Off-center impurities in a robust ferroelectric material: case of Li in KNbO3

R. MACHADO, RODRIGO; SEPLIARSKY. MARCELO; STACHIOTTI, MARCELO

PHYSICAL REVIEW B

AMER PHYSICAL SOC

Lugar: New York; Año: 2012 vol. 86 p. 941181 - 941186

1098-0121

The influence of Li impurities on the phase transition sequence of KNbO3 is investigated using an atomistic model with parameters fitted to first-principles calculations. We find that the replacement of K by Li ions increases local electric dipoles due to a large Li off-centering along [001] directions. Li doping strongly affects the transition temperatures of KNbO3 as a result of the coupling between the off-center Li relaxation dynamics and the macroscopic polarization of the host material. This coupling produces a decrease in the temperatures for the rhombohedral-orthorhombic and orthorhombic-tetragonal phase transitions, while the temperature of the cubic-tetragonal ferroelectric phase transition increases. The Li relaxation mechanism in the different phases of KNbO3 provides a simple framework to understand the transition temperature shifts.