Origin of ultrahigh piezoelectricity in relaxor-ferroelectrics - Dr. Gang Liu

DECEMBER 21, 2016

Over last 60 years, efforts to enhance piezoelectricity generally resort to tuning the long-range ferroelectric phase transition. In the work published in the recent issue of Nature Communications (doi:10.1038/ncomms13807), the researchers revealed that small amount of nanoscale local inhomogeneity may dramatically improve the piezoelectric responses (50-80%) of a ferroelectric crystal.

Relaxor ferroelectrics or relaxors - A ferroelectric material has electrical polarization that is reversed by application of an electric field, were discovered almost five decades ago among the complex oxides with perovskite structure. Relaxor ferroelectrics have revolutionized piezoelectric devices with much prominent properties due to ultra-high piezoelectric properties compared to the normal ferroelectrics, which makes it has great promise applications in medical ultrasound imaging.

“A key feature of the relaxor ferroelectrics, are the vibrations of inhomogeneous polar nanoregions, termed PNRs, which enable the enhanced/improved performance”, said Gang, co-authored the paper.

How the tiny regions makes relaxors so responsive is a more than 20-years-long challenge. Quantitative contribution of PNRs is lacking and the underlying mechanism for the ultrahigh piezoelectric responses of relaxor-based ferroelectrics has yet to be solved.

Now, scientists at Pennsylvania State University and their research partners have used a closely integrated experimental and computational investigation to solve this long-standing puzzle.

They successfully quantify the contributions of PNRs to the overall piezoelectric responses of relaxor ferroelectrics from investigations on three different types of relaxors. The contribution of PNRs to piezoelectric activity could account for up to 80% of the room temperature piezoelectric and dielectric responses.

This ultra-high piezoelectric responses of relaxor ferroelectrics are attributed to the “collinear” PNRs acted as “seeds” explained in the paper. The collinear PNRs will facilitate polarization rotation and therefore enhance the shear piezoelectric response.

Caption: A schematic plot showing the major finding of this work for the enhancement of dielectric/piezoelectric properties in relaxor–PT crystals (the temperature dependent piezoelectric/dielectric responses of the classical ferroelectrics is inferred from phenomenological theory and first-principle calculations of Pb(Zr_0.5Ti_0.5)O₃.

弛豫铁电单晶问世于上世纪90年代，相对于传统压电材料，弛豫铁电单晶由于具有超高的压电性能, 使其在医用超声成像技术中有着非常理想的应用前景。是过去20年铁电压电领域研究的热点材料,并被认为是研发下一代高性能换能器、传感器等器件的重要压电材料。弛豫铁电单晶不但压电常数可达2500 pC/N,约为传统Pb(Zr,Ti)O₃陶瓷的5倍, 其高压电性能的产生机理一直是铁电压电领域的研究热点。人们发现弛豫铁体中一个明显的特征是纳米极化区域的存在。那么，到底弛豫铁电体中的纳米极化区域是如何影响其压电性能的，一直未有确定的答案。通过实验及理论模拟相结合，本研究首次定量的给出了弛豫铁电体中纳米极化区对其介电、压电性能的影响。纳米区域的矩阵排列有助于实现极化旋转，进而提高其介电性能高达50%-80%。