A large body of work has been reported in the last 5 years on the development of lead-free piezoceramics in the quest to replace lead–zirconate–titanate (PZT) as the main material for electromechanical devices such as actuators, sensors, and transducers. In specific but narrow application ranges the new materials appear adequate, but are not yet suited to replace PZT on a broader basis. In this paper, general guidelines for the development of lead-free piezoelectric ceramics are presented. Suitable chemical elements are selected first on the basis of cost and toxicity as well as ionic polarizability. Different crystal structures with these elements are then considered based on simple concepts, and a variety of phase diagrams are described with attractive morphotropic phase boundaries, yielding good piezoelectric properties. Finally, lessons from density functional theory are reviewed and used to adjust our understanding based on the simpler concepts. Equipped with these guidelines ranging from atom to phase diagram, the current development stage in lead-free piezoceramics is then critically assessed.

Perspective on the Development of Lead-free Piezoceramics

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

Perovskite lead-free dielectrics for energy storage applications

The methods of preparation and formation of supermolecular structures in quiescent and sheared melts and the properties of the β-modification of isotactic polypropylene (β-iPP) are reviewed. The introduction of selective β-nucleants is the most reliable method for preparation of samples rich in β-modification or of pure β-iPP. The advantages and drawbacks of the known β-nucleating agents are summarized. It is emphasized that pure β-iPP can be prepared under laboratory and processing conditions in the presence of highly active and selective β-nucleants. Nevertheless, there are no literature data—apart from that of the author's groups—which evidenced unambiguously the formation of pure β-iPP. It hints at the insufficient selectivity of β-nucleants used or at the inappropriate crystallization or melting conditions applied by other scientists. The structure formation during the high-temperature hedritic crystallization is discussed comprehensively and illustrated by polarized light microscopy and scanning ele...

β-MODIFICATION OF ISOTACTIC POLYPROPYLENE: PREPARATION, STRUCTURE, PROCESSING, PROPERTIES, AND APPLICATION

Perovskite oxides with formula ABO3 or A2BO4 are a very important class of functional materials that exhibit a range of stoichiometries and crystal structures. Because of the structural features, they could accommodate around 90% of the metallic natural elements of the Periodic Table that stand solely or partially at the A and/or B positions without destroying the matrix structure, offering a way of correlating solid state chemistry to catalytic properties. Moreover, their high thermal and hydrothermal stability enable them suitable catalytic materials either for gas or solid reactions carried out at high temperatures, or liquid reactions carried out at low temperatures. In this review, we addressed the preparation, characterization, and application of perovskite oxides in heterogeneous catalysis. Preparation is an important issue in catalysis by which materials with desired textural structure and physicochemical property could be achieved; characterization is the way to explore and understand the textura...

Perovskite Oxides: Preparation, Characterizations, and Applications in Heterogeneous Catalysis

Sol-gel derived CaCu3Ti4O12 ceramics : Synthesis, characterization and electrical properties

The development and use of high-performance and environmentally friendly energy storage capacitors are urgently demanded. Despite extensive research efforts, the performance of existing lead-free dielectric ceramics is barely satisfactory. In this work, a novel lead-free 0.78NaNbO3–0.22Bi(Mg2/3Ta1/3)O3 (0.22BMT) linear-like relaxor ferroelectric with ultrahigh energy storage capability and ultrahigh efficiency was designed and synthesized via a local random field strategy. To our satisfaction, an ultrahigh recoverable energy density (Wrec, 5.01 J cm−3) and an ultrahigh energy efficiency (η) of 86.1% were achieved simultaneously, which are superior to those of other reported lead-free systems. In addition, excellent temperature, frequency and fatigue stabilities (variation of Wrec < 8% over 20–200 °C, Wrec < 3% after 1–100 Hz and 104 cycles) were observed. More importantly, the 0.22BMT ceramic exhibited a large current density (CD ∼ 537.9 A cm−2), an extremely high power density (PD ∼ 37.7 MW cm−3), and an ultrafast discharge time (t0.9 ∼ 23 ns). The impedance analysis demonstrated that the introduction of BMT was beneficial for the improvement of the insulation ability and breakdown strength (Eb) of the 0.22BMT ceramic. Additionally, nonisovalent Mg2+ and Ta5+-filled Nb5+ on the B-site with low average electronegativity generated a random local field, which enhanced the ion bonding, destroyed the long-range order and led to decreased remnant polarization (Pr). These results indicate that this new strategy is a feasible and efficacious means to simultaneously achieve ultrahigh Wrec, superior η and excellent thermal stability in NN-based lead-free ceramics. Furthermore, this work has further broadened the scope of research and the application of the NN-based ceramics.

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Realizing ultrahigh recoverable energy density and superior charge–discharge performance in NaNbO3-based lead-free ceramics via a local random field strategy

A new low loss spinel microwave dielectric ceramic with composition of ZnLi2/3Ti4/3O4 was synthesized by the conventional solid-state ceramic route. The ceramic can be well densified after sintering above 1075 °C for 2 h in air. X-ray diffraction data show that ZnLi2/3Ti4/3O4 ceramic has a cubic structure [Fd-3m (227)] similar to MgFe2O4 with lattice parameters of a = 8.40172 A, V = 593.07 A3, Z = 8 and ρ = 4.43 g/cm3. The best microwave dielectric properties can be obtained in ceramic with relative permittivity of 20.6, Q × f value of 106,700 GHz and τf value of −48 ppm/°C. The addition of BaCu(B2O5) (BCB) can effectively lower the sintering temperature from 1075 °C to 900 °C and does not induce much degradation of the microwave dielectric properties. Compatibility with Ag electrode indicates that the BCB added ZnLi2/3Ti4/3O4 ceramics are good candidates for LTCC applications.

Xiuli Chen

Papers

Sol-gel derived CaCu3Ti4O12 ceramics : Synthesis, characterization and electrical properties

Realizing ultrahigh recoverable energy density and superior charge–discharge performance in NaNbO3-based lead-free ceramics via a local random field strategy

ZnLi2/3Ti4/3O4: A new low loss spinel microwave dielectric ceramic

Effects of Na/K evaporation on electrical properties and intrinsic defects in Na0.5K0.5NbO3 ceramics

High energy storage density and power density achieved simultaneously in NaNbO3-based lead-free ceramics via antiferroelectricity enhancement