Ferroelastic Materials Research Articles

Ubiquity of avalanches: Crackling noise in kidney stones and porous materials

Systematic advances in the resolution and analytical interpretation of acoustic emission (AE) spectroscopy have, over the last decade, allowed for extensions into novel fields. The same dynamic failure patterns, which have been identified in earthquakes, magnetism, and switching of ferroelastic and ferroelectric materials, are shown, in this paper, to be equally important in medicine, and minerals, in the geological context, to give just two examples. In the first application, we show that biological samples, i.e., kidney stones, can be analyzed with acoustic emission and related to the progression of mechanical avalanches. Discrepancies between strong and weak AE signals are shown to have separate avalanche exponents for a urate kidney stone, with evidence of slight multi-branching. It is proposed that investigations of this nature can be adopted to the field of medicine, and in the case of kidney stones, can provide a blueprint for selecting ideal combinations of energy and frequency to instigate their destruction. In a second example, porous geological material failure is shown to proceed equally in avalanches, and precursors to catastrophic failure can be detected via AE. Warning signs of impeding macroscopic collapse, e.g., in mining activities, show systematic evolution of energy exponents. Ultimately, this behavior is a result of geological processes, man-made bio-mineralization, or the burning of carbon inclusions, creating pores and holes, causing cracks, and accelerating their interactions.

Two-Dimensional Ferroelasticity and Domain-Wall Flexoelectricity in HgX2 (X = Br or I) Monolayers

Electromechanical phenomena in two-dimensional (2D) materials can be related to sizable electric polarizations and switchable spontaneous ferroelasticity, allowing them to be used as miniaturized electronic and memory devices. Even in a parent centrosymmetric (nonpolar) ferroelastic (FE) material, non-zero polarization can be produced around the FE domain wall, owing to the strain-gradient-induced flexoelectricity. Compared with the negligibly weak flexoelectric effect in bulk compounds, significant electric polarizations can be expected in 2D FE materials that sustain a large elastic strain and a strain gradient. Using first-principles calculations, we predict that spontaneous 2D ferroelasticity and domain-wall flexoelectricity can be simultaneously realized in synthetic HgX2 (X = Br or I) monolayers. The FE phase renders three oriented variants, which form FE domain walls with a large strain gradient and the associated domain-wall flexoelectric polarizations. Our thermodynamic stability analysis and kinetic barrier simulations allow us to manipulate the domain-wall flexoelectricity via applied mechanical stress, thereby enabling future electromechanical applications in nanoelectronics.

Influence of Pd(II) Adsorption on High-Temperature Ferroelastic Phase Transition in (2-Amino-2-thiazolinium)PbBr3.

Ferroelastic materials have received special attention because of their great promise for mechanical switches, piezoelectric sensors, and data storage applications. Here, we report a novel ferroelastic semiconducting hybrid organic-inorganic perovskite (C3H7N2S)PbBr3 (1) [(C3H7N2S)+ is 2-amino-2-thiazolinium] with a ferroelastic phase transition at 395 K and an optical band gap of 3.43 eV. 1 has a one-dimensional BaNiO3-type structure and undergoes a high-temperature ferroelastic phase transition with an Aizu notation of mmmF2/m. Meanwhile, 1 exhibits dielectric switch near the phase transition temperature. By introducing the thioether group, the motion of the molecules or ions of 1 is hindered after the sorption of Pd(II) metal ions, which leads to the disappearance of the high-temperature ferroelastic phase transition and dielectric switch. This is the first reported ferroelastic semiconductor material with Pd(II) adsorption property, by studying the influence of Pd(II) adsorption on high-temperature ferroelastic phase transition, it may be enlightening to further uncover the mechanism of phase transition or the origin of ferroelasticity, which represents an important step toward multifunctional applications of lead-hybrid perovskite-based ferroelastic materials.

Strong spin-lattice entanglement in cobaltites

Strongly correlated electronic system contains strong coupling among multi-order parameters and is easy to efficiently tune by external field. Cobaltite (LaCoO<sub>3</sub>) is a typical multiferroic (ferroelastic and ferromagnetic) material, which has been extensively investigated over decades. Conventional research on cobaltites has focused on the ferroelastic phase transition and structure modulation under stress. Recently, researchers have discovered that cobaltite thin films undergo a paramagnetic-to-ferromagnetic phase transition under tensile strain, however, its origin has been controversial over decades. Some experimental evidence shows that stress leads the valence state of cobalt ions to decrease, and thus producing spin state transition. Other researchers believe that the stress-induced nano-domain structure will present a long-range ordered arrangement of high spin states, which is the main reason for producing the ferromagnetism of cobalt oxide films. In this paper, we review a series of recent researches of the strong correlation between spin and lattice degrees of freedom in cobalt oxide thin films and heterojunctions. The reversible spin state transition in cobalt oxide film is induced by structural factors such as thin-film thickness, lattice mismatch stress, crystal symmetry, surface morphology, interfacial oxygen ion coordination, and oxygen octahedral tilting while the valence state of cobalt ions is kept unchanged, and thus forming highly adjustable macroscopic magnetism. Furthermore, the atomic-level precision controllable film growth technology is utilized to construct single cell layer cobaltite superlattices, thereby achieving ultra-thin two-dimensional magnetic oxide materials through efficient structure regulation. These advances not only clarified the strong coupling between lattice and spin order parameters in the strongly correlated electronic system, but also provided excellent candidate for the realization of ultra-thin room temperature ferromagnets that are required by oxide spintronic devices.

Two-dimensional organic–inorganic hybrid perovskite ferroelastics: (PEA)2[CdCl4], (3-FPEA)2[CdCl4], and (4-FPEA)2[CdCl4

Three 2D organic–inorganic hybrid perovskites ferroelastics with dielectric switch. This work provides a new case for the preparation of 2D perovskite ferroelastic materials and the possibility for the application in actuators.

An anomalous ferroelastic phase transition arising from an unusual cis-/anti-conformational reversal of polar organic cations.

Hybrid ferroelastics have attracted increasing attention for their potential application as mechanical switches. The sporadically documented anomalous ferroelastic phase transitions, i.e., ferroelasticity that appears at a high-temperature phase rather than a low-temperature phase, are of particular interest but are not well understood at the molecular level. By judiciously choosing a polar and flexible organic cation (Me2NH(CH2)2Br+) with cis-/anti- conformations as an A-site component, we obtained two new polar hybrid ferroelastics, A2[MBr6] (M = Te for 1 and Sn for 2). These materials undergo distinct thermal-induced ferroelastic phase transitions. The larger [TeBr6]2- anions anchor the adjacent organic cations well and essentially endow 1 with a conventional ferroelastic transition (P21 → Pm21n) arising from a common order-disorder transition of organic cations without conformational changes. Moreover, the smaller [SnBr6]2- anions can interact with the adjacent organic cations in energetically similar sets of intermolecular interactions, enabling 2 to undergo an anomalous ferroelastic phase transition (P212121 → P21) arising from an unusual cis-/anti-conformational reversal of organic cations. These two instances demonstrate the importance of the delicate balance of intermolecular interactions for inducing anomalous ferroelastic phase transitions. The findings here provide important insights for seeking new multifunctional ferroelastic materials.

Increasing the ferroelastic phase transition temperature of hybrid perovskites through a mixed phosphonium and ammonium cation strategy.

[(CH3)3PCH2CH2CH3]2(n-C4H9NH3)Bi2Br9 (1) was obtained by a mixed organic cation strategy. The introduction of phosphonium cations increases the potential energy barrier for the motion of cations, which raises the ferroelastic phase transition temperature of 1 above room temperature, unlike the low-temperature ferroelasticity of [n-C4H9NH3]2[BiBr5]. This provides a new idea for exploring and designing molecular ferroelastic materials with excellent performance.

Frontispiece: Ferroelasticity in Organic–Inorganic Hybrid Perovskites

Organic-inorganic hybrid perovskite ferroelastics have received particular attention by taking advantages of their low-cost, light-weight, easy preparation, and mechanical flexibility. Different dimensional crystal structures, ferroelastic phase transition and ferroelastic-related properties have been highlighted. This review article summarizes the structural design strategies of organic-inorganic hybrid perovskite ferroelastic materials, as well as the opportunities and challenges in the future.

Wall-wall and kink-kink interactions in ferroelastic materials

Kinks interact with other kinks and antikinks elastically in ferroelastic domain walls and other interfaces in ferroic materials. In thin samples, suitable for transmission electron-microscopy, the interaction is purely dipolar with no indication of monopolar or higher order contributions. Kinks and antikinks attract each other while kink-kink interactions are repulsive. When the kinks are situated in two parallel twin walls, they display the same attraction/repulsion. We argue that this interaction constitutes, part or all, the elusive wall-wall interaction in ferroelastics. The dipolar interactions over distances $d$ between the kinks and between walls decay as $1/{d}^{2}$ when the samples have some nanoscale size. Nanoscale samples bend and tilt when kinks are introduced with typical bent regions of some 1 nm and tilt angles of some $1.{2}^{\ensuremath{\circ}}$. Multiple kinks will enhance the effect systematically and bent and modulated twin walls are predicted.

Integrated Reversible Thermochromism, High Tc , Dielectric Switch and Narrow Band Gap in One Multifunctional Ferroic.

Organic-inorganic Hybrid (OIH) materials for multifunctional switchable applications have attracted enormous attention in recent years due to their excellent optoelectronic properties and good structural tunability. However, it still remains challenging to fabricate one simple OIH compound with multi-functionals properties, such as dielectric switching, thermochromic properties, semiconductor characteristics and ferroelasticity. Under this context, we successfully synthesized [2-(2-fluorophenyl)ethan-1- ammonium]2 SnBr6 (compound 1), which has a higher phase transition temperature of 427.7 K. Additionally, it exhibits a semiconducting property with an indirect band gap of 2.36 eV. Combining ferroelastic, narrow band gap, thermochromic, and dielectric properties, compound 1 can be considered as a rarely reported multi-functional ferroelastic material, which is expected to give inspiration for broadening the applications in the smart devices field.

NH4+/K+-substitution-induced C–F–K coordination bonds for designing the highest-temperature hybrid halide double perovskite ferroelastic

Ferroelastic materials with switchable spontaneous strain possess widely potential applications in the field of energy and information conversion. Recently, organic-inorganic hybrid halide double perovskites (OIHHDPs) have become a charming new platform for developing various functional materials, such as ferroelectrics, fluorescence and X‑ray detection. Nevertheless, OIHHDP ferroelastic materials, especially high-temperature ones, are rare. Herein, we initially synthesized an OIHHDP ferroelastic, (2,2-difluoroethanamine)2[(NH4)InCl6] (1), which possesses a ferroelastic phase transition at 407 K. Moreover, thanks to the flexible B-site for OIHHDPs, we replaced the NH4+ ions within [(NH4)InCl6]n2n– formworks with K+ ions, which endows with coordination bonds between 2,2-difluoroethanamine organic cations and [KInCl6]n2n– formworks. Due to the existence of coordination bonds, the phase transition temperature of (2,2-difluoroethanamine)2[KInCl6] (2) can reach 458 K. As far as we know, this value is the highest reported in OIHHDP ferroelastics. This work offers inspiration for the design of high-temperature OIHHDP phase transition materials including ferroelectrics and ferroelastics.

Ferroelasticity in Organic–Inorganic Hybrid Perovskites

Molecular ferroelastics have received particular attention for potential applications in mechanical switches, shape memory, energy conversion, information processing, and solar cells, by taking advantages of their low-cost, light-weight, easy preparation, and mechanical flexibility. The unique structures of organic-inorganic hybrid perovskites have been considered to be a design platform for symmetry-breaking-associated order-disorder in lattice, thereby possessing great potential for ferroelastic phase transition. Herein, we review the research progress of organic-inorganic hybrid perovskite ferroelastics in recent years, focusing on the crystal structures, dimensions, phase transitions and ferroelastic properties. In view of the few reports on molecular-based hybrid ferroelastics, we look forward to the structural design strategies of molecular ferroelastic materials, as well as the opportunities and challenges faced by molecular-based hybrid ferroelastic materials in the future. This review will have positive guiding significance for the synthesis and future exploration of organic-inorganic hybrid molecular ferroelastics.

Observation of cation-specific critical behavior at the improper ferroelectric phase transition in Gd2(MoO4)3

Gadolinium molybdate is a classical example of an improper ferroelectric and ferroelastic material. It is established that the spontaneous polarization arises as a secondary effect, induced by a structural instability in the paraelectric phase, which leads to a unit cell doubling and the formation of a polar axis. However, previous x-ray diffraction (XRD) studies on gadolinium molybdate have been restricted by the limited ability to include a wide $2\ensuremath{\theta}$ range in the analysis, and thus, at atomic scale, much remains to be explored. By applying temperature-dependent XRD, we observe the transition from the paraelectric tetragonal phase to the orthorhombic ferroelectric phase. The ferroelastic strain is calculated based on the thermal evolution of the lattice parameters, and Rietveld refinement of the temperature-dependent data reveals that the displacement of different cations follows different critical behavior, providing insight into the structural changes that drive the improper ferroelectricity in gadolinium molybdate.

Probing the dynamic response of ferroelectric and ferroelastic materials by simultaneous detection of elastic and piezoelectric properties

Domain walls and precursors in ferroelectric and ferroelastic materials are of great importance for the optimization of ferroic devices and novel paradigms for domain switching. Any domain wall- or ferroic-precursor-based device requires knowledge about structural phase transitions and the formation and evolution of mesoscopic structures. In this review, Resonant Piezoelectric Spectroscopy (RPS) is shown to be a convenient investigative tool for the characterization of ferroic materials. RPS simultaneously measures elastic and piezoelectric properties related to domain walls and ferroic precursors and correlates the onset of phase transitions and the formation of mesoscopic structures with piezoelectric properties. Examples are given for ferroelastic, ferroelectric, and relaxor materials, including SrTiO3, BaTiO3, and PbMg1/3Nb2/3O3. Comparison of the data with incipient ferroelectric KTaO3 provides insights into the physical meaning of the coherence temperature and the Burns temperature in ferroelectrics, relaxors, and potentially other ferroic systems.

Underlying physics and chemistry of ferroic-photocatalysis: a critical review

The significance of ferroelectric and ferroelastic materials physico-chemistry is summarized and detailed for various photocatalytic reactions, followed by an outlook on future advancements.

Two-dimensional ferroelasticity and negative Poisson's ratios in monolayer YbX (X = S, Se, Te)

Two-dimensional ferroelastic materials and two-dimensional materials with negative Poisson's ratios have attracted great interest.

(C3N2H5)3Sb2I9 and (C3N2H5)3Bi2I9: ferroelastic lead-free hybrid perovskite-like materials as potential semiconducting absorbers.

We have synthesised and characterised novel organic-inorganic hybrid crystals: (C3N2H5)3Sb2I9 and (C3N2H5)3Bi2I9 (PSI and PBI). The thermal DSC and TG analyses indicate four structural phase transitions (PTs) at 366.2/366.8, 274.6/275.4, 233.3/233.3 and 142.8/143.1 K (on cooling/heating) for PSI and two reversible PTs at 365.2/370.8 and 252.6/257.9 K for PBI. Both analogues crystallize at room temperature in the orthorhombic Cmcm structure, which transforms, in the case of PBI, to monoclinic P21/n at low temperature. According to the X-ray diffraction results, the anionic component is discrete and built of face-sharing bioctahedra, [M2I9]3-, in both compounds, whereas cations exhibit distinct dynamical disorder over high temperature phases. Dielectric spectroscopy and 1H NMR spectroscopy have been used to characterise the dynamical state of the C3N2H5+ cations. The ferroelastic domain structure has been characterised by observations under a polarized optical microscope. Both compounds are semiconductors with narrow bandgaps of 1.97 eV (PBI) and 2.10 eV (PSI).

Toward tunable mechanical behavior and enhanced elastocaloric effect in NiTi alloy by gradient structure

Tailoring properties of engineering materials to meet various application requirements is a long-standing challenge in materials science. Here, we demonstrate an unprecedented strategy to achieve highly tunable mechanical behavior and significantly enhanced elastocaloric effect in superelastic NiTi via gradient structure fabricated by laser surface annealing on a severely deformed matrix. The gradient-structured (GS) NiTi sheet is characterized by a nanocrystalline core sandwiched between two coarse-grained layers with grain-size gradients enabled by progressive annealing within the thickness due to the natural degradation of heat penetration. Tailorable martensitic transformation characteristics, which gradually change from a uniform mode with quasi-linear stress-strain response to a nucleation and growth mode with plateau-type superelasticity, are readily realized through tuning the grain-size gradient. Furthermore, the GS NiTi exhibits more than 50% and 130% improvement in elastocaloric cooling capacity and efficiency compared to traditional nanocrystalline and coarse-grained NiTi with homogeneous microstructures, respectively. Such significant performance breakthroughs are attributed to the strong synergetic strengthening between fine and coarse grains in the GS NiTi, which cannot be offered by the freestanding components. The unique strengthening mechanism is activated, even in the absence of plastic deformation, by the high mechanical incompatibility among heterogeneous domains and the resultant pronounced strain gradient accommodated by martensite variants. The work opens a novel avenue for fabricating bulk GS materials with desired mechanical properties and inspires the microstructure optimization in a wide range of ferroelastic materials for giant caloric effects.

Mild fluctuations in ferroelastic domain switching

We study the avalanche dynamics of shear-induced ferroelasticity by molecular dynamics simulations and statistical analysis. The dynamics of ferroelastic domain switching proceeds by avalanches which are power-law distributed. These avalanches can therefore be classified as wild with an energy exponent near 3. Wildness originates from the interaction between domain boundaries and defects, and jamming between domain boundaries. Concomitantly, mild events also arise but their distributions do not follow power-laws so that these mild energy releases are not scale invariant and exhibit a characteristic energy. We identify several mild domain switching events, namely the motion of single kinks and highly nonlinear relaxations of solitonic waves. The solitonic waves are reflected by domain boundaries, kinks, junctions, and free surfaces. Relaxations during domain switching have different characteristic energies from those created during creep. We observe the coexistence of mild and wild events depending on the external forces acting on the ferroelastic material.

Simultaneously increasing the strength and decreasing the modulus in TiNi alloys via plastic deformation

It is challenging to simultaneously increase strength and decrease modulus, since they are often mutually exclusive. Here, we report an easy way to achieve a 140% increase of yield stress and a 59% decrease of Young's modulus in a shape memory alloy of Ti49.2Ni50.8 via tensile plastic deformation at T0(σ) ∼283 K (T0(σ) denotes an equilibrium temperature between austenite and martensite after deformation). Through integrating experiments and Landau theory, we reveal that besides the strength increase due to strain hardening, the modulus reduction results from a state change from an austenitic state to a special dual-phase state where austenite and stress-induced martensite have the same free energy and thus exhibit the lowest modulus at T0(σ). Similar results were also found in another ferroelastic Ti49Ni51 alloy, implying that the performance of other ferroelastic materials may be further optimized using the strategy of plastic deformation at T0(σ).