LOWER VALENCE FLUORIDES OF VANADIUM .3. STRUCTURES OF THE PSEUDO-HEXAGONAL KXVF3,RBXVF3,TIXVF3,CSXVF3 PHASES

Hexagonal tungsten bronze like Ax.VF3 compounds (A = K, Rb, Tl, or Cs) were prepared and their structures studied by using polarized microscopy and X-ray diffraction techniques. Superlattice reflections were observed on Debye-Scherrer films which made the a dimensions of Ax,VF3 twice those of AxWO3. Relative intensities of these reflections suggest ordering of A+ ions in partially filled sites. Weissenberg and Guinier-Hagg photographs revealed that KXVF3, RbxVF3, and T1xVF3are distorted slightly from hexagonal and are orthorhombic. The distortion ratio [formula-omited] demonstrates the magnitude and direction of the distortion, and for lower values of x, it is approximately 1.005. For samples of composition Rb0.32 VF3and T1030 VF3 (x is near its maximum theoretical value ⅓), the direction of the distortion is reversed, and the distortion ratios found were 0.996 and 0.991, respectively. Typical lattice constants: for K0.25 VF3 a = 12.895, b = 7.398, and c = 7.533 ∘ for Rb0.25 VF3 a = 12.904, b = 7.411, and c 7.550 ∘ for T10.30VF3 a = 12.928, b = 7.427, and c = 7.563 ∘ for Rb0.32 VF3 a = 12.874, b = 7.464, and c = 7.567 ∘; for Rb0.32 VF3 a = 12.841, b = 7.479, and c = 7.572 A. These orthorhombic compounds form domains which are oriented 120μ with respect to each other giving a macroscopic effect of hexagonal symmetry. X-ray photographs of CsxVF3 compounds display weak superlattice reflections; however, no distortion from hexagonal symmetry was observed. The lattice constants of this phase increase slightly with x. © 1979, American Chemical Society. All rights reserved.