Materials Science - General Information

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Materials Science - UNO

A. Goals.

The UNO Materials Science program is administered through the Physics
Department. It has as its goals the modeling, fabrication and testing of
novel materials. The theoretical component of the Group has been in
existence for over a decade and grew out of a long standing collaboration
between theorists at UNL and UNO. Over the past six years, using funds from
NRI and NSF-EPSCoR a significant experimental component has been
developed and the computational capabilities of the theory component has
improved greatly. The research efforts of the group currently encompass
a) fabrication of novel high-temperature superconductors and b) simulation
and fabrication materials with unique mechanical and electronic
properties, i. e. ferroelastic and ferroelectric compounds.

In recent years, the search for materials with exotic physical properties
that make them suitable for use in sophisticated detectors and transducers
or as energy storage or memory devices has been greatly increased. Part of
the group's efforts have been directed toward the study of new high
temperature superconductors, for example, which may eventually become
components in power transfer and levitation devices and as "containers" for
the plasmas used in fusion generators. Ferroelectric materials, which the
theory group has been studying for some time, are useful in many
applications. Since their structures can be "switched" using electric
fields, they are useful as computer memory elements and storage devices.
Their sensitivity to the presence of microwaves (radar) is also of obvious
usefulness. By continuing to develop methods of simulating materials such
as these on computers and synthesizing the materials in the laboratory,
this research group is making significant contributions to this "materials
revolution."

Computer facilities within the group presently allow computer simulations
of a variety of materials to be performed by the members of the theory
group, consisting of a total of five members at UNO and four at UNL.
Experimental facilities allow the materials being simulated to be
fabricated at UNO and studied using facilities at UNO and UNL. The
experimental group at UNO consists of two faculty members, a research
associate and two undergraduate students.

B. Collaborations.

The long-standing collaboration between UNL material scientists has been
intensified, in part due to NSF/EPSCoR funding. The theory group as a whole
collaborates with theorists at the Naval Research Laboratory, Washington
DC, Oak Ridge National Laboratory, Brigham Young University, National
Chaio-Tung University in Taiwan - Republic of China. The experimentalists
are making extensive use of equipment at UNL, at the Eppley Cancer
Institute at UNMC, and at the University of Oregon. Some of the high
temperature superconducting materials under investigation were
fabricated at the University of Oxford, U. K. and the Technische Universitat
Graz, Austria. Other collaborators are at Cray Research Inc., the Research
Reactor Center of University of Missouri - Columbia, the University of
Notre Dame and Louisiana State University.

C. Priorities for 1995-96

1) Experimental

Dr. Betanabhatla is continuing his work on bismuth-oxide based systems of
materials which are superconducting in the vicinity of 30K. He has shown
that with optimum stoiciometry the transition temperature can be raised
by as much as 5K by using high oxygen pressures in the annealing process.
During the coming year tese studies will be extended to other families of
materials, in particular, Sr-K-Bi-O systems. Dr. Mehta will assist him in
fabricating and testing these materials.

Dr. Smith (experiment) and Dr. Flocken (theory) have completed the first
combined experimental and theoretical study of solid solutions ever
performed by the group, or any other group, as far as we know. The study
shows that when Rb ions are used to randomly replace K ions in KCaF3, the
transition temperature drops almost linearly from 550K, for pure KCaF3 to
about 300K for a 50-50 concentration of Rb and K. Limitations on
equipment prevented us from obtaining experimental results below room
temperature, however, the computer simulation shows that as Rb
concentration continues to increase, the proper transition temperature for
pure RbCaF3 (195K) is obtained. The agreement between theoretical and
experimental results was excellent, demonstrating that for this class of
materials, computer simulations can be expected to provide accurate
predictions of phase transitions in solid solutions. A manuscript on this
study has been submitted to Physical Review Letters. Work has begun on
investigations of K-Na-Mg-F and Na-Li-Mg-F solutions, which will continue
in 1995-96.

Dr. Smith has also continued he synthesis and characteration of a range of
borate-based materials and has completed analysis of five materials of
this type.Data sets have been collected for six others. Analysis of these
data will continue in the coming year.

2) Theory

In addition to the combined study on solid solutions discussed above, we
are continuing preliminary investigations on more complex fluoride based
materials (A2BF4 compounds, for example). Work on solid solutions will be
done by Dr. Mei and Dr. Flocken with the aid of graduate and undergraduate
students hired using EPSCoR funds. Dr. Kulver has been using Monte Carlo
computer simulation techniques to study the switching mechanisms which
come into play when ferroelectric materials are placed in electric fields
that cause a reversal in polarization. He has obtained hysteresis loops for a
number of compounds and has found polarization values which are in good
agreement with experiment.


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