H. J. Goldsmid

Bio: H. J. Goldsmid is an academic researcher from University of New South Wales. The author has contributed to research in topics: Thermoelectric materials & Thermal conductivity. The author has an hindex of 6, co-authored 9 publications receiving 267 citations.

The Figure of Merit in Amorphous Thermoelectrics

Abstract: In some semiconductors, the mean free path can be greater for the phonons than for the charge carriers. When this is the case it is likely that the material will display a higher thermoelectric figure of merit in the amorphous rather than the crystalline form. Here we determine the general conditions that must hold for an amorphous material to be promising for thermoelectric applications. The most important quantity is undoubtedly the effective mass of the charge carriers. At room temperature it appears that this quantity is unlikely to be large enough for our purposes in any good thermoelectric material presently known. On the other hand, it seems quite possible that amorphous material may be useful in high-temperature thermoelectric generation. We suggest that our ideas may be demonstrated in amorphous or fine-grained skutterudites and half-Heusler alloys.

The thermal conductivity of polycrystalline Bi88Sb12

Abstract: Comprehensive thermogalvanomagnetic measurements have been made on polycrystalline samples of Bi 88 Sb 12 . The temperature has ranged from 100 to 300 K and a magnetic field of up to 1 T has been used. The samples have contained up to 1000 ppm of either tin or selenium. We have attempted to calculate the electronic component of the thermal conductivity from the data but have found that this sometimes leads to unacceptable values for the lattice conductivity. More reasonable lattice components are found from the variation of the total thermal conductivity with magnetic field. We confirm our observation of a fall in the lattice conductivity when the grain size is reduced below about 10 μm, but an even greater fall in the electrical conductivity means that the thermoelectric figure of merit is not improved.

The maximum possible conversion efficiency of silicon‐germanium thermoelectric generators

Abstract: The thermoelectric properties of N‐type and P‐type Si‐Ge alloys have been reviewed and detailed calculations for the efficiency of a thermoelectric generator made from a 70% Si‐30% Ge alloy have been made over the temperature range from 300 to 1300 K. A model employing one valence band and two conduction bands has been used. A generator of standard material, optimally doped, and infinitely segmented will have an efficiency of 12.1% operating over this range. If the lattice thermal conductivity can be reduced to its minimum value without upsetting the electrical properties, then the efficiency can be raised to an ultimate maximum of 23.3%. A more modest increase in efficiency to 14.7% could be obtained by a 2.4 volume percent of finely dispersed second‐phase precipitates which would act as phonon scatterers. The utility/futility of GaP additions and grain‐boundary scattering as methods to increase the efficiency is discussed.

Anomalously high thermoelectric figure of merit in Bi1−xSbx nanowires by carrier pocket alignment

Abstract: Electronic transport calculations were carried out for Bi1−xSbx nanowires (0⩽x⩽0.30) of diameters 10 nm⩽dW⩽100 nm at 77 K. A band structure phase diagram was generated, showing the dependence of the relative band edge positions on diameter and composition. Calculations of the thermoelectric figure-of-merit (ZT) predict that the performance of Bi1−xSbx nanowires is superior to that of Bi nanowires and to that of the bulk alloy. An exceptionally high value of ZT for p-type nanowires at 77 K was found for dW∼40 nm and x∼0.13, which is explained by the coalescence in energy of up to ten valence subband edges to maximize the density-of-states at the Fermi energy.

Grain Boundary Engineering for Achieving High Thermoelectric Performance in n-Type Skutterudites

Abstract: Grain or phase boundaries play a critical role in the carrier and phonon transport in bulk thermoelectric materials. Previous investigations about controlling boundaries primarily focused on the reducing grain size or forming nanoinclusions. Herein, liquid phase compaction method is first used to fabricate the Yb-filled CoSb3 with excess Sb content, which shows the typical feature of low-angle grain boundaries with dense dislocation arrays. Seebeck coefficients show a dramatic increase via energy filtering effect through dislocation arrays with little deterioration on the carrier mobility, which significantly enhances the power factor over a broad temperature range with a high room-temperature value around 47 μW cm−2 K−1. Simultaneously, the lattice thermal conductivity could be further suppressed via scattering phonons via dense dislocation scattering. As a result, the highest average figure of merit ZT of ≈1.08 from 300 to 850 K could be realized, comparable to the best reported result of single or triple-filled Skutterudites. This work clearly points out that low-angle grain boundaries fabricated by liquid phase compaction method could concurrently optimize the electrical and thermal transport properties leading to an obvious enhancement of both power factor and ZT.