**Abstract:**

Relaxor ferroelectric single crystals of Pb(Zn[inf 1/3]Nb[inf 2/3])O[inf 3] (PZN), Pb(Mg[inf 1/3]Nb[inf 2/3])O[inf 3] (PMN) and their solid solutions with normal ferroelectric PbTiO[inf 3] (PT) were investigated for ultrasonic transducer applications. Longitudinal coupling coefficients (k[inf 33]) as high as 94% and dielectric constants (K[inf 3][sup T]) in the range of 3500--6000 were achieved with low dielectric loss (<1%) using <001> oriented rhombohedral crystals of (1-x)PZN-xPT and (1-y)PMN-yPT, where x<0.09 and y<0.35. Dicing direction as well as poling direction was critical for high coupling under laterally clamped conditions. Dicing parallel to the (001) yields 90% of laterally clamped coupling (k[inf bar]) out of 94% longitudinal coupling (k[inf 33]) for PZN-8%PT. Thickness coupling (k[inf T]) as high as 64% and low dielectric constant (K[inf 3][sup T])<600 with low loss (<1%) could be achieved using tetragonal crystals of (1-x)PZN-xPT and (1-y)PMN-yPT, where x>0.1 and y>0.4. The performance gains associated with these ultra-high coupling coefficients and range of dielectric constants are evident in relations to broader bandwidth and electrical impedance matching. Using the KLM model, a pulse/echo response simulated a bandwidth of ~124% for a subdiced array element with a center frequency of 10 MHz. An optimized array design of the same geometry constructed of PZT 5H displayed 87% bandwidth. [Work supported by ONR, DARPA.]

ASA 133rd meeting - Penn State, June 1997