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Research Area Summary:
Ferroelectric perovskites play a key role in Navy technology,
particularly the transducers (sound producing and detecting elements)
in SONAR arrays, electronic applications and microwave circuits. We
are using computational methods to understand the properties of these
materials on an atomic-level basis, and are using this to identify
avenues for improving existing materials and to find new superior
compositions.
 | FIG. 1.
Zone boundary rotational mode in perovskites.
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Ferroelectric perovskites play a key role in Navy technology,
particularly the transducers (sound producing and detecting elements)
in SONAR arrays, electronic applications and microwave circuits.
We are using computational methods to understand the properties
of these materials on an atomic level basis, and are using this
to identify avenues for improving existing materials and to find
new superior compositions. Since ferroelectricity is intimately
connected with lattice instabilities and the interplay of competing
structural distortions, this requires the use of accurate
methodologies applied to realistic models of the perovskite
ferroelectric alloys. For this purpose, we primarily use
local density and generalized gradient approximation calculations
with the linearized augmented planewave method. However, for
some properties, these approximate density functionals are not
adequate. For example, the interplay between lattice distortions associated
with rotation of the perovskite octahedra and ferroelectric
distortions is very strongly volume dependent. Predicting this
interplay thus requires methodologies that can predict the
volume to within one percent or better. For this purpose, we use
the weighted density approximation as implemented using NRL
algorithms.
Examples of recent successes in this area are the unravelling of
the lattice instabilities in the Navy SONAR tranducer material
Pb(Zr,Ti)O3 near the morphotropic phase boundary, leading
to an understanding of the importance of octahedral rotational
modes -- a finding recently confirmed by experiments, and the
prediction that alloying Cd for Pb in PbTiO3 would favor
increases in the c/a ratio, implying potential for large displacement
actuation.
Further Reading:
- First Principles Analysis of Vibrational Modes in KNbO3. D.J. Singh and L.L. Boyer, Ferroelectrics 136, 95 (1992).
- Calculated Electric Field Gradients of Ferroelectric KNbO3. D.J. Singh, Solid State Commun. 88, 323 (1993).
- Weighted Density Approximation Ground State Studies of Solids D.J. Singh, Phys. Rev. B 48, 14099 (1993).
- Electric Field Gradients in BaTiO3 and KNbO3. D.J. Singh, Ferroelectrics 153, 183 (1994).
- Planewaves, Pseudopotentials and the LAPW Method. D.J. Singh (Kluwer Academic, Boston, 1994).
- Local Density and Generalized Gradient Approximation Studies of KNbO3 and BaTiO3. D.J. Singh, Ferroelectrics 164, 143 (1995).
- Structure and Energetics of PbZrO3 D.J. Singh, Phys. Rev. B 52, 12559 (1995).
- Stability and Phonons of KTaO3 D.J. Singh, Phys. Rev. B 53, 176 (1996).
- Density Functional Studies of PbZrO3, KTaO3 and KNbO3. D.J. Singh, Ferroelectrics 194, 299 (1997).
- Non-local density functionals and the linear response of the homogeneous electron gas I.I. Mazin and D.J. Singh, Phys. Rev. B 57, 6879 (1998).
- An alternative way of linearizing the APW method. E. Sjostedt, L. Nordstrom and D.J. Singh, Solid State Commun. 114, 15 (2000).
- Dielectric Response of Oxides in the Weighted Density Approximation N. Marzari and D.J. Singh, Phys. Rev. B 62, 12724 (2000).
- Possible Co-Existence of Rotational and Ferroelectric Distortions in Rhombohedral PbZrxTi1-xO3 M. Fornari and D.J. Singh, Phys. Rev. B 63, 092101 (2001).
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