Dehydration products of gypsum - positron-annihilation and dielectric measurements



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Serna Galán, Julio and Troev, T. and Petkov, M. and Alemany, C. (1994) Dehydration products of gypsum - positron-annihilation and dielectric measurements. Journal of Materials Science, 29 (4). pp. 865-869. ISSN 0022-2461

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Bassanite (CaSO_4•½ H_2O) and anhydrite (CaSO_4) are the low-temperature products of gypsum (CaSO_4·2H_2O) dehydration, which are obtained at about 373 and 433 K, respectively. These sulphates have non-centrosymmetric crystallographic point groups, but dielectric measurements do not reveal any piezo- or ferroelectric characteristic, and they practically behave like linear dielectrics. Positron lifetime spectra exhibit the existence of two different positron states, besides a free positron state. There is positronium formation in the three sulphates, and there is also evidence for the presence of a highly populated positron bound state which may be a complex state associated with positrons bound to SO_4^2- ions. Parameter S estimated from the Doppler curve and the average positron lifetime show unquestionably the sensitivity of positrons to the phase transitions gypsum-bassanite and bassanite-anhydrite.

Item Type:Article
Uncontrolled Keywords:Materials Science, Multidisciplinary
Subjects:Sciences > Physics > Optics
ID Code:22086
Deposited On:29 Jun 2013 16:37
Last Modified:29 Jun 2013 16:37

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