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(K,Na)NbO3-based ceramics are deemed among the most promising lead-free piezoelectric materials, though their overall piezoelectric performance still lags behind the mainstream lead-containing counterparts. Here, we achieve an ultrahigh piezoelectric charge coefficient d33 ∼ 807 pC·N−1, along with a high longitudinal electromechanical coupling factor (k33 ∼ 88%) and Curie temperature (Tc ∼ 245 °C) in the (K,Na)(Nb1-xSbx)O3-Bi0.5Na0.5ZrO3-BiFeO3 (KNN-xSb) system through structural flexibility and grain orientation strategies. Phenomenological models, phase field simulations and high-angle annular dark-field scanning transmission electron microscopy reveal that the structural flexibility originates from the high Coulomb force between K+/Na+ ions and Sb ions in the KNN-xSb system, while the grain orientation promotes the displacement of B-site cations leveraging the engineered domain configuration. As a result of its excellent comprehensive piezoelectric properties, the textured KNN-5Sb/epoxy 1-3 piezoelectric composite is found to possess a broader bandwidth BW = 60% and higher amplitude output voltage than commercial PZT-5 and other KNN counterparts. These findings suggest that the textured KNN-5Sb ceramics could potentially replace current lead-based piezoceramics in transducer applications. The authors achieve piezoelectric coefficient d33 ∼ 807 pC·N−1, along with high k33 ∼ 88 % and Tc ∼ 245 °C in (K,Na)(Nb1-xSbx)O3-Bi0.5Na0.5ZrO3-BiFeO3 system through structural flexibility and grain orientation strategies. [ABSTRACT FROM AUTHOR]

The great progress has been made in the research of the thermoelectric (TE) materials in recent years. The thermoelectric properties of the traditional Bi2Te3 and PbTe based materials have been improved, and a series of the original high-performance thermoelectric materials, such as SnSe and GeTe, have also been discovered. The thermoelectric properties of the thermoelectric materials not only depend on the composition, structure, and defects of the materials, but also are closely related to the preparation process. Mechanical alloying (MA) combined with spark plasma sintering (SPS) is an important method to synthesize the thermoelectric materials, which is simple and efficient to obtain the fine-grained microstructures and the nanostructures, leading to the reduced lattice thermal conductivity and the enhanced thermoelectric properties. In addition, the prepared bulk materials have the better mechanical properties, which can effectively enhance the life-time of the thermoelectric devices. The basic principle and key influencing factors of the thermoelectric material preparation by mechanical alloying and spark plasma sintering were introduced in this paper, and the research progress of the telluride, sulfide, and selenide based thermoelectric materials prepared by this method was summarized.

Piezoelectric materials are functional materials that can realize electromechanical coupling characteristics and are widely used in electronic information, sensors, ultrasonic transducer, nondestructive testing, and communication technology. However, the current dominant piezoelectric ceramics are lead zirconium titanate systems. These systems contain lead, which is a toxic element, and the content of lead oxide or lead tetroxide in lead-based piezoelectric ceramics is over 60%. Because of the volatile and water-soluble characteristics of lead, the production and disposal of traditional lead-based piezoelectric ceramics will result in different levels of lead pollution, which will severely harm the environment and human health. With the improvement of environmental protection and the sustainable development of human society, the harmful effects of lead-based piezoelectric ceramics have aroused increasing attention. Countries around the world have introduced legislation to ban or restrict the use of lead-based ceramics. Thus, lead-free piezoelectric ceramics have received much attention because they are environment-friendly and pollution-free. In the last decade, countries worldwide invested a large amount of funds and labor to search and develop environment-friendly lead-free piezoelectric ceramics, which can be used to replace lead-based piezoelectric ceramics in actuators, transducers, and sensors. In recent years, BiFeO3-BaTiO3 (BF-BT) lead-free solid solutions, which are considered as one of the most promising candidates for high-temperature piezoelectric applications, have received extensive attention from researchers because of their high-Curie temperature (TC) and large spontaneous polarization (Ps), as well as high piezoelectric coefficient (d33). This paper mainly reviewed recent advances in BF-BT ceramics, including the phase structure and piezoelectric property, as well as the magnetic property. In addition, the problems that need to be solved before these ceramics can be practically applied were also analyzed according to the knowledge of the authors.