Spatially resolved heat conduction in polar perhydrotriphenylene inclusion compounds studied by means of thermal waves

Abstract

Scanning pyroelectric microscopy was applied to study the local thermal diffusivity in polar perhydrotriphenylene ͑PHTP͒ inclusion compounds. A thermal wave technique with special heat flow and pyroelectric detection principles was used to measure the longitudinal (K ʈ) and transversal (K Ќ) thermal diffusivity of needle shaped crystals. As expected, we have found a higher thermal conductivity along the channel direction: K ʈ ϾK Ќ. K ʈ also showed a variation along the needle axis, the K ʈ values near the capping faces being higher than in the center region. Based on these observations we suggest a relation between the longitudinal thermal conductivity and the local density of orientational defects of the dipolar guest molecules which reaches a maximum in the area around the seed. These findings are in agreement with previous pyroelectric studies, revealing a macrodomain structure and a spatially dependent pyroelectric activity for two different PHTP inclusion compounds.

Scanning pyroelectric microscopy revealing the spatial polarity distribution in topologically centric crystals of trans-4-chloro-4′-nitrostilbene

“…The setup for the SPEM analysis used here has been described earlier. 15 For thermal excitation, an intensity modulated laser diode (LISA, HL25/M2, 635 nm, 5 mW) showed an incident laser beam diameter of B5 mm. The pyroelectric signal generated in the capacitor (Fig.…”

“…Further details on the electrostatic description of needle-shaped pyroelectrics can be found in ref. 15 and 17. Note that because of small tilt of the sample, the projected inner angles are not necessarily the same as provided in ref.…”

Vapour growth, morphology, absolute structure and pyroelectric coefficient ofmeta-nitroaniline single crystals

“…The first examples demonstrating reversal were acceptordonor-disubstituted biphenyls (Burgener et al, 2013(Burgener et al, , 2016Hulliger et al, 2014Hulliger et al, , 2017. The discovery of the reversal transition was possible because of an analysis taking into account (i) morphology, (ii) anomalous X-ray scattering, and (iii) scanning pyroelectric microscopy (SPEM) (Wü bbenhorst et al, 2000) and/or (iv) phase-sensitive second harmonic microscopy (Rechsteiner et al, 2000) and/or (v) scanning piezoelectric force microscopy (Batagiannis et al, 2010).…”