Kenichiro Yagi

X-Ray Diffraction Study on Glass Transition in K1-x(NH4)xI Mixed Crystal

X-ray diffraction study on K 1- x (NH 4 ) x I mixed crystal with x =0.5 has been carried out to determine the order parameter in the glassy phase. Deviation of the lattice parameter from the Debye approximation was seen in the glassy phase where the diffuse scattering was observed at the (500) reciprocal lattice point. Both the deviation of lattice parameter and the intensity of diffuse scattering increased with decreasing temperature. The results indicate that there is a local distortion which breaks the fcc symmetry in the glassy phase.

In situ studies of fast atom bombardment and annealing processes by reflection electron microscopy

Abstract The capability of reflection electron microscopy (REM) to characterize surface structures is applied to in situ studies of fast atom bombardment (FAB) and annealing process. A FAB gun (4–6 kV Ar) is attached to a UHV electron microscope. Heat cleaned Pt(111) and Si(111) surfaces are bombarded. Low temperature bombardment produces defects on surfaces and they mask images of surface atomic steps. Higher temperature annealing is required to get atomically flat surfaces for a longer time bombardment. In cases of high temperature bombardment, sputtering and annealing take place simultaneously and surface atomic steps move as a result of the sputtering.

Study of crystal structure at high temperature phase in KIO3 crystal by synchrotron powder X-ray diffraction

Abstract The accurate crystal structure of the I-phase in KIO 3 crystal has been obtained at 530 K, for the first time, by the MEM/Rietveld analysis from high-energy X-ray powder-diffraction data. The crystal structure of the I-phase is the rhombohedral perovskite structure (space group R3m; Z =1). The MEM charge-density distributions reveal that the shorter I–O bond exhibits a covalent bonding character and others (I–K, K–O and longer I–O bonds) an ionic.

Structural Phase Transition in (NMe4)2TCNQ3.

The structural properties of a neutral/radical 1 : 2 mixed compound, (NMe 4 ) 2 TCNQ 3 , are studied by the X-ray diffraction method in the temperature range between 25 and 150°C. The experimental ...

EXAFS study of phase transitions in KIO3.

The iodine K-edge EXAFS study of KIO3 was performed to clarify local structural changes on the successive phase transitions. The pair-distribution function of three oxygen atoms in an oxygen octahedron is almost independent on temperature like a covalent bond, whereas that of the other three is gradually reduced with increasing temperature like an ionic bond. The result indicates that iodine and oxygen atoms exist as an IO3- molecule in a pseudo-perovskite-type structure. The anomalous behavior in the Debye-Waller factor for the latter pair-distribution function appears around 50 K, which is associated with the orientational glass transition.

X-Ray Diffraction Study of KBr 1-x(NO 2)x Mixed Crystal

An X-ray diffraction study of KBr 0.64 (NO 2 ) 0.36 was performed to elucidate its structural glass-like properties and compare them to those of other mixed crystals. As the temperature decreases, the fundamental Bragg reflections begin to decrease and strong diffused scattering appears around the Brillouin-zone center of an face centered cubic (fcc) lattice, Γ-point. The results indicate that the local distortion of a lattice with only short-range ferroelectric correlation is induced by reorientational freezing of nitrite ions. The correlation length estimated from the diffused scattering is about 23 A at 100 K, which is much smaller than the coherence length of an X-ray.

X-ray diffraction study of domain reversal in relaxor Pb(Zn1/3Nb2/3)O3

The behavior of domain reversal in relaxor Pb(Zn 1/3 Nb 2/3 )O 3 single crystals was studied using X-ray diffraction measurements. After the electric field was switched instantaneously, the {222} B...

Phase Transitions of (Thiourea)3-CCl4 Clathrate Compound.

An X-ray diffraction study of a clathrate compound, (thiourea) 3 -CCl 4 , was performed to elucidate the mechanism of phase transitions which are characterized by the orientational ordering of CCl 4 molecules. A discontinuous change of lattice constants was observed at (39±2) K indicating the second-order phase transition and a continuous change at (64±2) K, the first-order one. Below the upper transition temperature, the space group of the lattice changed from R 3 c to C c . The lower two phases belong to the same space group C c , though the phase transition occurred. The orientation of CCl 4 molecules deduced from the structural symmetry agrees with that proposed from the previous heat capacity and NQR measurements.

Reflection Electron Microscopy with Use of CTEM: Studies of Au Growth on Pt(111)

Reflection electron microscopy (REM) and reflection high energy electron diffration (RHEED) in ultra-high vacuum (UHV) conditions have been found to be very powerful methods for the studies of surface structures and surface dynamic processes on bulk crystals, although REM images are foreshortened and the resolution is limited to some extent. The history of REM and its characteristics have been recently reviewed by one of the present authors [K.Y.][1] and are described in this book by many authors. Therefore, in this paper, we briefly review the characteristics of REM-RHEED with the use of conventional transmission electron microscopes (CTEM) and illustrate them by a recent study of growth of Au on Pt(111) surfaces. Scanning REM using a small scanning probe and a small solid angle detector (Cowley, Ichikawa and Doi, Bennett and Johnson in this book) which is equivalent by reciprocity theory to REM using a CTEM is not described.

Deglitching procedure for XAFS.

A computer program for eliminating artifacts such as glitches and Bragg peaks of the polarized XAFS spectra is presented. It permits to easily locate and to eliminate from the EXAFS spectra the additional signals originated from the Bragg scattering by crystalline samples. The test of the procedure on the spectra with specially introduced artifacts and on the experimental polarized XAFS spectra showed its high effectiveness.