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Complex system ceramics Pb(Sc/sub 1/2/Nb/sub 1/2/)O/sub 3/-Pb(Mg/sub 1/3/Nb/sub 2/3/)O/sub 3/-Pb(Ni/sub 1/2/Nb$ d1/sub /2/)O/sub 3/-(Pb/sub 0.965/,Sr/sub 0.035/) (Zr,Ti)O/sub 3/ (PSN-PMN-PNN-PSZT abbreviated PSMNZT) have been synthesized by the conventional technique, and dielectric and piezoelectric properties of the ceramics have been investigated for ultrasonic medical transducers. High capacitances of the transducers are desired in order to match the electrical impedance between the transducers and the coaxial cable in array probes. Although piezoelectric ceramics that have high dielectric constants (/spl epsiv//sub 33//sup T///spl epsiv//sub 0/) are produced in many foundries, the dielectric constants are insufficient. However, we have reported that low molecular mass B-site ions in the lead-perovskite structures are important in realizing better dielectric and piezoelectric properties. We focused on the complex system ceramics PSMNZT that consists of light B-site elements. The maximum dielectric constant, /spl epsiv//sub 33//sup T///spl epsiv//sub 0/ = 7,200, was confirmed in the ceramics, where k/sub 33/' = 69%, d/sub 33/ = 940 pC/N, and T/sub c/ = 135/spl deg/C were obtained. Moreover, pulse-echo characteristics were simulated using the Mason model. The PSMNZT ceramic probe showed echo amplitude about 5.5 dB higher than that of the conventional PZT ceramic probe (PZT-5H type). In this paper, the electrical properties of the PSMNZT ceramics and the simulation results for pulse-echo characteristics of the phased-array probes are introduced.