Evolution from Lead‐Based to Lead‐Free Piezoelectrics: Engineering of Lattices, Domains, Boundaries, and Defects Leading to Giant Response

Abstract

for piezoelectric devices was estimated to be worth $25.1 billion with a projected compounded annual growth rate (CAGR) of 6.2%. [6] However, the development of piezoelectrics took more than a century to evolve from quartz, which is among the first known piezoelectric materials, [7,8] to their current forms in the modern era. The evolution of piezoelectrics is, hence, rich with the exciting discoveries in fundamental physics, paving the way to the development of applications that changed the course of history. One such example is the invention of sonar by Paul Langevin and team in 1917 [9] which is still essentially implemented today for underwater acoustics and navigation. Later, the discovery of ferroelectricity in BaTiO 3 polycrystal in 1946 [10,11] and phase transition (now referred to as a morphotropic phase boundary (MPB)) in PbZrO 3 -PbTiO 3 solid solution in 1954 [12] stimulated a worldwide interest in gaining fundamental understanding of electromechanical coupling in ferroelectric materials to develop better and more reliable piezoelectric devices. [13][14][15] By contrast, the research on piezoelectrics in the past two decades has been driven mainly by the environmental and health concerns related to the toxicity of lead, which is a primary constituent of the widely used lead-based piezoelectric ceramics, [16,17] where the best known example is lead zirconium titanates (PZT). Consequently, the stringent regulations all over the world to restrict the use of lead [18] have resulted in the rise of "lead-free" ceramics which further gained popularity after Saito et al.'s discovery of large piezoelectric response in a lead-free piezoceramic. [19] These eco-friendly materials represent now although a relatively small part of the current piezoelectrics market, with a total estimate of around $172 million, but, their sales are projected to reach $443 million by 2024 with a CAGR of 20.8%. [6] ABO 3 -type perovskite oxide ferroelectrics hold great technical value owing to their large spontaneous polarization, which makes them highly suitable for piezoelectric applications. [1,3,20] In recent years, the research efforts have been primarily focused on developing new strategies to produce high-performance lead-free oxide piezoelectrics with properties at least comparable to or surpassing those of the lead-based counterparts, such as PZT. [20] These strategies have mainly Piezoelectric materials are known to mankind for more than a century, with numerous advancements made in both scientific understandings and practical applications. In the last two decades, in particular, the research on piezoelectrics has largely been driven by the constantly changing technological demand, and the drive toward a sustainable society. Hence, environmental-friendly "lead-free piezoelectrics" have emerged in the anticipation of replacing lead-based counterparts with at least comparable performance. However, there are still obstacles to be overcome for realizing this objective, while the efforts in this direction already seem to culminat...

Seeing Structural Mechanisms of Optimized Piezoelectric and Thermoelectric Bulk Materials through Structural Defect Engineering

“…Piezoelectrics, due to their ability of interconversion between electrical energy and mechanical strain, are widely applied in electro-mechanical devices. Environmental problems make it urgent to develop new lead-free piezoelectric materials with high performance [44,55,[113][114][115][116][117][118][119][120][121][122][123][124]. The lack of basic comprehension of the mechanisms at local level has hindered development.…”

Dehydration-activated structural phase transition in a two-dimensional hybrid double perovskite

“…However, on account of their toxicity and long-term instability, lead-based materials seriously affect the health of animals and plants, thus hindering their practical application 22 and meaning that the research on lead-free perovskites has become an important research hotspot. [23][24][25] Homo-valent replacement, as a popular lead-free solution using Ge and Sn, can be used to construct lead-free perovskites that show superior optical and electronic properties. [26][27][28] However, Ge-and Sn-based perovskites have still been criticized for their instability, prompting scientists to attempt hetero-valent replacement to produce materials with chemical stability.…”

Ultrahigh electric‐field‐induced strain in KNN‐based piezoelectric ceramics sintered in reducing atmosphere

“…In particular, piezoelectric actuators based on inverse piezoelectric effect are essential parts of electronic components in the field of precision manufacturing 1,2 . For a long time, lead‐based piezoelectric materials, represented by lead zirconate titanate, have occupied the main position in the piezoelectric equipment market 3 . However, the production, usage, and recycling of lead‐containing materials are detrimental to the natural environment and employee health 4 .…”

“…1,2 For a long time, lead-based piezoelectric materials, represented by lead zirconate titanate, have occupied the main position in the piezoelectric equipment market. 3 However, the production, usage, and recycling of lead-containing materials are detrimental to the natural environment and employee health. 4 Although directives such as "The Restriction of the use of certain Hazardous Substances in electrical and electronic equipment" and "Waste Electrical and Electronic Equipment" have been issued to restrict the use of lead in electronic components, piezoelectric-related applications were exempted because of challenges in the substitutability of lead-based piezoelectric ceramics.…”