Conventional porous piezoelectric ceramics can possess superior figures of merit only at very high values of porosity, leading to bad fragileness, small stiffness, low toughness, and the difficulty of polarization. To this end, this study for the first time shows that it is possible that the piezoelectric ceramic with ultra‐low porosity is capable of superior figures of merit based on the concept of auxetic piezoelectric ceramics. Owing to the ultra‐low porosity and auxetic effect, the auxetic piezoelectric ceramic shall also possess larger stiffness, higher toughness, and is more easily polarized. First, the auxetic piezoelectric ceramic with ultra‐low porosity is proposed to achieve highly tunable electromechanical properties on the basis of the rotating square mechanism. Then, using a multiscale finite element method, the effects of geometric architecture and polarization directions on the electromechanical properties including Poisson's ratios, elastic coefficients, piezoelectric stress coefficients, dielectric coefficients, and figures of merit in the auxetic piezoelectric ceramics are investigated in detail. Furthermore, the stress fields in conventional and proposed porous piezoelectric ceramics subjected to mechanical and electrical loads are compared and discussed. Finally, it can be concluded that the auxetic piezoelectric ceramic exhibits (a) giant negative Poisson's ratios (smaller than ‐5), (b) negative elastic coefficients, (c) more extensible, higher piezoelectric sensitivity, lower acoustic impedance, stronger crack resistance than conventional porous piezoelectric ceramics with the same porosity, and (d) larger stiffness than conventional porous piezoelectric ceramics with similar figures of merit.

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In this paper, the radiation defects induced by the swift heavy ions and the recoil atoms in amorphous SiO 2 were studied. The energy of recoil atoms induced by the incident Au ions in SiO 2 was calculated by using Monte Carlo method. Results show that the average energies of recoils reach the maximum (200 eV for Si and 130 eV for O, respectively) when the incident energy of Au ion is 100 MeV. Using Tersoff/zbl potential with the newly built parameters, the defects formation processes in SiO 2 induced by the recoils were studied by using molecular dynamics method. The displacement threshold energies (E d ) for Si and O atoms are found to be 33.5 and 16.3 eV, respectively. Several types of under-and over-coordinated Si and O defects were analyzed. The results demonstrate that Si 3 , Si 5 , and O 1 are the mainly defects in SiO 2 after radiation. Besides, the size of cylindrical damage region produced by a single recoil atom was calculated. The calculation shows that the depth and the radius are up to 2.0 and 1.4 nm when the energy of recoils is 200 eV. Finally, it is estimated that the Au ion would induce a defected track with a diameter of 4 nm in SiO 2 . ARTICLE HISTORY

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In this study, the ultra‐low porous auxetic piezoelectric composite made of lead zirconate titanate (PZT) and hollow polyvinylidine difluoride (PVDF) is first proposed by combining “additive” and “subtractive” approaches. The electromechanical properties of the auxetic piezoelectric composite are investigated by finite element analysis. It is found that the ultra‐low porosity in the composite may lead to great extensibility along with the excellent figures of merit obtained in conventional highly porous piezoelectric ceramics. The small amount of additional PVDF can greatly tune the electromechanical properties of composite and effectively reduce the maximum stress of PZT. To elucidate the role of Poisson’s ratio on the electromechanical properties of piezoelectric materials, the relationship expressions among some electromechanical coefficients are derived. Moreover, the semi‐empirical expression of “longitudinal” compliance coefficients and a simple strategy for predicting some electromechanical coefficients are presented to instruct design and application of the ultra‐low porous auxetic piezoelectric materials.