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									                                                                   CAREER: Fundamental Structure-Dielectric Property
                                                                      Relationships of Fluorite Related compounds
                                                                    Juan C. Nino, University of Florida, DMR 0449710



                             A2B2O7 Pyrochlore Structure
                                                                                                   Bi-based pyrochlores are among the most studied compounds in the family of
                                                                                                   fluorite-related structures due to their interesting dielectric properties. They
                                                                                         A         undergo a dielectric relaxation [time lag between electric field and
                                                                                                   polarization] that is temperature and frequency dependent. Given that
BO6                                                                                                bismuth is the dominant element on the A site of Bi-based pyrochlores, until
                                                                                                   recently, it was speculated that the observed relaxor dielectric behavior was
             O                                                                                     associated to the presence of Bi (with its lone electron pair).


                                                                                                              Dielectric relaxation in                                                    However, in collaboration with
                                                                                                         Ca1.469Ti1.469Nb1.037O7 pyrochlore                                               NIST, CNRS, and CSIRO, we
                               XRD profile confirming                                                                                                                                     have now shown that a
                                 pyrochlore phase                                                                   110                                                                   displacive cubic pyrochlore not
                                                                                                                                                                 0.14
                                                                                                                                                                                          containing bismuth, namely
                                                                                                                    100                                          0.12                     Ca1.469Ti1.469Nb1.037O7,      also
                                              (222)
Intensity (Abitrary Units)




                                                                                              Dielectric Constant




                                                                                                                                                                 0.10                     displays dielectric relaxation.




                                                                                                                                                                        Dielectric Loss
                                                                                                                    90
                                                                                                                                                                 0.08
                                                      Ca1.469Ti1.469Nb1.037O7                                                     Increasing the frequency                                This combined crystallographic
                                                                                                                                                                 0.06
                                                                                                                    80                                                                    and electrical characterization
                                                                                                                                                                 0.04
                                                                                                                                                                                          result provides an important
                                                                                                                    70                                           0.02                     new      insight    into     our
                                                                                                                                                                 0.00                     understanding of the nature of
                                (111)




                                                                         (622)
                                                      (400)




                                                                                 (444)




                                                                                                                    60
                                                                                                                     -200 -150 -100 -50   0   50   100 150 200 250                        the     dielectric    relaxation
                                                                                                                                  Temperature ( C)
                                                                                                                                                   o
                                                                                                                                                                                          behavior of pyrochlores.
                                        20   30               40   50   60               70
                                             2 (degrees)
                      CAREER: Fundamental Structure-Dielectric Property
                         Relationships of Fluorite Related compounds
                       Juan C. Nino, University of Florida, DMR 0449710

Education and Outreach
As part of the educational and outreach component of this
program, the PI organized and delivered the first in the
series of International Workshops on Electroceramics
across the Bolivarian countries in South America. This first
workshop took place in the Universidad del Valle, Cali,
COLOMBIA, from August 8-10, 2007. The local host was
Prof. Pedro Prieto, director of the Excellence Center in
Novel Materials (CENM). The workshop was attended by
68 participants including faculty, undergraduate and
graduate students from across Colombia..


                                                 Topics covered included dielectrics,
                                                 ferroelectrics,  fuel    cells,   and
                                                 thermoelectrics and were presented
                                                 by the PI Nino, P. Prieto, and faculty
                                                 from other Colombian universities
                                                 through a series of technical talks
                                                 and laboratory tours.


                                                     Besides the technical sessions, there was very fruitful
                                                     general discussion on opportunities for Colombian faculty
                                                     and students towards scientific collaboration and exchange
                                                     with University of Florida and the US in general.

								
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