Defect structure of Na0.5-xR0.5+xF2+2x (R = Ho,Yb) solid solutions (fluorite type)

The stnrcture of Na0.395H0.605F2.210 (I) and Na0.446Yb0.554F2.108 (II) crys tals has been studied by the neutron diffraction method. A low occupancy of the main positions of fluorine atoms (F-c) is established. Interstitial fl uorine atoms in crystal (I) occupy two positions, 48i and 32f, with the par ameter w = 0.293 (the so-called relaxed fluorine atoms). In crystal (LI), i nterstitial fluorine atoms occupy four positions, general 48i, 32f (w = 0.3 22), 32f(v = 0.414) positions and the special 4b position (1/2, 1/2, 1/2) i n the center of the large cubic void (the so-called Goldschmidt position). (C) 2000 MAIK "Nauka/Interperiodica".