HR: 0830h
AN: V11D-0529    [PDF]
TI: Atomistic Simulations of PbTiO$_{3}$, PMN, and PMN-PT: using shell model potentials fitted to first principles results
AU: * Asthagiri, A
EM: a.asthagiri@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd. NW, Washington, DC 20015 United States
AU: Wu, Z
EM: z.wu@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd. NW, Washington, DC 20015 United States
AU: Sepliarsky, M
EM: sepli@ifir.edu.ar
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd. NW, Washington, DC 20015 United States
AU: Sepliarsky, M
EM: sepli@ifir.edu.ar
AF: Instituto de Fisica Rosario, CONICET-UNR, 27 de Febrero 210 bis, Rosario, 2000 Argentina
AU: Cohen, R
EM: cohen@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd. NW, Washington, DC 20015 United States
AB: The origin of the high piezoelectric response observed in complex pervoskites such as PbZn$_{1/3}$Nb$_{2/3}$O$_{3}$--PbTiO$_{3}$ (PZN--PT) or PbMg$_{1/3}$Nb$_{2/3}$O$_{3}$--PbTiO$_{3}$ (PMN--PT) is not well understood. These systems are of both industrial and basic material science interest. In the past decade much progress has been made in understanding the behavior of ordered ferroelectrics using first-principles methods. The direct application of first-principles methods to examine finite-temperature properties of these larger, disordered systems is still not computationally feasible. One appealing approach is to fit interatomic potentials to select first-principles data of ordered structures, and then use Molecular Dynamics to simulate more relevant systems. We have developed a shell model potential to describe PbTiO$_{3}$ and PMN by fitting to first-principles results. At zero pressure, the model reproduces the temperature behavior of PbTiO$_{3}$, but with a smaller transition temperature than experimentally observed. We then fit a shell model potential for the complex PMN based on the transferability of the interatomic potentials. We have examined several proposed ordered and disordered structures for PMN. We find that even for ordered PMN, quenching the structure gives a non-polar state, but with local polarization (off-center ions) indicative of relaxor behavior. For certain structures, we have observed the loss of short-range polarization order at high temperatures, indicative of the experimentally observed Burns temperature. We will also discuss the affect of electric fields on the behavior of PMN. Due to the transferability of the potential we can directly simulate PMN-PT and we will report on preliminary results for this material.
DE: 3900 MINERAL PHYSICS
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting