Fig. 7 shows the ICP results of the variation of K and Na element contents after sintering, as well as the K/Na ratio. The measured contents are normalized to Nb element, which is considered as a non-volatized element during sintering. K and Na contents both decreased with the increasing of sintering temperature. It can be specifically manifested from the ICP results that the volatilization of potassium is much more severe than sodium, especially when the sintering temperature exceeded to 1115°C. This should be ascribed to the low melting point of KNbO3 (~1090oC) if compared with NaNbO3 (nearly 1420oC)[33].