Low-Temperature Sintering of Dense (Na,K)NbO3 Piezoelectric Ceramics Using the Citrate Precursor Technique

An aqueous-based citrate precursor technique has been applied to the synthesis of raw powders for use in the atmosphere sintering of nondoped Na0.5K0.5NbO3 (NKN) piezoelectric ceramics. The synthesized raw powders showed an efficient sinterability, and air-sintered NKN ceramics at a temperature as low as 1000 degrees C showed a dense microstructure of =4.46 g/cm3 (98.8% TD) as well as a saturated ferroelectric hysteresis loop of P-r=31.4 mu C/cm2 and E-c=17.3 kV/cm. The best piezoelectric properties of k(p)=0.44, Q(m)=280, and d(33)=161 pC/N were measured when the Na/K/Nb molar ratio in the precursor solution was fixed to 0.500/0.550/1.00 (NKN-550) to compensate the volatilization of K2O gas and to retain the (Na0.5K0.5)NbO3 composition after the sintering step. The present result indicates that the raw powders derived from the citrate precursor technique is significantly effective for a low-temperature sintering of lead-free NKN ceramics, showing a high density and excellent piezoelectric properties, even if no dopant is used.