Discovery of Environment-friendly High Performance Lead-free Piezoelectric Material

Surpassing Lead-containing PZT, the King of Piezoelectric Materials

2009.12.10

National Institute for Materials Science

A team led by Dr. Xiaobing Ren, Group Leader of the Ferro Physics Group, Sensor Materials Center, National Institute for Materials Science succeeded in developing the world’s first environment-friendly, high performance lead (Pb)-free piezoelectric material. This is the first time that a Pb-free piezoelectric material outperforms the “king of piezoelectrics”, the toxic Pb-containing piezoelectric material PZT which has been widely used for 50 years.

概要

  1. A team led by Dr. Xiaobing Ren, Group Leader of the Ferro Physics Group, Sensor Materials Center (Managing Director: Hajime Haneda), National Institute for Materials Science (President: Sukekatsu Ushioda) succeeded in developing the world’s first environment-friendly, high performance lead (Pb)-free piezoelectric material. This is the first time that a Pb-free piezoelectric material outperforms the “king of piezoelectrics”, the toxic Pb-containing piezoelectric material PZT (lead zirconate titanate), which has been widely used for 50 years. Furthermore, Dr. Ren also proposed a theory of high performance Pb-free piezoelectric materials, which has the potential to contribute to the discovery of other Pb-free piezoelectric materials with even higher piezoelectricity. As part of this achievement, Dr. Ren’s work shatters the myth that “toxic lead is essential to high piezoelectric properties,” and may initiate the worldwide shift from the toxic Pb-containing piezoelectric materials to environmental-friendly ones.
  2. Piezoelectric materials are an important class of energy-conversion materials, which generate electric voltage when mechanical force is applied, and conversely, produce shape change when a voltage is applied (reverse piezoelectric effect). Owing to this smart feature, piezoelectric materials have been used in a wide variety of sensors and actuators. The “king” of these materials is the lead-containing PZT, which has been used for the past 50 years and has found wide applications ranging from household appliances and general industrial products such as cell phones, personal computers, televisions, and automobiles, to Hi-tech equipment such as robots and the atomic force microscopes. However, because of the toxicity of Pb-containing materials, there has been increasingly strict legislative laws worldwide against the use of Pb-containing products. Therefore, developing high-performance Pb-free piezoelectric materials has become an urgent task and there have been intensive research activities over the past decade. Unfortunately, the existing Pb-free materials had been found to have inferior piezoelectricity, compared with that of the soft PZT. Despite the decade-long effort, the best Pb-free material available had reached merely about half the level of the soft PZT; this situation had given rise to the widely-held pessimistic myth that “toxic lead is essential for high piezoelectric properties.”. For this reason the toxic PZT has been temporally exempted from the restriction of the legislative laws, and our industry and our daily life had to rely on the harmful PZT.
  3. Dr. Ren’s team developed a novel Pb-free piezoelectric material, BZT-BCT (barium zirconate titanate- barium calcium titanate) and achieved a piezoelectric property (piezoelectric constant d33 = 620pC/N exceeding that of high-performance soft PZT. Dr. Ren also clarified the origin of the high piezoelectric property of this Pb-free piezoelectric material, based on which he proposed a theory of high performance piezoelectric materials. This theory may provide guidelines for the developing other Pb-free piezoelectric materials with even better piezoelectricity in the future.
  4. This result shatters the myth that “toxic lead is essential to the high piezoelectric properties,” and shows that it is possible to create practical Pb-free piezoelectric material which satisfy both environmental requirements and high performance, while the theory proposed by Dr. Ren holds the potential for the discovery of other Pb-free piezoelectric materials with even higher piezoelectricity. The present result is expected to have a big impact on the PZT-based piezoelectric industry and related huge industry and may mark the start of a more realistic substitution of the toxic PZT by environmental-friendly materials.
  5. This work will be published online in Physical Review Letters on December 11, 2009. The related international and Japanese patents are pending.