Potassium-sodium niobate lead-free piezoelectric materials: past, present, and future of phase boundaries.

After twenty years of partly quiet and ten years of partly enthusiastic research into lead-free piezoceramics there are now clear prospects for transfer into applications in some areas. This mimics prior research into eliminating lead from other technologies that resulted in restricted lead use in batteries and dwindling use in other applications. A figure of merit analysis for key devices is presented and used to contrast lead-containing and lead-free piezoceramics. A number of existing applications emerge, where the usage of lead-free piezoceramics may be envisaged in the near future. A sufficient transition period to ensure reliability, however, is required. The use of lead-free piezoceramics for demanding applications with high reliability, displacements and frequency as well as a wide temperature range appears to remain in the distant future. New devices are outlined, where the figure of merit suggests skipping lead-containing piezoceramics altogether. Suggestions for the next pertinent research requirements are provided.

Transferring lead-free piezoelectric ceramics into application

We present a critical review that encompasses the fundamentals and state-of-the-art knowledge of barium titanate-based piezoelectrics. First, the essential crystallography, thermodynamic relations, and concepts necessary to understand piezoelectricity and ferroelectricity in barium titanate are discussed. Strategies to optimize piezoelectric properties through microstructure control and chemical modification are also introduced. Thereafter, we systematically review the synthesis, microstructure, and phase diagrams of barium titanate-based piezoelectrics and provide a detailed compilation of their functional and mechanical properties. The most salient materials treated include the (Ba,Ca)(Zr,Ti)O3, (Ba,Ca)(Sn,Ti)O3, and (Ba,Ca)(Hf,Ti)O3 solid solution systems. The technological relevance of barium titanate-based piezoelectrics is also discussed and some potential market indicators are outlined. Finally, perspectives on productive lines of future research and promising areas for the applications of these ma...

BaTiO3-based piezoelectrics: Fundamentals, current status, and perspectives

Recent development in lead-free perovskite piezoelectric bulk materials

High strain piezoelectric ceramics are the state-of-the-art materials for high precision, positioning devices. A comprehensive review of the latest developments of the various types of perovskite piezoelectric ceramic systems is presented herein, with special attention given to three promising families of lead-free perovskite ferroelectrics: the barium titanate, alkaline niobate and bismuth perovskites. Included in this review are details of phase transition behavior, strain enhancement approaches, material reliabilities as well as the status of some promising applications. This current review describes both compositional and structural engineering approaches that are intended to achieve enhanced strain properties in perovskite piezoelectric ceramics. The factors that affect the strain behavior of high-strain perovskite piezoelectric ceramics are addressed. The reliability characteristics of these high-strain ferroelectrics as well as the recent approaches to the long-term electrical, thermal and time-stability enhancement are summarized. Several promising applications of high-strain perovskite materials are introduced, which take advantages of their characteristics; examples include high-energy storage, pyroelectric and electro-caloric effect and luminescent properties.

Progress in high-strain perovskite piezoelectric ceramics

Superior comprehensive energy storage properties in Bi0.5Na0.5TiO3-based relaxor ferroelectric ceramics

Sr0.7Bi0.2TiO3 (SBT) was introduced into Bi0.5Na0.5TiO3 (BNT) via a standard solid-state route to modulate its relaxation behaviour and energy storage performance. With increasing SBT content, the perovskite structure of BNT transforms from a rhombohedral phase to a weakly polarized pseudo-cubic phase, and the relaxation behaviour is enhanced. In particular, the EDBS is improved from 120 kV/cm of BNT to 160 kV/cm of 0.6BNT-0.4SBT, which displays a large recoverable energy storage density (Wrec = 2.20 J/cm3), implying a large potential ability of energy storage for the 0.6BNT-0.4SBT ceramic. Moreover, both dielectric properties (28–326 °C) and energy storage properties (20–140 °C) exhibit a good thermal stability for the same 0.6BNT-0.4SBT composition. These characteristics suggest 0.6BNT-0.4SBT ceramic could be a promising candidate to be applied in a pulse power system over a broad temperature range.

Enhanced energy density and thermal stability in relaxor ferroelectric Bi0.5Na0.5TiO3-Sr0.7Bi0.2TiO3 ceramics

Lead-free relaxor ferroelectric ceramics of (1 − x)(0.6Bi0.5Na0.5TiO3–0.4Sr0.7Bi0.2TiO3)–xAgNbO3 were fabricated by a conventional mixed oxide route. The multifunction of AgNbO3 (AN) doping into the 0.6Bi0.5Na0.5TiO3–0.4Sr0.7Bi0.2TiO3 (BNT–SBT) matrix can be divided into two main aspects. First, it enhances the breakdown electric field (Eb) as a result of reduced grain size and increased resistivity. Second, it improves η via enhancing the relaxation behavior and stabilizing the antiferroelectric (AFE) phase. Eventually, we achieved a large Wrec of 3.62 J cm−3 and a high η of 89% simultaneously under a moderate electric field of 246 kV cm−1 as the doping ratio x of AgNbO3 equals 0.05. In addition, the same sample also exhibits excellent temperature stability and good frequency stability, suggesting that AgNbO3 doped BNT–SBT ceramics could be an ideal candidate in high energy storage capacitors.

Bi0.5Na0.5TiO3-based relaxor ferroelectric ceramic with large energy density and high efficiency under a moderate electric field

Y2/3Cu3Ti4O12 ceramics were successfully prepared by the conventional solid-state reaction method. Effects of sintering conditions on microstructure, phase structure, and the dielectric properties of Y2/3Cu3Ti4O12 ceramics were investigated in detail. Y2/3Cu3Ti4O12 ceramics sintered at 1010°C for 25 h exhibited a giant dielectric constant (1.10 × 104) and a relatively low dielectric loss (0.033) around room temperature. The samples showed good temperature stability (ΔCT/C25∘C=-6.7% – 9.5%) in the temperature range from −60°C to 125°C at 10 kHz. It was also found that a new dielectric relaxation III appeared at higher temperatures (>200°C). The complex impedance spectroscopy analysis suggested that Y2/3Cu3Ti4O12 ceramics were electrically heterogeneous, and they consisted of semiconducting grains and insulating grain boundaries, which could be modeled to a first approximation on an equivalent circuit based on two parallel RC elements connected in series. The Cu2+/Cu3+ and Ti3+/Ti4+ aliovalences were observed in Y2/3Cu3Ti4O12 ceramics. The giant permittivity phenomenon could be explained by internal barrier layer capacitance (IBLC) effect.

Giant Dielectric Constant and Good Temperature Stability in Y2/3Cu3Ti4O12 Ceramics

Lead-free (Ba1−xCax)(Zr0.1Ti0.9)O3(BCZT) ceramics were synthesized by conventional solid-state sintering process. The Ca ion substitutions on phase transition behavior, microstructure, ferroelectric and piezoelectric properties of BCZT ceramics were systemically investigated. The diffuse phase transition (DPT) behavior was suppressed, while the orthorhombic → tetragonal (O→T) and rhombohedral → orthorhombic (R→O) phase transitions were observed when the Ca content is at x = 0.05. Further increasing the Ca content, the DPT behavior gradually enhanced, and both the O→T and R→O phase transitions gradually evolved into R→T phase transition when the Ca content increases up to 0.15 at 25 °C. This behavior was related with phase structure and morphology, which significantly impacted the ferroelectric and piezoelectric properties near the R→T phase boundary. As a result, the sample with Ca contents of 0.15 shows the outstanding piezoelectric properties (with d33 = 572 pC/N, kp = 57%, Qm = 125, er = 4821, and tan ...

Pengfei Liang

Papers

Superior comprehensive energy storage properties in Bi0.5Na0.5TiO3-based relaxor ferroelectric ceramics

Enhanced energy density and thermal stability in relaxor ferroelectric Bi0.5Na0.5TiO3-Sr0.7Bi0.2TiO3 ceramics

Bi0.5Na0.5TiO3-based relaxor ferroelectric ceramic with large energy density and high efficiency under a moderate electric field

Giant Dielectric Constant and Good Temperature Stability in Y2/3Cu3Ti4O12 Ceramics

Phase transition behavior and electrical properties of lead-free (Ba1−xCax)(Zr0.1Ti0.9)O3 piezoelectric ceramics