Simultaneous determination of thermal conductivity and heat capacity near solid state phase transitions by a photopyroelectric technique

An improved technique employing the photopyroelectric effect to measure thermal conductivity and heat capacity simultaneously near solid state phase transitions is reported. A calibration procedure adaptable to the use of a pyroelectric detector on a thermally thick backing medium is described in detail. A quantitative comparison of the predictions of the theory with experimental results on selected known samples is used to test the applicability of the method as a practical technique. The variations of the thermal diffusivity (α_s), thermal effusivity (e_s), thermal conductivity (K_s) and heat capacity (c_ps) near the para-ferroelectric phase transition in single-crystalline triglycine sulphate at 49.4 °C cut along various axes are reported and compared with available experimental data. The method can be adapted to the measurement of these parameters during any kind of phase transition in solids, the only limitation being the temperature range over which the sensitivity of the pyroelectric detector remains sufficiently high.