Control of crystalline structure and ferroelectric properties of Pb(ZrxTi/sub 1-X/)O3 films by pulsed laser deposition
We have investigated Pb(Zr/sub X/Ti/sub 1-X/)O/sub 3/ (PZT) films on Pt/SiO/sub 2//Si substrates formed by pulsed laser deposition (PLD) and subsequent rapid thermal annealing (RTA) under various growth conditions. X-ray diffraction analysis revealed that preferentially [100]-oriented perovskite PZT films with trigonal structure were formed after RTA from as-deposited films which had consisted of small grains with pyroclore structure. The degree of [100]-orientation of the PZT film increased with the oxygen partial pressure during PLD. The capacitors made from these films showed higher remnant polarization than those from randomly oriented films.
Laser Ablation of Alkaline Earth Metals Investigated by Time-of-Flight Mass Spectroscopy: Ion Desorption by Core-Electron Excitation
The time-of-flight distribution and the amount of desorbed monovalent ions have been measured in the laser ablation of alkaline earth metals. The obtained relationship between the amount of ions and the laser fluence indicates that the desorption is caused by 5-, 4- and 3-photon processes for Ca, Sr and Ba, respectively when an ArF excimer laser is used as a light source. On the basis of the results, a model is proposed in which the laser ablation of the alkaline earth metals is triggered by excitation of the core electrons at the highest energy level.
Neutron Residual Stress Measurements on Rail Sections for Different Production Conditions
Rail sectioning with subsequent neutron diffraction experiments has been used to assess residual stresses in the rails. In this study we present the results of neutron stress measurements performed at the NIST Center for Neutron Research (NCNR) on rail sections from rails that were produced under various conditions. Specifically, these are air-cooled, air-cooled and roller-straightened, head-hardened and head-hardened and roller-straightened. More significantly, a head-hardened and roller-straightened rail was also studied after service to elucidate evolution of the service-induced residual stresses. In the latter case both a transverse-cut slice and the central region of a 0.53 m long piece were studied. Measurements on this piece are the first in which triaxial stresses have been determined for an intact rail. Neutron strain measurements with 3×3×3 mm3 spatial resolution were successfully employed for transversally cut slices to verify the difference in the stress state depending on the production process. Although examination of slices allows determination of only two-dimensional stresses in the plane of the slice, additional measurements on obliquely-cut slices, which were also carried out, and utilization of FEM gives the possibility of reconstructing the full triaxial stress distribution. Together, these approaches provide a better understanding of rail fabrication and the possibility of improving the durability and safety of rails in the future.Copyright © 2004 by ASME