We report that R martensite isothermally forms with time in a solution-treated Ti(48.7)Ni(51.3) single crystal. This abnormal formation originates from the growth of a short-range ordered R phase with time, i.e., the "crystallization" of strain glass. The established time-composition-temperature Ti-Ni diagram shows a time evolution of the R phase and composition-temperature phase diagram. The presence or absence of the R phase in this new diagram, as well as in other conditions (like doping Fe or aging), is explained in a unified framework of free-energy landscape. Our finding suggests a new mechanism for the isothermal martensite formation, which could be applied to other metal and ceramic martensitic systems to find new phases and novel properties.
Ferroelectric transition involves tiny shift of ions within unit cell, thus being intrinsically a very fast process without apparent time-dependence. Contrary to this conventional wisdom, here we report a time-dependent ferroelectric transition, which occurs in hours. The system studied was Pb(1−x)(Zr0.4Ti0.6)(1−x/4)O3 − xLa system with relaxor-forming dopant La3+. The time-dependent ferroelectric transition occurs at the ferroelectric/relaxor crossover composition range of 0.09 < x ≤ 0.16. In these compositions, in situ Raman spectroscopy and transmission electron microscopy reveal very slow growth of ferroelectric phase. Dielectric measurement shows isothermal kinetics of the transition. The slow ferroelectric transition can be understood as being caused by the slowing-down of the otherwise fast growth of polar nano-domains due to the random local field caused by La3+, so that long time is needed to achieve long-range order macroscopic ferroelectric phase.
The morphotropic phase boundary (MPB) in leadfree ferroelectrics, starting from a quadruple point (QP), often displays large piezoelectric responses due to the flattened freeenergy profiles. In this work, we found that the QP composition rendering most flattened energy profiles could also exhibit abnormally low piezoelectric constants in Hf-doped BaTiO 3 . Such an anomaly in the strength of piezoelectricity can be ascribed to the progressive influence of additional strain heterogeneity induced by the substitution of Hf 4+ for Ti 4+ in BaTiO 3 , which was overlooked previously. An intermediate level of strain heterogeneity can form an invisible ferroelectric crossover consisting of both micro-and nanodomains, resulting in a large elastic softening and high piezoelectricity. With a further increase in the level of strain heterogeneity, the extinction of regular ferroelectric domain structures and pinned polar dynamics resulted in the feeble piezoelectric outputs near the QP composition. Impressively, a giant d 33 of ∼610 pC/N has been accordingly obtained through employing a ferroelectric crossover at off-QP composition in Zr-doped BaTiO 3 , further underpinning the critical role of uncovered ferroelectric crossover on piezoelectricity along MPB. This work offers another degree of freedom in the design of high-performance eco-friendly piezoelectric ceramics.
We report a glass-ferroic composite (in short "glass-ferroic") in ferroic materials, an analog of the composite of glassy and crystalline phases (glass-crystal composite, e.g., semicrystalline polymer). The formation of glass-ferroic (i.e., the existence of residual ferroic glass) stems from a time-dependent crystallization of the ferroic glass. Moreover, glass-ferroics show two types of transition characteristics depending on the thermal hysteresis of crystallization transition as exemplified in Ti 48.7 Ni 51.3 and Pb 0.87 La 0.13 Zr 0.4 Ti 0.6 O 3. Based on experimental results, a generic phase diagram is established to include all ferroic states, i.e., ferroic crystal, ferroic glass, and glass-ferroic. Being the third class of ferroic materials, glass-ferroics may open a new avenue for achieving novel properties and designing ferroic phase-change memory devices.
The current approach to achieving superior energy storage density in dielectrics is to increase their breakdown strength, which often incurs heat generation and unexpected insulation failures, greatly deteriorating the stability and lifetime of devices. Here, a strategy is proposed for enhancing recoverable energy storage density (Wr) while maintaining a high energy storage efficiency (η) in glassy ferroelectrics by creating super tetragonal (super‐T) nanostructures around morphotropic phase boundary (MPB) rather than exploiting the intensely strong electric fields. Accordingly, a giant Wr of ≈86 J cm−3 concomitant with a high η of ≈81% is acquired under a moderate electric field (1.7 MV cm−1) in thin films having MPB composition, namely, 0.94(Bi, Na)TiO3‐0.06BaTiO3 (BNBT), where the local super‐T polar clusters (tetragonality ≈1.25) are stabilized by interphase strain. To the knowledge of the authors, the Wr of the engineered BNBT thin films represents a new record among all the oxide perovskites under a similar strength of electric field to date. The phase field simulation results ascertain that the improved Wr is attributed to the local strain heterogeneity and the large spontaneous polarization primarily is originated from the super‐T polar clusters. The findings in this work present a genuine opportunity to develop ultrahigh‐energy‐density thin‐film capacitors for low‐electric‐field‐driven nano/microelectronics.
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