Crystal-chemical characterization of KAlSi3O8 with the hollandite structure.

Abstract

The synthesis of a high-P phase of KAlSi3O8 with the hollandite structure was carried out at P >14 GPa. The unit cell parameters are a 9.3244(4), c 2.7227(3) A; space group I4/m; D(calc.) 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 build up a dense array which forms square 'tunnels'. Potassium atoms are situated in the tunnels and are in the eightfold coordination. A comparison with calcium ferrite structure is made.-T.Y.