First-Principles Determination of Chain-Structure Instability in KNbO 3
Abstract
A complete mapping in the Brillouin zone of the structural instability associated with the ferroelectric phase transitions of KNbO
3
has been obtained by first-principles calculations using an LAPW linear response approach. The wavevector dependence of the instability reveals pronounced two-dimensional character, which corresponds to chains oriented along
⟨100⟩
\ directions of displaced Nb atoms. The results are discussed in relation to models of the ferroelectric phase transitions.