2022-08-08 アメリカ・ローレンスリバモア国立研究所(LLNL)
この実験では、リニアックコヒーレント光源に設置されたMatter in Extreme Conditionsというユニークな装置を用いて、ピコ秒スケールの圧縮ショック上昇とそれに続く約100 psの持続的圧縮による炭素の相転移挙動を探りました。
チームメンバーは、生成物相が初期相と強く相関している相転移を見ました。彼らは、圧縮後20ピコ秒以内に、高度にテクスチャー化した、ほぼ単結晶の生成物を観察しました。
＜関連情報＞
超高速X線回折による高規則性グラファイト（HOPG）から六方晶ダイヤモンド（ロンズデライト）への相転移のピコ秒時間スケールでの観察 Highly ordered graphite (HOPG) to hexagonal diamond (lonsdaleite) phase transition observed on picosecond time scales using ultrafast x-ray diffraction
Michael R. Armstrong, Harry B. Radousky, Ryan A. Austin, Oliver Tschauner, Shaughnessy Brown, Arianna E. Gleason, Nir Goldman, Eduardo Granados, Paulius Grivickas, Nicholas Holtgrewe, Matthew P. Kroonblawd, Hae Ja Lee, Sergey Lobanov, Bob Nagler, Inhyuk Nam, Vitali Prakapenka, Clemens Prescher, Evan J. Reed, Elissaios Stavrou, Peter Walter, Alexander F. Goncharov, and Jonathan L. Belof
Journal of Applied Physics Published:01 August 2022
DOI:https://doi.org/10.1063/5.0085297
ABSTRACT
The response of rapidly compressed highly oriented pyrolytic graphite (HOPG) normal to its basal plane was investigated at a pressure of ∼80 GPa. Ultrafast x-ray diffraction using ∼100 fs pulses at the Materials Under Extreme Conditions sector of the Linac Coherent Light Source was used to probe the changes in crystal structure resulting from picosecond timescale compression at laser drive energies ranging from 2.5 to 250 mJ. A phase transformation from HOPG to a highly textured hexagonal diamond structure is observed at the highest energy, followed by relaxation to a still highly oriented, but distorted graphite structure following release. We observe the formation of a highly oriented lonsdaleite within 20 ps, subsequent to compression. This suggests that a diffusionless martensitic mechanism may play a fundamental role in phase transition, as speculated in an early work on this system, and more recent static studies of diamonds formed in impact events.
