INVESTIGADORES
KOVAL Sergio Fabian
congresos y reuniones científicas
Título:
Study of Slater and Takagi Defects in KDP from first-principles
Autor/es:
S. KOVAL; J. LASAVE; N. S. DALAL
Lugar:
Iguazú
Reunión:
Conferencia; 11th International Meeting on Ferroelectricity - IMF11; 2005
Resumen:
Abstract:We performed ab initio
electronic structure calculations to study the stability of the Slater
and Takagi protonic defects in the ferroelectric phase of KH2PO4.
We show that the Slater defects are stabilized only when they are
aligned forming chains of defects in the lattice, in accordance with the
displacive model of the transition. In contrast, the Takagi defects are not stable in the lattice. The ab initio
energy estimation for the Takagi defect (≈54 meV) is in fair good
agreement with previous phenomenological estimates. However, the
calculated uncorrelated Slater
defect energy (≈17 meV) is larger than that from previous model
assignments (5.2 meV), while the latter agrees well with our result for
the correlated value per formula unit. This suggests that the earlier
estimates contain considerable contribution from correlations between
configurations of different H2PO4 groups. Our ab initio
results show that the formation of chains of Slater defects is
accompanied by phosphate rotations, and a concomitant lattice
contraction in the basal plane. Therefore, we propose that the as yet
unexplained anomalous lattice contraction observed in the neighborhood
of the phase transition is due to an increase of the Slater defect
population.