Thermoelectric properties of Bi2Sr2Co2O9 whiskers under hydrostatic pressure
We report the temperature dependence of thermopower (S) in the ab plane of Bi2Sr2Co2O9 (BC-222) single crystalline whiskers under high pressure up to 1.2 GPa. Special modifications were made to our high-pressure transport measurement system to improve the measurement accuracy of S for whiskers with high resistance. Pressure improved the contact resistance dramatically. We observed a slight decrease of S and four-wire electrical conductivity (σ) under high pressure. As a result, the power factor (S2σ) was decreased less than 20% by pressure. From the temperature dependence of σ, the band gap of BC-222 whiskers increase very slightly under high pressure.
The photopyroelectric method in a non contact detection configuration is proposed to study water migration in starch sheets. This allows the exchange of humidity between the moist atmosphere and the starch sample during the experiment. The sensitivity for the total water content measurement was about 0.3%. A theoretical model was developed, taking into account a continuous depth profile of humidity in the starch sample. A water profile in the material and its evolution in time were evidenced when exposing one side of the sample to a humid atmosphere.