Abstract :
The resultant Seebeck coefficient a of the
touching p- and n-type M/Bi–Te/M (M = Cu and Ni)
composites was measured as a function of z at a scan
step of 0.5 mm using thermocouples set at three
different intervals of s = 4, 6.5 and 8 mm, where s is the
interval between two probes and z is the distance from
the center of Bi–Te compound to the middle of two
thermocouples. Bi–Te compounds have a thickness of
tBi–Te = 6 mm but the thickness tM of both end metals
sandwiching their compounds was varied from 0.5 mm
to 6 mm. The composites were compacted tightly at a
force of about 10 N by a ratchet. When two probes are
placed on both end metals, the resultant a was significantly
enhanced and exhibited a tendency to increase
as s approaches tBi–Te, like the welded composites. The
enhancement in a is attributed to the contribution from
the barrier thermo-emf generated near the interface.
When the thickness t0 of metal outside two probes set
at s = 6.5 mm was increased from 0.25 mm to 5.75 mm,
the averaged a for M = Cu and Ni was increased by
3.8% in the p-type composite, while reversely it was
decreased by 4.8% in the n-type one. It was first
observed that t0 also has a significant influence on
the resultant a. The maximum a of the p- and n-type
Ni/Bi–Te/Ni composites then reached great values of
264 lV/K at tM = 6 mm (corresponding to t0 = 5.75 mm)
and –280 lV/K at tM = 1.2 mm (corresponding to
t0 =0.95 mm), respectively, which are 29% and 23%
larger in absolute value than their intrinsic a values.
These maximum a were barely changed with time. It
was thus found that the barrier thermo-emf is generated
steadily even in touching composites and the
resultant a is highly sensitive to the position of leads
connected to the metal electrode of a thermoelement.
