Frustration of tilts and A-site driven ferroelectricity in KNbO3-LiNbO3 alloys.

Density functional calculations for K(0.5)Li(0.5)NbO(3) show strong A-site driven ferroelectricity, even though the average tolerance factor is significantly smaller than unity and there is no stereochemically active A-site ion. This is due to the frustration of tilt instabilities by A-site disorder. There are very large off centerings of the Li ions, which contribute strongly to the anisotropy between the tetragonal and rhombohedral ferroelectric states, yielding a tetragonal ground state even without strain coupling.