Matsunaga, Toshiyuki*; Yamada, Noboru*; Kojima, Rie*; Shamoto, Shinichi; Sato, Masugu*; Tanida, Hajime*; Uruga, Tomoya*; Kohara, Shinji*; Takata, Masaki*; Zalden, P.*; et al.
Advanced Functional Materials, 21(12), p.2232 - 2239, 2011/06
Thermal properties of the amorphous and crystalline state of phase-change materials show remarkable differences such as higher thermal displacements and a more pronounced anharmonic behavior in the crystalline phase. These findings are related to the change of bonding upon crystallization.
Kohara, Shinji*; Kato, Kenichi*; Kimura, Shigeru*; Tanaka, Hitoshi*; Usuki, Takeshi*; Suzuya, Kentaro; Tanaka, Hiroshi*; Moritomo, Yutaka*; Matsunaga, Toshiyuki*; Yamada, Noboru*; et al.
Applied Physics Letters, 89(20), p.201910_1 - 201910_3, 2006/11
The three-dimensional atomic configuration of amorphous GeSbTe were derived by reverse Monte Carlo simulation with synchrotron-radiation X-ray diffraction data. The authors found that amorphous GeSbTe can be regarded as "even-numbered ring structure", because the ring statistics is dominated by four- and six-fold rings analogous to the crystal phase. On the other hand, the formation of Ge-Ge homopolar bonds in amorphous GeTe constructs both odd- and even-numbered rings. They believe that the unusual ring statistics of amorphous GeSbTe is the key for the fast crystallization speed of the material.
Shamoto, Shinichi; Yamada, Noboru*; Matsunaga, Toshiyuki*; Proffen, T.*
Physica B; Condensed Matter, 385-386(1), p.574 - 577, 2006/11
Crystal structures of optical recording materials GeSbTe and GeBiTe have been studied in terms of the fast phase transition mechanism by both of real and reciprocal space Rietveld analyses of pulsed neutron powder diffraction data. These crystalline phases had large local lattice distortions. In addition, the crystallite size of GeBiTe was very small (about 150). These results suggest that the similarity of entropy between crystalline and amorphous phases plays an important role in terms of the fast phase transition mechanisms.
Shamoto, Shinichi; Yamada, Noboru*; Matsunaga, Toshiyuki*; Proffen, T.*; Richardson, J. W.*; Chung, J.-H.*; Egami, Takeshi*
Applied Physics Letters, 86(8), p.081904_1 - 081904_3, 2005/02
Local structure of NaCl-type crystalline GeSbTe has been studied by the atomic pair distribution function analysis of pulsed neutron powder diffraction data. We have found the large displacement of germanium atoms in this crystalline phase. Usually, such a large lattice distortion has disadvantage for the electric conductivity. The electronic band structure, however, implies that this significant distortion in addition to the lattice defect at Na site reduces only thermal conductivity, while the highly ordered tellurium atoms at Cl site keep high electric conductivity.
Shamoto, Shinichi; Taguchi, Tomitsugu; Matsunaga, Toshiyuki*; Yamada, Noboru*; Ishii, Kenji; Inami, Toshiya
Materials Research Society Symposium Proceedings, Vol.840, p.125 - 130, 2005/00
Metastable cubic GeSbTe samples, which are widely used as optical recording materials, have been studied by both of pulsed neutron and X-ray powder diffraction measurements. The crystalline cubic phases are found to coexist with two types of amorphous phases, depending on their antimony contents. One has the same first sharp diffraction peak (FSDP) as the amorphous antimony at the higher Q position. Another has a new FSDP at a lower Q position. The origin of the peak shift is discussed in terms of their constituents.
Sugiyama, Koichi*; Go, Shintaro*; Tomimatsu, Taro*; Kai, Tamito*; Nagae, Daisuke*; Ishibashi, Yuichi*; Matsunaga, Sotaro*; Nagata, Yuto*; Nishibata, Hiroki*; Washiyama, Kohei*; et al.
no journal, ,
We have successfully performed in-beam gamma-ray spectroscopy using the isomer-scope technique to study excited-state structure of neutron-rich heavy-actinide nuclei. The neutron-rich heavy-actinide nuclei were produced in the multinucleon-transfer reactions with a Cm target and O projectiles accelerated with the JAEA tandem accelerator. Projectile-like scattered particles were detected with Si E-E telescopes placed at the backward angle, and target-like scattered particles of isomers were caught by an annular aluminum plate placed at about 60-mm downstream from the target. Four Ge detectors and 4 LaBr detectors were placed at the periphery of the aluminum plate, and detected gamma rays from the isomers. Gamma rays emitted from the actinide isomers were successfully observed with a good sensitivity owing to the tungsten shield placed between the target and the detectors.