  KTaO_3-based solid solutions exhibit a variety of interesting physical
phenomena. To better understand these phenomena, we performed first-principles
calculations on [K_{1-x}, Li_x]TaO_3 (KLT) and K[Ta_{1-x}, Nb_x]O_3 (KTN)
supercells. Our results show Li displacements and potential barrier heights in
KLT that are in excellent agreement with values obtained from experimental
fits. Dramatic changes in B-site dynamical charges occur in KTN in response to
changes in near neighbor (nn) coordination. These effects can be explained by
heterogeneity in the local electronic dielectric permittivity.
