Ferroic Phase Transitions Research Articles

Composite quadrupole order in ferroic and multiferroic materials

The formalism of composite and intertwined orders has been remarkably successful in discussing the complex phase diagrams of strongly correlated materials and high-$T_c$ superconductors. Here, we propose that composite orders are also realized in ferroelectric and ferromagnetic materials when lattice anisotropy is taken into account. This composite order emerges above the ferroic phase transition, and its type is determined by the easy axis of magnetization or polarization, respectively. In multiferroic materials, where polarization and magnetization are coupled, composites of both orders are possible. This formalism of composite orders naturally accounts for magnetoelectric monopole, toroidal, and quadrupole orders. More broadly, composite orders may explain precursor phenomena in incipient (multi)ferroic materials, arising at temperatures above the ferroic phase transition and potentially contributing to the characterization of currently hidden orders.

Ferroic phase transition molecular crystals

Recent developments in ferroic phase transition molecular crystals (ferroelectrics, ferroelastics, and multiferroics) are highlighted.

Rippling Ferroic Phase Transition and Domain Switching In 2D Materials.

Ripples are a class of native structural defects widely existing in 2D materials. They originate from the out-of-plane flexibility of 2D materials introducing spatially evolving electronic structure and friction behavior. However, the effect of ripples on 2D ferroics has not been reported. Here a molecular dynamics study of the effect of ripples on the temperature-induced ferroic phase transition and stress-induced ferroic domain switching in ferroelastic-ferroelectric monolayer GeSe is presented. Ripples stabilize the short-range ferroic orders in the high-temperature phase with stronger ferroicity and longer lifetime, thereby increasing the transition temperature upon cooling. In addition, ripples significantly affect the domain switching upon loading, changing it from a highly correlated process into a ripple-driven localized one where ripples act as source of dynamical random stress. These results reveal the fundamental role of ripples on 2D ferroicity and provide theoretical guidance for ripple engineering of controlled phase transition and domain switching with potential applications in flexible 2D electronics.

Origin of Terahertz Soft-Mode Nonlinearities in Ferroelectric Perovskites

Soft modes are intimately linked to structural instabilities and are key for the understanding of phase transitions. The soft modes in ferroelectrics, for example, map directly the polar order parameter of a crystal lattice. Driving these modes into the nonlinear, frequency-changing regime with intense terahertz (THz) light fields is an efficient way to alter the lattice and, with it, the physical properties. However, recent studies show that the THz electric-field amplitudes triggering a nonlinear soft-mode response are surprisingly low, which raises the question on the microscopic picture behind the origin of this nonlinear response. Here, we use linear and two-dimensional terahertz (2D THz) spectroscopy to unravel the origin of the soft-mode nonlinearities in a strain-engineered epitaxial ferroelectric SrTiO3 thin film. We find that the linear dielectric function of this mode is quantitatively incompatible with pure ionic or pure electronic motions. Instead, 2D THz spectroscopy reveals a pronounced coupling of electronic and ionic-displacement dipoles. Hence, the soft mode is a hybrid mode of lattice (ionic) motions and electronic interband transitions. We confirm this conclusion with model calculations based on a simplified pseudopotential concept of the electronic band structure. It reveals that the entire THz nonlinearity is caused by the off-resonant nonlinear response of the electronic interband transitions of the lattice-electronic hybrid mode. With this work, we provide fundamental insights into the microscopic processes that govern the softness that any material assumes near a ferroic phase transition. This knowledge will allow us to gain an efficient all-optical control over the associated large nonlinear effects.Received 14 September 2020Revised 20 January 2021Accepted 12 March 2021DOI:https://doi.org/10.1103/PhysRevX.11.021023Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasDielectric propertiesElectric polarizationElectronic excitation & ionizationElectronic transitionsFerroelectricityLight-matter interactionNonlinear opticsPhononsStrong electromagnetic field effectsUltrafast phenomenaTechniquesTerahertz time-domain spectroscopyUltrafast pump-probe spectroscopyCondensed Matter, Materials & Applied PhysicsNonlinear DynamicsAtomic, Molecular & Optical

Ferroelastic phase transition in the family of double fluoride crystals by Raman spectroscopy

In order to clarify ordering mechanisms of ferroic phase transitions in double fluoride salts (NH4)3SnF7, (NH4)3GeF7 and (NH4)3TiF7, their Raman scattering spectra have been studied in wide ranges of frequencies (20–3400 cm−1) and temperatures (8–410 K). Substitution of the central ion in the octahedron groups was found to change not only the phase transition types and sequences, but to modify the types of structural disorder as well, which is a special feature of these high-symmetry fluoride crystals.

Microstructure and giant baro-caloric effect induced by low pressure in Heusler Co51Fe1V33Ga15 alloy undergoing martensitic transformation

Solid-state refrigeration based on the magneto- or mechano-caloric effect, including elasto- and baro-caloric in ferroic phase transition materials is promising to replace the current vapor compression refrigeration in consideration of environmental-friendliness and energy-saving. However, both high driven field and small thermal changes in all of these caloric materials hinder the development of solid-state refrigeration. Here we report a giant baro-caloric effect near room temperature induced by a low hydrostatic pressure in Co-based Co51Fe1V33Ga15 Heusler alloy. The maximum adiabatic temperature change under the applied pressure change of Δp = 0.1–100 MPa can be as high as ΔTadMax= 7.7 K (ΔTadMax/Δpreaches up to ∼7.7 K kbar−1), surpassing the ΔTadMax/Δpvalue reported hitherto in baro-caloric alloys. In addition, the microstructure is also studied by using the electron microscopes. Along with the austenite and martensite, the submicron V-rich particles are precipitated in this alloy, which are believed to account for enhancing mechanical properties.

Orthorhombic to monoclinic phase transition in NbNiTe2

The high-temperature structural phase transition of the potential topological material ${\mathrm{NbNiTe}}_{2}$ has been studied in detail. At high temperatures, the structure is centrosymmetric with orthorhombic space-group $P\frac{2}{m}\frac{2}{n}\frac{{2}_{1}}{a}(Pmna)$, and distorts at 373 K to a monoclinic structure with space-group $P11\frac{{2}_{1}}{a}(P{112}_{1}/a)$. A small signature in specific heat and commensurate small release of entropy are observed at the phase transition. The low-temperature monoclinic structure retains its inversion center and the symmetries associated with the orthorhombic $c$ axis. At high temperatures, ${\mathrm{NbNiTe}}_{2}$ shows phonon instabilities at $\mathrm{\ensuremath{\Gamma}}$ and $X$, which are removed by the structural phase transition. The electronic structure of ${\mathrm{NbNiTe}}_{2}$ is only slightly affected, indicating this ferroic phase transition is primarily due to steric effects.

Caloric Effects in Perovskite Oxides

AbstractPerovskite oxides show an amazing diversity of electronic and magnetic properties along with a myriad of structural variants and phase transitions. Large thermal changes may be driven near the ferroic phase transitions in perovskite oxides using magnetic, electric, and stress fields to manipulate conjugate order parameters. The ensuing magnetocaloric, electrocaloric, and mechanocaloric effects can be utilized for environment‐friendly and high‐efficiency solid‐state cooling applications. In this review the details of these caloric effects in perovskite oxides both from a chronological perspective and from the viewpoint of the recent advances in multiple caloric phenomena are described. The authors highlight the role of interfaces in oxide thin films for the different caloric effects and address some of the outstanding challenges for the fundamental understanding and practical implementation of perovskite oxides in solid state refrigeration.

Mechanosynthesis of the Whole Y1-xBixMn1-xFexO3 Perovskite System: Structural Characterization and Study of Phase Transitions.

Perovskite BiFeO3 and YMnO3 are both multiferroic materials with distinctive magnetoelectric coupling phenomena. Owing to this, the Y1−xBix Mn1−xFexO3 solid solution seems to be a promising system, though poorly studied. This is due to the metastable nature of the orthorhombic perovskite phase of YMnO3 at ambient pressure, and to the complexity of obtaining pure rhombohedral phases for BiFeO3-rich compositions. In this work, nanocrystalline powders across the whole perovskite system were prepared for the first time by mechanosynthesis in a high-energy planetary mill, avoiding high pressure and temperature routes. Thermal decomposition temperatures were determined, and structural characterization was carried out by X-ray powder diffraction and Raman spectroscopy on thermally treated samples of enhanced crystallinity. Two polymorphic phases with orthorhombic Pnma and rhombohedral R3c h symmetries, and their coexistence over a wide compositional range were found. A gradual evolution of the lattice parameters with the composition was revealed for both phases, which suggests the existence of two continuous solid solutions. Following bibliographic data for BiFeO3, first order ferroic phase transitions were located by differential thermal analysis in compositions with x ≥ 0.9. Furthermore, an orthorhombic-rhombohedral structural evolution across the ferroelectric transition was characterized with temperature-dependent X-ray diffraction.

Caloric Effects in Ferroic Materials: New Concepts for Cooling

AbstractRefrigeration is one of the primary uses for electrical energy and an important contributor to worldwide CO2 emissions. Both of these issues can be mitigated if caloric effects in solid materials are fully utilized. In particular, materials with ferroic phase transitions, which give rise to magneto‐, electro‐, and elasto‐caloric effects, are promising candidates. Because these refrigerants are in the solid state, the corresponding cooling technology also eliminates the need for halo‐carbon refrigerants with high global warming potential. This Special Issue gives an overview on recent breakthroughs in the research on magnetocaloric, elastocaloric, and electrocaloric materials and their implementation in more efficient cooling devices, as obtained within the German Priority Program Ferroic Cooling (SPP 1599). As a brief introduction to the in‐depth Reviews and Full Papers included in the Special Issue, a ferroic cooling cycle is sketched and the influences of magnetic, electric, and stress fields on ferroic materials are summarized in this Editorial.

An Unusual Phase Transition Driven by Vibrational Entropy Changes in a Hybrid Organic–Inorganic Perovskite

The driving forces for the phase transitions of ABX3 hybrid organic-inorganic perovskites have been limited to the octahedral tilting, order-disorder, and displacement. Now, a complex structural phase transition has been explored in a HOIP, [CH3 NH3 ][Mn(N3 )3 ], based on structural characterizations and ab initio lattice dynamics calculations. This unusual first-order phase transition between two ordered phases at about 265 K is primarily driven by changes in the collective atomic vibrations of the whole lattice, along with concurrent molecular displacements and an unusual octahedral tilting. A significant entropy difference (4.35 J K-1 mol-1 ) is observed between the low- and high-temperature structures induced by such atomic vibrations, which plays a main role in driving the transition. This finding offers an alternative pathway for designing new ferroic phase transitions and related physical properties in HOIPs and other hybrid crystals.

An Unusual Phase Transition Driven by Vibrational Entropy Changes in a Hybrid Organic–Inorganic Perovskite

AbstractThe driving forces for the phase transitions of ABX3 hybrid organic–inorganic perovskites have been limited to the octahedral tilting, order–disorder, and displacement. Now, a complex structural phase transition has been explored in a HOIP, [CH3NH3][Mn(N3)3], based on structural characterizations and ab initio lattice dynamics calculations. This unusual first‐order phase transition between two ordered phases at about 265 K is primarily driven by changes in the collective atomic vibrations of the whole lattice, along with concurrent molecular displacements and an unusual octahedral tilting. A significant entropy difference (4.35 J K−1 mol−1) is observed between the low‐ and high‐temperature structures induced by such atomic vibrations, which plays a main role in driving the transition. This finding offers an alternative pathway for designing new ferroic phase transitions and related physical properties in HOIPs and other hybrid crystals.

Giant barocaloric effects over a wide temperature range in superionic conductor AgI

Current interest in barocaloric effects has been stimulated by the discovery that these pressure-driven thermal changes can be giant near ferroic phase transitions in materials that display magnetic or electrical order. Here we demonstrate giant inverse barocaloric effects in the solid electrolyte AgI, near its superionic phase transition at ~420 K. Over a wide range of temperatures, hydrostatic pressure changes of 2.5 kbar yield large and reversible barocaloric effects, resulting in large values of refrigerant capacity. Moreover, the peak values of isothermal entropy change (60 J K−1 kg−1 or 0.34 J K−1 cm−3) and adiabatic temperature changes (18 K), which we identify for a starting temperature of 390 K, exceed all values previously recorded for barocaloric materials. Our work should therefore inspire the study of barocaloric effects in a wide range of solid electrolytes, as well as the parallel development of cooling devices.

Theory of antiferroelectric phase transitions

At variance with structural ferroic phase transitions which give rise to macroscopic tensors coupled to macroscopic fields, criteria defining antiferroelectric (AFE) phase transitions are still under discussion due to the absence of specific symmetry properties characterizing their existence. They are recognized by the proximity of a ferroelectric (FE) phase induced under applied electric field, with a double hysteresis loop relating the induced polarization to the electric field and a typical anomaly of the dielectric permittivity. Here, we show that there exist indeed symmetry criteria defining AFE transitions. They relate the local symmetry of the polar crystallographic sites emerging at an AFE phase transition with the macroscopic symmetry of the AFE phase. The dielectric properties of AFE transitions are deduced from a Landau theoretical model in which ferroelectric and ferrielectric phases are shown to stabilize as the result of specific symmetry-allowed couplings of the AFE order- parameter with the field-induced polarization.

Multiple ferroic glasses via ordering

Structural glasses are characterized by the loss of long-range translational and rotational symmetry. In the last two decades, however, it has been discovered that materials that exhibit ferroic (ferromagnetic, ferroelectric and ferroelastic) phase transformations may also exhibit glassy behavior, in which the ferroic degrees of freedom (magnetization, polarization, strain) exhibit a loss of long-range translational symmetry. A consequence of this loss of long-range symmetry is the suppression of the ferroic phase transitions. Moreover, these unique glassy systems exhibit dynamic and thermodynamic behavior analogous to regular structural glasses. Conventionally, the onset of glassy behavior is brought about by the introduction of spatial heterogeneities, typically originating from point defects, particularly in the case of strain glasses. Here, we demonstrate, for the first time, that configurational order/disorder in a single ferromagnetic alloy (Ni45Co5Mn36.6In13.4) can be used to stabilize both strain and magnetic glasses. The control of the degree of configurational order – through simple heat treatment schedules –, and simultaneous application of stress and magnetic field enabled us to observe a Kauzmann point, that is, the collapse of the entropy difference between a crystalline and a glassy phase. Systematic investigation of the transformation behavior in this system as a function of heat treatment enabled us to observe four kinds of solid–solid phase transitions (ferromagnetic–paramagnetic, martensitic transformation, strain and magnetic glass) in a single composition. The alloy investigated can be used to further elucidate the nature of ferroic glass transitions and their coupling.

Primary ferrotoroidicity in antiferromagnets

Antiferromagnetic ordering does not give rise to a measurable macroscopic symmetry-breaking order parameter such as the magnetization in a ferromagnet. An exception is the case of antiferromagnets with a vortexlike toroidal alignment of the magnetic moments in the unit cell because this gives rise to the formation of a spontaneous macroscopic toroidal moment which can be measured as a magnetoelectric effect. It is a long-standing question whether the toroidal moment is merely a side effect of the antiferromagnetic state or whether it can become the primary order parameter in a ferroic phase transition. Here we report the magnetoelectric properties of ${\mathrm{LiFeSi}}_{2}{\mathrm{O}}_{6}$ and show that they point to the role of the toroidal vector moment as the primary order parameter. Based on Landau theory we distinguish it from primary antiferromagnetic order. We thus justify the proposal that along with ferromagnets, ferroelectrics, and ferroelastics the ferrotoroidics constitute a new class of primary ferroics.

Variations in elastic and anelastic properties as indicators of static and dynamic strain relaxation phenomena associated with phase transitions

Almost all phase transitions are accompanied by some degree of lattice strain, typically varying between a few per mil to a few per cent, but extending to 5–10% for martensitic transitions. It is inevitable, therefore, that there will also be changes in elastic properties and, because the elastic moduli are susceptibilities, these are typically in the range of 10’s of per cent. At the same time, the associated transformation microstructures may be mobile under the action of external stress and therefore give rise to anelastic losses in a dynamical mechanical measurement. It has turned out that Resonant Ultrasound Spectroscopy, in a frequency window ∼0.1–2 MHz, is a particularly powerful method for characterizing elastic and anelastic behavior as functions of temperature and magnetic field for ferroic and multiferroic phase transitions in a wide range of materials. Examples of recent collaborative studies, relating to magnetoelastic effects in EuTiO3, multiferroic transitions in Pb(Fe0.5Nb0.5)O3, the influence of grain size on Jahn-Teller × charge ordering in La0.5Ca0.5MnO3, ferroelectric and ferroelastic transitions in metal organic frameworks, and martensitic transitions in Heusler alloys, will be used to demonstrate specific mechanisms and kinetics of static and dynamic strain relaxation phenomena.

Temperature Dependence of Magnetization in Nickel Thin Film Sputtered onto Ferroelastic Gadolinium Molybdate Substrate

The influence of the substrate Gd2(MoO4)3 ferroic phase transition on the magnetization of ferromagnetic nickel thin film was investigated using vibrating sample magnetometer. We have compared experimental results with micromagnetic simulations.Our measurements showed strong magnetization change at Curie Point. We have shown by simulations, taking into consideration magnetoelastic contribution to free energy, that this phenomenon results from the strain-driven spin reorientation transitions.

Caloric materials near ferroic phase transitions.

A magnetically, electrically or mechanically responsive material can undergo significant thermal changes near a ferroic phase transition when its order parameter is modified by the conjugate applied field. The resulting magnetocaloric, electrocaloric and mechanocaloric (elastocaloric or barocaloric) effects are compared here in terms of history, experimental method, performance and prospective cooling applications.

Ferroic phase transition of tetragonal Pb0.6−xCaxBi0.4(Ti0.75Zn0.15Fe0.1)O3 ceramics: Factors determining Curie temperature

In this paper, ferroelectric phase transitions of Pb0.6−xCaxBi0.4(Ti0.75Zn0.15Fe0.1)O3 with x ≤ 0.20 ceramics were experimentally measured and a change from first-order to relaxor was found at a critical composition x ∼ 0.19. With increasing Ca content of x ≤ 0.18, Curie temperature and tetragonality was found decrease but piezoelectric constant and dielectric constant increase in a quadratic polynomial relationship as a function of x, while the ferroic Curie temperature and ferroelastic ordering parameter of tetragonality are correlated in a quadratic polynomial relationship. Near the critical composition of ferroic phase transition from first-order to relaxor, the Pb0.42Ca0.18Bi0.4(Ti0.75Zn0.15Fe0.1)O3 and 1 mol % Nb + 0.5 mol % Mg co-doped Pb0.44Ca0.16Bi0.4(Ti0.75Zn0.15Fe0.1)O3 ceramics exhibit a better anisotropic piezoelectric properties than those commercial piezoceramics of modified-PbTiO3 and PbNb2O6. At last, those factors including reduced mass of unit cell, mismatch between cation size and anion cage size, which affect ferroic Curie temperature and ferroelastic ordering parameter (tetragonality) of tetragonal ABO3 perovskites, are analyzed on the basis of first principle effective Hamiltonian and the reduced mass of unit cell is argued a more universal variable than concentration to determine Curie temperature in a quadratic polynomial relationship over various perovskite-structured solid solutions.