The structural behaviour of the nepheline family: (1) Sr and Ba

ABSTRACT. The structural relations of solid solutions in the series (Srl _~,Bax)Al204 were studied using room- and high-temperature X-ray methods, infra-red spectroscopy, and DTA. At room temperature, SrA1204 and solid solutions with x up to 0.31 are monoclinic, between x = 0.31 and 0.43 monoclinic and hexagonal forms coexist, and between x = 0.43 and 1.0 only hexagonal forms occur. On heating, a member of the monoclinic series of solid solutions transforms to hexagonal sym-metry over a range of temperature within which both monoclinic and hexagonal forms coexist. The proportion of the hexagonal form increases instantaneously as the temperature is raised. The transformation temperature decreases with increasing BaA1204 in solid solution and, in addition, the temperature width of the region o