Sample

Two sets of hot pressed Bi₂Te₃, p- and n-type. Diameter 12 mm, thickness ca 3.5 mm.

Approach

Basic testing at room temperature. Kapton sensor 7577 selected to match sample size. 2 mm sensor radius allows 4 mm radial and 3.5 mm axial probing depth, thus the thickness limits the available probing depth. Sample surfaces lightly sanded to ensure smooth interfaces and good thermal contact. Sensor centred and firmly clamped between the sample halves.

Testing

One initial test with measurement time 4 s and heating power 50 mW performed for each sample set. Said heating power confirmed to yield a suitable final temperature increase, close to 3 K, for both p- and n-type samples. Measurement time shortened to 3 s for the n-type sample, to keep probing depth within sample boundaries.

Sharp tests carried out in accordance with the following table, 15 minutes between repeated tests:

 

Sample Measurement
Time
Heating
Power
Sensor Number of
Measurements
P-type 4 s 50 mW 7577 6
N-type 3 s 50 mW 7577 6

Results

Final results acquired after calculation (points 40-180), as presented in table below:

Sample Thermal conductivity [W/m/K] Standard deviation [W/m/K] Thermal diffusivity [mm²/s] Standard deviation [mm²/s] Volumetric SPecific Heat [MJ/m³K] Standard deviation [MJ/m³K]
P-type 0.833 0.0009 0.732 0.0046 1.137 0.0077
N-type 0.952 0.0022 0.982 0.0143 0.969 0.0146

 

The n-type Bi₂Te₃ shows a significantly higher thermal conductivity, compared to the p-type sample. The volumetric specific heat is just below theoretical (1.187 MJ/m³K) for the p-type sample, while more reduced for the n-type specimen. This is likely explained by lower density or larger anisotropy in the n-type sample.