High-resolution simultaneous photothermal measurements of thermal parameters at a phase transition with the photopyroelectric technique

Abstract

Photothermal techniques allow, under particular experimental conditions, the simultaneous determination of specific heat, thermal conductivity, and thermal diffusivity. A comparison has been made between measurements performed with the gas-microphone (P) configuration and the photopyroelectric (PPE) one at a liquid-crystal second-order phase transition. An increase in the sensitivity with respect to thermal parameter variation has been observed in the case of PPE.

Critical behavior of the paramagnetic to antiferromagnetic transition in orthorhombic and hexagonal phases ofRMnO3(R=SmOleaga1, Salazar2, Prabhakaran3 et al. 2012Phys. Rev. B576490View full textAdd to dashboardCite

“…In particular, using the standard back-detection configuration, 22,23 simultaneous measurements of thermal diffusivity D and specific heat c p can be carried out. As performed in the laboratory in Spain for the case of solid materials, in this configuration an acoustooptically modulated He-Ne laser beam of 5 mW illuminates the front surface of the sample under study.…”

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“…If the test sample is highly opaque, in which the optical absorption length is much smaller than sample thickness, this approach is further simplified by considering only heat source generated on the sample surface 12 . Thus, the resulting thermal wave is independent of the optical properties of the sample.…”

Characterization of Ferroelectric Materials by Photopyroelectric Method

“…This is an advantage compared with adiabatic types of calorimetry, for example. If we compare PPE with differential scanning calorimetry (DSC), PPE is more accurate in detecting the critical temperature (Curie point for ferroelectrics), due to the possibility of scanning very slow (few mK/min -see for example Marinelli et al, 1992) the temperature of the detection cell. In the case of DSC, it is known that the sensitivity increases with increasing temperature variation rate (decreasing the accuracy in measuring the critical temperature).…”

“…Marinelli et al, 1992 tried to compare the performances of the PPE technique in detecting phase transitions, with another photothermal technique largely used for phase transitions investigations: the photoacoustic (PA) method. If we follow only the phase channels, they are given in the standard configuration, with optically opaque and thermally thick sample by the equations (Zammit et al, 1988;Marinelli et al, 1992 An analysis of Eqs. (5.3.a,b) leads to the conclusion that the maximum sensitivity of the PA technique is reached when p=0 and has the value ½.…”

“…Consequently, it is expected that the PPE technique is suitable to detect both first and second order phase transitions, by measuring the critical anomalies of the thermal parameters. In time, the PPE technique was applied to detect first or second (Marinelli et al,1992) order phase transitions. For second order phase transitions the PPE results were used to calculate the critical exponents of the thermal parameters and to validate the existing theories (Marinelli et al, 1992, Chirtoc and).…”