Crystal-chemical characterization of KAlSi3O8 with the hollandite structure.

Abstract

The synthesis of a high pressure phase of KAlSi3O8 with the hollandite structure was carried out at pressures higher than 14 GPa. The unit cell parameters are: a=9.3244(4) A, c=2.7227(3) A and V=236.73(3) A3 with the space group I4⁄m. Calculated density is 3.905(1) g/cm3.The refinement of crystal structure was performed by the ordinary powder X-ray method. Double chains of edge shared MO6 octahedra run parallel to the c-axis. They share corners to built up dense array which forms square “tunnels”. Potassium atoms are situated in the tunnels and are in the eightfold coordination.The comparison with the calcium ferrite structure was made.