Using mechanochemical activation, a homogeneous (K0.485Na0.485Li0.03)(Nb0.8Ta0.2)O-3 (KNLNT) solid solution can be obtained after subsequent calcination and sintering. The present study aims to elucidate the origin of the high homogeneity of the activated powder and its relation to the synthesis of KNLNT ceramics. To investigate the effect of the milling conditions, the high-energy milling experiments were performed under different regimes, distinguished by the extent of the impact and frictional force components acting on the powder particles. In addition to this, each one of the starting compounds were also activated separately and then mixed together so as to avoid mechanochemical interactions. This enables us to verify whether the reaction between the constituents during high-energy milling has an effect on the synthesis of KNLNT. The results show that during the activation of the mixture, the symmetry of the CO(3)2- ions, present initially in K2CO3 and Na2CO3, is lowered. This is induced mechanochemically by the reaction with Nb2O5 and Ta2O5. As a result, an amorphous carbonato complex is formed, which plays a crucial role in obtaining highly homogeneous KNLNT ceramics.