Near-equilibrium polymorphic phase transformations in praseodymium under dynamic compression

Abstract

The authors report the first experimental observation of sequential, multiple polymorphic phase transformations occurring in praseodymium dynamically compressed using a ramp wave. The experiments also display the signatures of reverse transformations occurring upon pressure release and reveal the presence of small hysteresis loops. The results are in very good agreement with equilibrium hydrodynamic calculations performed using a thermodynamically consistent, multiphase equation of state for praseodymium, suggesting a near-equilibrium transformation behavior.

Dynamic compression of Ce and Pr with millisecond time-resolved X-ray diffraction

“…These new dDAC results span nearly 4 orders of magnitude in compression rate, bridging the gap between traditional “static” DAC experiments (time scales of minutes to hours) and dynamic shock and ramp compression experiments (µs–ns time scales). These results are consistent with the shock compression studies of Pavlovskii et al 34 who report that the VC transition in Ce occurs at 0.76 GPa, and also with ramp compression experiments on Pr by Bastea and Reisman 35 , who report a 5–10% over-compression at both the PrI-PrII(III) and the PrII(III)-PrIV phase transformations. As discussed above, this observation is not likely related to significant heating of the sample under rapid compression in the dDAC.…”

“…Our results are also consistent with the proposed dislocation induced diffusionless growth mechanism proposed by Decremps et al 22 , but they do not allow us to distinguish between the proposed Mott transition or Kondo screening models. In contrast, the onset transition pressure of the Pr-III to Pr-IV VC transition increases as the compression rate increases , in agreement with results from the ramp compression study of Bastea and Reisman 35 . Similar behavior was observed in Bi, where the Bi-III to Bi-V transition is observed at higher pressures at faster compression rates 16 .…”

“…Conversely, the bulk modulus of Pr behaves “normally”, under compression by increasing and a discontinuous increase in the bulk modulus is observed across the VC transition 25 . While both Ce and Pr have been extensively studied under static compression conditions 20 – 22 , 25 – 32 , far fewer dynamic compression studies have been reported 33 – 35 , and to-date there have been no studies at compression rates that are in-between static and dynamic shock or ramp compression regimes.…”

High pressure phase transformation in iron under fast compression

“…Well known concepts of phase nucleation and growth are being revisited and refined [1][2][3] due to their importance in geophysics, metallurgy, materials science [4][5][6][7] and many other fields, while new experimental techniques, particularly at high pressures, continue to open new vistas of research and exploration [8][9][10][11][12][13][14]. The study of phase transition kinetics under high pressures has a long history, with the earliest reported measurements being performed under static conditions by Bridgman [15].…”

Use of the Z Accelerator for Condensed Matter Studies at Multi-Mbar Pressures

“…resolidification in tin [27,31]; optical properties of sapphire [28]; and determination of strength properties during isentropic loading [15]. The magnetically driven flyer plate technique has been used to study the high-…”