Alignment of microscopic impurities in incipient ferroelectrics

Periodic boundary conditions were applied to compute polarization in solid solutions of KTaO3 : Li. Supercells of sizes 3 x 3 x 3, 4 x 4 x 4 and 5 x 5 x 5 lattice constants were considered. The polarization energy of the host lattice was found to be very sensitive to the wave vector which correspond s to alignment of the microscopic impurities. This alignment was shown to i ncrease with increasing impurity concentration. This phenomenon can be expl ained by a strong enhancement of the interaction between the Li dipoles due to the lattice polarization of the incipient ferroelectric KTaO3. The resu lts obtained are consistent with the experiment and consequences stemming f rom previous cluster computations of other authors.