Multiple experimental studies have been performed to investigate structural stability of Group IVB metals titanium (Ti), zirconium (Zr), and hafnium (Hf), at high pressure conditions.  As a result, it has been well established that Ti, Zr, and Hf undergo a structural phase transformation from ambient pressure hexagonal close packed (α) phase to an intermediate hexagonal (ω) phase with three atoms per unit cell [1], as they move toward the expected bcc (β) phase at high pressure.  Subsequent experiments have also shown that the onset pressure of α-ω transformation is significantly influenced by sample impurities, both substitutional and interstitial.  Likewise, corresponding computational work has shown that the presence of interstitial and substitutional impurities changes the energy barrier of α-ω transformation [2].

With ongoing advances in experimental techniques, especially developments associated with large scale multi-user x-ray sources, we are able to perform measurements that continue to shed light on various aspects of the high pressure α-ω transformation.  For example, in the work that will be presented here, during our recent experiments we were able to utilize DAC coupled with piezoelectric and/or gas membrane loading system to perform in situ time resolved x-ray diffraction (t-XRD) measurements of α-ω transformation in Zr.  From t-XRD spectra we are able to extract α-ω phase ratio directly and show the influence of compression rate (i.e. pressure-jump across α-ω) on the transformation-kinetics.  Likewise, we have ongoing developmental work investigating Zr at high pressure using DAC white-beam Laue diffraction measurement at the synchrotron x-ray High Pressure Collaborative Access Team (HPCAT) facility at the Advanced Photon Source, that could be used to provide additional insight into the transformation mechanisms, as well as the effect of varying compression rate on these mechanisms.

1. J. C. Jamieson,  Science 140, 2 (1963).

2. R. G. Hennig, D. R. Trinkle, J. Bouchet, S. G. Srinivasan, R. C. Albers, and J. W. Wilkins, Nature Materials 4, 129 (2005).