Photothermoelectric (PTE) detection of magnetic phase transitions based on liquid thermoelectric (LTE) materials as sensors

The paper proposes a new application of the liquid thermoelectrics (LTE): the detection of phase transitions. Cr2O3 single crystal was selected as a sample, because it is a well-known antiferromagnetic material involved in a phase transition at a Neel temperature around 34°C. In order to detect its antiferro-paramagnetic phase transition, we used as a sensor a liquid thermoelectric material (octanol + 10-2 mol/l tetrabutylammonium nitrate (TBAN)) with a Seebeck coefficient of about 4 mV/K. In the paper, the photothermoelectric (PTE) method, in back detection configuration was applied in order to obtain the critical behaviour of the static volume specific heat and dynamic thermal diffusivity, conductivity and effusivity of Cr2O3. Due to the fact that, usually, the Seebeck coefficient of the LTE materials is larger than that of solid TEs, a comparison with the same type of investigation, based on a solid thermoelectric sensor was performed. In the experimental arrangement proposed in the paper, no clear advantage of using LTE sensor was found; a new design of the PTE cell involving a direct sample/sensor thermal contact is necessary. A second comparison with the results obtained by using the classical photopyroelectric (PPE) method indicates that the PPE method is still more accurate for such type of investigations.