Serna Galán, JulioTroev, T.Petkov, M.Alemany, C.2023-06-202023-06-201994-02-150022-246110.1007/BF00351403https://hdl.handle.net/20.500.14352/58603Bassanite (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.journal articlehttp://dx.doi.org/10.1007/BF00351403http://link.springer.com/metadata only access535Materials ScienceMultidisciplinaryÓptica (Física)2209.19 Óptica Física