Two structures of Ag[sub 2[minus]x]V[sub 4]O[sub 11], determined by high resolution electron microscopy

High resolution microscopy and X-ray powder diffraction have been applied to determine the structure and microstructure of Ag[sub 2[minus]x]V[sub 4]O[sub 11]. This compound adopts two structures. Both structures consist of V[sub 4]O[sub 11] slabs, but they differ in the way these slabs are stacked. One stacking leads to a C-centered monoclinic unit cell (C2/m) with dimensions a = 1.451(1), b = 0.35766(3), c = 0.9564(8) nm, [beta] = 128.74(1)[degrees] (Phase I) which is dominant and the other stacking to a C-centered monoclinic unit cell with dimensions a = 1.53, b = 0.360, c = 0.76 nm, [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. Frequent stacking defects occur in the C[sup *] direction due to switching from the Phase I to the Phase II structure and due to (001) twinning.