The results of low-temperature linear and nonlinear susceptibilities and polarization measurements of the KLT-4.3%Li crystalline sample are presented. The following model of the mechanism of the ferroelectricity in the K0.957Li0.043TaO3 (KLT-4.3%Li) solid solution is proposed. Static quasi-frozen clusters of Li+ dipoles affect the ordering process of the remainder of the system: a dynamical correlation of the off-center motions of Ta ions along one of the equivalent off-center sites in the < 111 > cubic direction in the octahedral environment of O ions occurs and leads to the formation of a reversible spontaneous polarization. (C) 2016 Elsevier Ltd. All rights reserved.