Light-induced phase transformation from realgar to pararealgar has been studied by means of single-crystal X-ray diffraction and X-ray photoelectron spectroscopy. The photochemical degradation causes the increase of As4S4 intermolecular distances and the production of the As4S5 molecules. The results suggest the following cyclic process. 1st : an S atom in the As4S5 is released from one of the As-S-As linkages in As4S5 which becomes the As4S4 pararealgar molecule, 2nd : the free S atom is re-attached to another As4S4 realgar molecule and reproduces an As4S5 molecule, and 3rd : the As4S5 is again divided into an As4S4 pararealgar molecule and an S atom.
The development of radiation tolerant materials is of technological importance for the immobilization and long-term storage of surplus actinides and high-level radioactive wastes such as spent fuel from nuclear reactors. Complex oxide ceramics represent an important class of candidate materials for nuclear-waste hosts, and therefore much effort has been devoted to assess radiation damage behavior in these materials. Recent research has centered on a class of materials that possess structures related to the fluorite (CaF2) crystal structure (called fluorite structural derivatives), because certain fluorite-structured oxides, such as UO2 and cubicstabilized zirconia, behave quite robustly in a radiation environment. In an effort to study systematically radiation effects in fluorite structural derivatives, we recently initiated investigations into radiation damage effects in M7O12 compounds (M represents a metal cation, while O refers to an oxygen anion) . Many M7O12 compounds are known to crystallize in a so-called delta (δ) crystal structure, a structure closely related to fluorite. In this article, our recent study on ion-beam-induced structural transformations in δ-Sc4Zr3O12 was reported.
The interplays between crystal structures and physical properties in BiCoO3, PbVO3 and BiNiO3 are investigated. It is found that the t2g1 and t2g4eg2 electronic configurations of V4+ and Co3+ ions are the origin of the large tetragonal distortions in BiCoO3 and PbVO3. High pressure neutron diffraction measurements and Bond valence sum calculations on BiNiO3 with unusual oxidation state of Bi3+0.5Bi5+0.5Ni2+O3 show that the pressure-induced melting of the charge disproportionated state leads to a simultaneous charge transfer from Ni to Bi, so that the high pressure phase is metallic Bi3+Ni3+O3.
A polarized-neutron-diffraction study has been performed on a single crystal sample of TbMnO3, where the ferroelectricity and spiral magnetic order coexist. The spin helicity, detected as the change in intensities of magnetic satellites with the spin direction of incident neutrons, can be controlled by the poling electric field alone. The temperature dependence of the change well agrees with that of the electric polarization. These results establish that an inverse effect of the Dzyaloshinskii-Moriya interaction is the origin of spontaneous electric polarization in the spiral ordered phase of TbMnO3.
Recent development of synchrotron powder diffractometry with a high resolution powder diffractometer with multiple-detector system (MDS) on the beemline BL-4B2 at the KEK Photon Factory (PF) in Tsukuba is described. Practical methods for analyzing the MDS data, including (i) precise evaluation and correction for counting-loss of detection systems, (ii) connection of segmented intensity data, (iii) deconvolution of instrumental aberration, and (iv) evaluation and removal of asymmetry in the spectroscopic distribution of the source X-ray, have been originally developed for the MDS diffractometer. It is shown that the KEK-PF MDS powder diffractometer has become a more advanced tool for precise and detailed evaluation of crystalline materials.
High angular resolution of a powder diffractometer enables the precise structural analysis of crystalline materials. Here we review the results of precise analyses of crystal structure and electron density in some inorganic materials such as barium-doped α-tricalcium phosphate (Ba-α-TCP), α-silicon nitride, tantalum oxynitride TaON photocatalyst and zirconium oxide nano-particles. These studies were carried out with a multi-detector system at the beam line 4B2 of Photon Factory, KEK. In Ba-α-TCP, Ba atoms are located at three crystallographic Ca sites among eighteen Ca sites. Covalent bonding is visualized in TaON, α-silicon nitride and zirconium oxide. A new furnace to measure the diffraction profile up to 1800 K is available at the 4B2 beam line.
The Photon Factory currently operates four synchrotron beamlines for protein crystallography and two more beamlines are scheduled to be constructed in the next years. Over the last years these beamlines have been upgraded and equipped with a fully automated beamline control system based on a robotic sample changer. The current system allows for remote operation, controlled from the user's area, of sample mounting, centering and data collection of pre-frozen crystals mounted in Hampton-type cryo-loops on goniometer head. New intuitive graphical user interfaces have been developed so as to control the complete beamline operation. Furthermore, algorithms for automatic sample centering based on pattern matching and X-ray beam scanning are being developed and combined with newly developed diffraction evaluation programs in order to complete entire automation of the data collection.