Thermal Effusivity Investigations of Solid Thermoelectrics Using the Front Photopyroelectric Detection

The front photopyroelectric configuration (FPPE), making use of air as a coupling fluid between the sample and sensor, was applied to measure the thermal effusivity of some solid thermoelectric materials. The investigated samples were ZnO, CuCrO2, Cu4Sn7S16, TiS3 and two samples of high manganese silicide (HMS) thermoelectric materials. Most of these materials are porous and consequently, the classical PPE method, making use of standard coupling fluids between sensor and sample, cannot be used due to the fact that the coupling fluid penetrates inside the sample and leads to incorrect results. With this work we extend (to thermoelectric solids) the area of application of a method, recently proposed by Salazar et al. (Measurement 121: 96, 2018). Experimentally, the thermal effusivity is obtained from a multi-parametric fit of the phase of the FPPE signal as a function of the modulation frequency (with sample’s thermal effusivity, thickness of the sensor-sample air gap and heat losses by convection and radiation, as fitting parameters). It was demonstrated that, in some particular cases, the three parameters are independent and consequently, the solution of the fit is unique. Where possible, the obtained results have been compared with data from the literature and good agreement was found.