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Abstract:
In this report an alternative approach for optimization of the
thermoelectric properties of half-Heusler compounds is presented. The
common approaches are partial substitution of elements by elements of
nearby groups and substitution with homologs. In this approach we
substitute one element by one neighboring element with fewer valence
electrons and by one with more electrons. The amounts of the
substitutions are chosen such that the amount of deficiency and excess
electrons are compensated. In the solid solution
TiCo(x)(Ni(0.5)Fe(0.5))(1-x)Sb, Co was substituted equally by Fe and Ni.
The aim of the substitution was to improve the figure of merit by a
reduction of the thermal conductivity accompanied by an unchanged high
Seebeck coefficient. The solid solution TiCo(x)(Ni(0.5)Fe(0.5))(1-x)Sb,
Co was synthesized by arc-melting. The structure of the as-cast samples
was analyzed by x-ray diffraction. Rietveld refinements yielded the
TiCo(x)(Ni(0.5)Fe(0.5))(1-x)Sb, Co structure type with a small amount of
antisite disorder between Co and Sb. The thermoelectric properties of
the solid solution were investigated in the temperature range from 2 K
to 400 K. A Seebeck coefficient of TiCo(x)(Ni(0.5)Fe(0.5))(1-x)Sb, Co at
400 K and a reduction of the thermal conductivity to
TiCo(x)(Ni(0.5)Fe(0.5))(1-x)Sb, Co were measured. The figure of merit
was enhanced by a factor of about seven to a value of 0.04 at 400 K for
TiCo(x)(Ni(0.5)Fe(0.5))(1-x)Sb, Co.
