Ferroelastic domain walls in the incommensurate phase of γ-KCoP04

Ferroelastic domains in γ-KCoP04 were studied by polarized light microscopy and by X-ray methods. These domains appear upon cooling as a result of a phase transition at about 449°C from an orthorhombic normal (N) phase (with probable space group Pnma) to a incommensurate phase (IC) which is monoclinic and has a average structure isotypic with CsLiS04 with space group P21/c. The modulation of the monoclinic structure decreases and the cell parameters change when the crystals are ground to a grain size of less than 7 μm and heated and cooled several times through the phase transition. A Rietveld refinement of the structure of γ-KCoP04 was achieved on a powder pattern. The cell parameters are: a = 5.3052(3), b = 8.5571(4), c = 10.3926(6), β = 120.833(2)° in [A] and Z = 4.