Temperature-induced Structural Phase Transition Research Articles

Oxide Strontium-Barium Perovskites Ceramics: Examinations of Structural Phase Transitions and Potential Application as Oxygen Carriers

The structural properties of selected (Ba1−xSrx)PbO3 ceramics were examined at 14–1148 K using X-ray powder diffraction (XRD). These materials are attractive due to their variety of applications, such as, for example, high-temperature thermoelectric energy conversion. Attention was paid to this paper as a continuation of the previous examinations of higher Sr2+ concentrations. The type of perovskite distortion and temperatures of the structural phase transitions (SPTs) were determined from the splitting of certain pseudocubic lines. At this point, for example (Ba0.3Sr0.7)PbO3 showed three temperature-induced SPTs. When the amount of Sr increased in the samples, no phase transition was observed, which is contrary to the data previously demonstrated in the literature. The quality of the ceramics was examined by scanning electron microscopy-energy dispersion X-ray spectroscopy (SEM-EDS), demonstrating their homogeneity and uniform elements dispersion. As a result of profound crystal investigations, confirmed by thermogravimetric analysis and quadrupole mass spectroscopy (TGA-QMS), a phase diagram was prepared for the (Ba1−xSrx)PbO3 system based on our former and recent study. Also, the investigation of a new application for the (Ba1−xSrx)PbO3 family is presented in this paper for the first time. The TGA analysis was conducted on Illinois#6 hard coal to evaluate the capability of perovskites to be used in the chemical looping combustion (CLC) process in a range of temperatures 1073–1173 K. Due to its thermal stability and reactivity, Ba0.9Sr0.1PbO3 is the material with the greatest potential to be applied as an oxygen carrier. The combination of strontium and barium offers encouraging results compared to the pure barium and strontium lead oxide perovskites.

Orientational deformations leading to temperature-induced structural phase transition in Prehnite using Raman, Infrared, and Terahertz spectroscopy

Understanding molecular and structural properties of naturally extracted minerals under varying thermodynamic parameters such as pressure (P) and temperature (T) helps us to explore vital information regarding various geological processes. Here, we present the comprehensive results of Raman, infrared (IR), and Terahertz (THz) spectroscopic investigations on Prehnite (Ca2Al(AlSi3O10)(OH)2) mineral from ambient (25 °C) to 1000 °C in the 6.6 – 4000 cm−1 wide spectral range. The results indicate a substantial distortion in orientation between AlO6 octahedron and SiO4 tetrahedron layer leads to the strengthening of hydrogen bonds (HBs) in the Prehnite structure around 800 °C. Consequently, the disappearance of Raman active modes and abrupt change in frequency (ω) of Far-IR modes (obtained using THz spectroscopy) around 800 °C are spectral signatures of symmetry change in the structure. Eventually, these orientational changes at the molecular level trigger structural phase transition around 800 °C, supported by X-ray diffraction (XRD) measurements. Thus, the present study depicts the pivotal role of inter- and intra-molecular interactions in Prehnite, which determines its bonding and structural characteristics and hence its physicochemical properties under diverse environments.

Repeatable Actuations of Organic Single Crystal Fibers Driven by Thermosalient-Phase-Transition-Induced Buckling.

Thermosalient crystals are molecular solids that exhibit explosive motions, such as sudden breaks and jumps, due to temperature-induced structural phase transitions between two polymorphs. Therefore, the development of molecular actuators with superior speed and power by deriving mechanical work from explosive motion is a fascinating concept. However, thermosalient transitions often cause crystal disintegration, which hampers repeatable phase transitions between the polymorphs. Here, it is reported that single crystal nano/microfibers of 1, 2, 4, 5-tetrabromobenzene (TBB), whose bulk crystals exhibit thermosalient behavior at ≈40°C, can repeatedly transform between the low and high temperature polymorphs without disintegration. The structural tolerance against phase transition is attributed to the high flexibility of the nano/microfibers. It is observed that a structure consisting of a TBB fiber with both ends pinned to the substrate repeatedly buckles and straightens when the temperature is varied between 30 and 40°C. It is demonstrated that buckling can lead to large displacement actuation as compared to a simple length change of the fiber. Moreover, the force generated by the buckling fiber is estimated and it is found that it can generate a force large enough to flick an object ≈104 times heavier than the fiber itself into the air against gravity.

Temperature-induced structural transition in an organic–inorganic hybrid layered perovskite (MA)2PbI2−xBrx(SCN)2

A temperature-induced structural phase transition is reported in layered hybrid perovskite (MA)2PbI2−xBrx(SCN)2 (0 ≤ x ≤ 1.2). The observed transition temperature decreases with Br substitution, suggesting a weakening of bonding interaction between the molecular ions.

Temperature-Induced Structural Phase Transitions in Self-Assembled Hydrogen Bonded Networks at the Liquid/Solid Interface

Temperature-Induced Structural Phase Transitions in Self-Assembled Hydrogen Bonded Networks at the Liquid/Solid Interface

Fully Controllable Structural Phase Transition in Thermomechanical Molecular Crystals with a Very Small Thermal Hysteresis

The construction of a practical crystalline molecular machine faces two challenges: to realize a collective molecular movement, and to amplify this movement into a precisely controlled mechanical response in real time and space. Thermosalient single crystals display cooperative molecular movements that are converted to strong macroscopic mechanical responses or shape deformations during temperature-induced structural phase transitions. However, these collective molecular movements are hard to control once initiated, and often feature thermal hystereses that are larger than 10°C, which greatly hamper their practical applications. Here, it is demonstrated that the phase boundaries of the thermomechanical molecular crystal based on a fluorenone derivative 4-DBpFO can be used to finely control its structural phase transition. When this phase transition is triggered at two opposite crystal faces, it is accompanied by two parallel phase boundaries that can be temperature controlled to move forward, backward, or to halt, benefitting from the stored elastic energy between the parallel boundaries. Moreover, the thermal hysteresis is greatly decreased to 2-3°C, which allows for circular heating/cooling cycles that can produce a continuous work output.

Negative thermal expansion coefficient of Sc-doped indium tungstate ceramics synthesized by co-precipitation

Co-precipitation was successfully applied to synthesize the Sc3+ doped In2-xScx (WO4)3 (x = 0, 0.3, 0.6, 0.9 and 1.2) compounds. The composition- and temperature-induced structural phase transition and thermal expansion behaviors of Sc3+ doped In2(WO4)3 were investigated. Results indicate that In2-xScx (WO4)3 crystalizes in a monoclinic structure at 300 °C for x ≤ 0.3 and changes into hexagonal structure for x ≥ 0.6. Hexagonal In1.1Sc0.9(WO4)3 displays negative thermal expansion (NTE) with an average linear coefficient of thermal expansion (CTE) of −1.85 × 10−6 °C −1. After sintering at 700 °C and above, a phase transition from hexagonal to orthorhombic phase was observed in In2-xScx (WO4)3 (x ≥ 0.6). Sc3+ doping successfully reduce the temperature-induced phase transition temperature of In2-xScx (WO4)3 ceramics from 250 °C (x = 0) to room temperature (x = 0.9). When x = 0.9 and 1.2, the average linear CTEs of In2-xScx (WO4)3 ceramics are −5.45 × 10−6 °C−1 and -4.43 × 10−6 °C−1 in a wider temperature range of 25–700 °C, respectively.

Helical magnetic ordering in Sr(Co1−xNix)2As2

SrCo2As2 is a peculiar itinerant magnetic system that does not order magnetically, but inelastic neutron scattering experiments observe the same stripe-type antiferromagnetic (AF) fluctuations found in many of the Fe-based superconductors along with evidence of magnetic frustration. Here we present results from neutron diffraction measurements on single crystals of Sr(Co1-xNix)2As2 that show the development of long-range AF order with Ni-doping. However, the AF order is not stripe-type. Rather, the magnetic structure consists of ferromagnetically-aligned (FM) layers (with moments laying in the layer) that are AF arranged along c with an incommensurate propagation vector of (0 0 tau), i.e. a helix. Using high-energy x-ray diffraction, we find no evidence for a temperature-induced structural phase transition that would indicate a collinear AF order. This finding supports a picture of competing FM and AF interactions within the square transition-metal layers due to flat-band magnetic instabilities. However, the composition dependence of the propagation vector suggests that far more subtle Fermi surface and orbital effects control the interlayer magnetic correlations.

Temperature-Induced Structural Phase Transitions in Two New Postperovskite Coordination Polymers

We presented two new ABX3 postperovskite coordination polymers, (C5H13NCl)[M(dca)3] (dca = N(CN)2–, M = Mn2+ for 1 and Cd2+ for 2), as well as their phase transition behaviors disclosed by using differential scanning calorimetry measurements, variable-temperature single-crystal X-ray analyses, dielectric measurements, and Hirshfeld surface analyses. Both 1 and 2 have same structure (Cmcm) at room temperature, in which their A-site organic cations are fourfold disordered about two mirror planes and undergo order–disorder phase transition mainly caused by the freezing of A-site cations upon cooling. The different metal ions endow them distinct structural flexibility, resulting in different phase transition behaviors and dielectric responses; that is, the smaller and coordinatively rigid Mn2+ ion results in two-step Cmcm (Z = 4) ↔ Pbcm (Z = 4) ↔ Pbca (Z = 8) transitions accompanied with obvious dielectric relaxation, whereas the larger and coordinatively flexible Cd2+ ion results in one-step Cmcm (Z = 4) ↔ P...

Excellent Energy Storage and Charge-discharge Performances in PbHfO3 Antiferroelectric Ceramics

Single phase PbHfO3 antiferroelectric ceramics were prepared via rolling process. It is revealed that the rolling process can reduce the grain size and increase the bulk density, which lead to the enhanced breakdown strength up to 268 kV/cm versus 219 kV/cm of samples using the conventional solid-state method. As a result, high recoverable energy density of 7.6 J/cm3 with an efficiency of 80.8 % was achieved. Meanwhile, a large current density of 1381 A/cm2 and an ultrahigh peak power density up to 170 MW/cm3 were observed under 250 kV/cm. In addition, unique electrical polarization response characteristics at different electric fields and temperature-induced structural phase transitions were also investigated. The energy storage performance and charge-discharge properties of PbHfO3 were first studied in this communication and all the results indicate that PbHfO3 ceramic is a promising candidate for pulse power applications.

Optical bistability in shape-memory nanowire metamaterial array

Non-volatile temperature-induced structural phase transitions such as those found in chalcogenide glasses are known to lead to strong changes in optical properties and are widely used in rewritable optical disk technology. Herein, we demonstrate that thermally activated optical memory can be achieved via the nanostructural reconfiguration of a metallic nanowire metamaterial array made from a shape-memory alloy: A nickel-titanium film of nanoscale thickness structured on the subwavelength scale exhibits bistability of its optical properties upon temperature cycling between 30 °C and 210 °C. The structure, comprising an array of NiTi nanowires coated with a thin film of gold to enhance its plasmonic properties, can exist in two non-volatile states presenting an optical reflectivity differential of 12% via nanoscale mutual displacements of alternating nanowires in the structure. Such all-metal shape-memory photonic gratings and metamaterials may find applications in bistable optical devices.

Crystal structure and temperature dependent structural phase transitions in (Ba1-xSrx)PbO3 (x = 0, 0.2, 0.6) perovskite ceramics

The structural properties of (Ba1-xSrx)PbO3 (x = 0, 0.2 and 0.6) ceramics were examined in a wide range of temperatures, from 14 K to 1223 K, using the X-ray powder diffraction method. The type of distortion of the pseudo-cubic perovskite cell was determined from the splitting of the main diffraction lines and from the analysis of the superlattice peaks. Temperature-induced structural phase transitions at high temperatures were observed. On the other hand at temperatures starting as low as 14 K, the examined ceramics did not show any phase transitions. The effect of Sr doping was evaluated and showed that with an increase in the amount of Sr2+ ions in the crystal lattice the number of SPT's decreases. Additionally, the temperatures at which these SPT's occur are shifted towards higher values. The following sequences of structural phase transitions, written using Glazer's notation, were proposed:I2/m (a-b0c-) → Ibmm (a-b0a-)→ I4/mcm (a0a0c-)→ Pm3¯m(a0a0a0) for BaPbO3I2/m (a-b0c-) → I4/mcm (a0a0c-) → Pm3¯m(a0a0a0) for (Ba0.8Sr0.2)PbO3and I2/m (a-b0c-)→ I4/mcm (a0a0c-)→ Pm3¯m(a0a0a0) for (Ba0.4Sr0.6)PbO3.These SPT's were used as trial models in refinement procedures based on the Rietveld method.

Mn-Doped Maghemite (γ-Fe2O3) from Metal-Organic Framework Accompanying Redox Reaction in a Bimetallic System: The Structural Phase Transitions and Catalytic Activity toward NOx Removal.

Mn-doped maghemite (γ-Fe2O3) particles were generated from a binary metal (Fe,Mn)-based metal–organic framework (MOF) via thermal decomposition under air. The X-ray photoelectron spectroscopy analysis revealed that the synthesis of Fe/Mn-MOF accompanied the reduction of the metal ions. The existence of Mn ions in this synthetic process leads to thermally stable maghemite particles under air. A temperature-induced structural phase transition from γ-Fe2O3 to α-Fe2O3 was observed through a mixed phase with another structure. Mn-doped γ-Fe2O3 and α-Fe2O3 exhibit superparamagnetic behavior. The sample annealed at 600 °C showed a mixed magnetic hysteresis loop indicating the existence of an intermediate structural phase between γ-Fe2O3 and α-Fe2O3 during the phase conversion from FeMn-MOF. The constructed Mn-doped iron oxides are active toward reducing nitric oxide with NH3. The NO conversion is 97% over Mn-doped γ-Fe2O3 calcined at 320 °C.

Temperature-induced structural phase transition in hydrated minerals Na6 M(SO4)4 (M = Co, Ni)

Temperature-induced structural phase transition in hydrated minerals Na₆ <i>M</i>(SO₄)₄ (<i>M</i> = Co, Ni)

Temperature-induced reversible structural phase transition and X-ray diffuse scattering in 2-amino-3-nitropyridinium hydrogen sulfate.

The novel polar material 2-amino-3-nitropyridinium hydrogen sulfate, C5H6N3O2(HSO4) (abbreviated as 2A3NP-HS), was obtained and structurally characterized by means of single-crystal X-ray diffraction. At room temperature, 2A3NP-HS crystallizes as a non-centrosymmetric disordered phase (I) in the orthorhombic Pna21 space group. On cooling below 298 K, 2A3NP-HS undergoes a reversible phase transition to phase (II) with the monoclinic non-centrosymmetric P21 space group. This transition might be classified as an `order-disorder' type. The structural details in both phases are analysed. Additionally, for phase (I), in the 304-365 K temperature range, diffuse scattering was found to be present in the form of elongated streaks parallel to the a* direction. This can be unravelled when implementing a short-range order affecting anionic cationic ribbons occurring in the structure, with correlations acting both in the a-direction and in the bc-plane. The results of Monte Carlo simulations, adapting a two-dimensional Ising-type model, reveal the formation of domains, which are b-elongated and thin along a. Locally, the stacking of the ribbons in the domains reflects the ordered arrangement observed in the low-temperature monoclinic phase (II).

Raman signatures of inversion symmetry breaking and structural phase transition in type-II Weyl semimetal MoTe2.

Transition metal dichalcogenide MoTe2 is an important candidate for realizing the newly predicted type-II Weyl fermions, for which the breaking of the inversion symmetry is a prerequisite. Here we present direct spectroscopic evidence for the inversion symmetry breaking in the low-temperature phase of MoTe2 by systematic Raman experiments and first-principles calculations. We identify five lattice vibrational modes that are Raman-active only in the low-temperature noncentrosymmetric structure. A hysteresis is also observed in the peak intensity of inversion symmetry-activated Raman modes, confirming a temperature-induced structural phase transition with a concomitant change in the inversion symmetry. Our results provide definitive evidence for the low-temperature noncentrosymmetric Td phase from vibrational spectroscopy, and suggest MoTe2 as an ideal candidate for investigating the temperature-induced topological phase transition.

Concentration- and Temperature-Induced Phase Transitions in PrAlO3-SrTiO3 System.

Single-phase mixed aluminates-titanates Pr1−xSrxAl1−xTixO3 (x = 0.1, 0.2, 0.3, 0.5, 0.7) with rhombohedral perovskite structure were prepared by solid-state reaction technique at 1823–1873 K. Morphotropic rhombohedral-to-cubic phase transition in Pr1−xSrxAl1−xTixO3 series is predicted to occur at x = 0.88. The temperature-induced structural phase transition R overline{3} с − Pm overline{3} m in Pr0.5Sr0.5Al0.5Ti0.5O3, detected at 930 K by in situ high-temperature X-ray synchrotron powder diffraction, occurs at considerably lower temperature as the corresponding transformation in the parent compound PrAlO3 (1770 K). Such remarkable drop of the transition temperature is explained by gradual decrease of the perovskite structure deformation in the Pr1−xSrxAl1−xTixO3 series with increasing Sr and Ti contents as a consequence of the increasing Goldschmidt tolerance factor. For Pr0.3Sr0.7Al0.3Ti0.7O3 phase, a sequence of the low-temperature phase transformation R overline{3} с − Immb(C2/m) − I4/mcm was detected.

Synthesis and Temperature-Induced Structural Phase and Spin Transitions in Hexadecylboron-Capped Cobalt(II) Hexachloroclathrochelate and Its Diamagnetic Iron(II)-Encapsulating Analogue.

Template condensation of dichloroglyoxime with n-hexadecylboronic acid on the corresponding metal ion as a matrix under vigorous reaction conditions afforded n-hexadecylboron-capped iron and cobalt(II) hexachloroclathrochelates. The complexes obtained were characterized using elemental analysis, MALDI-TOF mass spectrometry, IR, UV-vis, (1)H and (13)C{(1)H} NMR, (57)Fe Mössbauer spectroscopies, SQUID magnetometry, electron paramagnetic resonance, and cyclic voltammetry (CV) and by X-ray crystallography. The multitemperature single-crystal X-ray diffraction, SQUID magnetometry, and differential scanning calorimetry experiments were performed to study the temperature-induced spin-crossover [for the paramagnetic cobalt(II) complex] and the crystal-to-crystal phase transitions (for both of these clathrochelates) in the solid state. Analysis of their crystal packing using the molecular Voronoi polyhedra and the Hirshfeld surfaces reveals the structural rearrangements of the apical long-chain alkyl substituents resulting from such phase transitions being more pronounced for a macrobicyclic cobalt(II) complex. Its fine-crystalline sample undergoes the gradual and fully reversible spin transition centered at approximately 225 K. The density functional theory calculated parameters for an isolated molecule of this cobalt(II) hexachloroclathrochelate in its low- and high-spin states were found to be in excellent agreement with the experimental data and allowed to localize the spin density within a macrobicyclic framework. CV of the cobalt(II) complex in the cathodic range contains one reversible wave assigned to the Co(2+/+) redox couple with the reduced anionic cobalt(I)-containing species stabilized by the electronic effect of six strong electron-withdrawing chlorine substituents. The quasireversible character of the Fe(2+/+) wave suggests that the anionic iron(I)-containing macrobicyclic species undergo substantial structural changes and side chemical reactions after such metal-centered reduction.

Polymorphism of resorcinol explored by complementary vibrational spectroscopy (FT-RS, THz-TDS, INS) and first-principles solid-state computations (plane-wave DFT).

The polymorphism of resorcinol has been complementary studied by combining Raman, time-domain terahertz, and inelastic neutron scattering spectroscopy with modern solid-state density functional theory (DFT) calculations. The spectral differences, emerging from the temperature-induced structural phase transition, have been successfully interpreted with an emphasis on the low-wavenumber range. The given interpretation is based on the plane-wave DFT computations, providing an excellent overall reproduction of both wavenumbers and intensities and revealing the source of the observed spectral differences. The performance of the generalized gradient approximation (GGA) functionals in prediction of the structural parameters and the vibrational spectra of the normal-pressure polymorphs of resorcinol has been extensively examined. The results show that the standard Perdew, Burke, and Ernzerhof (PBE) approach along with its "hard" revised form tends to be superior if compared to the "soft" GGA approximation.

Temperature-induced reversible structural phase transition of 1,4-dimethyl-1,4-diazabicyclo[2.2.2]octane bis(perchlorate)

A novel molecular-based phase change material was synthesized. The phase transition from a room temperature to a low temperature paraelectric phase might be driven by the order–disorder transition of ClO4− anions and the ordering of twisting motions of the dabco ring.