Formation Of Ferroelastic Domains Research Articles

Lattice match between coexisting cubic and tetragonal phases in PMN-PT at the phase transition

(1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) perovskite-like solid solutions are recognized for their outstanding electromechanical properties, which are of technological importance. However, some significant aspects of the crystal structures and domain assemblages in this system and the role of these characteristics in defining the functional performance of PMN-PT remain uncertain. Here, we used synchrotron x-ray diffraction to investigate the phase transition linking the paraelectric (cubic) and ferroelectric (tetragonal) phases in a single crystal of 0.65PMN-0.35PT. We analyzed the evolution of reciprocal-space maps across this transition. These maps were collected using small temperature step (1 K) and a high reciprocal-space resolution to reveal changes in the splitting of Bragg peaks caused by the formation of ferroelastic domains in the low-symmetry phase. Our results uncovered a two-phase state, cubic plus tetragonal phases, which exists over a narrow temperature range of only ≈4 K and exhibits a thermal hysteresis of ≈1.8 K. Remarkably, within this state, the lattice parameter of the cubic phase, aC, matches the orientational average of the lattice parameters for the tetragonal polymorph, 23aT+13cT. We discuss the implications of this matching, highlighting the possibility of it being realized by the formation of an assemblage of tetragonal twin domains separated from the cubic phase by a strain-free {110} boundary, as in the “adaptive phase” but without domain miniaturization.

Photoinduced Strain in Organometal Halide Perovskites.

There is a lack of fundamental understanding of mechano-electro-optical multifield coupling for organometallic halide perovskites (OHPs). In this study, the effect of light irradiation on OHPs' mechanical properties was investigated by atomic force microscopy. In the dark, an MAPbI3 film was dominated by grains with a Young's modulus of approximately 5.94 GPa, which decreased to 2.97 GPa under light illumination. The photoinduced strain distribution within the polycrystalline MAPbI3 film was not uniform, and the maximum strain generated inside individual grains was 5.8%. Furthermore, the illumination-induced strain promoted the formation of ferroelastic domains. The Young's modulus of one domain increased from 8.99 to 25.27 GPa, whereas the Young's modulus of an adjacent domain decreased from 14.9 to 1.30 GPa. According to the density-functional-theory calculations, the observed photoinduced strain-promoted variations in mechanical properties were caused by the reversible migration of MA+ cations. These findings can help establish the relationship among the mechanical-chemical-optoelectronic characteristics of OHPs.

Raman imaging of ferroelastically configurable Jahn\u2013Teller domains in LaMnO3

The Jahn–Teller (JT) effect, through geometric deformation of molecules or local ionic lattices, lowers the overall energy of the system by removing electron degeneracy from partially occupied orbitals. Crystal symmetry lowered by JT distortion inevitably creates multiple variants of elastic and orbital-anisotropic states. Visualization and control of the domain/wall textures create a cornerstone to understand various correlated phenomena and explore wall properties. Here, we report the real-space observation of JT phonon and orbiton-related domains in a LaMnO3 thin film using confocal Raman spectromicroscopy. The characteristic symmetries of the JT-originated Raman modes allow us to detect and visualize the local population and orientation of the JT planes. Combined with a crystal structural analysis, we find that the formation of ferroelastic domains with W or W’ walls provides the basic framework for understanding JT domain textures. Furthermore, we demonstrate the JT domains can be manipulated by applying local external stress. Our findings provide a useful pathway for mechanically-tunable orbitronic applications.

Inducing ferroelastic domains in single-crystal CsPbBr3 perovskite nanowires using atomic force microscopy

Understanding and controlling the formation and dynamics of ferroelastic domains can be key to enhance metal halide perovskite device performance, but established methods lack spatial control at the level of single domains. Here, the authors induced the formation of ferroelastic domains in CsPbBr${}_{3}$ nanowires using an atomic force microscope tip, and studied the structural changes using nanofocused x-ray diffraction with a 60-nm beam. The applied stress locally induced lattice tilts that define room temperature-stable ferroelastic domains, which spread spatially and terminated at {112}-type domain walls. While pristine regions show an orthorhombic (004) reflection; regions exposed to higher forces exhibit {220}-type reflections.

In Situ Imaging of Ferroelastic Domain Dynamics in CsPbBr3 Perovskite Nanowires by Nanofocused Scanning X-ray Diffraction.

The interest in metal halide perovskites has grown as impressive results have been shown in solar cells, light emitting devices, and scintillators, but this class of materials have a complex crystal structure that is only partially understood. In particular, the dynamics of the nanoscale ferroelastic domains in metal halide perovskites remains difficult to study. An ideal in situ imaging method for ferroelastic domains requires a challenging combination of high spatial resolution and long penetration depth. Here, we demonstrate in situ temperature-dependent imaging of ferroelastic domains in a single nanowire of metal halide perovskite, CsPbBr3. Scanning X-ray diffraction with a 60 nm beam was used to retrieve local structural properties for temperatures up to 140 °C. We observed a single Bragg peak at room temperature, but at 80 °C, four new Bragg peaks appeared, originating in different real-space domains. The domains were arranged in periodic stripes in the center and with a hatched pattern close to the edges. Reciprocal space mapping at 80 °C was used to quantify the local strain and lattice tilts, revealing the ferroelastic nature of the domains. The domains display a partial stability to further temperature changes. Our results show the dynamics of nanoscale ferroelastic domain formation within a single-crystal perovskite nanostructure, which is important both for the fundamental understanding of these materials and for the development of perovskite-based devices.

Study of the Phase Transition in Hg2Cl2 Crystals Using Anomalous X-Ray Transmission

The small-angle X-ray scattering in calomel (univalent mercury chloride Hg2Cl2) single crystals at low temperatures has been investigated. Data on the size of superstructural ferroelectric domains have been obtained for the first time. Lang measurements with anomalous X-ray transmission have made it possible to trace the temperature dynamics of crystal lattice of the high-temperature D4h phase of Hg2Cl2 from 300 K to the Curie temperature (186 K) and the formation of ferroelastic domains in the temperature range of 186–100 K. The lowering of paraphase symmetry in the closest vicinity of the phase transition temperature is indicative of tricritical point transition.

Orientation control and domain structure analysis of {100}-oriented epitaxial ferroelectric orthorhombic HfO2-based thin films

Orientation control of {100}-oriented epitaxial orthorhombic 0.07YO1.5-0.93HfO2 films grown by pulsed laser deposition was investigated. To achieve in-plane lattice matching, indium tin oxide (ITO) and yttria-stabilized zirconia (YSZ) were selected as underlying layers. We obtained (100)- and (001)/(010)-oriented films on ITO and YSZ, respectively. Ferroelastic domain formation was confirmed for both films by X-ray diffraction using the superlattice diffraction that appeared only for the orthorhombic symmetry. The formation of ferroelastic domains is believed to be induced by the tetragonal–orthorhombic phase transition upon cooling the films after deposition. The present results demonstrate that the orientation of HfO2-based ferroelectric films can be controlled in the same manner as that of ferroelectric films composed of conventional perovskite-type material such as Pb(Zr, Ti)O3 and BiFeO3.

On the magnetostructural transition in MnCoGeBx alloy ribbons

The magnetostructural transition in the Mn0.96Co1.04GeB0.02 ribbon alloy was investigated. Chemical, structural, microstructural, and magnetic studies were performed on the samples which were annealed at different temperatures. The resulting samples underwent a first-order phase transition in which the characteristic structural transition temperature shows a near-linear and inversely proportional dependence to the annealing temperature. The magnetostructural transition occurs through a simultaneous ferroelastic–magnetic transition between the ferroelastic–paramagnetic and paraelastic–ferromagnetic phases. Our results suggest that the crystal structure of the hexagonal high temperature phase allows the formation of ferroelastic domains, and the domain walls act as the natural nucleation site of the low temperature paraelastic–ferromagnetic phase.

The influence of ferroelastic domain formation on thermal conductivity in Li2TiGeO5 ceramics

We show, through thermal conductivity coefficient measurements of Li2TiGeO5 ceramics, that the anomaly associated with the ferroelastic phase transition can be distinguished. We correlate this anomaly with the measurement of the domain structure observed in the vicinity of phase transition temperature Tc. Near the Tc, the appearance of ferroelastic domains which become new scattering centers for thermal waves, strongly affect the thermal conductivity in Li2TiGeO5 ceramics.

A variable temperature synchrotron X-ray diffraction study of the ferroelastic double perovskite Ba2GdMoO6

A study of the magnetic and structural properties of the double perovskite Ba2GdMoO6 has been performed. The crystal structure distorts from the ideal cubic (Fm3m) structure to the tetragonal space group I4/m at 220 K, before undergoing a second distortion to a triclinic system (I1) at 80 K. The phase transition to triclinic symmetry is also evident in magnetic susceptibility measurements. The variable temperature synchrotron powder X-ray diffraction results reveal that Ba2GdMoO6 is ferroelastic, with the onset of ferroelastic domain formation occurring at the cubic-tetragonal phase transition. A number of Rietveld refinement techniques for modelling diffuse scattering from ferroelastic domain boundaries have been explored.

Domain annihilation due to temperature and thickness gradients in single-crystal BaTiO3

The manner in which 90. ferroelectric-ferroelastic domains respond to changes in temperature has been mapped in BaTiO3 single crystals using atomic force microscopy. Domain periodicity remains unaltered until approximately 2 degrees C below the Curie temperature (T-C), whereupon domains coarsened dramatically. This behavior was successfully rationalized by considering the temperature dependence of the parameters associated with standard models of ferroelastic domain formation. However, while successful in describing the expected radical increase in equilibrium period with temperature, the model did not predict the unusual mechanism by which domain coarsening occurred; this was not continuous at a local level but instead involved discrete domain annihilation events. Subsequent insights from a combination of free energy analysis for the system and further experimental data from an analogous situation, in which domain period increases with increasing crystal thickness, suggested that domain annihilation is inevitablewhenever a component of the relevant gradient that affects domain period is orientated parallel to the domain walls. Consistent with this thesis, we note that, for the observations presented herein, the thermal gradient possessed a significant component parallel to the domain walls. We suggest that domain annihilation is a general feature of domain structures in gradient fields.

Rhombohedral LSMO films – a unique case of ferroelastic domain formation

AbstractFerroelastic domain formation in thin films of rhombohedral La1–xSrxMnO3 (LSMO), coherently grown on (001) or (011) oriented SrTiO3 (STO), is suggested to occur during film deposition at elevated temperatures, unlike other common perovskite films where structural phase transition and domain formation take place only during cooling. Due to a comparatively small lattice parameter misfit, the LSMO/STO system should be an ideal case for the experimental observation of domain formation without additional strain relaxation effects including misfit dislocation formation. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

35Cl NMR studies of the domain structure of tetramethylammoniumcadmium chloride (TMCC) at lower temperatures

Quadrupolar perturbed 35Cl NMR and 35Cl NQR investigations are performed onsingle crystals of tetramethylammonium cadmium chloride, (CH3)4NCdCl3 (TMCC),in order to study the formation of ferroelastic domains in the ferroelasticphase II below 118 K in which the hexagonal symmetry of the high temperaturephase I is lost. The experimental results cannot simply be explained in termsof the well known monoclinic domain structure but additionally a twin domainstructure is found to exist in phase II: six orientational domains areverified from the NMR rotational pattern at 113 K in contrast to the expectednumber of three for a classical 6/mF2/m transition. The rotational angleΘ between the epitaxially grown twins is calculated from the strain tensors ofthe three orientation states, applying an algebraic approach. The theoreticalvalue Θ = 3.5° is in very good correspondence with the experimental result fromthe 35Cl NMR studies (~4°). Similar results were also derived in recentx-ray studies in phase II. In the low temperature phase III below 104 K thenumber of non-equivalent Cl positions is consistent with both the space groupof phase III and the sixfold enlarged size of the unit cell in phase III withrespect to that in phase I as observed in XRD studies.

87RbNMR study of phase transitions below room temperature in aLiK0.9Rb0.1SO4mixed crystal

${}^{87}\mathrm{Rb}$ NMR spectra in a mixed ${\mathrm{LiK}}_{0.9}{\mathrm{Rb}}_{0.1}{\mathrm{SO}}_{4}$ single crystal have been investigated in the temperature range from 300 to 80 K. From the electric field gradient analysis, one can suggest that the Rb impurity replaces the K site in the mixed crystal. The temperature dependence of the central NMR frequency of ${}^{87}\mathrm{Rb}$ $(I=\frac{3}{2})$ demonstrates the phase transition at 255 K which occurs without a change of the ${\mathrm{Rb}}^{+}$ site symmetry. In the temperature range from 215 to 176 K, the NMR result shows a mixed phase, our tentative proposal. Another phase transition below 140 K indicates a sudden change in symmetry at the rubidium site in the crystal and a phase transition to a new phase with lower symmetry with the formation of ferroelastic domains. These phase transition temperatures are different from the ${}^{39}\mathrm{K}$ NMR study in the pure ${\mathrm{LiKSO}}_{4}$ and are not in agreement with an optical study in ${\mathrm{LiK}}_{1\ensuremath{-}x}{\mathrm{Rb}}_{x}{\mathrm{SO}}_{4}$ $(x=0.1,0.2).$ From the angular dependence of the second order quadrupole shift of the central transition of ${}^{87}\mathrm{Rb}$ NMR, the quadrupole coupling constant and the asymmetry parameter are determined at 300 and 135 K, respectively. The differential scanning calorimeter results clearly show the phase transitions near 257 and 173 K, respectively, but cannot discriminate other phase transitions.

The low-temperature phase sequence gamma - delta - epsilon in halide perovskite tetramethylammonium trichlorogermanate(II) studied by X-ray diffraction

The halide perovskite tetramethylammonium trichlorogermanate(II), N(CH3)4GeCl3, undergoes a structural phase transition at 200 K from an orthorhombic room-temperature phase to an incommensurately modulated orthorhombic phase and at 170 K a further transition to a phase characterized by the coexistence of a monoclinic and an orthorhombic Bravais lattice. It is proposed that the superposition of the two Bravais lattices results from the low bulk modulus (9 GPa) in conjunction with the formation of ferroelastic domains. Local stresses implied by adjacent monoclinic domains allow the soft material to form orthorhombic domain boundaries. Two order parameters xi and eta governing the phase transition at 170 K can be related to a translational and a rotational part of the displacive modulation of the rigid GeCl3 and tetramethylammonium molecules. Experimental evidence suggests that the displacive modulation in the incommensurate phase is related to short-range disorder observed in the room-temperature phase.

Extremely early stage of ferroelastic domain formation observed by laser refraction.

The initial domain formation process in a ferroelastic crystal ${\mathrm{KD}}_{3}$(${\mathrm{SeO}}_{3}$${)}_{2}$ is observed by a method that utilizes laser light refraction at the ferroelastic domain structures. The high sensitivity of this method enables us to detect the refracted light even above the transition point (${\mathit{T}}_{\mathit{c}}$). The intensity level extends down three orders of magnitude smaller than that caused by the domains below ${\mathit{T}}_{\mathit{c}}$. This implies the embryos of the ferroelastic domains already exist in the high-temperature phase as the inhomogeneous strain field.

Ferroelastic phase transition and elastic properties of orthorhombic betaine hydrogen maleinate, (CH 3) 3NCH 2COO·(CH) 2(COOH) 2

Crystals of the title compound undergo a ferroelastic transition at about 194 K. The transition has been detected by the measurement of temperature derivatives of elastic constants employing ultrasonic methods. Two elastic shear stiffnesses, c 44 and c 66, decrease strongly approaching the transition temperature from above. c 66 exhibits a sharp minimum at the transition, whereas c 44 reaches still smaller values down to 0.012 × 10 10Nm -2. Below 194 K elastic waves connected with c 44 are strongly attenuated indicating the formation of ferroelastic domains with monoclinic symmetry. The temperature dependence of c 44 is approximated by c 44=a· log( T T 0 ) with a = 0.446 × 10 10Nm −2 and T 0 = 184 K. The constants c 44 and c 66 even possess negative pressure derivatives. At 293 K the transition is induced by a pressure of 3495 bar. The transition is of strongly second order, as no spontaneous variation of the lattice constants is observed.

Ferroelastic phase transitions in Csr(MoO4)2-CsR(WO4)2 with R = Dy, Ho, Er, Tm, Yb, and Lu

The phase transitions, phase S-T diagrams and domain structure in CsR(MoO4)2 - CsR(WO4)2 system of crystals were studied. The phase transitions were found to be displacement structural phase transitions, attended by a jump of the dielectric constant and formation of ferroelastic domains.