Successive Structural Transitions Research Articles

Electronic transport evolution across the successive structural transitions in Ni50–xFexTi50 shape memory alloys

Abstract TiNi-based shape memory alloys have been extensively investigated due to their significant applications, but a comprehensive understanding of the evolution of electronic structure and electrical transport in a system with martensitic transformations (MT) is still lacking. In this work, we focused on the electronic transport behavior of three phases in Ni50−x Fe x Ti50 across the MT. A phase diagram of Ni50−x Fe x Ti50 was established based on x-ray diffraction, calorimetric, magnetic, and electrical measurements. To reveal the driving force of MT, phonon softening was revealed using first-principles calculations. Notably, the transverse and longitudinal transport behavior changed significantly across the phase transition, which can be attributed to the reconstruction of electronic structures. This work promotes the understanding of phase transitions and demonstrates the sensitivity of electron transport to phase transition.

Peculiarity of magnetocaloric and magnetoresistance effects in Ni–Mn–Sn–Fe alloy with successive metamagnetic structural transitions

Magnetocaloric and magnetoresistance properties originated from a metamagnetic structural transition were investigated in a Fe-doped Ni46.8Mn38.1Sn11.6Fe3.5 alloy. After annealing, the alloy exhibited the intermartensite phase that contributed to the multiple abrupt magnetization and resistivity changes during heating process of martensite transformation. As a result, three successive magnetic entropy change ΔSM peaks of 10.7, 14.5 and 9.7 J/kg·K at temperatures 275, 279 and 285 K respectively were observed, which was responsible for a wide working temperature span ΔTFWHM of 273–287 K and thus a large effective refrigeration capacity RCeff of 98.1 J/kg under 5.0 T. At the same time, a large negative magnetoresistance MR (e.g. over 26.7% at 275 K) was also revealed during heating process under 5.0 T. Such multi-functional magnetocaloric and magnetoresistance effects render Ni–Mn–Sn–Fe alloys promising working materials for magnetic refrigerants, information storage and thermal magnetoelectricity conversions.

Electronic states of metallic electric toroidal quadrupole order in Cd2Re2O7 determined by combining quantum oscillations and electronic structure calculations

Pyrochlore oxide ${\mathrm{Cd}}_{2}{\mathrm{Re}}_{2}{\mathrm{O}}_{7}$ exhibits successive structural transitions upon cooling that break its inversion symmetry. The low-temperature noncentrosymmetric metallic phases are believed to be some odd-parity multipole ordered states that are associated with a Fermi-liquid instability due to the strong spin-orbit interaction (SOI) and electronic correlation. However, their microscopic ordering pictures and the driving force of the phase transitions are still unclear. We determined the electronic structure of the lowest temperature phase of ${\mathrm{Cd}}_{2}{\mathrm{Re}}_{2}{\mathrm{O}}_{7}$ by combining quantum oscillation measurements with electronic structure calculations. The observed Fermi surfaces were well reproduced based on the optimized crystal structure, and we demonstrated the strong influence of the antisymmetric SOI. From the mass enhancement factor, we elucidated the strongly correlated nature of the electronic states. In addition, we visualized the microscopic picture of the $3{z}^{2}\ensuremath{-}{r}^{2}$-type metallic electric-toroidal-quadrupole (ETQ) order characterized by the Re-O bond order. These results corroborate that the metallic ETQ order is driven by a Fermi-liquid instability associated with the strong SOI and electronic correlation, as has been theoretically proposed. Our results provide the basis for exploring unconventional phenomena expected in the metallic ETQ order.

Quasihydrostatic versus nonhydrostatic pressure effects on the electrical properties of NiPS3

We report combined x-ray diffraction (XRD) and electrical transport studies of the van der Waals (vdW) insulator ${\mathrm{NiPS}}_{3}$ to elucidate a pressure-induced insulator-to-metal transition (IMT). On application of quasihydrostatic pressure, two successive structural transitions occur at 10 and 29.4 GPa, as evidenced by the XRD and resistivity measurements. The concomitant IMT with a monoclinic-to-trigonal structural transition near 29.4 GPa turns out to be a common feature of the ${\mathrm{MPS}}_{3}$ family (M=transition metals). Under uniaxial-like pressure, the critical pressure for IMT is drastically reduced to $P=12.5$ GPa. These results showcase that the IMT is susceptible to strain and hydrostatic environments and that pressure offers a new venue to control a dimensional crossover in layered vdW materials.

Successive Structural Transitions of CrSe<sub>2</sub> with Anomalous Valent Chromium

Successive Structural Transitions of CrSe<sub>2</sub> with Anomalous Valent Chromium

Linear Trimer Formation with Antiferromagnetic Ordering in 1T-CrSe2 Originating from Peierls-like Instabilities and Interlayer Se-Se Interactions.

Anomalous successive structural transitions in layered 1T-CrSe2 with an unusual Cr4+ valency were investigated by synchrotron X-ray diffraction. 1T-CrSe2 exhibits dramatic structural changes in in-plane Cr-Cr and interlayer Se-Se distances, which originate from two interactions: (i) in-plane Cr-Cr interactions derived from Peierls-like trimerization instabilities on the orbitally assisted one-dimensional chains and (ii) interlayer Se-Se interactions through p-p hybridization. As a result, 1T-CrSe2 has the unexpected ground state of an antiferromagnetic metal with multiple Cr linear trimers with three-center-two-electron σ bonds. Interestingly, partial substitution of Se for S atoms in 1T-CrSe2 changes the ground state from an antiferromagnetic metal to an insulator without long-range magnetic ordering, which is due to the weakening of interlayer interactions between anions. The unique low-temperature structures and electronic states of this system are determined by the competition and cooperation of in-plane Cr-Cr and interlayer Se-Se interactions.

The crystal structure and phase transitions of LiBaPO4

Polymorphism in lithium barium phosphate (LiBaPO4) was investigated by synchrotron X-ray diffraction (sXRD) and high temperature X-ray diffraction (HT-XRD). Two modifications were isolated using different cooling rates from the synthesis temperature to room temperature. The slowly-cooled sample exhibited a monoclinic structure with a Cc space group (denoted as M-LiBaPO4) while the quenched sample belonged to a trigonal system with a P31c space group (denoted as T-LiBaPO4). In both structures, LiO4 and PO4 tetrahedra are linked alternatively by sharing each corner in the lattice, forming tridymite-type six-membered rings. The voids in the anionic framework are filled by Ba atoms. The monoclinic distortion in M-LiBaPO4 can be attributed to “polyhedral tilting” which shifts the axial bridging oxygens from the centroid of the PO4 tetrahedron, breaking the three-fold symmetry in the trigonal structure. The HT-XRD data upon heating from 298 to 1373 K indicate successive structural transitions as follows; M-LiBaPO4 (Cc) → T-LiBaPO4 (P31c) → H-LiBaPO4 (P63) → O-LiBaPO4 (Pmcn). H-LiBaPO4 and O-LiBaPO4 denote the phases exhibiting the hexagonal and orthorhombic systems, respectively. The thermal evolution of the crystal structure of LiBaPO4 is quite similar to that of LiKSO4. The sequences of space group change in both compounds are nearly identical and only the transition temperatures differ.

Novel stable structure of Li3PS4 predicted by evolutionary algorithm under high-pressure

By combining theoretical predictions and in-situ X-ray diffraction under high pressure, we found a novel stable crystal structure of Li3PS4 under high pressures. At ambient pressure, Li3PS4 shows successive structural transitions from γ-type to β-type and from β-type to α type with increasing temperature, as is well established. In this study, an evolutionary algorithm successfully predicted the γ-type crystal structure at ambient pressure and further predicted a possible stable δ-type crystal structures under high pressure. The stability of the obtained structures is examined in terms of both static and dynamic stability by first-principles calculations. In situ X-ray diffraction using a synchrotron radiation revealed that the high-pressure phase is the predicted δ-Li3PS4 phase.

Pressure-induced structural transitions of a room temperature ionic liquid—1-ethyl-3-methylimidazolium chloride

In this paper, structural evaluations of a room temperature ionic liquid, 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl), were systematically investigated at high pressures. Our Raman spectra, infrared spectra, and synchrotron X-ray diffraction investigations show that crystalline [EMIM]Cl experienced structural instabilities at high pressures and underwent at least four successive structural transitions at around 5.8, 9.3, 15.8, and 19.1 GPa, respectively. Notably, the abrupt emergence of photoluminescence from the sample at around 19.3 GPa, originated from the pressure-induced polymerization of the [EMIM]+ cations, as confirmed by the mass spectrometry experiments. Our results also indicate that high pressure significantly affected the conformational equilibrium of the [EMIM]+ cations. The structural transitions are influenced by the ion stacking modes determined by the hydrogen bonds and possibly by some chemical reactions in addition to the cation conformational isomers.

Possible origin of stabilized monoclinic structure of KNbO3 nanomaterials at room temperature

We have investigated the structural phase transition and phase stability of newly discovered monoclinic crystal structure of KNbO3 nanomaterials. Through x-ray diffraction, Raman scattering, and neutron diffraction measurements, we have found that the KNbO3 grown at low temperature undergoes a successive structural transition from monoclinic, tetragonal, to cubic, while the KNbO3 grown at high temperature does from monoclinic, orthorhombic, tetragonal, to cubic with the increase of temperature. After heat treatment, the monoclinic structure of KNbO3 is transformed to an orthorhombic structure at room temperature. Accompanying the structural transformation, the Raman peaks corresponding to surface and lattice hydroxyl groups are strongly suppressed. These results imply that the hydroxyl defects should play a crucial role for the monoclinic structure of KNbO3 at room temperature.

Preparation, Characterization, and Lithium Intercalation Behavior of LiVO3 Cathode Material for Lithium-Ion Batteries

A variety of LiVO3 compounds (LVO-350, LVO-400, LVO-450, and LVO-500) have been synthesized via a resorcinol-formalin assisted sol–gel method. The LiVO3 cathodes calcined at different temperatures are characterized by XRD, SEM, and galvanostatic charge/discharge to investigate the effects of annealing on the structure, morphology, and electrochemical characteristics. The results show that both crystallinity and morphology play important roles in the Li-storage properties of LiVO3; the sample annealed at 450 °C (LVO-450) has high crystallinity, moderated particle size, and thus exhibits the best electrochemical performance among the four electrodes. Furthermore, the Li-ion intercalation/deintercalation mechanism for LiVO3 is investigated by ex situ XRD, TEM, Raman spectroscopy, and XPS. The characterizations on the pristine and cycled LVO-450 reveal that the initial lithium insertion/extraction reaction of LiVO3 based on V5+/V4+ redox couple undergoes a successive structural transition: monoclinic LiVO3 tr...

Thermotropic phase transitions in Pb1−xSrx(Al1/3Nb2/3)0.1(Zr0.52Ti0.48)0.9O3 ceramics: Temperature dependent dielectric permittivity and Raman scattering

The phase transitions of Pb1−xSrx(Al1/3Nb2/3)0.1(Zr0.52Ti0.48)0.9O3 (Sr-modified PAN-PZT) ceramics with Sr compositions of x = 2%, 5%, 10% and 15% have been investigated using X-ray diffraction (XRD), temperature dependent dielectric permittivity and Raman scattering. The XRD analysis show that the phase transition occurs between Sr composition of 5% and 10%. Based on the broad dielectric peaks at 100 Hz, the diffused phase transition from tetragonal (T) to cubic (C) structure shifts to lower temperature with increasing Sr composition. The dramatic changes of wavenumber and full width at half-maximum (FWHM) for E(TO4)′ softing mode can be observed at morphotropic phase boundary (MPB). Moreover, the MPB characteristic shows a wider and lower trend of temperature region with increasing Sr composition. It could be ascribed to the diminishment of the energy barrier and increment of A-cation entropy. Therefore, the Sr-modified PAN-PZT ceramics unambiguously undergo two successive structural transitions (rhombohedral-tetragonal-cubic phase) with temperature from 80 to 750 K. Correspondingly, the phase diagram of Sr-modified PAN-PZT ceramics can be well depicted.

Valence-lattice interaction on YbPd

An intermediate valence compound YbPd undergoes successive structural transitions at 105 K and 125 K. The recent inelastic X-ray scattering measurement have revealed softening of longitudinal acoustic (LA) mode around X point, q = (0, 0, 0.5). We have attempted to reproduce this softening from first-principles calculations. The calculated results with fixed valence Yb do not show any anomaly in the LA mode around X. To include valence change in the lattice vibrations, the nearest-neighbor valence-lattice interaction has been added. The interaction reduces the energy of the LA mode around X as observed by the experiment. This soft mode leads to the structure below 105 K. On the other hand, the lowest energy is found at the slightly different wavevector, q = (0.1, 0.1, 0.5). This wavevector corresponds to the superlattice reflection observed by the experiment in the intermediate incommensurate phase between 105 K and 125 K. Therefore, the successive structural transitions of YbPd can be correctly reproduced by including this valence-lattice interaction.

Orbital Order and Structural Phase Transitions in Vanadium Spinel FeV2O4

Orbital degrees of freedom plays an important role in condensed matter physics because it is strongly related with phase transitions and induces the fascinating physical properties. A spinel oxide FeV2O4is one of the peculiar examples because this compound has double orbital degrees of freedom at both Fe2+and V3+ions. Furthermore, this material represents exotic physical properties [1,2], i.e.; multiferroic, large magnetostriction, and successive structural transitions with decreasing temperature: cubic - tetragonal (c < a: tetraHT, 138K) - orthorhombic (orthoHT, 108 K) - tetragonal (c > a: tetraLT, 68 K). However, the origin of structural transitions and physical properties is controversial until now. In order to clarify the origin, we have performed synchrotron x-ray diffraction experiments at low temperatures at beamline BL02B2 (for the powder samples) in SPring-8 and BL-4C (for the single crystal) of the Photon Factory, KEK. Furthermore, we have carried out the magnetization and the specific heat measurements using polycrystalline samples and single crystal of FeV2O4. We have firstly found another orthorhombic phase (orthoLT) below 30 K in the polycrystalline sample of FeV2O4, shown in figure 1. The Rietveld analysis was performed, and the overall qualities of fittings were fairly good. In order to investigate the details of the orbital state of Fe2+and V3+in FeV2O4, we have performed the normal mode analysis, which is based on static displacements of the tetrahedron of FeO4and octahedron of VO6. In the orthoLT phase, we found the orbital order of Fe2+ions, which is mixture of 3z2-r2and y2-z2orbitals, without change of orbital order of V3+ions. This result indicates that the origin of the orthoLT phase is derived from the competition between cooperative Jahn-Teller effect and relativistic spin-orbit coupling of Fe2+ions. We also discuss the origins of the other phase transitions considering the orbital state of V3+and Fe2+ions, and then the orbital dilution effect, where the structural and magnetic properties are investigated by using powder samples substituted for Fe2+and V3+ions by other ions (Mn2+and Fe3+) with no orbital degrees of freedom.

Structural and magnetic properties of spinel compound Fe1+xCoxV2O4

Vanadium spinel oxides AV2O4have attracted much attention for recent years because they show the peculiar physical properties which are caused by competition and cooperation of spin, orbital and lattice degrees of freedom. Among such compounds, FeV2O4is a unique compound showing successive phase transitions: cubic to tetragonal (c < a) at ~140 K, from tetragonal to orthorhombic accompanied by ferrimagnetic transition at ~110 K and from orthorhombic to tetragonal (c > a) at ~70 K with decreasing temperature. It is suggested that these phase transitions originate from the orbital degrees of freedom of both Fe2+ions at A-site (tetrahedral site) and V3+ones at B-site (octahedral site), however, the origin remains controversial. In the present study, we investigate the substitution effect of Fe2+with Co2+having no orbital degrees of freedom to clarify the role of the orbital degree of Fe2+at the A-site. We carried out magnetization and specific heat measurements and synchrotron powder diffraction experiments by the Debye-Scherrer camera at the beamline BL-8B at Photon Factory in KEK. For x ≤ 0.1, the successive structural transitions similar to that observed in FeV2O4occur although the transition temperature of cubic-to-tetraLT transition rapidly decreases with increasing x. For 0.2≤ x ≤ 0.6, the only structural transition from cubic to tetragonal (c < a) was observed, however, the transition temperatures were somewhat different from the ferrimagnetic transition ones. On the other hand, for x ≥ 0.7, the crystal structure remains cubic down to 10 K similar to that of CoV2O4. These structural properties are discussed in terms of the orbital states of Fe2+ions obtained by the normal mode analysis, and they are compared with the results of the specific heat and magnetization measurements.

Successive Pressure-Induced Structural Transitions in Relaxor Lead Indium Niobate

We employed Raman scattering and x-ray diffraction to investigate the behavior of disordered perovskite-type Pb(In1/2Nb1/2)O3 (PIN) under high pressure up to 50 GPa at 300 K. The sharp peak centered at 380 cm−1 increases its intensity with pressure. Two Raman peaks around 550 cm−1 merge at 16 GPa and their linewidths increase with pressure. The structural phase transition is associated with a splitting of the 50 cm−1 peak above 16 GPa. The pressure evolution of the diffraction patterns for PIN shows obvious splitting above 16 GPa and 33 GPa, particularly for the pseudo-cubic (110), (200), and (211) diffraction peaks, indicative of a symmetry-lowering transition. Our results demonstrate that PIN undergoes successive structural phase transitions: a pseud-cubic to orthorhombic at 0.5 GPa; a transition from orthorhombic to orthorhombic at 16 GPa due to enhanced octahedra tilting and change in linear compressibility; the transition at 33 GPa is plausibly a transition to a monoclinic phase.

Structural transitions in asymmetric poly(styrene)-block-poly(lactide) thin films induced by solvent vapor exposure.

Successive structural transitions in thin films of asymmetric poly(styrene)-block-poly(lactide) (PS-PLA) block copolymer samples upon exposure to tetrahydrofuran (THF) vapors have been monitored using atomic force microscopy (AFM) and both in situ and ex situ grazing incidence small-angle X-ray scattering (GISAXS). A direct link was established between the structure in the swollen state and the morphology formed in the dried state post solvent evaporation. This was related to the high incompatibility between the constituting blocks of the copolymer that thwarted the system from reaching the homogeneous disordered state in the swollen state under the specific conditions utilized in this study. Upon rapid solvent removal, the morphologies formed in the swollen state were trapped due the fast evaporation kinetics. This work provides a better understanding of the mechanisms associated with block copolymer thin film morphology changes induced by solvent vapor annealing.

LiFe(MoO4)2 as a novel anode material for lithium-ion batteries.

Polycrystalline LiFe(MoO4)2 is successfully synthesized by solid-state reaction and examined as anode material for lithium-ion batteries in terms of galvanostatic charge-discharge cycling, cyclic voltammograms (CV), galvanostatic intermittent titration technique (GITT), and electrochemical impedance spectroscopy (EIS). The LiFe(MoO4)2 electrode delivers a high capacity of 1034 mAh g(-1) at a current density of 56 mA g(-1) between 3 and 0.01 V, indicating that nearly 15 Li(+) ions are involved in the electrochemical cycling. LiFe(MoO4)2 also exhibits a stable capacity of 580 mAh g(-1) after experiencing irreversible capacity loss in the first several cycles. Moreover, the Li-ion storage mechanism for LiFe(MoO4)2 is suggested on the basis of the ex situ X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) at different insertion/extraction depths. A successive structural transition from triclinic structure to cubic structure is observed, and the tetrahedral coordination of Mo by oxygen in LiFe(MoO4)2 changes to octahedral coordination in Li2MoO3, correspondingly. When being discharged to 0.01 V, the active electrode is likely to be composed of Fe and Mo metal particles and amorphous Li2O due to the multielectron conversion reaction. The insights obtained from this study will benefit the design of new anode materials for lithium-ion batteries.

Absence of pressure-induced electron spin-state transition of iron in silicate glasses upon compression

Upon compression, silicate melts in the Earth’s interior are expected to be subject to successive structural transitions with multiple densification mechanisms that are distinct from those of their crystalline analogs. Experimental verification of this phenomenon remains a major target of glass-melt studies. Early studies of Fe spin-state transitions in silicate glasses under compression used synchrotron X-ray emission spectroscopy (XES) to develop seemingly irreconcilable interpretations that vary from complete transitions to low spin states at high pressure to a prevalence of high spin states. In an effort to reconcile the controversy, Mao et al. (February–March 2014 issue of American Mineralogist ) showed that the XES data must be properly handled with a correct reference spectrum for each spin state and suggested that the subtle effect of pressure-induced broadening in the spectra be considered. Based on the new analyses, they concluded that no pressure-induced spin-state transitions exist in iron-bearing silicate glasses at high pressure, relevant to Earth’s deep lower mantle. Thanks to several series of experimental studies, the elusive spin state in glasses under compression is being revealed, rendering the spin state of iron among the best understood for glasses at high pressure.

Observation of hysteretic magnetic phase transitions coupled with orientation motion of ions and dielectric relaxation in a one-dimensional nickel-bis-dithiolene molecule solid

The second polymorph, the β-crystal, of the nickel-bis-dithiolene compound [4'-CF3bzPy][Ni(mnt)2], where 4'-CF3bzPy = 1-(4'-trifluoromethylbenzyl)pyridinium and mnt(2-) = maleonitriledithiolate, was obtained. The variable-temperature single crystal structures, magnetic behavior in 1.8-300 K and dielectric nature in 123-373 K have been investigated for the β-crystal. This polymorph experiences two hysteretic magnetic phase transitions in a narrow temperature region (190-217 K) with the thermal hysteresis loops ca. 6 K and ca. 11 K. The two hysteretic magnetic phase transitions are coupled with two isostructural phase transitions (IPTs), respectively, which are driven by the novel step-wise dynamic orientation motion of the anion and cation in the β-crystal. There is an absence of a dielectric anomaly in the structural transformation temperature interval. However, a dielectric relaxation, related to the dipole motion of polar CF3 groups in the cations under an ac electrical field, emerges in the high-temperature phase.