Raman spectroscopic study of phase transitions in undoped morphotropic PbZr1−xTixO3

Several PbZr_1−xTi_xO₃ (PZT) compositions in the proximity of the morphotropic phase boundary (MPB) were examined by means of Raman spectroscopy in the 15–800 K temperature range. Previous studies performed by other researchers using various techniques evidenced that, in the phase diagram of PZT, areas with rhombohedral/monoclinic and tetragonal/monoclinic phases coexist across the MPB. For these compositions, either long‐range or short‐range symmetry ordering of the monoclinic phase should be considered, so that no true rhombohedral–monoclinic–tetragonal phase boundary exists. In addition, the onset of antiferrodistortive phase transitions between high‐T and low‐T perovskite phases has been predicted by ab initio calculations and experimentally reported. In the present work, low‐T and high‐T Raman scattering spectra were collected on undoped PbZr_1−xTi_xO₃ with compositions x = 0.42, 0.45, 0.465, 0.48 and 0.53 in an attempt to clarify the current open issues on the phase diagram of PZT. Spectra clearly belonging to the respective phases were observed in the rhombohedral, monoclinic and tetragonal areas, thus confirming that monoclinic ordering is long‐range only for a narrow range of compositions. Raman measurements at cryogenic temperatures allowed detecting all predicted low‐T phases, including the tetragonal one. These results are in good agreement with both ab initio calculations and experimental results obtained by other authors on the same compositions. Copyright © 2010 John Wiley & Sons, Ltd.     

Real-time freight locomotive rescheduling and uncovered train detection during disruption

This paper discusses rescheduling of freight train locomotives when dealing with a disrupted situation in the daily operations in Japan. Within the current framework of dispatching processes, passenger railway operators modify the entire timetables and an adjusted freight train timetable is distributed to a freight train operator. For this timetable, we solve the locomotive rescheduling problem by changing the assignment of the locomotives to all the trains and considering their periodic inspections. We then solve the uncovered train detection problem that selects unassigned trains according to their value if the rescheduling phase fails.     

Formation and characterization of polyperinaphthalenic organic semiconductor nanoparticles by laser ablation of mixture targets of a perylene derivative with cobalt powder at 355 nm

Laser ablation of mixed targets of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) with cobalt powder (PTCDA-Co) was carried out using the third harmonic of a Nd:YAG laser (355 nm) in order to prepare nanoparticles consisting basically of polyperinaphthalene (PPN), a member of the low dimensional graphite family. The optimized content ratio of Co to PTCDA (Co:PTCDA) for effective elimination reaction of anhydride groups of PTCDA was determined. We found that the ablation at Co:PTCDA of 4:1 and 8:1 enabled us to eliminate the side groups effectively. Furthermore, surface enhanced Raman spectroscopy with a tip of an atomic force microscope was carried out to investigate the molecular structure of each nanoparticle. Amplification of the Raman intensity by more than 100 times compared with conventional micro Raman spectroscopy was achieved by tip enhancement. A nanoparticle having a diameter of approximately 70 nm prepared by this method was found to possess PPN structure. PACS 81.05.Uw; 81.16.Mk; 07.79.-v     

Proportional counter operated at 13–300 K and its application to CEMS

The operation of a proportional counter was investigated at temperatures between 13–300K. It was found that the suitable gases filled in the counter are purified belium at temperatures below 22K, purified neon at temperatures between 22–53K and He+5%N₂ or He+10%CO at temperatures above 46 or 47K, respectively. This experimental technique was applied to CEMS with natural iron and with a thin foil of iron oxide.     

CEMS measurements at low temperatures with Fe-Implanted sapphire

A single crystal of sapphire was implanted with 100-keV⁵⁷Fe to a dose of 3.4×10¹⁵ ions/cm². The charge states of iron ions were investigated with the CEMS technique at low temperatures. The formation of the observed charge states Fe²⁺(1) and Fe²⁺(2) were elucidated in terms of crystal structure.     

Theoretical DFT study of the structure and chemical activity of small indium(III) oxide clusters

The B3LYP/Lanl2dz and B3LYP/SDD levels of DFT have been used to describe the structural properties of small stoichiometric indium(III) oxide clusters. It was shown that the most stable structures for the monomer and dimer are linear and cubic, respectively, in origin. The most stable trimer is due to the formation of three eight-membered and two six-membered rings with alternation of In and O atoms. Among neutral and monocation tetrameric structures, formation of an ??arrowhead?? isomer is energetically less favorable than the global minimum structure that has eight six-membered and six four-membered rings. In the pentamer and octamer, a few centers of higher coordination number and a variety of In?CO bond lengths are observed. The other centers cannot be fitted to the characteristic bixbyite structure, however, so the larger octamer cannot be a good model for mimicking the properties of the In₂O₃ crystal structure. An H-terminated cluster model consisting of In₁₃O₂₇H₁₅ is proposed that well describes basic features of indium oxide and tin-doped indium oxide (ITO) structures.     

Laser-induced phase change in Langmuir films observed using nanosecond pump-probe Brewster angle microscopy

A technique is described to observe transient events in thin interfacial films and monolayers. p-polarized light has minimum reflectivity at the Brewster angle. When an interface is viewed with light that is both incident and reflected at the Brewster angle the resulting image is dark. However, small refractive index changes can increase the reflectivity producing a high-contrast image of an altered interface with a dark background level. Using this phenomenon, with imaging optics, photo-induced phase change in Langmuir films was monitored. Two synchronized 5-ns pulsed lasers were used in the pump–probe configuration to induce changes at an air–liquid interface and to monitor the resulting morphology changes at selected time delays after photo-excitation. The photo-responsive layers were made from photochromic spiropyrans, having long aliphatic chain substituents. When irradiated with UV light the closed form of the molecule converts to a more planar ring open merocyanine form. This results in the layers changing their morphology in order to accommodate the new molecular form.     

A convenient preparation of nitriles by reaction of free sulfimide with aldehydes

Diphenyl free sulfimide was found to react readily with aldehydes affording the corresponding nitriles in high yields.