It should be noted that the path 1 samples are obtained by diluting the subsaturated MF2 solution, where there are certain amounts of CIPs (Fig. ). As a consequence, they might be preserved in the dilution. While for the samples of path 2, they are prepared by a physical mixture of NaF solution and M 2+ salt solution, where there is no M 2+ -F -CIPs initially. These indicate that the transformation from SIPs to CIPs is dynamics-controlled. There is an energy barrier that prevents the transformation.