The crystallographic problem and method of solutionThe DBWS program, the latest version of which is 9807a (Young et al., 1999), an upgraded version of DBWS-9411, described by Young et al. (1995), is written in Fortran and can carry out Rietveld re®nements using digitized data (from a neutron or X-ray diffractometer) stored in a text ®le. It also requires an Input Control File (ICF), constructed by the user, which stores information about the material and program execution. The ICF is a text ®le that contains crystallographic information about the material and program settings in lines and columns. Given the size of the input ®le needed by DBWS, compiling it can be confusing, dif®cult and time consuming (an ICF for quartz plus alumina, which has only two phases, uses an ICF with more than 60 lines). Most users edit new ICFs by opening previously used ®les in a non-formatted text editor (such as Microsoft Notepad or DOS Edit) and then substituting the old values for new ones. Editing these ®les manually can be confusing because the user needs to know the placement of each parameter in the ICF; furthermore, small errors in the format of the ICF may cause problems when the program runs. After the program has run, a text ®le containing the re®ned data is returned, along with, optionally, a binary ®le that is used to plot the diffraction pattern using a graphics program such as DMPlot (Marciniak, 1997).To solve the aforementioned problems, a graphical interface for DBWS (which works with versions 9411 and 9807 and runs under Windows 95/98/NT) has been developed. Known as DBWS Tools, the program makes DBWS much easier to use and manages each step of the process, from the creation of the ICF to the plotting of the diffraction pattern using the external program DMPlot. In this way, the user need not consult the program manual every time a new sample is analysed (because the meaning of each data ®eld is shown on screen) and the entire process is much faster and user-friendly. DBWS ToolsDBWS Tools was compiled using Borland C++ Builder and runs under Windows 95/98/NT (as a Windows-based program, it cannot run under DOS). It compiles ICFs and manages DBWS and DMPlot execution. The ®rst and most important function of the program is the ICF editor. It collects data entered by the user in a series of ®elds arranged in windows, with descriptions of each option so that the User's Guide is not needed for the task. The input ®les generated by DBWS Tools are identical to those shown in the DBWS User's Guide (versions 9411 and 9807). The interface arranges data correctly, no matter what order the user enters them.`Default' buttons are included in the windows so that the user can bypass the typing of the most common values. The program also runs DBWS in a DOS window using the ®les indicated by the user. Optionally, the diffraction pattern can be plotted using DMPlot, which is a shareware program that uses plot ®les produced by DBWS and has a wide range of options when working with these ®les. DBWS Tools can deal with the complete pro...
Columbite route for synthesis of P3MgNb2O9 (PMN) allows the suppression of secondary phases in PMN powders. These phases, having low dielectric constant, affect negatively the dielectric properties of PMN ceramics. Aiming to get reactive PMN powders, the partial oxalate method was used to precipitate lead oxalate over MgNb2O6 particles. The columbite (NM) powders were prepared using polymeric precursor based on Pechini's method. Two processing routes were used to prepare PMN powders. In the first one the NM-lead oxalate co-precipitate was washed in water and ethanol and calcined at several temperatures. In the second route, the NM-lead oxalate co-precipitate was washed in water and isopropyl alcohol, ball milled for 30 min and calcined at several temperatures. The second route leads to practically pyrochlore free PMN. Powders morphologies observed by SEM showed the formation of agglomerates, which sizes depend on the processing route.
Calcium copper titanate, CaCu 3 Ti 4 O 12 , CCTO, thin films with polycrystalline nature have been deposited by RF sputtering on Pt/Ti/SiO 2 /Si (100) substrates at a room temperature followed by annealing at 600°C for 2 h in a conventional furnace. The crystalline structure and the surface morphology of the films were markedly affected by the growth conditions. Rietveld analysis reveal a CCTO film with 100 % pure perovskite belonging to a space group Im3 and pseudo-cubic structure. The XPS spectroscopy reveal that the in a reducing N 2 atmosphere a lower Cu/Ca and Ti/Ca ratio were detected, while the O 2 treatment led to an excess of Cu, due to Cu segregation of the surface forming copper oxide crystals. The film present frequency-independent dielectric properties in the temperature range evaluated, which is similar to those properties obtained in single-crystal or epitaxial thin films. The room temperature dielectric constant of the 600-nm-thick CCTO films annealed at 600°C at 1 kHz was found to be 70. The leakage current of the MFS capacitor structure was governed by the Schottky barrier conduction mechanism and the leakage current density was lower than 10-7 A/cm 2 at a 1.0 V. The current-voltage measurements on MFS capacitors established good switching characteristics.
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