2 STRUCTURES OF AG2-XV4O11, DETERMINED BY HIGH-RESOLUTION ELECTRON-MICROSCOPY

High resolution electron microscopy and X-ray powder diffraction have been applied to determine the structure and microstructure of Ag2-xV4O 11. This compound adopts two structures. Both structures consist of V4 O11 slabs, but they differ in the way these slabs are stacked. One sta cking leads to a C-centered monoclinic unit cell (C2/m) with dimension s a = 1.451(1), b = 0.35766(3), c = 0.9564(8) nm, beta = 128.74(1)-deg rees (Phase I) which is dominant and the other stacking to a C-centere d monoclinic unit cell with dimensions a = 1.53, b = 0.360, c = 0.76 n m, beta = 102-degrees (Phase II). Ion milling leads to a change in the c axis and beta, which is suggested to be caused by a loss of Ag. Fre quent stacking defects occur in the c direction due to switching from the Phase I to the Phase II structure and due to (001) twinning. (C) 1994 Academic Press, Inc.