Work

Structural Phase Stability in Group Iv Metals Under Static High Pressure

Year: 2009

Type: conference-paper

Abstract: Group IV metals, titanium (Ti), zirconium (Zr), and hafnium (Hf), are all known to undergo a structural phase transition from a ductile alpha (hexagonal closed packed) to a brittle omega (hexagonal structure with three atoms per unit cell) phase at high pressure.Although the alpha to omega structural phase transition is well established there still remains a large discrepancy in the transition pressure reported in the literature.Some of the disparity has been attributed to experimental conditions (Le.hydrostatic vs. non-hydrostatic) and has been shown that shear deformation in non-hydrostatic experiments drives alpha to omega transition and decreases the transition pressure [1].Impurities can also aid or suppress this transition.By performing x-ray diffraction experiments on samples contained in a diamond anvil cell we show that interstitial impurities, such as carbon, nitrogen, and oxygen obstruct alpha to omega structural phase transition and help increase transition pressure.Likewise, reduction in the initial grain size of our sample appears to help reduce some of the shear deformation effects, which helps stabilize alpha phase to higher pressure under nonhydrostatic experimental conditions.Regardless of impurity concentration or sample grain size, we show that careful examination of the whole diffraction pattern, obtained using angle dispersive x-ray diffraction technique and an area detector, is needed to accurately detect the onset of alpha-omega structural phase transition.

Source: AIP conference proceedings

DOI: 10.1063/1.3295022