Determination of the pyroelectric coefficient within pyroelectric materials by using space charge measurements

摘要

In this paper, a new theory allowed calculating the pyroelectric coefficient “p” using the diffusion of a thermal wave within materials having a pyroelectric effect. The demonstration is performed on materials composed by various percentages of a cycloaliphatic epoxy (CE) resin and of a flexibilizing comonomer (1,6-hexanediol diglycidyl ether — HDGE). By using an electric field measurement technique (the Thermal Step Method — TSM), the signal obtained on these materials (a current) presents an atypical form, which requires the modification of the theoretical model of the TSM. Indeed, the theory of the TSM technique has been initially developed for insulating materials with a high dielectric time constant. An adaptation of the technique is thus necessary to analyze the behavior of materials, which present a modification of their molecular structure during the application of the thermal wave. During a space charge characterization performed on these materials, we have observed an atypical shape for the thermal step currents. To help in the interpretation, the broadband dielectric spectroscopy and the Differential Scanning Calorimetry technique (DSC) were used to obtain additional information. Considering these results, a circuit containing a resistor and a capacitor in series has been used for modeling the materials. This equivalent circuit constitutes the beginning of the new theory, which is developed in this paper. The pyroelectric coefficient generated by the thermal step diffusion, due to the presence of a pyroelectric effect of these studied materials, has been calculated using the detailed model.