October 1996 through September 1997 - Oak Ridge National ...

oxide file1 cells and solid-state sensors. The Micristar unit was successfully substituted for the Biihler
controller, which allowed the adjustment of the control settings, digital readout of temperature, and
programming of tempcratiire schedule. This rrnit may be controlled via an RS-232 interface, and it is
hoped that such an interface will be set up in tlie fiitiire between the VAX computer and the Micristar
to integrate the temperature control with the goniometer software.
2.4.2 Intensity Enhanced at HFlK Bearnline HE4
This year, the Solid-state Division at ORNL installed a vertically focusing Ge(51 I )
inonochroniator on the HB-4 diffractometcr that resulted in a tlux increase of a factor of three for
small samples. For large samples, a 30% increase in flux was also realized, thanks to the better
perforinatice of tlie new monochromator. ‘This upgrade opens neu opportunitics for all HTMI, users,
especially in the areas of high temperature studies, where the peak intensities are inherently low due
to broadening and thermal diffuse scattering and for cases where a large sample is not available.
2.4.3 New Software Developed for High-Temperature X-ray Data Collection
The capabilities offered by DUC were enhanced by the development of new software for
temperature control and data acquisition bq ail engineering student from Michigan ‘Technological
Unikersitj employed at thc Il’T’ML under the Science arid Engineering Research Semester (SERS)
program. The new software, written in C+ t with a graphical user interface and running tinder
Windows NT. better utilizes the rapid data acquisition rates made possible bj an existing position
sensitive detector. Data download times have been reduced by a factor of twenty, which was the slow
step in existing coinniercial software. ‘This same softwarc is capable of controlling 1 ITXRD
experiments using an identical position sensitive detector atid teinperature controller at thc OKNI,
X14A synchrotron beainlinc at BNI,. Jhe next development phase will add scanning capabilities to
the data collection package. This development allows real-time studies of phase transforniations by
high temperatiire X-ray diffraction at HTML.
2.5 FWSIDUAL STRESS USER CENTER (KSUC) HIGHLIGHTS
2-51 First In Situ Neutron Diffraction Strain Measurements on Electrostrictive Ceramics
Clectrostrictive materials are considered good candidates to replace piezoelectrics because of their
increased strain response \.tith electric tield. but the application of these materials has been limited by
poor electromechanical coupling: IJsers from Alfred IJniversity and the University of Cincinnati
recently utilized the strain-mapping facilities of the 11 TML, to study samples of polycrystalliiie
Pb(Mg,,,N b2,j)0,-PbTiO~-(Ba,Sr)TiO: (PMN) produced by Lxkheed-Martin Syracuse. Neutron
diffraction provides a means of determining strain as a function of direction and hkl within bulh
electrobtrictive materials tinder applied dc fields. which may be used to correlate microscopic strains
with macroscopic strains measured using strain gages. Strain components nornial and parallel to the
field were measured as a fiinction of applied field up to 1.2 kV/mm. The (400) (220), (3 lo), and
(222) reflections of PMN were nieasiired and used to determine the inaxinium microscopic strain
response of polycrystalline PMN. The neutron diffraction strain data will be compared to the
macroscopically-measured strains determined using strain gauges as an initial step towards
irnderstanding the poor electroinechanical coupling of PMN materials. Futurc research proposals are
anticipated to study the electrostrictive response as a function of dopant levels, processing, and eveii
under ac fields.
2-7