Highly tailorable electromechanical properties of auxetic piezoelectric ceramics with ultra‐low porosity

Abstract

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.

Electromechanical properties of ultra‐low porous auxetic piezocomposite: from the perspective of Poisson’s ratio

“…In this section, we will provide new insight on the relationship among piezoelectric strain and stress coefficients, figures of merit by introducing Poisson’s ratio to instead of some compliance coefficients. The crystal symmetry in common piezoelectric ceramics is 6mm or 4mm, but Tang et al 18 . indicated that the auxetic architecture may change the crystal symmetry into 2mm.…”

“…This phenomenon can be attributed to the fact that the large deformation near the slits is undergone by PVDF, resulting in smaller stresses distributed in the PZT. Moreover, it has been demonstrated that auxetic porous structures have greater crack resistance than conventional porous structures 14,18,42,43 . Therefore, it is suggested that the auxetic architecture together with an appropriate amount of PVDF can effectively improve the deformability of piezoelectric materials, and ensure that the composite still has excellent electromechanical properties.…”

“…[11]. Recently, based on the rotating square mechanism, Tang et al 18 advanced the auxetic piezoelectric ceramic with ultra‐low porosity, it was found that the auxetic piezoelectric ceramic can be characterized by giant negative Poisson’s ratios, great extensibility, moderate stiffness, excellent figures of merit, strong crack resistance. However, the stress concentration in the piezoelectric ceramics near the slits may be not conducive to long‐term use of the auxetic piezoelectric ceramic.…”

“…The deformability and extensibility of auxetic porous PZT/PVDF composite may be much better than the auxetic piezoelectric ceramic in Ref. [18]. To the best knowledge of authors, the extremely high electric field is demanded to actuator the deformation of dielectric elastomer, which easily gives rise to the pull‐in failure and electrical breakdown in dielectric elastomer 20 .…”

“…Even so, the available viewpoints regarding the relationship between Poisson’s ratio and piezoelectric properties only keep true for the transversely isotropic piezoelectric materials with positive Poisson’s ratios. Evidently, the crystal symmetry in auxetic piezoelectric materials can be changed, as a result of the presence of distinctive auxetic structure 18 . To this end, it is necessary to investigate the relationship between Poisson’s ratio and piezoelectric coefficients in the present auxetic piezoelectric materials with other crystal symmetries.…”