Thermal characterization of II–VI binary crystals by photopyroelectric calorimetry and infrared lock-in thermography

In this paper, a complete thermal characterization (measurement of all static and dynamic thermal parameters) of some selected II-VI binary crystals was carried out. The semiconductors under investigation were grown from the melt by high-pressure/high-temperature modified Bridgman method. The contact photopyroelectric (PPE) method in back configuration (BPPE) and non-contact infrared lock-in thermography technique were used in order to get the thermal diffusivity of the investigated crystals. The thermal effusivity of the samples was obtained by using the PPE technique in the front configuration (FPPE), together with the thermal wave resonator cavity (TWRC) method. Knowing the values of the thermal effusivity and thermal diffusivity, the remaining two thermal parameters, i.e., thermal conductivity and specific heat were calculated

Thermal characterization of ZnBeMnSe mixed compounds by means of photopyroelectric and lock-in thermography methods

In this work a thermal characterization (measurement of dynamic thermal parameters) of quaternary Zn1-x-yBexMnySe mixed crystals was carried out. The crystals under investigation were grown from the melt by the modified high pressure Bridgman method with different Be and Mn content. The effect of Be and Mn content on thermal properties of Zn1-x-yBexMnySe compounds was analyzed, by using the photopyroelectric (PPE) method in the back configuration (BPPE) for thermal diffusivity measurements, and the PPE technique in the front configuration (FPPE) for thermal effusivity investigations. Infrared lock-in thermography (IRT) was used in order to validate the BPPE results. The measured thermal effusivity and diffusivity allowed the calculation of thermal conductivity of the investigated materials

On the optimization of experimental parameters in photopyroelectric investigation of thermal diffusivity of solids

In this paper, the possibility of optimizing the experimental conditions for a correct photopyroelectric evaluation of the thermal diffusivity of solid samples is studied. For this purpose, a glassy carbon sample, with known thermal properties, was selected as test material and two types of techniques were applied in order to get the value of its thermal diffusivity: (i) the photopyroelectric calorimetry in back detection configuration and (ii) the infrared thermography. Assuming that the values of thermal diffusivity obtained by thermography are correct (a non-contact technique), we studied how to eliminate the underestimation (due to the presence of the coupling fluid) of the results in the back photopyroelectric calorimetry investigations. Experiments with different types of coupling fluids and numerical simulations were performed in order to evaluate the influence of the coupling fluid on the value of the thermal diffusivity. The conclusion is that a proper choice of the type of coupling fluid and some improvements performed in the experimental design of the photopyroelectric calorimetry detection cell (with the purpose of reducing the coupling fluid’s thickness), can eliminate the difference between the results obtained with the two photothermal (contact and non-contact) techniques

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

Improved Photopyroelectric (PPE) Configuration for Thermal Effusivity Investigations of Porous Solids

A new photopyroelectric detection configuration is proposed in order to measure the thermal effusivity of porous solids. Compared with the previously reported detection scheme this configuration makes use of a transparent window in front of the pyroelectric sensor. In such a way, the heat losses by convection at the sensor’s irradiated surface are eliminated, and consequently, the conduction remains the only process responsible for the heat propagation in the whole detection cell. In the paper, the mathematical model for this new configuration is developed, with the main conclusion that the sample’s thermal effusivity can be finally obtained via a fitting procedure with only two fitting parameters (instead of three as previously reported); in such a way, the possible degeneracy of the results is eliminated. The suitability of the method is demonstrated with application on some porous building materials and cellulose-based pressed powders