Prof. Takamitsu Yamanaka [Osaka University, Japan]
Title: J-PARC neutron diffraction facility for high-pressure experiment and its application to Mn-ferrite
Time: 10:00 - 11:00 AM, Thursday, June 2, 2016
Place: Auditorium Room 410, HPSTAR (Shanghai)
Host: Dr. Ho-Kwang Mao
Abstract:
X-rays interact primarily with the electron cloud surrounding each atom. Synchrotron radiation with highly collimated and strong incident source is an effective tool to analyze the electron density distribution in the matter even under extreme conditions.
The contribution to the diffracted X-ray intensity is larger for atoms with larger atomic number. Then an anbiguity and difficulty come out in the atomic positions or detection of light elements in the compounds composed of heavy and light elements such as metal and hydrogen. On the other hand, neutrons interact directly with the nucleus of the atom. The scattering length varies from isotope to isotope rather than linearly with the atomic number. Non-magnetic neutron diffraction is directly sensitive to the positions of the nuclei of the atoms, same structure analysis by X-ray diffraction.
The scattering power of an atom does not fall off with the scattering angle as it does for X-rays. Therefore, neutron diffraction peaks are strong and well defined even at high angles. Combination of X-ray and neutron diffraction is a complementary technique for studies under extreme conditions.
Beam Line 11 (PLANET) of the spallation neutron source facilities in Japan Proton Accelerator Research Complex (J-PARC) is especially designed for the researches under the high-pressure and high-temperature.
Example of experiment in J-PARC
The high-pressure phase transitions of Mn1-xFe2+xO4 spinels (post-spinels) are of high relevance, because of the occurrence of their polymorphs in nature. These structures are very similar, several ambiguities and inconsistencies appear in high-pressure studies, leading to many problems that are yet to be solved, because X-ray scattering powers (scattering factor) of these two atoms Fe (atom No 26) and Mn (atomic No. 25) are very similar. Neutron diffraction has an effective source for precise diffraction study of these solid solutions because of big difference in the scattering lengths. Mn has a negative coherent scattering length of -3.73fm, (which is an extremely rare case in the all elements.) On the other hand Fe has 9.54fm. By making use of this great advantage, we aim the following two powder diffraction studies under high-pressure and high-temperature: I. magnetic structure analysis and II. Jahn-Teller effect at extreme conditions.
Biography of the Speaker:
Prof. Takamitsu Yamanaka's experimental works have been focusing to X-ray diffraction, absorption and resonance using synchrotron radiation for 20 years in PF-KEK and SPring-8 in Japan. One of his science interests is crystal physics facing to electron-lattice and spin-lattice correlation in earth’s interiors under extreme conditions. His visit to the Lab aims at the improvement of high-pressure crystallography in Geophysical Laboratory.
Takamitsu was a Professor in the Department of Earth and Space Science and Professor at the Center for Quantum Science and Technology under Extreme Conditions in Osaka University. He is Emeritus Professor of Osaka University. He is a Member of National Science Council of Japan belonging to Japanese cabinet since 2003. He is President of International Mineralogical Association (IMA). He in an active member of the organizing committee of International Union of Crystallography (IUCr-2008 at Osaka).