Multiscale Structure Engineering for High-Performance Pb-Free Piezoceramics

Abstract

Metrics & MoreArticle Recommendations CONSPECTUS:The increasing world energy crisis drives humans to harvest the energy in nature as much as possible without heavily damaging the environment. However, most of the energy in nature cannot be used directly. Therefore, pursuing technologies or matter that can directly interconvert different energies has been one of the most cutting-edge fields in science and technology. Such a magic ability exists in true-life piezoelectric materials that generate charge when being given a force and vice versa, rendering them highly promising for energy harvesting and conversion because of the tremendous mechanical energy on the earth, such as tide energy. Thus, piezoelectric materials, represented by the lead zirconate titanate (Pb(Zr, Ti)O 3 , PZT) family, have been largely used in various traditional and burgeoning fields, such as electronic information, biomedical treatment, and wearable flexible electronic devices, and are one of the most important favorites in multidisciplinary fields. However, Pb is highly toxic.Driven by environmental protection and concern for human health, Pb-free piezoceramics are rapidly being developed to hopefully replace Pb-based ones. In particular, the renewal of Restriction of the use of certain Hazardous Substances (e.g., RoHS 2), issued by the European Union, declared that replacement of PZT "...may be scientifically and technologically practical to a certain degree...". Therefore, developing high-performance Pb-free piezoceramics has become more urgent than ever. In this context, some Pb-free piezoceramics, represented by potassium sodium niobate ((K, Na)NbO 3 , KNN), barium titanate (BaTiO 3 , BT), bismuth barium titanate ((Bi, Na)TiO 3 , BNT), and bismuth ferrite (BiFeO 3 , BFO), stand out because of their unique or similar traits. However, several key challenges, including an inferior overall performance compared to Pb-based counterparts and an unclear structure−property relationship from multiscale viewpoints, have severely hindered the development of Pb-free piezoceramics for a long time.Pb-based piezoceramics possess decent performance due to the strategy of phase boundary engineering, which inspired the researchers to pursue it in Pb-free counterparts. In the last 10 years, our group has been aiming at the new phase boundary (NPB) and new physical phenomenon in Pb-free piezoceramics. This Account presents our recent contributions to the development of Pbfree piezoceramics concerning the good performance and emerging phenomenon. First, we introduce the construction of the NPB in KNN-based piezoceramics by emphasizing the role of some key elements (i.e., Bi, Sb, Zr, and Hf). Then, we summarize the effects of the NPB on KNN-and BT-based ceramics and the new physical phenomenon in BNT-based ceramics. The NPB boosts the piezoelectric properties and temperature stability of KNN-and BT-based piezoceramics, comparable to some Pb-based piezoceramics. Combining the NPB and the multilayer ceramics substantially enhances the temperature stability of t...

Deciphering the atomic-scale structural origin for large dynamic electromechanical response in lead-free Bi0.5Na0.5TiO3-based relaxor ferroelectrics

“…By introducing local disorder and randomness, the phenomenon of deviations from the perfection occurring at the nanoscale, breaks the long-range correlation and average symmetry, providing enormous freedoms for modifying the properties of matter 2 . This strategy has been successfully established in perovskite relaxor ferroelectrics—complex oxides exhibiting the frequency-dependent diffusive phase transition that can substantially enhance dielectric and electromechanical properties 3 – 5 . Although these improved properties are often attributed to local (nanoscale) symmetry breaking, due to the lack of a clear understanding of their underlying structures, correlating the microscopic physical nature to material performance remains a decisive challenge in these “mess” systems (Fig.…”

“…Growing environmental concerns over lead toxicity have driven the search for lead-free alternatives in recent years 5 , 10 . Inspired by the heterovalent B-site cations (Mg 2+ , Nb 5+ ) in the canonical relaxor system PbMg 1/3 Nb 2/3 O 3 (PMN), lead-free Bi 0.5 Na 0.5 TiO 3 (BNT)-based relaxor systems with heterovalent A-site cations (Bi 3+ , Na + ) are expected to achieve comparable electromechanical properties that have been reported in Pb-based counterparts 11 .…”

Crystallographic texture and phase structure induced excellent piezoelectric performance in KNN‐based ceramics

“…For a few examples, piezoelectric coefficients ( d 33 ) of 525 and 650 ± 20 pC/N were successively achieved at the PPB composition in KNNS–BNKH and KNNS–BNKZ–Fe–AS systems, respectively, which are comparable to those of commercial PZT ceramics 16,17 . The excellent piezoelectric properties have been verified to originate from the flattening energy barrier induced by PPB, benefiting the polarization reversal 13,14,17 . In addition, controlling the crystal orientation has proven to be a more effective method to improve the piezoelectric and electromechanical coupling properties by advantageously utilizing the strong anisotropy of crystals.…”

“…Extensive research has shown that the polymorphic phase boundary (PPB) in KNN‐based ceramics is beneficial for enhancing the piezoelectric response. In the region of multiphase coexistence, the domain wall is easily oriented under an external electric field, and the samples exhibit excellent piezoelectric properties, analogs to the morphotropic phase boundary in PZT 12,13 . The PPB can be successfully constructed at approximately room temperature by elevating the phase transition temperature between the rhombohedral (R) and orthorhombic (O) phases, and simultaneously decreasing the phase transition temperature between the orthorhombic and tetragonal (T) phases.…”

Phase Character and Dielectric Properties of Amphoteric Holmium‐Doped Ba0.90Ca0.10(Ti0.95Zr0.05)2O5 Polycrystalline Ceramics

“…[3] Thus, suitable lead-free ferroelectric alternatives have been developed. [4][5][6][7] BaTi 2 O 5 (BT2) materials have gained increased research attention because of the analogical T C and promising ferroelectricity similar to PZT materials. [8] BT2 materials exhibit state-of-the-art relative dielectric constant and ferroelectricity along with the b-axis of the crystallography in a single crystal [9] ; however, they could not be easily prepared by a conventional process.…”