NIST pings key material in sonar, closes gap on structural mystery

Using a neutron beam as a probe, researchers working at the National Institute of Standards and Technology (NIST) have begun to reveal the crystal structure of a compound essential to technologies ranging from sonar to computer memory. Their recent work* provides long-sought insight into just how a widely used material of modern technology actually works. (* D. Phelan, X. Long, Y. Xie, Z.-G. Ye, A.M. Glazer, H. Yokota, P.A. Thomas and P.M. Gehring. Single crystal study of competing rhombohedral and monoclinic order in lead zirconate titanate. Physical Review Letters, Nov. 8, 2010, DOI: 10.1103/PhysRevLett.105.207601)

Piezoelectrics like PZT are important in the construction of actuators, such as those used to read data from computers' hard disks. A better fundamental understanding of PZT may one day allow scientists to create better piezoelectric materials from the ground up.

The compound is a "piezoelectric," a material capable of changing one kind of energy into another - mechanical to electrical, or vice versa. Long employed in sonar systems to detect sound waves, more recently piezoelectrics have been applied in devices that require minuscule changes in position, such as the head that reads data from your computer's hard drive.

For decades, the industry standard piezoelectric has been PZT, a compound that contains titanium,zirconium, lead and oxygen.

Crystals of PZT change a tiny fraction of a percent in size when a sound wave strikes them, and thisshape change creates an electrical impulse. Decades ago, it was discovered that PZT performs at its best when the titanium and zirconium appear in approximately equal proportions, but no one really understood why.

"The theories frequently concern what happens at the transition line between having a surplus of zirconium and one of titanium," says Peter Gehring of the NIST Center for Neutron Research (NCNR). "Some theories suggest that right near the transition zone, the atoms take on a special configuration that allows certain atoms to move more freely than they can otherwise. But because it's been hard to grow a crystal of PZT large enough to analyze, we couldn't completely test these ideas."