Dehydration products of gypsum: positron annihilation and dielectric measurements

✍ Scribed by T. Troev; M. Petkov; C. Alemany; J. Serna

• Publisher: Springer
• Year: 1994
• Tongue: English
• Weight: 475 KB
• Volume: 29
• Category: Article
• ISSN: 0022-2461
• DOI: 10.1007/bf00351403

✦ Synopsis

Bassanite (CaS04 "1 H20) and anhydrite (GAS04) are the low-temperature products of gypsum (CaS04-2H20) 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~-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.