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allied
academies
November 22-23, 2018 | Paris, France
Journal of Materials Science and Nanotechnology | Volume: 2
Materials Physics and Materials Science
International Conference on
Characterization of commercial Bi
2
Te
3
thermoelectric materials
Karl Heinz Gresslehner
University of Applied Sciences Upper Austria, Austria
I
nthisworkwepresent resultsof experimental investigations
of commercially available n- and p-type Bi
2
Te
3
alloys. The
as delivered samples are slabs with a diameter of D~31mm
and thicknesses of L = 1.5 – 2mm. They were analyzed by
energy dispersive X-ray analysis (EDX) to estimate the
elemental composition, by spectroscopic ellipsometry in
the IR and UV-VIS to estimate the real and imaginary part
of the refractive index and by IR-thermography to estimate
the thermal diffusivity as well as a potential anisotropy. For
SE analysis the samples were mechanically polished. By
mass fractions the empirical formula of the compound is
Bi
2
Te
2
.
7
Se
0.3
. In the case p-type samples the empirical formula
of the compound is Bi
0.4
6Sb
1.54
Te
3
. For IR thermography the
samples were instantaneously heated on the front side
by a pulsed diode laser with a peak wavelength of 808nm
and an operating power between 12W and 33W. The
pulse duration was in the range from 10msec to 100msec.
To estimate the absorbed energy of the incident laser
pulse the temperature rise at the end of the heating phase
on the front side was evaluated for several heating times.
From theoretical point of view the temperature rise is
proportional. Based on this the absorbed energy lies in the
range of 3 to 10% of the incident energy. The temperature
evolution was measured with an IR camera which is a cooled
1280 x 1024pixel FPA with a thermal resolution of typically
18mK and sensitive in the spectral range of 1.5-5μm. A frame
rate of 333.33Hz was chosen and the spatial resolution was
4.33pixel / mm. From thermal imaging on the front side no
anisotropy in the in-plane thermal diffusivity was detected.
To obtain the thermal diffusivity in z-direction temperature
measurements were carried out at the rear side of the
samples (z = L, transmission mode). The measured (red)
and modelled (black) temperature rise above ambient for a
pulse heating of 100msec of a n-type sample. The thermal
diffusivity was evaluated with Parker’s method, which was
modified to consider the finite heat duration. With this, a
thermal diffusivity of 1.01x10
-6
m
2
/s was obtained. This
leads to a thermal conductivity of 1.2W/m.K for a density of
7700kg/m³ and a specific heat capacity of 154 J/kg.K. From
SE measurement the imaginary part of the refractive index
is n’’≈ 4 at = 808nm. From that the absorption coefficient
was estimated at 6.2 x 10
-5
cm
-1
which leads to a penetration
depth of the laser light of 16nm. Therefore, the absorption
of the laser pulse takes place at the front side (z = 0) and can
be modelled as a Dirac Delta function (z).
Speaker Biography
Karl Heinz Gresslehner have completed his PhD in the field of semiconductor physics in
1981 at the Johannes Kepler University in Linz. He was working more than 10 years in the
industry and 24 years as a teacher at a school for higher technical education (HTL). Since
2016 he is a professor at the University of Applied Sciences in Upper Austria and is the head
of the research group Thermoelectricity.
e:
karl.gresslehner@fh-wels.at