X-ray scattering study of temperature dependence of a structural incommensurability of theωphase in Ti-V alloys

Abstract

The incommensurate $\ensuremath{\omega}$ phase in titanium alloys has been revisited. A mechanism of the formation relevant to electron-lattice coupling has been re-investigated in terms of an x-ray-scattering technique on three kinds of single crystals, each containing 20, 24, and 27 mass % of vanadium respectively. The superlattice reflections of all systems observed for reduced wave vector $\mathbit{q}=(2∕3+\ensuremath{\Delta},2∕3+\ensuremath{\Delta},2∕3+\ensuremath{\Delta})$ at temperature $\ensuremath{\cong}30\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ reveal the following three effects for their intensity distribution with increasing temperature, where $\ensuremath{\Delta}$ has a nonzero value giving the incommensurability: (1) decrease of the intensities, (2) increase of the distribution widths, and (3) reduction of the $\ensuremath{\Delta}$ values. The results suggest unstabilization of the lock-in state. A temperature region which indicates a notion of the transition is lowered with increasing concentration, implying excess of the valence electrons which prohibits lock-in nesting of the charge density wave. This idea was supported by molecular-orbital population analysis using cluster models of the two phases.