Ultrafast, Light, Soft Martensitic Materials

Abstract

Martensitic transformations are well documented in metals and alloys where the atoms connected via metallic bonds rearrange concertedly and rapidly; however, due to the metal atoms, these materials are inherently very dense and add significant weight and bulkiness to actuating devices. Here, remarkably rapid lattice switching of molecular martensitic materials is reported where the rate of structural transformation exceeds other phase transitions several orders of magnitude. With a determined speed in the range of 0.3-0.6 m s −1 , the new phase advances throughout the crystal about ten thousand times faster relative to spin-crossover transitions, and about hundred to hundred thousand times faster than other common structural phase transitions. Macroscopic crystals of these materials respond by rapid expansion or contraction of about 0.02 m s −1 for unrestrained crystals and 0.02-0.03 m s −1 for clamped crystals. Monte-Carlo simulation of the spatiotemporal profile of the transition and of the local distribution of elastic and kinetic energies induced by domain growth reveals the critical role of the dynamic phase boundary and the lattice edges in the structure switching. Within a broader context, this study indicates that the martensitic organic crystals are prospective lightweight substitutes of metals for ultrafast and clean energy transduction.

Room-temperature martensitic actuation profited from one-dimensional hybrid perovskite structure

“…Both the two transformations show features of concerted, non-displacive, and rapid structure phase transitions, accompanied by remarkable structural rearrangements. 32 These characteristics, together with temperature hysteresis exhibited in DSC curves, suggest the rst-order nature of the martensitic transitions.…”

Smart molecular crystal switches

“…High phase‐front propagation speed (concerted transition) is a known characteristic of a martensitic transition. The switching of a smart molecular thermoswitch is normally completed within a second, and occurs in some cases on a millisecond time scale, which is much faster than the propagation of other solid‐state transitions such as those triggered by a spin crossover [35a] . Among the molecular crystalline martensites, the structures that include strong intermolecular interactions are faster compared to those triggered by an order‐disorder transition.…”

“…Among the molecular crystalline martensites, the structures that include strong intermolecular interactions are faster compared to those triggered by an order‐disorder transition. For example, the phase front in crystals of the terephthalic acid and pyroglutamic acid can propagate up to 500 mm/s during a transition, which is fast enough to generate detectable acoustic burst [35] . In contrast, the propagation speeds are usually below 1 mm/s in case of side chain order–disorder driven transitions [33] …”

“…The actuators made of molecular crystal thermoswitches have several advantages over actuators based on other materials. The group of Naumov has highlighted that molecular crystal thermoswitches are beneficial for being low‐density materials because they are normally purely organic [35a] . They compared organic actuating crystals to other actuators and concluded that the rigid and martensitic nature of the smart molecular crystals turns them into ultra‐fast switching actuators with high power density [17,35] .…”

Stimuli-responsive flexible organic crystals

“…They are emerging as a new research direction in materials science, ''crystal adaptronics'', which provides an opportunity to develop smart crystal materials. [11][12][13][14][15][16][17][18][19][20][21][22][23][24] Compared to traditional amorphous materials, organic crystalline materials have intrinsic advantages as stimuli-responsive smart materials. Firstly, due to few internal defects and long-range structural order, crystalline materials have faster response speed and higher energy transfer efficiency.…”