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

Materials Science & Engineering

CAREER: Fundamental Structure-Dielectric Property Relationships of Fluorite Related compounds

Juan C. Nino, University of Florida, DMR 0449710

Based on dielectric permittivity measurements as a function of temperature, it was determined that as the average lanthanide ionic radius in the Ln3NbO7 compounds decreases, there is an increase in the temperature coefficient of capacitance (TCC) with a transition from negative to positive TCC around 1.06 Å.

The Ln3NbO7 compounds that exhibit a dielectric relaxation have an associated phase transition involving off-center displacements within the rare earth coordination polyhedra (LnO8). A correlation between the magnitude of the off-center displacement of the lanthanide ions and the temperature of the phase transition was established.

This study focuses on the understanding of the origin of dielectric relaxation in the fluorite-related compounds (A2B2O7, A and B are cations), with particular focus on Ln3NbO7 (Ln3+ = lanthanides) compounds. To date there have been two key crystal-structural findings and two fundamental structure-dielectric property relationships have been identified

Within the Ln3NbO7 compounds, it was found that all the materials crystallizing with a defect fluorite crystal structure show no dielectric relaxation while those crystallizing with a weberite-type crystal structure exhibit a characteristic temperature and frequency dependent dielectric relaxation similar to that observed in bismuth pyrochlores.

Juan C. Nino - NSF Highlights 2010 - DMR-0449710

1.12 1.08 1.04 1.00 0.96

-400

-300

-200

-100

0

100

200

300

400

500

Er

Yb

Y

Average ionic radius of Ln3+ ( Å )

Temperature coefficient of capacitance

1.16 1.12 1.08 1.04 1.00 0.963.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

GdYbSmYb

NdYb

LaYb

LaErLaDy

La

Nd

Gd

Dy Er

Yb

weberite-type defect fluorite

Y

Ion

pola

rizab

ility

(Å

3 )

Dielectric Relaxation

Ionic radius (Å)

NoRelaxation

0 100 200 300 400 5000.0

0.1

0.2

0.3

Gd3NbO

7

La3NbO

7

Nd3NbO

7

Off

-cen

ter d

ispl

acem

ent

(Å)

Temperature (K)

LnO8

Materials Science & Engineering

CAREER: Fundamental Structure-Dielectric Property Relationships of Fluorite Related compounds

Juan C. Nino, University of Florida, DMR 0449710

Education and Outreach

During the last year, the main graduate student in this project, Lu Cai, graduated with her Ph.D. in Materials Science and Engineering. Her dissertation “Fundamental Structure-Dielectric Property Relationships of Fluorite-Related Compounds” is now available in electronic format online via the UF library system. Lu is now a postdoctoral scientist at Oak Ridge National Laboratory.Two new graduates Roberto Esquivel and Nathan Wysk have joined the project and will build on Lu’s prior work. Alex Luis Arias continues his work on the characterization of single crystal growth of TGS-TGSe as part of his senior undergraduate research thesis.

As part of the educational and outreach component of this project, the PI organized the third in the series of International Workshops on Electroceramics across the Bolivarian countries in South America. This third workshop took place at the Universidad Simón Bolívar (USB) in Caracas, VENEZUELA, South America in July 8-10, 2009. The local host was Professor Carlos Borrás. There were several presentations and lab tours from researchers across USB. There were 50 student participants from Chemistry, Physics and Materials Science Departments. Key areas for future academic and research collaboration were identified and initiated.

International Workshop on Electroceramics, Caracas, VENEZUELA 2009

Juan C. Nino - NSF Highlights 2010 - DMR-0449710