Ferroelastic Crystals Research Articles

A Multidirectional Superelastic Organic Crystal by Versatile Ferroelastical Manipulation

AbstractMechanical twinning changes atomic, molecular, and crystal orientations along with directions of the anisotropic properties of the crystalline materials while maintaining single crystallinity in each domain. However, such deformability has been less studied in brittle organic crystals despite their remarkable anisotropic functions. Herein we demonstrate a direction‐dependent mechanical twinning that shows superelasticity in one direction and ferroelasticity in two other directions in a single crystal of 1,3‐bis(4‐methoxyphenyl)urea. The crystal can undergo stepwise twinning and ferroelastically forms various shapes with multiple domains oriented in different directions, thereby affording a crystal that shows superelasticity in multiple directions. This adaptability and shape recoverability in a ferroelastic and superelastic single crystal under ambient conditions are of great importance in future applications of organic crystals as mechanical materials, such as in soft robotics.

Characterization of BiVO4 nanoparticles prepared by sonochemical process

Nowadays, environment highly encounters various pollutants including toxic gases, organic volatiles and water pollutant. Many scientists have taken the effort to reduce or eliminate pollutant using photocatalytic materials. Due to good ferroelectric property in ferroelastic crystal as a result of the reduction in symmetry between the paraelastic and ferroelastic phases, it makes bismuth vanadate (BiVO4) one of attractive ferroelectric materials. In addition, BiVO4 with low optical band gap could be activated by visible light illumination so that it would be a potential candidate as a visible light driven photocatalyst. This work was carried out to synthesize BiVO4 nanoparticles by simple but effective method via sonochemical process through chemical route assisted by ultrasonic irradiation. The crystalline structure and surface morphologies of the synthesized products were observed by X-ray diffraction technique and Scanning Electron Microscope, respectively. Raman spectroscopy and Fourier Transform Infrared spectroscopy were used to approve the BiVO4 chemical bonding and relevant crystalline formation. Photocatalytic activity was studied by mean of the degradation of organic dye assigned as organic compound under visible light irradiation.

Degenerate (identity) chemical reactions in ferroelastic crystals

The presence of degenerate chemical reactions in crystals is discussed. They take place in some order-disorder phase transitions in crystals. The other category of identity (degenerate) chemical reactions in crystals includes a few examples of domain reorientations with simultaneous hopping of atoms/ions in some ferroelastic crystals. The product of the hopping maybe either identical with the reactant though in a different orientation or a conjugated enantiomorph. In these examples, the hopping atom is either situated in a special position or disordered about it in the paraelastic phase. The article also discusses the definition of identity (degenerate) chemical reactions which do not take into cosideration the reactions in which the reactant and the product are enantiomers or enantiomorphs.

Lattice Dynamics and Baric Behavior of Phonons in the Hg2Br2 Model Ferroelastics

Raman spectra of Hg2Br2 model improper ferroelastic crystals have been investigated in a wide range of high hydrostatic pressures. Baric dependences of the phonon frequencies have been obtained; of greatest interest are the observed soft mode originating from the slowest TA1 acoustic branch at the Brillouin zone boundary (X point) of the tetragonal phase and the anomalous behavior of this mode. In the ferroelastic phase spectra, the ignition of the second acoustic TA2 from the same point has also been detected and its baric behavior has been studied. Under sufficiently high pressures, splitting of doubly degenerate phonons with the Eg symmetry has been observed and explained. The parameters of the Gruneisen constants have been determined from the baric dependences of the phonon frequencies and discussed.

Динамика решеток и барическое поведение фононов в модельных сегнетоэластиках Hg-=SUB=-2-=/SUB=-Br-=SUB=-2-=/SUB=-

AbstractRaman spectra of Hg_2Br_2 model improper ferroelastic crystals have been investigated in a wide range of high hydrostatic pressures. Baric dependences of the phonon frequencies have been obtained; of greatest interest are the observed soft mode originating from the slowest TA _1 acoustic branch at the Brillouin zone boundary ( X point) of the tetragonal phase and the anomalous behavior of this mode. In the ferroelastic phase spectra, the ignition of the second acoustic TA _2 from the same point has also been detected and its baric behavior has been studied. Under sufficiently high pressures, splitting of doubly degenerate phonons with the E _ g symmetry has been observed and explained. The parameters of the Grüneisen constants have been determined from the baric dependences of the phonon frequencies and discussed.

Euhedral crystals of Na2TiGeO5with switchable translucency and reorientable microstructure

Crystal twinning in euhedral crystals reveals anomalous optical properties.

High-Temperature Ferroelastic Phase Transition in an Organic–Inorganic Hybrid: [(CH3)3NCH2Br]2–ZnBr4

Molecular ferroelastic materials with high-temperature reversible crystal phase transition behavior are very rare and have currently become one of the hotspots in the field of ferroelastic materials. However, it is still a great challenge to synthesize a high-temperature ferroelastic phase transition material due to the insufficient theoretical knowledge about the structure transition. Here, we try to combine molecular design and crystal engineering to design molecular ferroelastic crystals with high phase transition temperatures. As expected, a new organic–inorganic hybrid, [(CH3)3NCH2Br]2–ZnBr4 (1), is synthesized by molecular modifications, in which the directionality of the halogen···halogen interactions seems to play a crucial role in achieving a much higher temperature phase transition behavior. Intriguingly, the strip-type ferroelastic domains of 1 were observed at room temperature.

Crystal Adaptronics: Mechanically Reconfigurable Elastic and Superelastic Molecular Crystals.

Mechanically reconfigurable molecular crystals-ordered materials that can adapt to variable operating and environmental conditions by deformation, whereby they attain motility or perform work-are quickly shaping a new research direction in materials science, crystal adaptronics. Properties such as elasticity, superelasticity, and ferroelasticity, which are normally related to inorganic materials, and phenomena such as shape-memory and self-healing effects, which are well-established for soft materials, are increasingly being reported for molecular crystals, yet their mechanism, quantification, and relation to the crystal structure of organic crystals are not immediately apparent. This Minireview provides a condensed topical overview of elastic, superelastic, and ferroelastic molecular crystals, new classes of materials that bridge the gap between soft matter and inorganic materials. The occurrence and detection of these unconventional properties, and the underlying structural features of the related molecular materials are discussed and highlighted with selected prominent recent examples.

Manifestations of structural phase transition in ab initio molecular dynamics of (C3N2H5)2SbF5 crystal

Structural and electronic properties of the ferroelastic crystal (C3N2H5)2SbF5 characterized by first-order phase transition were studied by ab initio methods in the framework of density functional theory. The molecular dynamics calculations were performed at different temperatures in the range TC - 70 ÷ TC + 70° containing the phase transition point TC. In this approach, atomic scale (microscopic) manifestations of this transition were obtained. The quasi continuous temperature changes of some microscopic properties in the relatively wide temperature range around TC were observed in spite of sharp experimental temperature dependences of several macroscopic properties of (C3N2H5)2SbF5 near the first order phase transition point TC (latent heat flow, dielectric permittivity). The latter peculiarities may be regarded as the microscopic precursors of the first order phase transition in (C3N2H5)2SbF5. Different specific kinetic energies (energy per one atom) for five constituting chemical elements (C, N, H, Sb and F) of the crystal have been detected for the first time, indicating for different abilities of the interatomic energy exchange.

Statistics of twinning in strained ferroelastics

In this review, we show that the evolution of the microstructure and kinetics of ferroelastic crystals under external shear can be explored by computer simulations of 2D model materials. We find that the nucleation and propagation of twin boundaries in ferroelastics depend sensitively on temperature. In the plastic regime, the evolution of the ferroelastic microstructure under strain deformation maintains a stick-and-slip mechanism in all temperature regimes, whereas the dynamic behavior changes dramatically from power-law statistics at low temperature to a Kohlrausch law at intermediate temperature, and then to a Vogel–Fulcher law at high temperature. In the yield regime, the distribution of jerk energies follows power-law statistics in all temperature regimes for a large range of strain rates. The non-spanning avalanches in the yield regime follow a parabolic temporal profile. The changes of twin pattern and twin boundaries density represent an important step towards domain boundary engineering.

Strain phase separation: Formation of ferroelastic domain structures

Phase decomposition is a well-known process leading to the formation of two-phase mixtures. Here we show that a strain imposed on a ferroelastic crystal promotes the formation of mixed phases and domains, i.e., domain and phase de-strain with local strains determined by a common tangent construction on the free energy versus strain curves. It is demonstrated that a domain structure can be understood using the concepts of domain/phase rule, lever rule, coherent and incoherent de-strain within the de-strain model description, in a complete analogy to phase decomposition. The proposed de-strain model is validated using phase-field simulations and experimental observations of PbTiO_3 and BiFeO_3 thin films as examples. The de-strain model provides a simple tool to guide and design domain structures of ferroelastic systems.

Domain glasses: Twin planes, Bloch lines, and Bloch points

Ferroelastic materials can develop complex domain structures, which have properties of glassy systems (non‐ergodicity, glass dynamics, glass transitions, and freezing). Four characteristic temperatures are defined for such domain glasses: the dynamical nucleation temperature Td where local correlated clusters can form glass states within a (tweed‐) nano structure, To the Vogel–Fulcher temperature of these precursor nano‐structures, Tpt the phase transition temperature where the (ferroelastic) transition occurs, and TK the Kauzmann temperature where the complex domain structure freezes. Td exists in most ferroelastic materials whereas the other transitions depend on the complexity of the domain patterns and hence on their thermal history. Shear collapse and rapid thermal quench of ferroelastic crystals preferentially lead to domain glasses whereas slow anneal produces mostly highly correlated pattern such as stripe patterns or single domain crystals. Domain glasses are compared with structural glasses and several examples for domain glass features are discussed.

Tweed, Twins, and Holes: A link between mineralogy and materials science

The paper entitled “Tweed, Twins, and Holes,” by Ekhard K.H. Salje [2015, vol. 100(2–3)] gives a comprehensive overview on experiments, theory, and computer simulations of microstructures in ferroelastic and multiferroic minerals and synthetic crystals, with special emphasis on domain wall properties. Such materials are highly interesting for technological applications as well as from a more fundamental point of view, bearing a lot of open questions. Domain boundaries are nanometer-sized objects that very often exhibit physical properties quite different from the bulk. This can lead to completely new functionalities as compared to single domain crystals.

Pressure behavior of phonons and phase transition effects in Hg2I2 model virtual ferroelastics

The Raman spectra of virtual ferroelastic Hg2I2 crystals have been studied in a broad range of hydrostatic pressures. Linear pressure dependences of phonon frequencies are obtained at P Pc) in various polarizations exhibit the excitation of new lines from the X point of the Brillouin zone, including transverse (TA) and longitudinal (LA) acoustic phonons. Based on analysis of the experimental and theoretical results, the Raman spectra of ferroelastic Hg2I2 crystals are interpreted and a model of the phase transition in these crystals is proposed.

Successive phase transitions and kink solutions in ϕ(8), ϕ(10), and ϕ(12) field theories.

We obtain exact solutions for kinks in ϕ(8), ϕ(10), and ϕ(12) field theories with degenerate minima, which can describe a second-order phase transition followed by a first-order one, a succession of two first-order phase transitions and a second-order phase transition followed by two first-order phase transitions, respectively. Such phase transitions are known to occur in ferroelastic and ferroelectric crystals and in meson physics. In particular, we find that the higher-order field theories have kink solutions with algebraically decaying tails and also asymmetric cases with mixed exponential-algebraic tail decay, unlike the lower-order ϕ(4) and ϕ(6) theories. Additionally, we construct distinct kinks with equal energies in all three field theories considered, and we show the coexistence of up to three distinct kinks (for a ϕ(12) potential with six degenerate minima). We also summarize phonon dispersion relations for these systems, showing that the higher-order field theories have specific cases in which only nonlinear phonons are allowed. For the ϕ(10) field theory, which is a quasiexactly solvable model akin to ϕ(6), we are also able to obtain three analytical solutions for the classical free energy as well as the probability distribution function in the thermodynamic limit.

Studying the ferroelastic phase transition in Sb5O7I crystals

The specific heat of a ferroelastic Sb5O7I crystal in the vicinity of the ferroelastic phase transition is studied. It is shown that the phase transition in such a crystal is of the first order.

Dynamically strained ferroelastics: Statistical behavior in elastic and plastic regimes

The dynamic evolution in ferroelastic crystals under external shear is explored by computer simulation of a two-dimensional model. The characteristic geometrical patterns obtained during shear deformation include dynamic tweed in the elastic regime as well as interpenetrating needle domains in the plastic regime. As a result, the statistics of jerk energy differ in the elastic and plastic regimes. In the elastic regime the distributions of jerk energy are sensitive to temperature and initial configurations. However, in the plastic regime the jerk distributions are rather robust and do not depend much on the details of the configurations, although the geometrical pattern formed after yield is strongly influenced by the elastic constants of the materials and the configurations we used. Specifically, for all geometrical configurations we studied, the energy distribution of jerks shows a power-law noise pattern $P(E)\ensuremath{\sim}{E}^{\ensuremath{-}(\ensuremath{\gamma}\ensuremath{-}1)}(\ensuremath{\gamma}\ensuremath{-}1=1.3\ensuremath{-}2)$ at low temperatures and a Vogel-Fulcher distribution $P$($E$) \ensuremath{\sim} exp-($E/{E}_{0}$) at high temperatures. More complex behavior occurs at the crossover between these two regimes where our simulated jerk distributions are very well described by a generalized Poisson distributions $P(E)\ensuremath{\sim}{E}^{\ensuremath{-}(\ensuremath{\gamma}\ensuremath{-}1)}$ exp-($E/{E}_{0}$)${}^{n}$ with $n$ $=$ 0.4--0.5 and \ensuremath{\gamma}\ensuremath{-}1 \ensuremath{\approx} 0 (Kohlrausch law). The geometrical mechanisms for the evolution of the ferroelastic microstructure under strain deformation remain similar in all thermal regimes, whereas their thermodynamic behavior differs dramatically: on heating, from power-law statistics via the Kohlrausch law to a Vogel-Fulcher law. There is hence no simple way to predict the local evolution of the twin microstructure from just the observed statistical behavior of a ferroelastic crystal. It is shown that the Poisson distribution is a convenient way to describe the crossover behavior contained in all the experimental data without recourse to specific scaling functions or temperature-dependent cutoff lengths.

The kinetic relation for twin wall motion in NiMnGa—part 2

A combined theoretical and experimental investigation of twin wall motion in ferromagnetic shape memory alloy (FSMA) NiMnGa is presented. A general analysis of twinning dynamics in ferroelastic and ferroelectric crystals reveals that different kinetic relations for sidewise twin wall motion appear under different ranges of the driving force. All these relations are shown to be governed by several nano-scale properties of the twin wall. For high values of the driving force with respect to a crystal's Peierls barrier, uniform viscous motion is obtained. Recently (Faran and Shilo, 2011), we reported on a pioneering experimental demonstration of this important kinetic relation through magnetically induced twin wall motion in NiMnGa. In the lower driving force range, twin wall propagates through thermally activated nucleation and growth of twin wall steps. Here, we present a model for step nucleation that leads to an exponential-type kinetic relation that is governed by the values of the step's physical properties. Comparison of experimental results for type I and type II twin walls with model predictions allow for the extraction of all the fundamental material properties that govern twinning dynamics in NiMnGa. In addition, the effect of demagnetization energy on twin wall motion and local variations in viscosity values are presented and discussed.

Giant domain wall response of highly twinned ferroelastic materials

Many ferroelastic crystals display at sufficiently low measurement frequencies a huge elastic softening below Tc which is caused by domain wall motion. Materials range from perovskites to iron based superconductors and shape memory materials. We present a model—based on Landau-Ginzburg theory including long range elastic interaction between needle shaped ferroelastic domains—to describe the observed superelastic softening. The theory predicts that the domain wall contribution to the elastic susceptibility is different for improper and proper ferroelastic materials. A test of the theory against experimental data on SrTiO3, KMnF3, LaAlO3, LaAlO3,La1-xNdxP5O14, and NH4HC2O4·12H2O yields excellent agreement.

Crystal structure and characterization of a novel ferroelastic ionic crystal: 1-Aminopyridinium iodide (C5H7N2)+I−

1-Aminopyridinium iodide (API) undergoes a reversible first-order phase transition (PT) II→I at 384K. The single-crystal X-ray diffraction studies have been carried out at 110, 280 and 401K. The compound crystallizes in the monoclinic space group P21/c (phase II) and exhibits ferroelastic properties. High temperature paraelastic phase (I) is described by the trigonal symmetry (space group R3¯m) with the 6-site cations disorder. The mechanism of PT is governed by both cationic dynamics and shifts of the I− anions. The conductivity that emerges when approaching the PT temperature is believed to be associated with the charge transfer from I− anion to the 1-aminopyridinium cation.