| Electron Spin-Lattice Relaxation in Polymers and Crystals Related to Disorder and Structure Defects |
| S.K. Hoffmann, W. Hilczer, T. Radczyk Institute of Molecular Physics, Polish Academy of Sciences, M. Smoluchowskiego 17, 60-179 Poznań, Poland and I. Polus A. Cieszkowski Agriculture University, Faculty of Wood Technology Department of Chemistry, Wojska Polskiego 75, 60-625 Poznań, Poland |
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| Received: August 16, 2002; revised version November 21, 2002; in final form December 18, 2002 |
| Temperature dependences (4--300 K) of the electron spin-lattice relaxation have been determined by electron spin echo technique for free radicals in two polymeric systems: phenol-formaldehyde resin and polyhydrazodisulphide. The dependences are described in terms of dynamics specific for amorphous systems involving two-level tunnelling states at low temperatures, exchange-coupled clusters of paramagnetic centres and local oscillators. Some universal temperature behaviour of the spin-lattice relaxation of amorphous systems is suggested, with a strong increase in relaxation rate with temperature at low temperatures and much weaker increase above 50 K with characteristic linear temperature dependence in a broad temperature range and cosech(Δ/kT)-type behaviour. It is also shown that the amorphous-type behaviour appears in low temperatures relaxation studies of single crystals but it is due to a non-uniform distribution of doped paramagnetic ions. Such behaviour we have found in Tutton salt crystals doped with Cu 2+ , as well as for free radical centres produced by ionising irradiation in (NH 4 ) 3 H(SeO 4 ) 2 and Li(N 2 H 5 )SO 4 single crystals, where extended phonons are suppressed around radiation damage centres suggesting a local amorphisation of the crystal structure. |
| DOI: 10.12693/APhysPolA.103.373 PACS numbers: 61.41.+e, 61.80.--x, 76.30.--v |