다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

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

Dielectric energy-storage capacitors have received increasing attention in recent years due to the advantages of high voltage, high power density, and fast charge/discharge rates. Here, a new environment-friendly 0.76NaNbO3–0.24(Bi0.5Na0.5)TiO3 relaxor antiferroelectric (AFE) bulk ceramic is studied, where local orthorhombic Pnma symmetry (R phase) and nanodomains are observed based on high-resolution transmission electron microscopy, selected area electron diffraction, and in/ex situ synchrotron X-ray diffraction. The orthorhombic AFE R phase and relaxor characteristics synergistically contribute to the record-high energy-storage density Wrec of ≈12.2 J cm−3 and acceptable energy efficiency η ≈ 69% at 68 kV mm−1, showing great advantages over currently reported bulk dielectric ceramics. In comparison with normal AFEs, the existence of large random fields in the relaxor AFE matrix and intrinsically high breakdown strength of NaNbO3-based compositions are thought to be responsible for the observed energy-storage performances. Together with the good thermal stability of Wrec (>7.4 J cm−3) and η (>73%) values at 45 kV mm−1 up to temperature of 200 °C, it is demonstrated that NaNbO3-based relaxor AFE ceramics will be potential lead-free dielectric materials for next-generation pulsed power capacitor applications.

Ultrahigh Energy‐Storage Density in NaNbO3‐Based Lead‐Free Relaxor Antiferroelectric Ceramics with Nanoscale Domains

Highly dense (1−x)(Na0.5K0.5)NbO3–x(Bi0.5Na0.5)TiO3 (NKN-BST) solid solution piezoelectric ceramics have been fabricated by ordinary sintering. All compositions show pure perovskite structures, showing room-temperature symmetries of orthorhombic at x⩽0.02, of tetragonal at 0.03⩽x⩽0.09, of cubic at 0.09 0.20. A morphotropic phase boundary (MPB) between orthorhombic and tetragonal ferroelectric phases was identified in the composition range of 0.02<x<0.03. The materials near the MPB exhibit a strong compositional dependence, owning peak values of the planar electromechanical coupling factor kp∼43%, the piezoelectric constant d33∼195pC∕N, and the Curie temperature of 375°C comparable to that of commercial lead zinconate titanate ceramics. The results indicate that NKN-BST ceramic is a promising lead-free piezoelectric candidate material.

Phase structures and electrical properties of new lead-free (Na0.5K0.5)NbO3–(Bi0.5Na0.5)TiO3 ceramics

Superior Energy-Storage Capacitors with Simultaneously Giant Energy Density and Efficiency Using Nanodomain Engineered BiFeO3-BaTiO3-NaNbO3 Lead-Free Bulk Ferroelectrics

A novel lead-free relaxor ferroelectric ceramic of (0.67−x)BiFeO3–0.33BaTiO3–xBa(Mg1/3Nb2/3)O3 [(0.67−x)BF–0.33BT–xBMN, x = 0–0.1] was prepared by a solid-state reaction method. A relatively high maximum polarization Pmax of 38 μC/cm2 and a low remanent polarization Pr of 5.7 μC/cm2 were attained under 12.5 kV/mm in the x = 0.06 sample, leading to an excellent energy-storage density of W ~1.56 J/cm3 and a moderate energy-storage efficiency of η ~75%. Moreover, a good temperature stability of the energy storage was obtained in the x = 0.06 sample from 25°C to 190°C. The achievement of these characteristics was basically attributed to an electric field induced reversible ergodic to ferroelectric phase transition owing to similar free energies near a critical freezing temperature. The results indicate that the (0.67−x)BF–0.33BT–xBMN lead-free realxor ferroelectric ceramic could be a promising dielectric material for energy-storage capacitors.

Novel BiFeO3–BaTiO3–Ba(Mg1/3Nb2/3)O3 Lead-Free Relaxor Ferroelectric Ceramics for Energy-Storage Capacitors

A new ternary lead-free (0.67-x)BiFeO3-0.33BaTiO3-xLa(Mg1/2Ti1/2)O3 ferroelectric ceramic exhibited an obvious evolution of dielectric relaxation behavior. A significantly enhanced energy-storage property was observed at room temperature, showing a good energy-storage density of 1.66 J/cm3 at 13 kV/mm and a relatively high energy-storage efficiency of 82% at x = 0.06. This was basically ascribed to the formation of a slim polarization-electric field hysteresis loop, in which a high saturated polarization Pmax and a rather small remnant polarization Pr were simultaneously obtained. Particularly, its energy storage properties were found to depend weakly on frequency (0.2 Hz–100 Hz), and also to exhibit a good stability against temperature (25 °C–180 °C). The achievement of these characteristics was attributed to both a rapid response of the electric field induced reversible ergodic relaxor to long-range ferroelectric phase transition and a typical diffuse phase transformation process in the dielectric maxima.

Ruzhong Zuo

Papers

Ultrahigh Energy‐Storage Density in NaNbO3‐Based Lead‐Free Relaxor Antiferroelectric Ceramics with Nanoscale Domains

Phase structures and electrical properties of new lead-free (Na0.5K0.5)NbO3–(Bi0.5Na0.5)TiO3 ceramics

Superior Energy-Storage Capacitors with Simultaneously Giant Energy Density and Efficiency Using Nanodomain Engineered BiFeO3-BaTiO3-NaNbO3 Lead-Free Bulk Ferroelectrics

Novel BiFeO3–BaTiO3–Ba(Mg1/3Nb2/3)O3 Lead-Free Relaxor Ferroelectric Ceramics for Energy-Storage Capacitors

Enhanced energy storage properties in La(Mg1/2Ti1/2)O3-modified BiFeO3-BaTiO3 lead-free relaxor ferroelectric ceramics within a wide temperature range