Temperature-dependent deformation behavior of dual-phase medium-entropy alloy; In-situ neutron diffraction study

Gu, G. H.*; Jeong, S. G.*; Heo, Y.-U.*; Harjo, S.; Gong, W.; Cho, J.*; Kim, H. S.*; 4 of others*

Journal of Materials Science & Technology, 223, p.308 - 324, 2025/07

https://doi.org/10.1016/j.jmst.2024.11.057

Detailed computational models for nuclear criticality analyses on the first startup cores of NSRR: A TRIGA annular core pulse reactor

Yanagisawa, Hiroshi; Motome, Yuiko

JAEA-Research 2025-001, 99 Pages, 2025/06

JAEA-Research-2025-001.pdf:1.98MB

The detailed computational models for nuclear criticality analyses on the first startup cores of NSRR (Nuclear Safety Research Reactor), which is categorized as a TRIGA-ACPR (Annular Core Pulse Reactor), were created for the purposes of deeper understandings of safety inspection data on the neutron absorber rod worths of reactivity and improvement of determination technique of the reactivity worths. The uncertainties in effective neutron multiplication factor (k) propagated from errors in the geometry, material, and operation data for the present models were evaluated in detail by using the MVP version 3 code with the latest Japanese nuclear data library, JENDL-5, and the previous versions of JENDL libraries. As a result, the overall uncertainties in k for the present models were evaluated to be in the range of 0.0027 to 0.0029 k. It is expected that the present models will be utilized as the benchmark on k for TRIGA-ACPR. Moreover, it is confirmed that the overall uncertainties were sufficiently smaller than the values of absorber rod worths determined in NSRR. Thus, it is also considered that the present models are applicable to further analyses on the absorber rod worths in NSRR.

Neutron capture cross-section measurement at TC-Pn in KUR for holmium among nuclides in decommissioning

Nakamura, Shoji; Endo, Shunsuke; Rovira Leveroni, G.; Kimura, Atsushi; Shibahara, Yuji*

KURNS Progress Report 2024, P. 31, 2025/06

no abstracts in English

Crystal structures and phase stability of antiferroelectric phases in undoped and Ca-modified sodium niobates

Aso, Seiyu*; Matsuo, Hiroki*; Yoneda, Yasuhiro; Morikawa, Daisuke*; Tsuda, Kenji*; Oyama, Kenji*; Ishigaki, Toru*; Noguchi, Yuji*

Physical Review B, 111(17), p.174114_1 - 174114_12, 2025/05

https://doi.org/10.1103/PhysRevB.111.174114

We investigate the crystal structures, phase transitions, and phase stability of undoped and Ca-modified NaNbO through a combined analysis of high-resolution synchrotron radiation X-ray and neutron diffraction, convergent-beam electron diffraction, and density functional theory (DFT) calculations. It is demonstrated that the antiferroelectric (AFE)- phase is stabilized over a wide temperature range of 200 to 800 K by Ca modification, and that the NaNbO is stabilized by temperature-driven isostatic pressure accompanied by lattice expansion, whereas the Ca-modified NaNbO is induced by composition-induced chemical pressure along with lattice shrinkage.

Synthesis of BaSiH hydridosilicate at high pressures; A Bridge to BaSiH polyhydride

Beyer, D. C.*; Spektor, K.*; Vekilova, O. Y.*; Grins, J.*; Barros Brant Carvalho, P. H.*; Leinbach, L. J.*; Sannemo-Targama, M.*; Bhat, S.*; Baran, V.*; Etter, M.*; et al.

ACS Omega (Internet), 10(15), p.15029 - 15035, 2025/04

https://doi.org/10.1021/acsomega.4c10502

Hydridosilicates featuring SiH octahedral moieties represent a rather new class of compounds with potential properties relating to hydrogen storage and hydride ion conductivity. Here, we report on the new representative BaSiH obtained from reacting the Zintl phase hydride BaSiH with H fluid at pressures above 4 GPa and subsequent decompression to ambient pressure. It consists of complex SiH ions, which are octahedrally coordinated by Ba counterions. The arrangement of Ba and Si atoms deviates only slightly from an ideal fcc NaCl structure. IR and Raman spectroscopy showed SiH bending and stretching modes in the ranges 800-1200 and 1400-1800 cm, respectively. BaSiH is thermally stable up to 95C above which decomposition into BaH and Si takes place. DFT calculations indicated a direct band gap of 2.5 eV. The discovery of BaSiH consolidates the compound class of hydridosilicates, accessible from hydrogenations of silicides at gigapascal pressures (10 GPa). The structural properties of BaSiH suggest that it presents an intermediate (or precursor) for further hydrogenation at considerably higher pressures to the predicted superconducting polyhydride BaSiH.

Enhanced strength and ductility in an additively manufactured Al10SiMg alloy at cryogenic temperatures

Naeem, M.*; Rehman, A. U.*; Romero Resendiz, L.*; Salamci, E.*; Aydin, H.*; Ansari, P.*; Harjo, S.; Gong, W.; Wang, X.-L.*; 3 of others*

Communications Materials (Internet), 6, p.65_1 - 65_13, 2025/04

https://doi.org/10.1038/s43246-025-00793-4

Crystal structures of ReO under hydrostatic pressure; A Combined neutron, X-ray, Raman, and first-principles calculation study

Efthimiopoulos, I.*; Klotz, S.*; Kunc, K.*; Baptiste, B.*; Chauvigne, P.*; Hattori, Takanori

Physical Review B, 111(13), p.134103_1 - 134103_13, 2025/04

https://doi.org/10.1103/PhysRevB.111.134103

We present a comprehensive study of the high pressure behaviour of ReO using X-ray and neutron diffraction, Raman scattering and first-principles calculations to 15 GPa. We show that the ambient pressure structure converts at 0.7 GPa in a continuous phase transition directly to a cubic phase with space group and rhombohedral structures in this pressure range are an artifact due to an alteration of the sample by high-flux synchrotron X-ray radiation. The structural pressure dependence of the O samples are presented. The data shed light onto the unusual transition and densification mechanism due to progressive tilting of essentially rigid ReO octahedra.

Robustness of ferromagnetism in van der Waals magnet FeGeTe to hydrostatic pressure

Wang, Y.*; Zeng, X.-T.*; Li, B.*; Su, C.*; Hattori, Takanori; Sheng, X.-L.*; Jin, W.*

Chinese Physics B, 34(4), p.046203_1 - 046203_6, 2025/03

https://doi.org/10.1088/1674-1056/adb26f

Two-dimensional van der Waals ferromagnet FeGeTe (FGT) holds a great potential for applications in spintronic devices, due to its high Curie temperature, easy tunability, and excellent structural stability in air. In this study, we have performed high-pressure neutron powder diffraction (NPD) up to 5 GPa, to investigate the evolution of its structural and magnetic properties with hydrostatic pressure. The NPD data clearly reveal the robustness of the ferromagnetism in FGT, despite of an apparent suppression by hydrostatic pressure. As the pressure increases from 0 to 5 GPa, the Curie temperature is found to decrease monotonically from 225(5) K to 175(5) K, together with a dramatically suppressed ordered moment of Fe, which is well supported by the first-principles calculations. Although no pressure-driven structural phase transition is observed up to 5 GPa, quantitative analysis on the changes of bond lengths and bond angles indicate a significant modification of the exchange interactions, which accounts for the pressure-induced suppression of the ferromagnetism in FGT.

A Decade of neutron diffraction study of iron hydrides

Aoki, Katsutoshi*; Machida, Akihiko*; Saito, Hiroyuki*; Hattori, Takanori

Koatsuryoku No Kagaku To Gijutsu, 35(1), p.4 - 11, 2025/03

https://doi.org/10.4131/jshpreview.35.4

Iron reacts with hydrogen to form solid solutions with body-centered cubic, face-centered cubic, hexagonal close packed, and double hexagonal close packed structures at high temperatures and high pressures. Neutron diffraction is the most powerful tool for determining the occupation sites and occupancies of hydrogen atoms dissolved in a metal lattice. Structural parameters, including hydrogen occupation sites and occupancies, are refined via Rietveld analysis for neutron diffraction data. We present our expertise in Rietveld refinement of iron hydrides accumulated over 10 years.

Monte Carlo and experimental assessment of the optimal geometry of the source and collimator for a table-top NRTA system for small nuclear material measurement

Guembou Shouop, C. J.; Tsuchiya, Harufumi

Nuclear Instruments and Methods in Physics Research A, 1072, p.170189_1 - 170189_14, 2025/03

https://doi.org/10.1016/j.nima.2024.170189