Frustration of Tilts and A-Site Driven Ferroelectricity in KNbO₃-LiNbO₃ Alloys...

Density functional calculations for K0.5Li0.5NbO3 show strong a-site driven ferroelectricity, even though the average tolerance factor is significantly smaller than unity and there is no sterochemically active A-stie 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.