DIFFERENT ASPECTS OF THE CRYSTAL-STRUCTUR E OF YBV4O8 - III - DOMAIN-STRUCTURE FROM PARALLEL COALESCENCE OF ALPHA-PHASE AND BETA-PHASE AND GROUP-THEORETIC EXAMINATION OF THEIR SYMMETRY

The crystal structure of a multiple domain crystal of composition YbV4 O8 has been determined and refined as a commensurate composite crystal with two subsystems. Subsystem 1 is formed by the V2O4 atoms, subsyst em 2 contains the Yb atoms. All reflections in the diffraction pattern can be indexed using a lattice with a = 9.057(1)Angstrom, b = 21.238( 5)Angstrom and c = 5.7560(9)Angstrom yet three different types of doma ins have to be taken into account to explain the diffraction pattern. Domains I and II correspond to two twin domains of beta-YbV4O8 with sy mmetry A2(1)/d11 (=P2(1)/n11) while domain III with symmetry P12(1)/n1 has the structure of alpha-YbV4O8. Refinement was carried out in high er dimensional space using the reflections of all domains simultaneous ly and converged at a final R(F) value of 0.050 (R-w(F)= 0.038). The r esults are discussed.