Pyroelectric diacetylenes

Whereas several pyroelectric diacetylenes were identified, uniform ferroelectric phases seem to be rather the exception, according to our experience with many new substitutions of diacetylenes [92]. The ferroelectric low-temperature phase of the symmetrically disubstituted diacetylene DNP, i.e. l,6-bis(2,4-dinitrophenoxy)-2,4-hexadiyne (Tab. 9.2), turned out to be one of the rare and interesting exceptions [93-98]. 

IPUDO (for the molecular structure see Tab. 9.2) is an example of a symmetrically substituted diacetylene. For the monomer as well as polymer crystals, non-centrosymmetrical orthorhombic crystal structures can be found already at room temperature [84]. The c-axis is the polar axis of the monomer crystal. IPUDO can only be polymerized by y radiation ( °Co). For 85% polymerized crystals pyroelectric properties were observed only in b direction. The permittivity of IPUDO is highly anisotropic, with maximum values of 8.5 for the... 

Sample defects can be another origin of piezo and pyroelectric phenomena in substituted diacetylenes, which generally can be identified via sample dependence and smaller size of these effects [88]. Bloor et al. discussed such spurious pyroelectric effects, which seemed to be correlated with the occurrence of macroscopic deformations, such as screw dislocations in TS single crystals [90]. Similarly the analysis of weak polarization, caused by molecular distortion during solid state polymerization of TS, was reported by Bertault et al. [91]. We have observed comparable weak pyroelectric phenomena for TS/FBS [87]. 

P. Gruner-Bauer, P. Strohriegl, E. Dormann Dielectric and pyroelectric properties of substituted diacetylenes, in Electrical, Optical and Acoustic Properties of Polymers, (The Plastics and Rubber Institute, Conference Publication, Canterbury, UK), 11/1 (1988)... 

H. Winter, E. Dormann The pyroelectric phase transition of DNP", a disubstituted diacetylene single crystal, in A. Blumen et al. (eds.) Dynamical processes in condensed molecular systems, World Scientific Publishing Co., 214 (1990)... 

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