Losses in Ferroelectric Materials - Dr. Gang Liu

Shanghai, February 14, 2015— Energy loss (or energy dissipation)  is one of most critical issues in ferroelectric materials for engineering applications. This loss including elastic, piezoelectric and dielectric, associated with elasticity, dielectric relaxation and piezoelectric hysteresis in ferroelectrics, have brought many controversies/confusions in the past several decades.  In a newly published study led by Dr. Gang Liu from Center of High Pressure Science and Technology Advanced Research, reviewed how the energy losses happened in ferroelectrics, fully tracked the origin of energy losses, and proposed a general theoretical model to describe the inherent relationships among elastic, dielectric, piezoelectric and mechanical losses.

Ferroelectric materials are materials possessing a natural charge polarization that can be reversed by an external electric field, known as the switching process. Over 250 compounds have been found to display such characteristics since the discovering of ferroelectricity in Rochelle salt in 1920. Leadtitanate, PbTiO3, and related compounds are most focused systems.

Ferroelectric  draws its name by analogy with ferromagnetism, which describes permanent magnetic materials based on iron that are found in nature. Ferroelectric materials have been widely used as resonators, actuator, transducers, transformers, sensors, non-volatile FeRAM, capacitors, etc. But they’ve faced one major obstacle­­­—Energy loss (or energy dissipation), which is one of the most key problems in ferroelectrics for high power devices, such as therapeutic ultrasonic transducers, large displacement actuators, SONAR projectors, and high frequency medical imaging transducers. Energy loss may cause significant heat generation in electromechanical devices under strong field driving condition, leading to device failure, especially in high-power transducers and ultrasonic motors.

For decades, scientists have made impressive progresses to reduce energy losses in ferroelectrics using kinds of methods. Several possible mechanisms have been proposed, with many open questions still remaining.

Now, in new research published in Materials Science and Engineering: R: Reports, led by Dr. Gang liu, provided a comprehensive review on the energy losses in ferroelectrics by comparing related intrinsic and extrinsic mechanisms, characterization techniques on serials offerroelectric materials, mainly on relaxor-PbTiO3, to provide a deep understanding of correlative reasons involved.

According to the relationship between the mechanical quality factor and measured quality factors, easy polarization variations and domain wall motions related to the intrinsic and extrinsic contributions, are supposed to be responsible for the enhanced functional properties and decreased quality factors in ferroelectric single crystals, explained in the work.

“Our work shows that the phase boundary region and related structural instability are critical factors for the easy polarization variations, leading to decreased quality factors but enhanced piezoelectric properties,” said Gang Liu, the lead author of this research, “For polycrystalline piezoceramics, grain boundaries and grain size both play critical roles in dominating the loss behavior in these materials”.

“We are proposing a general model to correlate all three types of losses and obtain individual elastic, dielectric, piezoelectric losses”, Liu added, “ Our study have important implications in both scientific ressearch and industry applications”.

The other co-authores are Shujun Zhang and Wenhua Jiang from Department of Mathematics and Materials Research Institute, the Pennsylvania State University,　USA， and Wenwu Cao from Condensed Matter Science and Technology Institute, Harbin Institute of Technology China & Department of Mathematics and Materials Research Institute, the Pennsylvania State University, USA.