The equilibrium at 200 ℃ favouring the perovskite phase (Fig. 5) was different from that at 170 ℃ and below favouring the K8Nb6O19·10H2O phase. The phase equilibrium did not seem to be affected when the synthesis temperature decreased from 170 to 60 ℃, which did not change the ratio of KNbO3 and Nb2O5 in the obtained main product of K8Nb6O19·10H2O, based on the XRD patterns in Fig. 2. This ratio was also similar to our previous results at 9 mol/L KOH [26]. The above synthesis probably occurred in the KOH - Nb2O5 - H2O system via a dissolution-precipitation process according to the following reactions [29,30]: