C. Uher

Anomalous barium filling fraction and n-type thermoelectric performance of BayCo4Sb12

Barium-filled skutterudites BayCo4Sb12 with an anomalously large filling fraction of up to y=0.44 have been synthesized. The lattice parameters increase linearly with Ba content. Magnetic susceptibility data show that Ba0.44Co4Sb12 is paramagnetic, which implies that some of the Co atoms in BayCo4Sb12 have acquired a magnetic moment. The presence of the two different valence states of Co (Co3+ and Co2+) leads to the anomalously large barium filling fraction even without extra charge compensation. All samples show n-type conduction. The electrical conductivity increases with increasing the Ba filling fraction. The lattice thermal conductivity of BayCo4Sb12 is significantly depressed as compared to unfilled Co4Sb12. The dimensionless thermoelectric figure of merit, ZT, increases with increasing temperature reaching a maximum value of 1.1 for Ba0.24Co4Sb12 at 850 K.

Origin of the High Performance in GeTe-Based Thermoelectric Materials upon Bi2Te3 Doping

As a lead-free material, GeTe has drawn growing attention in thermoelectrics, and a figure of merit (ZT) close to unity was previously obtained via traditional doping/alloying, largely through hole carrier concentration tuning. In this report, we show that a remarkably high ZT of ∼1.9 can be achieved at 773 K in Ge0.87Pb0.13Te upon the introduction of 3 mol % Bi2Te3. Bismuth telluride promotes the solubility of PbTe in the GeTe matrix, thus leading to a significantly reduced thermal conductivity. At the same time, it enhances the thermopower by activating a much higher fraction of charge transport from the highly degenerate Σ valence band, as evidenced by density functional theory calculations. These mechanisms are incorporated and discussed in a three-band (L + Σ + C) model and are found to explain the experimental results well. Analysis of the detailed microstructure (including rhombohedral twin structures) in Ge0.87Pb0.13Te + 3 mol % Bi2Te3 was carried out using transmission electron microscopy and crystallographic group theory. The complex microstructure explains the reduced lattice thermal conductivity and electrical conductivity as well.

Recent advances in high-performance bulk thermoelectric materials

Thermoelectric (TE) materials facilitate direct heat-to-electricity conversion. The performance of a TE material is characterised by its figure of merit zT (=S2 σT/κ) that depends on both electronic transport properties, i.e. the Seebeck coefficient S and the electrical conductivity σ, and on thermal transport properties, i.e. the thermal conductivity κ of a material. The intrinsically counter-correlated behaviour between electronic and thermal transport properties makes the enhancement of zT a very challenging task. In the past 10 years, the zTs in bulk TE materials have been significantly enhanced due to intensive exploratory efforts, the discovery of new physical phenomena and effects, and applications of advanced synthesis methods. In this review, we summarise the recent progress in bulk TE materials. After the introduction of fundamental principles of thermoelectricity, the recently achieved enhancements in the TE performance encompassing the use of electronic band structure engineering, lattice phonon engineering and nanostructure tailoring will be emphasised. Next, the highlights of typical TE materials will be presented, focusing especially on the great progress achieved during the past decade. Finally, new techniques and approaches developed to fabricate TE materials will be outlined and their impact on the performance and economic viability of large-scale TE applications will be considered. The progress made during the past dozen or so years provides great opportunities for the use of bulk TE materials in a much broader range of applications and bodes well for a more efficient utilisation of energy.

Low-temperature ferromagnetic properties of the diluted magnetic semiconductor Sb2-x Crx Te3 .

We report on magnetic and electrical transport properties of

Influence of fullerene dispersion on high temperature thermoelectric properties of BayCo4Sb12-based composites

{\mathrm{Sb}}_{2\ensuremath{-}x}{\mathrm{Cr}}_{x}{\mathrm{Te}}_{3}

Anomalous barium filling fraction and n-type thermoelectric performance of Ba{sub y}Co{sub 4}Sb{sub 12}

single crystals with

Electrical resistance and the time-dependent oxidation of semicontinuous bismuth films

0\ensuremath{\leqslant}x\ensuremath{\leqslant}0.095

YBa2Cu3O7-δ films: Calculation of the thermal conductivity and phonon mean-free path

over temperatures from

Enhanced thermoelectric performance of a quintuple layer of Bi2Te3

2\phantom{\rule{0.3em}{0ex}}\mathrm{K}

Epitaxial strain, metastable structure, and magnetic anisotropy in Co-based superlattices (invited)

to