Abstract
The large-scale modeling of the atomic and electronic structure of
KNbxTa1-xO3 (KTN) perovskite solid
solutions is performed using the Intermediate Neglect of the
Differential Overlap (INDO) method based on the Hartree-Fock formalism.
It is found that periodic Nb impurities in KTaO3 reveal
coherent off-center displacements already at the smallest calculated
concentration, x=0.125. The calculated magnitude of < 111 > Nb
off-center displacement is 0.27 a.u., which is close to the XAFS
observation at 70 K and x=0.09. In contrast, Ta impurities in
KNbO3 remain on-center, due to higher ionicity of Ta, as
compared to Nb. Using the calculated energy gain caused by the
off-center displacements of Nb atoms, the non-empirical
Ginzburg-Landau-Devonshire functional with concentration-dependent
coefficients is constructed. Analysis of INDO results for several Nb
concentrations in KTN allows calculate the lowest critical Nb
concentration, xcr=0.025, corresponding to the quantum
displacive limit for the paraelectric-ferroelectric transition at 0 K.
This value is only slightly higher than the experimental one.
Original language | English |
---|---|
Title of host publication | AIP Conference Proceedings |
Pages | 231-240 |
Volume | 677 |
DOIs | |
State | Published - 1 Aug 2003 |
Externally published | Yes |
Keywords
- Niobates titanates tantalates PZT ceramics etc.
- Phase transitions and Curie point