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Title: Reinvestigation of high pressure polymorphism in hafnium metal

There has been a recent controversy about the high pressure polymorphism of Hafnium (Hf). Unlike, the earlier known α→ω structural transition at 38 ± 8 GPa, at ambient temperature, Hrubiak et al. [J. Appl. Phys. 111, 112612 (2012)] did not observe it till 51 GPa. They observed this transition only at elevated temperatures. We have reinvestigated the room temperature phase diagram of Hf, employing x-ray diffraction (XRD) and DFT based first principles calculations. Experimental investigations have been carried out on several pure and impure Hf samples and also with different pressure transmitting media. Besides demonstrating the significant role of impurity levels on the high pressure phase diagram of Hf, our studies re-establish room temperature α→ω transition at high pressures, even in quasi-hydrostatic environment. We observed this transition in pure Hf with equilibrium transition pressure P{sub o} = 44.5 GPa; however, with large hysteresis. The structural sequence, transition pressures, the lattice parameters, the c/a ratio and its variation with compression for the α and ω phases as predicted by our ab-initio scalar relativistic (SR) calculations are found to be in good agreement with our experimental results of pure Hf.
Authors:
;  [1] ; ;  [2] ;  [3] ;  [4]
  1. High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Mumbai-400 085 (India)
  2. Materials Science Division, Bhabha Atomic Research Centre, Mumbai-400 085 (India)
  3. Geophysical Laboratory, Carnegie Institution of Washington, Washington, D.C. 20015 (United States)
  4. Indian National Science Academy, New Delhi-110 002 (India)
Publication Date:
OSTI Identifier:
22303993
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 115; Journal Issue: 23; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; AMBIENT TEMPERATURE; COMPRESSION; COMPUTERIZED SIMULATION; DENSITY FUNCTIONAL METHOD; EQUILIBRIUM; HAFNIUM; HYSTERESIS; LATTICE PARAMETERS; PHASE DIAGRAMS; PRESSURE RANGE GIGA PA; RELATIVISTIC RANGE; TEMPERATURE RANGE 0273-0400 K; X-RAY DIFFRACTION