresis loops in 2 H − NbSe 2

{mathrm{KCr}}_{3}{(mathrm{OD})}_{6}{(mathrm{S}mathrm{O}}_{4}{)}_{2}

New compounds with MgAgAs-type structure: NbIrSn and NbIrSb

which contains

Stable and metastable vortex states and the first-order transition across the peak-effect region in weakly pinned 2 H − NbSe 2

{mathrm{Cr}}^{3+}

Single crystalline pentacene solar cells

S=3/2

Peak effect, plateau effect, and fishtail anomaly: The reentrant amorphization of vortex matter in 2 H − NbSe 2

ions on a kagome lattice. In a sample with