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.

Deformation mechanism of a strong and ductile maraging steel investigated using X-ray synchrotron diffraction

Li, H.*; Liu, Y.*; Zhao, W.*; Liu, B.*; Tominaga, Aki; Shobu, Takahisa; Wei, D.*

International Journal of Plasticity, 165, p.103612_1 - 103612_20, 2023/06

https://doi.org/10.1016/j.ijplas.2023.103612

In order to clarify the strength properties of Co-free maraging steel, tensile experiment using high energy synchrotron X-ray diffraction was performed. Diffraction profiles from the martensitic and austenitic phases were obtained, and their strength and width were observed to vary as loading. Analysis of the diffraction profiles showed that the content of martensite in the as-aged material decreased slowly at low stress levels and decreased rapidly at high stress levels. On the other hand, the austenite phase in the as-solution materials was significantly transformed the martensite phase as the stress increased. It was clarified to be responsible for their respective strength properties.

Feasibility study of magnetic-domain observation by means of non-resonant magnetic X-ray diffraction

Inami, Toshiya*; Shobu, Takahisa; Ishii, Kenji*

IEEE Transactions on Magnetics, 57(3, Part 2), p.6400105_1 - 6400105_5, 2021/03

https://doi.org/10.1109/TMAG.2020.3046006

Hydrostatic compression behavior and high-pressure stabilized -phase in -based titanium aluminide intermetallics

Liss, K.-D.*; Funakoshi, Kenichi*; Dippenaar, R. J.*; Higo, Yuji*; Shiro, Ayumi*; Reid, M.*; Suzuki, Hiroshi; Shobu, Takahisa; Akita, Koichi

Metals, 6(7), p.165_1 - 165_22, 2016/07

https://doi.org/10.3390/met6070165

Titanium aluminides find application in modern light-weight, high-temperature turbines, such as aircraft engines, but suffer from poor plasticity during manufacturing and processing. Huge forging presses enable materials processing in the 10 GPa range and hence, it is necessary to investigate the phase-diagrams of candidate materials under these extreme conditions. Here we report on an in-situ synchrotron X-ray diffraction study in a large-volume-press of a modern ( + ) two-phase material, Ti-45Al-7.5Nb-0.25C, under pressures up to 9.6 GPa and temperatures up to 1686 K. At room temperature, the volume response to pressure is accommodated by the transformation rather than volumetric strain, expressed by apparently high bulk moduli of both constituent phases. Crystallographic aspects, specifically lattice strain and atomic order are discussed in detail. It is interesting to note that this transformation takes place despite an increase in atomic volume, which is due to the high ordering energy of . Upon heating under high pressure, both the eutectoid and -solvus transition temperatures are elevated, and a third, cubic -phase is stabilized above 1350 K. Earlier research has shown that this -phase is very ductile during plastic deformation, essential in near-conventional forging processes. Here, we were able to identify an ideal processing window for near-conventional forging, while the presence of the detrimental -phase is not present under operating conditions. Novel processing routes can be defined from these findings.

Structure of GaAs(001)-c(44); Comparison of X-ray diffraction and first-principles calculation

Takahashi, Masamitsu; Kratzer, P.*; Penev, E.*; Mizuki, Junichiro

Surface Science, 600(18), p.4099 - 4102, 2006/09

https://doi.org/10.1016/j.susc.2006.01.127

The GaAs(001)-c(44) has been studied by synchrotron surface X-ray diffraction. The atomic coordinates and Debye-Waller factors were determined up to the sixth layer from the surface. The results support the formation of the Ga-As heterodimers. The resultant atomic coordinates were compared with those given by a first-principle calculation. In spite of the theoretical prediction of the stability of the single-heterodimer structure, our data fit best a three-heterodimer model where three heterodimers are present in one unit cell. The preference of the formation of the three heterodimers will be discussed in the relationship with the transition process from the 24 to the c(44) structures.

Precise Measurement of density and structure of undercooled molten silicon by using synchrotron radiation combined with electromagnetic levitation technique

Higuchi, Kensuke*; Kimura, Kakuryo*; Mizuno, Akitoshi*; Watanabe, Masahito*; Katayama, Yoshinori; Kuribayashi, Kazuhiko*

Measurement Science and Technology, 16(2), p.381 - 385, 2005/02

https://doi.org/10.1088/0957-0233/16/2/008

X-ray diffraction and density measurements have been simultaneously performed to investigate the atomic structure of molten silicon in wide temperature range including undercooling region by using the electromagnetic levitation technique. The density was obtained from the mass and the shape of levitated sample by non-contact method based on the image analysis technique. X-ray diffraction experiments were performed by using the synchrotron radiation at SPring8, Japan. From structural analysis of undercooled molten silicon, first nearest neighbour coordination numbers and interatomic distances were about 5 and 2.48 with no dependence on temperature in the range of 1900-1550 K. We conclude as a result that the short-range order based on tetrahedral bonds of undercooled molten silicon does not change with the degree of undercoolings but medium-range order changes by the degree of undercoolings.

X-ray diffraction study on GaAs(001)-24 surfaces under molecular-beam epitaxy conditions

Takahashi, Masamitsu; Yoneda, Yasuhiro; Mizuki, Junichiro

Applied Surface Science, 237(1-4), p.219 - 223, 2004/10

https://doi.org/10.1016/j.apsusc.2004.07.018

The GaAs(001)- reconstructed surface was investigated by in situ surface X-ray diffraction. The sample was subjected to measurements under molecular-beam epitaxy conditions without being transferred another chamber. Several X-ray diffraction patterns were measured with increasing the substrate temperature within the -phase of GaAs(001)- in a constant As flux of 510 Torr. At relatively low temperatures up to 545C, the observed X-ray diffraction patterns agree well to the 2(24) surface. However, a different X-ray diffraction pattern was obtained at 585C, while the periodicity still persited. This change is explained by partial As-dimer desorption which results in a mixture of the 2(24) and 2(24) structures.

Application of a portable pulsed magnet to synchrotron radiation experiments

Matsuda, Yasuhiro*; Ueda, Yuji*; Nojiri, Hiroyuki*; Takahashi, Toshiharu*; Inami, Toshiya; Owada, Kenji; Murakami, Yoichi; Arima, Takahisa*

Physica B; Condensed Matter, 346-347, p.519 - 523, 2004/04

https://doi.org/10.1016/j.physb.2004.01.139

A very small capacitor bank and miniature pulsed magnets have been developed to perform high-field synchrotron radiation experiments. A 20T pulsed field can be generated using an energy of 1kJ with typical pulse duration about 1ms. Electron spin resonance experiments in millimeter wave range and high-field X-ray diffraction experiments have been done successfully.

Phase relations of AgI under high pressure and high temperature

Otaka, Osamu*; Takebe, Hitoshi*; Yoshiasa, Akira*; Fukui, Hiroshi*; Katayama, Yoshinori

Solid State Communications, 123(5), p.213 - 216, 2002/08

https://doi.org/10.1016/S0038-1098(02)00290-9

Using a multi-anvil high-pressure device and synchrotron radiation, X-ray observations of AgI high pressure and high temperature up to 6.0 GPa and 1000 K have been performed to investigate the phase relations between -AgI, rocksalt-type, disordered rocksalt-type, and liquid phases. The three phases of -AgI, disordered rocksalt-type, and liquid meet in a triple point in the vicinity of 823 K and 1.3 GPa. The melting curve of the disordered rocksalt phase is linear with a positive slope. The transition between rocksalt and the disordered rocksalt phases is a broad and diffuse disordering type within the same structure. The formation of the disordered rocksalt phase has been hence estimated with the variation of a relative intensity ratio of (111) and (200) diffraction from the rocksalt phase. With increasing pressure the rocksalt phase becomes stabel at high temperature. At 6.0 GPa the rocksalt phase directly melts without the transition to the disordered rocksalt phase.

Amorphization from the quenched high-pressure phase in III-V and II-VI compounds

Mori, Yuki*; Kato, Sayuri*; Mori, Hiroko*; Katayama, Yoshinori; Tsuji, Kazuhiko*

Review of High Pressure Science and Technology, 7, p.353 - 355, 1998/03

http://ci.nii.ac.jp/naid/10002690121

The temperature dependence of phase transitions in GaSb, AlSb, GaAs, GaP, InAs, ZnSe, and CdTe are studied by X-ray diffraction measurements under pressure upto 30 GPa at temperatures of 90-300K. The phase transitions depend on paths in a pressure-temperature phase diagram. The structure of the recovered phase after decompression depends on the ionicity in bonding: amorphous for small ionicity, the stable zincblende structure for large ionicity, and microcrystalline or moderate ionicity. These results are discussed by using a configuration-coordinate model.