Polymorphic forms of bismuth phosphate

Abstract

Bismuth phosphate has long been known to crystallize with the monazite-type structure. It is now possible to report the existence of two other modifications, and to describe their crystal structure. One type is hexagonal, and has the CePO 4 · ½ H 2 O structure. The other is a monoclinic high-temperature form which very slowly converts to the monazite-type structure at ordinary temperatures. The structure of the hexagonal crystal has been determined from Weissenberg single-crystal data, and that of the high-temperature form from powder-diffraction data. The three structures preserve certain features in common, and intercomparison seems to indicate that the transformation from one to the other must be predominantly displacive rather than disruptive in character.