  It has been demonstrated that InSb nanoinclusions, which are formed in situ,
can simultaneously improve all three individual thermoelectric properties of
the n-type half Heusler compound (Ti,Zr,Hf)(Co,Ni)Sb [Xie et al., Acta Mater.
58, 4795 (2010)]. In the work presented herein, we have adopted the same
approach to the p-type half Heusler compound Ti(Co,Fe)Sb. The results of
resistivity, Seebeck coefficient, thermal conductivity, and Hall coefficient
measurements indicate that the combined high mobility electron injection, low
energy electron filtering, and boundary scattering, again, lead to a
simultaneous improvement of all three individual thermoelectric properties:
enhanced Seebeck coefficient and electrical conductivity as well as reduced
lattice thermal conductivity. A figure of merit of ZT=0.33 was attained at 900
K for the sample containing 1 atomic percent InSb nanoinclusions, a 450 percent
improvement over the nanoinclusion-free sample. This represents a rare case
that the same nanostructuring approach successfully works for both p-type and
n-type thermoelectric materials of the same class, hence pointing to a
promising materials design route for higher performance half-Heusler materials
in the future and hopefully will realize similar improvement in TE devices
based on such half Heusler alloys.
