hide
Free keywords:
-
Abstract:
Polycrystalline samples of the type-I clathrate Ba8NixGe46-x-y square(y)
were synthesized for 0.2 <= x <= 3.5 by melt quenching and for 3.5 < x
<= 6.0 by melting with subsequent annealing at 700 degrees C. The
maximum Ni content in the clathrate framework at this temperature was
found to be x approximate to 4.2 atoms per unit cell. Thermoelectric and
thermodynamic properties of the type-I clathrate were investigated from
300 to 700 K by means of electrical resistivity, thermopower, thermal
conductivity and specific heat measurements. As the Ni content
increases, the electronic properties gradually evolve from a metallic
character (x < 3.5) towards a highly doped semiconducting state (x >=
3.5). Below x approximate to 4.0 transport is dominated by electrons,
while further addition of Ni (x approximate to 4.2) switches the
electrical conduction to p-type. Maximum value of the dimensionless
thermoelectric figure of merit ZT approximate to 0.2 was achieved at
500K and 650K for x approximate to 2.0 and x approximate to 3.8,
respectively.
