Most oxide ceramics are known to be brittle macroscopically at room temperature with little or no dislocation‐based plasticity prior to crack propagation. Here, we demonstrate the size‐dependent brittle to ductile transition in SrTiO ₃ at room temperature using nanoindentation pop‐in events visible as a sudden increase in displacement at nominally constant load. We identify that the indentation pop‐in event in SrTiO ₃ at room temperature, below a critical indenter tip radius, is dominated by dislocation‐mediated plasticity. When the tip radius increases to a critical size, concurrent dislocation activation and crack formation, with the latter being the dominating process, occur during the pop‐in event. Beyond the experimental examination and theoretical justification presented on SrTiO ₃ as a model system, further validation on α‐Al ₂ O ₃ , BaTiO ₃ , and TiO ₂ are briefly presented and discussed. A new indentation size effect, mainly for brittle ceramics, is suggested by the competition between the dislocation‐based plasticity and crack formation at small scale. Our finding complements the deformation mechanism in the nano‐/microscale deformation regime involving plasticity and cracking in ceramics at room temperature to pave the road for dislocation‐based mechanics and functionalities study in these materials.

Significance: We demonstrate the micropillars of normally brittle BaTiO₃(BTO) are superelastic as well as fatigue resistant over 1 million cycles without accumulating residual strains or noticeable variation in stress–strain curves over cycles. The mechanism of reversible 90° domain switching identified in our work is advantageous over the conventional phase transition mechanism as found in ZrO₂and shape memory alloys, and it is not limited to BTO. Therefore, our work offers a promising strategy for realizing fatigue-resistant superelasticity in otherwise brittle ferroelectric materials.

This paper proposed a piezoelectric energy harvester based on a spring-mass-spring oscillator, of which the piezoelectrics operate in the d₃₃ mode. Theoretical analysis reveals that the spring-mass-spring oscillator can not only generate a larger vibration than that of the ambient system but also buffer the force of possible accidental impact applied on the piezoelectric stacks. By using lead zirconate titanate (PZT-4) ceramics as model materials, we systematically characterized the performance of the energy harvester. Results show that at the resonance frequency, the harvester can output a satisfactory electric field. In addition, it has excellent fatigue resistance, e.g., under 9 g vibration acceleration for a long time about 12 h, the electric voltage output of the harvester nearly kept constant and only a slight fluctuation was observed.

Cellular electrets polymer is a new ferroelectret material exhibiting large piezoelectricity and has attracted considerable attentions in researches and industries. Property characterization is very important for this material and current investigations are mostly on macroscopic properties. In this work, we conduct nanoscale piezoelectric and ferroelectric characterizations of cellular polypropylene (PP) films using piezoresponse force microscopy (PFM). First, both the single-frequency PFM and dual-frequency resonance-tracking PFM testings were conducted on the cellular PP film. The localized piezoelectric constant d₃₃ is estimated to be 7–11pC/N by correcting the resonance magnification with quality factor and it is about one order lower than the macroscopic value. Next, using the switching spectroscopy PFM (SS-PFM), we studied polarization switching behavior of the cellular PP films. Results show that it exhibits the typical ferroelectric-like phase hysteresis loops and butterfly-shaped amplitude loops, which is similar to that of a poly(vinylidene fluoride) (PVDF) ferroelectric polymer film. However, both the phase and amplitude loops of the PP film are intensively asymmetric, which is thought to be caused by the nonzero remnant polarization after poling. Then, the D-E hysteresis loops of both the cellular PP film and PVDF film were measured by using the same wave form as that used in the SS-PFM, and the results show significant differences. Finally, we suggest that the ferroelectric-like behavior of cellular electrets films should be distinguished from that of typical ferroelectrics, both macroscopically and microscopically.