Doping effects of CuO additives on the properties of low-temperature-sintered PMnN-PZT-based piezoelectric ceramics and their applications on surface acoustic wave devices

To develop the anisotropic ceramic substrate with low sintering temperature for surface acoustic wave (SAW) applications, the low cost and feasible material with moderate piezoelectric properties, good dielectric properties, and higher Curie temperature were explored. The piezoelectric ceramics with compositions of Pb[(Mn_1/3Nb_2/3)_0.06-(Zr_0.52Ti_0.48)0.94] O₃ (PMnN-PZT) + 0.5 wt.% PbO + x wt.% CuO (0.05les times les 0.3) had been prepared by the conventional mixed-oxides method. CuO dopants were used as the sintering aid to improve the bulk density under low sintering temperature (i.e., 980-1040degC). The phase structures, microstructures, frequency behavior of dielectric properties (up to 50 MHz), piezoelectric properties, ferroelectric properties, and temperature stability with the amount of CuO additive were systematically investigated. Experimental results showed that the sintering temperature could be lowered down to 1020degC and still keep reasonably good piezoelectric activity (i.e., high electromechanical coupling factor k_p, k_t) and dielectric and ferroelectric properties. The preferable composition, obtained at x = 0.1, presented the values of the electromechanical coupling factor (k_p) (k_t), mechanical quality factor (Q_m), piezoelectric charge constant (d₃₃), dielectric constant, dielectric loss, temperature coefficient of resonant frequency (TCF_B), and Curie point (T_c) of 0.54, 0.48, 850, 238 pc/N, 1450, 0.0023, 1.1 kV/mm, 26 coul/cm², -150 ppm/degC, and 348degC. Using this developed low-temperature-sintered material to make the piezoelectric substrate, the SAW filter was fabricated and its properties were measured. Results showed that this device possessed very high value of k²(7.13%) with a good TCF (-40.15 ppm/degC), and a surface wave velocity (V_P) of 2196 m/s.