EXPERIMENTAL-DETERMINATION OF THE SURFACE-ACOUSTIC-WAVE PROPERTIES OF NEW FINE-GRAIN PIEZOELECTRIC CERAMICS

The surface acoustic wave (SAW) properties, i.e., free surface wave velocity, surface coupling coefficient, and static surface permittivity, of a lead titanate composition modified with an additive of samarium and processed by hydrothermal synthesis are determined. The effective permittivity of the piezoelectric ceramic was calculated, and the SAW properties were extracted from the analysis of the curve. In particular, the relations between the square coupling coefficient, the effective permittivity, and the usual definition k(s)2=2DELTAV/V are discussed. In parallel, experimental measurements of the SAW properties were carried out by developing a curve-fitting algorithm on the real and imaginary parts of a unapodized single electrode SAW transducer. A free surface wave velocity of 2595 m/s, a coupling coefficient of 1.8%, and a static permittivity of 196 are found which were predicted by the analysis of the effective permittivity curves. The SAW properties of a Y+128-degrees cut lithium niobate single crystal are also presented and-are in agreement with those found in literature. These results are discussed and suggest that the present ceramic has the potential as a substrate for SAW devices.