The origin of the highly crystallized face-centered cubic YH3 high-pressure phase when quenched to ambient condition. (June 2022)

• Record Type: Journal Article
• Authors: Kataoka, Riki; Taguchi, Noboru; Kitta, Mitsunori; Takeichi, Nobuhiko; Utsumi, Reina; Saitoh, Hiroyuki; Nozaki, Masashi; Kamegawa, Atsunori
• Is Part Of: Materials today communications. Volume 31(2022)
• Publication Date: 2022-06
• Subjects: Rare earth -- Hydride -- High-pressure phase -- STEM -- In situ XRD; Materials science -- Periodicals; 620.11
• DOI: 10.1016/j.mtcomm.2022.103265
• Languages: English
• ISSNs: 2352-4928

Abstract

Abstract: The origin of the face-centered cubic (FCC) structure in yttrium trihydride stabilized (or quenched) at ambient pressure was investigated using transmission electron microscopy (TEM) and in situ synchrotron x-ray diffraction (XRD) measurements under high pressures in the gigapascal range. Although the FCC-YH 3 high-pressure phase is normally unstable at ambient pressure, in this study, we found that the FCC-YH 3 phase, with high crystallinity, could be obtained via sintering at 1373 K for 24 h under 6 GPa, and subsequent quenching at a rate greater than 1000 K/min. The XRD profile of the FCC-YH 3 phase showed sharp peak patterns, i.e., it had a high crystallinity; however, the TEM observations revealed that the surfaces of the particles were significantly disordered. It was observed that these surface defects played an important role in keeping the FCC-YH 3 high-pressure phase present at the ambient pressure. In situ XRD measurements during high-pressure and temperature processing confirmed that the YH 3 phase structure had completely transformed from HCP to FCC at 1173 K and 9 GPa; however, the amount of HCP-YH 3 ambient pressure phase increased continuously during cooling and depressurization. The sample cooling rate during in situ measurements was 90 K/min, which was more than ten times slower than that in the ex situ experiments. Since the defects introduced into the surface of the particles during the slow cooling process were insufficient, a reversal of the HCP-FCC reversible structural change was observed during the depressurization after sintering. Graphical abstract: Highlights: FCC-YH 3 high-pressure phase with high crystallinity was observed. The FCC phase could be obtained by rapidly cooling at high pressure. Quenching introduced defects into the particle surfaces.