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

The surface acoustic wave (SAW) properties, i.e., free surface wave ve locity, 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 particula r, the relations between the square coupling coefficient, the effectiv e permittivity, and the usual definition k(s)2=2DELTAV/V are discussed . In parallel, experimental measurements of the SAW properties were ca rried out by developing a curve-fitting algorithm on the real and imag inary parts of a unapodized single electrode SAW transducer. A free su rface 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 anal ysis of the effective permittivity curves. The SAW properties of a Y+1 28-degrees cut lithium niobate single crystal are also presented and-a re in agreement with those found in literature. These results are disc ussed and suggest that the present ceramic has the potential as a subs trate for SAW devices.