KCr3(SO4)2(OH)6: Synthesis, characterization, powder diffraction data, and structure refinement by the Rietveld technique and a compilation of alunite-type compounds

Abstract

The new compound, KCr3(SO4)2(OH)6, was prepared by low-hydrothermal synthesis. The structure was refined by the Rietveld technique in space group(Z= 3),a=7.2416(3) Å,c= 17.0788(9) Å,V= 775.63 Å3,Rp= 7.7,Rwp=10.1,RB= 6.8. The compound is isotypic with alunite, KAl3(SO4)2(OH)6. The temperature of decomposition under nitrogen atmosphere to a hitherto unknown form is about 550 K. The water content of alunite-type compounds is discussed.