Topotaxy relationships in the transformation phosgenite-cerussite

Abstract

The crystallization of phosgenite (Pb2ClzCO 3) and cerussite (PbCO 3) has been carried out by counter diffusion in a silica hydrogel at 25°C. The crystallization of both phases is strongly controlled by the pH of the medium. Under certain conditions the physicochemical evolution of the system determines that phosgenite crystals become unstable and transform into cerussite. The transformation is structurally controlled and provides an interesting example of topotaxy. The orientational relationships are (110)ph║[001]cer, (110)ph [100]cer, and (001)ph ║(010)cer. In this paper, a study of the topotactic transformation and the crystal morphology is worked out. The topotactic relationships are interpreted on the ground of geometrical and structural considerations.