An X-ray crystallographic study of V₂D

Abstract

Both superlattice and fundamental reflections have been used in an X‐ray determination of the vanadium‐atom displacements induced by selected ordering of interstitial deuterium in a multi‐domain crystal of V2D. The magnitudes of these displacements along X and Z directions of the pseudo‐tetragonal (b.c.t.) unit cell are designated DAX and DAZ respectively, where Z is along the tetragonal c axis. Measurements of the lattice parameters yield DAX≃0.03 and DAZ≃0.17 Å. From intensity measurements, the best values for the displacements are DAX = 0.03±0.01 and DAZ = 0.15±0.02 Å, and the purely thermal Debye–Waller factor was found to be 2B = 0.025 Å2. The temperature dependences of both the long‐range‐order parameter, S, and the lattice parameters of the b.c.t. unit cell were also investigated. Both verify that the phase transition from β (monoclinic) to α (b.c.c.) is first order in character with no intervening ɛ (tetragonal) phase as in V2H. There is additional evidence that the disordering process includes random occupancy of both Z octahedral and random tetrahedral sites.

Hydrogen-induced lattice expansion of vanadium in a Fe/V (001) single-crystal superlattice

“…In bulk vanadium the volume expansion, i.e., three-dimensional lattice expansion, is given by the coefficient k b ͓k b ϭ0. 19(1), Ref. 16͔.…”

Change from a bulk discontinuous phase transition in V2H to a continuous transition in a defective near-surface skin layer

“…The ferromagnetic sites of a metamagnet can thereby be compared to occupied O z1 sites and the antiferromagnetic coupling between the layers to the alternating occupation of O z sites [1]. The occupation of mainly O z1 sites in every other (0 k/2 k/2) plane leads to a periodic distortion of the vanadium (V) host lattice and thus to {0 k/2 k/2} superstructure peaks (pseudo bct notation) [14,16,17]. In this ordering process, ¶ Present address: Max-Planck-Institut für Metallforschung, D-70569 Stuttgart, Germany.…”

Large-angle convergent-beam electron diffraction; a simple technique for the study of modulated structures with application to V2D

“…Therefore, superstructure reflections appear at the 1/2 1/2 0, 3/2 3/2 0 etc. (Westlake, Mueller & Knott, 1973;Jo, Moss & Westlake, 1980). Using the monoclinic unit cell these superstructure reflections are the 100, 300 etc.…”

“…However, instead of a parallel incident beam of white radiation, we use a convergent beam of monochromatic electrons. We demonstrate the technique of large-angle convergent-beam electron diffraction (LACBED) by studying the D-induced static displacement of the V atoms in/3-V2D, a system used by Jo, Moss & Westlake (1980) in earlier X-ray diffraction studies on a multidomain crystal of V twinned because of loading with D.…”