High temperature rare earth and Si-Ge thermoelectric materials

Thumbnail Image
Han, Sang Hyun
Major Professor
Karl A. Gschneidner, Jr.
Committee Member
Journal Title
Journal ISSN
Volume Title
Research Projects
Organizational Units
Organizational Unit
Materials Science and Engineering
Materials engineers create new materials and improve existing materials. Everything is limited by the materials that are used to produce it. Materials engineers understand the relationship between the properties of a material and its internal structure — from the macro level down to the atomic level. The better the materials, the better the end result — it’s as simple as that.
Journal Issue
Is Version Of
Materials Science and Engineering

The preparation of the metastable crystalline high temperature and high pressure polymorphs of R[subscript]2S[subscript]3, where R = Y, Dy, Er, Tm, Yb and Lu, was investigated at room temperature by mechanical milling (MM). For Dy[subscript]2S[subscript]3 the pure metastable high temperature [gamma]-phase was obtained by MM. For Y[subscript]2S[subscript]3, Er[subscript]2S[subscript]3 and Yb[subscript]2S[subscript]3 the pure metastable high pressure [gamma]-phase was obtained, whereas for the Tm[subscript]2S[subscript]3 and Lu[subscript]2S[subscript]3 samples the metastable high pressure [gamma]-phases coexisted with the corresponding equilibrium ambient polymorphic phase. In case of Dy[subscript]2S[subscript]3 and Y[subscript]2S[subscript]3 the [gamma]-cubic phase was present even after 160 hour MM;The Seebeck coefficient, electrical resistivity, and Hall effect have been studied in Cu[subscript]x(Dy[subscript]2S[subscript]3)[subscript]1-x compounds with the [eta]-orthorhombic structure in the composition range 0.006≤ x≤ 0.15 in order to determine their potential as high temperature (25 to 1000°C) thermoelectric materials. In this temperature and composition range Cu-doped Dy[subscript]2S[subscript]3 behaves as a degenerate semiconductor and shows itinerant conduction. The electrical resistivity and the Seebeck coefficient increased with increasing temperature and then reached the maximum values of 4.35 to 7.13 m[omega]-cm and -163 to -177 [mu]V/°C, respectively. The maximum power factor of 7.9 [mu]W/cm-°C[superscript]2 at Cu[subscript]0.039(Dy[subscript]2S[subscript]3)[subscript]0.961 was obtained at 690°C;The electrical activity of phosphorus in Si[subscript]80Ge[subscript]20 by two non-conventional doping processes has been measured over the temperature range 25-1250°C. Both solid state (mechanical alloying) and gaseous phase doping processes were found to extend the electrical activity of phosphorus in Si[subscript]80Ge[subscript]20 alloys beyond the maximum equilibrium activity (2.1x 10[superscript]20/cm[superscript]3) to 2.5 to 2.9x 10[superscript]20/cm[superscript]3 within the temperature range 900-1200°C. It is likely that this extended electrical activity of phosphorus is associated with a high density of defects.

Wed Jan 01 00:00:00 UTC 1992