Effect of Li+ and Nb5+ impurities on phase transition in potassium tantalate

Monocrystals Ksub(1-x)Lisub(x)TaO(KLT) (x=0-0.3), KTasub(1-y)Nbsub(y)Osub(3) (y=0.1; 0.15) and Ksub(0.95)Lisub(0.05)Tasub(0.9)Nbsub(0.1)Osub(3) were investigated in a wide range of frequencies (10-2.5x1010 Hz) and in the 80-300 K temperature range using dielectric spectroscopy methods. The K-Li and Ta-N substitutions are shown to affect the KTaO3 properties in different ways. Li introduction suppresses the low-temperature soft mode in potassium tantalate but induces a new transition related to the ordering of noncentral impurity ions. Nb introduction contributes to the critical lattice vibration and appearance of a ferroelectric phase transition of the displacement type, but suppresses the order-disorder phase transition in KLT. Effects associated with noncentral impurities are very sensitive to the properties of a crystal lattice - matrix