INCOMMENSURATE PHASES IN THE SOLID-SOLUTIONS (NH4)2(BEF4)0.08(SO4)1-0.08 AND (NH4)2(BEF4)0.18(SO4)1-0.18

An X-ray study of the phase transitions in the solid solutions (HH4)2(Bef4)x(SO4)1-xis presented for the compounds with x=0.08 and x=0.18 in the case of x=0.18, the ininvenstigated sample presents a complex transition sequence. at a guven temperature 3 phases are simulteneously observed: 2 incommensurate phases and a commensurate phases are 7 K and 14 K, respeotively. An analogous sequence is observed in the case of a sample oorresponding to the composition x=0. 08, but now the temperature ranges of the two incommensurate phases are smaller. In another sample of the same composition x=0. 08, but now the temperature ranges of the two incommensurate phases are 7K and 14 K, respeotively. An analogous sequence is observed in the case of a sample corresponding to the composition x=0.008, but now the temprature ranges of the two incommensurate phases are smaller. In another sample of the same composition x=0.08 and grown in the same condition, only one incommensurate phase is found. In this case a time evolution of the diffraction profile corresponding to the incommensurate surstrousture is observed. © 1990, Taylor & Francis Group, LLC. All rights reserved.