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

The long-standing popularity of thermoelectric materials has contributed to the creation of various thermoelectric devices and stimulated the development of strategies to improve their thermoelectric performance. In this review, we aim to comprehensively summarize the state-of-the-art strategies for the realization of high-performance thermoelectric materials and devices by establishing the links between synthesis, structural characteristics, properties, underlying chemistry and physics, including structural design (point defects, dislocations, interfaces, inclusions, and pores), multidimensional design (quantum dots/wires, nanoparticles, nanowires, nano- or microbelts, few-layered nanosheets, nano- or microplates, thin films, single crystals, and polycrystalline bulks), and advanced device design (thermoelectric modules, miniature generators and coolers, and flexible thermoelectric generators). The outline of each strategy starts with a concise presentation of their fundamentals and carefully selected examples. In the end, we point out the controversies, challenges, and outlooks toward the future development of thermoelectric materials and devices. Overall, this review will serve to help materials scientists, chemists, and physicists, particularly students and young researchers, in selecting suitable strategies for the improvement of thermoelectrics and potentially other relevant energy conversion technologies.

Advanced Thermoelectric Design: From Materials and Structures to Devices

Lead zirconate titanate (PZT) based piezoelectric materials are well known for their excellent piezoelectric properties. However, considering the toxicity of lead and its compounds, there is a general awareness for the development of environmental friendly lead-free materials as evidenced from the legislation passed by the European Union in this effect. Several classes of materials are now being considered as potentially attractive alternatives to PZTs for specific applications. In this paper, attempts have been made to review the recent developments on lead-free piezo materials emphasizing on their preparation, structure–property correlation, etc. In this context, perovskite systems such as bismuth sodium titanate, alkali niobates (ANbO3), etc. and non-perovskites such as bismuth layer-structured ferroelectrics are reviewed in detail. From the above study, it is concluded that some lead-free compositions show stable piezoelectric responses even though they do not match the overall performance of PZT. This has been the stimulant for growing research on this subject. This topic is of current interest to the researchers worldwide as evidenced from the large number of research publications. This has motivated us to come out with a review article with a view that it would give further impetus to the researchers already working in this area and also draw the attention of the others.

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Review: environmental friendly lead-free piezoelectric materials

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

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

The phase transition behavior and piezoelectric properties of (Ba1−xCax)(Zr0.1Ti0.9)O3 and (Ba0.85Ca0.15)(ZryTi1−y)O3 ceramics were investigated in this work to find out the potential factors contributing to large piezoelectricity. It was found that the morphotropic phase boundary (MPB) of (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 ceramics was closely related to the presence of an intermediate phase (considered as orthorhombic phase in this work) between rhombohedral (R) and tetragonal (T) phases at a narrow region, which could be carefully adjusted by the temperature and contents of Ca and Zr in the composition. In addition, the maximum piezoelectric and electromechanical coupling coefficients (with d33 = 572 pC/N and kp = 0.57) were observed near the MPB region close to T phase side, which might be intimately related to the presence of the intermediate phase. This investigation yielded a new sight to understand the mechanism of enhanced piezoelectricity near the MPB.

Phase Transition Behavior and Large Piezoelectricity Near the Morphotropic Phase Boundary of Lead‐Free (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 Ceramics

Regulation of energy density and efficiency in transparent ceramics by grain refinement

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.

Xiaolian Chao

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

Phase Transition Behavior and Large Piezoelectricity Near the Morphotropic Phase Boundary of Lead‐Free (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 Ceramics

Regulation of energy density and efficiency in transparent ceramics by grain refinement

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