The Gibbs free energies of reaction △ r GTof KNbO3 and NaNbO3 were calculated and then that of KxNa1-xNbO3 was estimated. On the ba-sis of the thermodynamic calculation results, the hydrothermal temperatures were designed at 100, 160, and 230°C respectively. However, NaNbO3 was prepared when the heating temperature was higher than 160°C, and KNbO3 and KxNa1-xNbO3 were obtained at 230°C, sug-gesting that only at a higher temperature the kinetic requirement is satisfied. According to the X-ray diffraction results, both the solid solu-tions, NaNbO3-based solid solution, Na1-xKxNbO3, and KNbO3-based solid solution, K1-xNaxNbO3, were hydrothermally synthesized in 6 mol/L alkali (NaOH and KOH) solution at 230°C.
Based on the thermodynamic study of β-SiAlON and one section of Si-Al-O-N phase diagram for Si/Al=9 at 1773 K, the pure β-SiAlON (Si6-ZAlZOZN8-Z) ceramics with different Z values (viz. 1.4, 1.8, 2.2, 2.6, 3.0) were synthesized at different temperatures using the pressure-less technique. The relationship of the experimental-saturated Z value (the maximum Z value at a constant temperature) with temperature was then discussed. The experimental results indicated that there is a good linear relationship between Z value and temperature, which is Z=_10.76+0.0071T (R=0.9985). The β-SiAlON stability regions at different temperatures were exhibited in a sketch phase diagram of Si3N4-SiO2-Al2O3-AlN system. In addi- tion, the relationship between experimental-saturated Z value and the lattice parameters was also characterized, and the linear regression results a=7.604+0.02872Z and c=2.908+0.02496Z were obtained, respectively.
