Virginia Tech team tests alternative to lead-based piezoelectric materials
For post-doctoral researcher Deepam Maurya, getting the lead out is not a colloquialism for working fast.
Lead zirconate titanate, known as PZT, is one of the world's most often used piezoelectric ceramic materials — and is made up of more than 50 percent lead.
Working with Shashank Priya, the Robert E. Hord Jr. Professor of Mechanical Engineering and faculty director for materials and sustainable energy at the Institute for Critical Technology and Applied Science (ICTAS), Maurya has worked to find an alternative to lead-based piezoelectric ceramic materials since earning his Ph.D. from Virginia Tech in 2012.
Hoping to find a way to get more lead out of the environment, Maurya has spent the last eight years working to solve the problem of replacing the lead with a suitable piezoelectric material that will meet the working thresholds of PZT. The current lead-heavy composition is used in the automotive, medical, and electrical fields, among others, to make sensors, filters, actuators, and other products.
“People have been working on this topic for more than 20 years,” said Maurya, of Shahjahanpur, India. “If we can reduce the amount of lead being used in products and disposed of in landfills, we’ll be making a positive impact on the ecosystem.”
While PZT components are normally very small in dimensions, the number of these lead-based products is staggering. Finding a suitable replacement will yield enormous economic and environmental benefits. But finding a suitable replacement for the high properties of lead-based compositions has been a problem.
“The toxicity of lead is a big concern that needs to be addressed as the lead from discarded components can mix with soil and eventually underground water systems,” Maurya explained.
“In many parts of the world there is a growing demand for the elimination of lead from all consumer items. Cellphones, auto-focus cameras, fuel injectors, the Hubble Space Telescope, they all utilize lead-based piezoelectric actuators,” Maurya explained. “Lead-based piezoelectric materials allow for very precise control, but with ecological consequences. What we’ve discovered is that we can achieve similar properties such as high piezoelectric response and high temperature stability in a lead-free material which is necessary for a suitable lead replacement.”
The patented lead substitute, which Maurya calls "NBT-based ceramics" is a significant improvement over previous compounds as the mixture. When combined with a special synthesis process that aligns the grains in the ceramic along a preferred crystallographic direction this material exhibits excellent temperature stability, giant electric field induced strain, and ultra-low hysteresis. In short, it achieves the optimum combination of most of the relevant electromechanical parameters necessary to be a viable alternative to traditional PZT.
“We used the knowledge of previous studies to develop a theory that combines phase transformations, dopant engineering, and microstructure engineering — which led to the material with a high transition temperature and high piezoelectric coefficient,” Maurya said. “We based our process on current industry accepted manufacturing techniques and it is quite scalable.”
“Replacing lead by a suitable piezoelectric material in many of our consumer products can make a big difference in creating a sustainable environment, said Roop L. Mahajan, the executive director of ICTAS. “This has the potential to be a transformative technology.”
The road from laboratory to products is long, Maurya said, but they are starting the process of validating the compound for material-specific applications. The NBT-based ceramics are currently being investigated by some of the industrial members of the National Science Foundation Industry and University Cooperative Research Program “Center for Energy Harvesting Materials and Systems.”
The pair had a paper published on their work in 2015 that can be found in Scientific Reports.
Written by Rosaire Bushey.