LAUSR

Trace amounts of samarium greatly improve materials used in sonar and ultrasound imaging Piezoelectrics change in length when an electric field is applied, and good materials have large piezoelectric coefficients, the ratio of elongation to applied field strength. The most advanced piezoelectric devices, such as underwater sonars and medical ultrasound imaging instruments, typically use a perovskite oxide crystal, Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT). The properties and manufacture of this material have been optimized in the past 20 years (1–4). The increase of the piezoelectric coefficient of PMN-PT by a factor of 2 (to ∼4000 pC/N), reported on page 264 of this issue by Li et al. (5), is thus an unexpected result. The authors achieved this improved piezoelectric performance by adding only about one samarium (Sm) atom per thousand atoms of the parent PMN-PT crystal, and the piezoelectric properties of this doped crystal are more homogeneous than those of the undoped material.