Dopant doubles a crystal’s piezoelectricity

Piezoelectric materials generate mechanical strain under an applied electric field, and vice versa. Over the past 20 years, these materials have come into wide use in inkjet printers, guitar pickups, and devices that generate ultrasound waves for medical imaging, among other applications. Boosting the piezoelectric charge coefficient of these materials could lead to new kinds of medical imaging, improving the resolution of ultrasound and making it possible to generate the frequencies needed to image the eye and other parts of the body currently invisible to the method, says University of Wollongong materials engineer Shujun Zhang. Along with collaborators at Xi’an Jiaotong University and Pennsylvania State University, Zhang has been working for years to improve one of the best piezoelectric materials, a lead titanate crystal called PMN-PT, by engineering its structure. This material’s high piezoelectric charge coefficient arises from heterogeneity in its crystal structure. Zhang says previous research by his lab and collaborators showed that adding small amounts of rare-earth dopants should encourage this heterogeneity. So they experimented with several elements, eventually landing on samarium as the most promising. Now, they’ve grown single crystals of PMN-PT doped with Sm. The dopant doubles the crystal’s piezoelectricity to 3,400 picocoulombs per newton. It also doubles the yield of usable crystal, Zhang says (Science 2019, DOI: 10.1126/science.aaw2781).