High-temperature Structural Phase Transition Research Articles

A notable reversible thermochromic (3,3-difluoropyrrolidinium)2[CuCl4] with ferroelectricity and ferroelasticity

The design and fabrication of sensitive and reversible thermochromics (TCs) remain challenging although they own enormous applications. Especially, there is a tough task to introduce multifold physical properties to them. Here, a temperature-response organic–inorganic metal halide hybrid (OIHM) (3,3-Difluoropyrrolidium)2CuCl4 ((DFP)2CuCl4) 1 is fabricated, utilizing a self-assembly method based on Cu2+ inorganic salt and fluoropyrrolidinium dexterously. It possesses two reversible phase transitions (PTs) comprising a ferroelectric to paraelectric PT at 194 K and a ferroelastic to paraelastic PT at 351 K. The ferroelastic and ferroelectric properties are mainly derived from the order–disorder transitions in the microstructure and the displacement of the charge center. Importantly, the high-temperature structural phase transition is accompanied by a reversible color change. Its crystals can be directly applied in reversible thermochromic materials, exhibit an obvious color change (green to yellow–brown at 351 K) with full reversibility, and are successfully used as inks for hand-painting. To the best of our knowledge, 1 is the first Cu(II)-based OIMH TC with both ferroelectricity and ferroelasticity. This work laid the foundation for further development of alternative TCs, ferroics and practical applications for TCs.

Phase Transitions in a Perovskite Thin Film Studied by Environmental In Situ Heating Nano‐Beam Electron Diffraction (Small Methods 9/2021)

Structural Phase Transition In article number 2100464, Seibt and co-workers studied a high-temperature structural phase transition in a perovskite thin film using environmental transmission electron microscopy. The reaction path is controlled via the ambient condition and both reversible behavior as well as irreversible is found depending on the oxygen partial pressure (picture courtesy of Lukas Kroll).

Monoclinic SmAl3(BO3)4: synthesis, structural and spectroscopic properties.

Single crystals of SmAl3(BO3)4 were synthesized by the group growth on seeds method. The crystal structure was solved using a single-crystal experiment and the purity of the bulk material was proved by the Rietveld method. This borate crystallizes in the monoclinic C2/c space group with unit-cell parameters a = 7.2386 (3), b = 9.3412 (5), c = 11.1013 (4) Å and β = 103.2240 (10)°. IR and Raman spectroscopic analyses confirmed the monoclinic structure of SmAl3(BO3)4. Under 532.1 nm excitation, luminescence spectra exhibit bands assignable to the transitions from 4G5/2 to 6H5/2, 6H7/2, 6H9/2 and 6H11/2. The similarity of the luminescence spectra of the trigonal and monoclinic polymorphs is explained by the minor role of Sm-O bond distortion and the primary role of rotational distortion of SmO6 octahedra. The smaller covalency of the Sm-O bond in alumoborates is deduced in comparison with galloborates. Calorimetric measurements did not reveal high-temperature structural phase transitions up to a temperature of 720 K.

High-temperature structural phase transition and infrared dielectric features of La2CoMnO6

In this paper, we present the temperature-dependent far-infrared reflectivity spectra of partially ordered magnetodielectric La2CoMnO6 from room temperature to 673 K. We demonstrate a clear first-order structural phase transition (SPT) from a monoclinic structure with P21/n symmetry to a rhombohedral phase with R3¯ symmetry from the behavior of the polar phonon modes at TC ∼ 590 K. The temperature-dependent transversal and longitudinal phonon branches, dielectric strengths, and damping of the strongest dielectric modes support the significant contribution of the phonon modes to the SPT and reveal an important lattice anharmonicity, especially for the low-frequency modes. Also, these investigations showed that structural ordering does not inhibit the SPT and provided valuable information regarding the polar phonons and their effects on the intrinsic dielectric constant in double perovskites and related compounds.

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.

The two-dimensional metallic triangular lattice antiferromagnet CeCd3P3

Single crystals of $R{\mathrm{Cd}}_{3}{\mathrm{P}}_{3}$ ($R=\mathrm{La}$ and Ce) have been investigated by magnetization, electrical resistivity, the Hall coefficient, and specific heat. Magnetization measurements of ${\mathrm{CeCd}}_{3}{\mathrm{P}}_{3}$ demonstrate clear quasi-two-dimensional magnetic behavior. Electrical resistivity and Hall coefficient measurements suggest that $R{\mathrm{Cd}}_{3}{\mathrm{P}}_{3}$ compounds are low-carrier-density metallic systems, in strong contrast to an earlier study of polycrystalline material. Specific heat and electrical resistivity measurements of ${\mathrm{CeCd}}_{3}{\mathrm{P}}_{3}$ reveal a high-temperature (structural) phase transition at ${T}_{s}=127$ K and antiferromagnetic ordering below ${T}_{N}=0.41$ K. Upon applying magnetic field in the easy-plane ($H\ensuremath{\parallel}ab$) the magnetic ordering temperature increases to 0.43 K at $H\ensuremath{\sim}15$ kOe, demonstrating partial lifting of the magnetic frustration. The large electronic specific heat persists in an unusually wide range of temperature above ${T}_{N}$ due to the frustrated spins. The observation of conventional metallic behavior in the electrical resistivity suggests that the $f$ electrons in ${\mathrm{CeCd}}_{3}{\mathrm{P}}_{3}$ undergo negligible hybridization with the conduction electrons. Thus, ${\mathrm{CeCd}}_{3}{\mathrm{P}}_{3}$ may be a model system for exploring the complex interplay between magnetic frustration and Ruderman-Kittel-Kasuya-Yosida physics on a low-carrier-density Ce triangular lattice.

Room temperature crystal structure and high temperature structural and magnetic phase transitions in Sr(Fe0.5Nb0.5)O3 ceramic

The room temperature structure of the perovskite Sr(Fe0.5Nb0.5)O3 ceramic has been investigated by Rietveld structure refinement using high resolution X-ray diffraction (XRD) data. The correct structure is determined to be tetragonal in the space group I4/mcm ruling out orthorhombic (Pbnm), tetragonal (P4 mm), and monoclinic structures previously reported by authors. The high temperature structural phase transition has been studied by Rietveld analysis using the high resolution XRD data in the temperature range of 300–850 K. A high temperature structural phase transition is observed from tetragonal (I4/mcm) to cubic (Pm3̅m) phase around ∼630 K. This phase transition was also confirmed by the heat flow experiment using differential scanning calorimetry. To confirm the nature of phase transition, we have studied the variation of integrated intensity (ISL) of superlattice peak and the oxygen octahedral tilt angle (φ) in a tetragonal structure with temperature. The temperature variations of these two parameters provide evidence for the tricritical nature of the phase transition. A magnetic phase transition is discovered in temperature dependence of magnetization M(T) around ∼708 K, which coincides with the dielectric anomaly temperature in loss tangent.

High temperature structural phase transition and dielectric relaxation in an organic–inorganic hybrid compound: (4-methylpiperidinium)CdCl3

A new organic–inorganic hybrid perovskite-type compound, (4-MPD)CdCl3 (1, 4-MPD = 4-methylpiperidinium), demonstrating high temperature phase transition at around 364 K and prominent dielectric relaxation behavior, can be considered as a potential high temperature relaxor-type dielectric material. Systematic characterization techniques have been performed including variable-temperature structural analyses, differential scanning calorimetry (DSC) measurements, dielectric measurements and powder X-ray diffraction (PXRD) measurements. The structural phase transition coupled with the dielectric relaxation property is mainly ascribed to the order–disorder changes of organic cations. The studies of dielectric relaxation between 25 kHz and 1000 kHz disclose a significant Debye relaxation process above room temperature, which is well fitted by the Cole–Cole function.

High-temperature antiferroelectric and ferroelectric phase transitions in phase pure LaTaO4

Phase-pure LaTaO4 ceramics was prepared by solid-state reaction. Dielectric spectroscopic data as well as differential scanning calorimetric experiments showed the existence of a sequence two high-temperature first-order structural phase transitions. The first phase transition occurs above 160°C (on heating), from the monoclinic P21/c space group at room temperature to the polar orthorhombic Cmc21 group, exhibiting a very large thermal hysteresis probably linked to the reconstructive nature of the structural transition. The second transition occurs around 225°C to the orthorhombic Cmcm space group, with a small thermal hysteresis. Vibrational Raman spectroscopic analyses confirmed these two sequential phase transitions, as well as the thermal hysteresis observed for both first-order transitions in repeated heating and cooling cycles. The existence of a strong monoclinic distortion at room temperature could be related to the presence of defects (oxygen vacancies) in LaTaO4 ceramics, after sintering. Dielectric spectroscopy showed a strong influence of the electric conductivity on the dielectric response with activation energy of dc component of conductivity (0.62eV) compatible with the presence of oxygen vacancies. Far-infrared data confirmed that the extra modes observed in the Raman spectra are forbidden bands, which were activated by defects into the structure.

High-temperature structural phase transitions in neighborite: a high-resolution neutron powder diffraction investigation

The nature of the apparently continuous structural phase transition at 1,049 K in the perovskite-structured, MgSiO3 isomorph, neighborite (NaMgF3), from the orthorhombic (Pbnm) hettotype phase to the cubic (\( Pm\overline{3} m \)) aristotype structure, has been re-investigated using high-resolution, time-of-flight neutron powder diffraction. Using data collected at 1 K intervals close to the nominal phase transition temperature, the temperature dependence of the intensities of superlattice reflections at the M point \( \left( {\frac{2\pi }{a}\left[ {\frac{1}{2},\frac{1}{2},0} \right]} \right) \) and the R point \( \left( {\frac{2\pi }{a}\left[ {\frac{1}{2},\frac{1}{2},\frac{1}{2}} \right]} \right) \) of the pseudocubic Brillouin zone indicate the existence of a new intermediate tetragonal phase in space group P4/mbm, with a narrow phase field extending from ~1,046.5 to ~1,048.5 K, at ambient pressure. Group theoretical analysis shows that the structural transitions identified in this study, Pbnm–P4/mbm, and P4/mbm–\( Pm\overline{3} m \), are permitted to be second order. The observation of the tetragonal phase resolves the longstanding issue of why the high-temperature phase transition, previously identified as Pbnm–\( Pm\overline{3} m \), and which would be expected to be first order under Landau theory, is in fact found to be continuous. Analysis of the pseudocubic shear strain shows it to vary with a critical exponent of 0.5 implying that the phase transition from Pbnm to P4/mbm is tricritical in character. The large librational modes that exist in the MgF6 octahedron at high temperature, and the use of Gaussian probability density functions to describe atomic displacements, result in apparent bond shortening in the Mg–F distances, making mode amplitude determination an unreliable method for determination of the critical exponent from internal coordinates. Crystal structures are reported for the three phases of NaMgF3 at 1,033 K (Pbnm), 1,047 K (P4/mbm) and 1,049 K (\( Pm\overline{3} m \)).

Commissioning the Neutron Laue Diffractometer in Berlin

The Fast Acquisition Laue Camera for Neutrons (FALCON) is a thermal neutron Laue diffractometer situated in the experimental hall of the BER-II reactor at HZB in Berlin. The thermal beamtube, D1S, delivers a stream of neutrons direct to FALCON just 8m from the reactor core but with a low gamma radiation count. FALCON benefits from a beam that does not pass through any objects upstream whilst a beam definer delivers a highly focused neutron beam to the instrument with <10divergence. The instrument comprises two scintillator plate detectors coupled to four iCCD cameras each. The neutron beam passes through the detector units enabling one detector to be placed in the backscattering position and the second detector in the transmission position. The image-intensified CCDs are capable of obtaining 20-bit digitization Laue images in under ten seconds and variable sample table and detector positions allow a full range of sample environments to be utilised. Scientifically, FALCON offers the opportunity to study samples from a wide range of fields for example; low-temperature magnetic studies, high-temperature structural phase transitions, in-situ kinetics studies and point-defect analysis in compound semiconductors. Data from FALCON can be used to solve crystallographic structures and as a neutron instrument it has all the advantages of neutrons as a probe for condensed matter, for instance, identification of the location of hydrogen atoms within structures and differentiation between electronically similar elements. FALCON will now enter the commissioning phase using in-house samples to test both ambient and sample environment conditions on the instrument. We present here details of the upcoming commissioning tests and invite users to submit proposals for Laue diffraction experiments.

A case study of parameterized Rietveld refinement:The structural phase transition of CuInSe2

Abstract The ferroelastic high temperature structural phase transition of CuInSe2, from tetragonal chalcopyrite to cubic sphalerite structure type has been reinvestigated in detail by sequential and parametric Rietveld refinement using in-situ high energy synchrotron powder diffraction data. For the description of the structural changes, a symmetry mode based approach is used. The temperature dependence of the isotropic displacement parameters and of all symmetry modes influencing lattice parameters, atomic coordinates, and occupancies, has been modeled with a phenomenological power law model according to the Lanädau theory in order to get direct access to the temperature dependence of the order parameter leading to a more detailed understanding of the nature of the phase transition. The results of this study reveal superior statistics and much higher stability of parametric as compared to sequential Rietveld refinement, offering exciting possibilities in the analysis of ferroelastic phase transitions.

Direct Hydrothermal Synthesis and Physical Properties of Rare-Earth and Yttrium Orthochromite Perovskites

We describe a systematic study of the hydrothermal synthesis of rare-earth orthochromites, RCrO3 (R = La, Pr, Sm, Gd, Dy, Ho, Yb, and Lu) and YCrO3. All nine of these materials can be prepared in a single step by hydrothermal treatment of an amorphous mixed-metal hydroxide at temperatures above 300 °C upon heating around 24 h, with no post-synthesis annealing needed. The as-made materials are highly crystalline powders with submicrometer particle size. In the case of LaCrO3 the addition of solution additives to the hydrothermal synthesis allows some modification of crystallite form of the material, and in the presence of sodium dodecylsulfate nanocrystalline powders are produced. Profile refinement of powder X-ray diffraction (XRD) data show that each of the RCrO3 materials adopts an orthorhombic distorted (Pbmn) perovskite structure. Detailed, magnetization studies as a function of temperature reveal the high quality of the specimens, with low temperature antiferromagnetic behavior seen by direct current (DC) magnetization, and TN values that correlate with the structural distortion. A high temperature structural phase transition (∼ 540 K to rhombohedral R3̅c) seen by variable temperature XRD in the hydrothermally prepared LaCrO3 is consistent with the reported behavior of the same composition prepared using conventional high temperature synthesis.

High-temperature structural phase transition in [formula omitted] studied by in-situ X-ray diffraction and transmission electron microscopy

Ca 2 Fe 2 O 5 shows a first-order phase transition from space group Pnma to a modulated structure described in superspace group Imma ( 00 γ ) s 00 . The transition starts at 947 K during heating and the reverse transition in cooling conditions starts at 923 K, as determined from differential thermal analysis. In-situ high-temperature single-crystal X-ray diffraction experiments revealed a phase coexistence over a range of ca. 25 K. Data collected in this range show a good fit to a combined model of the two simultaneously occurring phases, which was refined using the software Jana2006. In-situ high-temperature transmission electron microscopy (selected area diffraction, dark field and high resolution images) was utilized to prove the existence of Pnma and Imma ( 00 γ ) s 00 domains within the temperature range of the phase coexistence. Remaining planar defects were observed within the Pnma phase at temperatures below the phase transition. From the analysis of high-resolution electron micrographs, these defects were proven to be antiphase boundaries with a displacement vector of R = 1 2 [ 111 ] .

Analysis of Phase Transition Pathways in X3H(SO4)2 (X = Rb, NH4, K, Na): Variable Temperature Single-Crystal X-ray Diffraction Studies

Evaluation of phase transitions in a series of hydrogen sulfates (Rb3H(SO4)2, (NH4)3H(SO4)2, K3 H(SO4)2, and Na3H(SO4)2) based on the single-crystal structure analysis has revealed the exact nature of such transitions and has sorted out the various ambiguities involved in earlier literature. Rb3H(SO4)2 at 293 K is C2/c. It is isostructural to its ammonium analogue, (NH4)3H(SO4)2, at room temperature. However, the variable temperature single-crystal diffraction studies indicate that the phase transition mechanism is different. When cooled to 100 K, the structure of Rb3H(SO4)2 remains C2/c. When heated to 350 K, it transforms to C2/m (with double the volume at room temperature), which changes to C2/c (with 4 times the volume at room temperature) at 425 K. The high-temperature (420 K) structural phase transition in (NH4)3H(SO4)2 is shown to be Rm. The structure of Na3H(SO4)2 remains invariant (P21/c) throughout the range of 100-500 K except for the usual contraction of the unit cell at 100 K and expansion at 500 K. The structural phase transitions with temperature for the compound K3H(SO4)2 are very different from those claimed in earlier literature. The hydrogen atom participating in the crucial hydrogen bond joining the two sulfate tetrahedra controls the structural phase transitions at low temperatures in all four compounds. The distortion of the SO4 tetrahedra and the coordination around the metal atom sites control the phase evolution in the Rb compound, while the Na and K analogues show no phase transitions at high temperature, and the NH4 system transforms to a higher symmetry space group resulting in a disorder of the sulfate moiety.

Some are different from others: high temperature structural phase transitions in ternary chalcopyrites

The high temperature behaviour of AIBIIIX2VI chalcopyrites (A = Cu; B = Al, Ga und In; X = S, Se, Te) was studied by in-situ high temperature synchrotron radiation X-ray diffraction. Structural phase transitions from the α phase with chalcopyrite structure to the β phase with sphalerite structure were obtained in the compounds CuInX2 and CuGaTe2. The driving force of this order-disorder transition is a Cu–In anti site occupancy starting in the critcal temperature region, nearly 10 K before the transition temperature. The order parameter of the phase transition, expressed as Δne = |ne (disordered) – ne(ordered)|, goes within the critical region to zero according to |T – Ttrans|β with the critical exponent β = 0.35(7). Structural transitions were also obtained in CuAlTe2 and CuGaSe2, but they show a different character. In the first compound it goes with the occurrence of a small two phases region, in the second with the formation of an other, unknown phase. Furthermore neither critical behaviour nor an anti site occupancy of the cations is observed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

High-temperature orbital, charge, and structural phase transitions in the cation-ordered manganitesTbBaMn2O6andYBaMn2O6

The high-temperature structures and phase transitions of the cation-ordered manganite perovskites TbBaMn2O6 and YBaMn2O6 have been studied by powder neutron diffraction and differential scanning calorimetry. TbBaMn2O6 undergoes an unprecedented transition from a charge and antiferro-orbitally ordered phase to a charge and ferro-orbitally ordered structure at 94.5 °C, and the charge and orbital ordering melts at 200 °C. An orthorhombic Cmmm phase with rotational order of MnO6 octahedra is observed above the transition, and at 514 °C this transforms to the aristotype tetragonal P4/mmm arrangement. YBaMn2O6 is charge and ferro-orbitally ordered up to 225 °C. Above this charge ordering transition, a C2/m phase with two rotational orders is found. This transforms to the Cmmm structure at 437 °C. Discontinuities in volume and volume expansion, and a limited phase coexistence region are observed at the charge ordering transitions, whereas the other transitions are continuous.

High temperature structural phase transitions in SrSnO 3 perovskite

Three high temperature structural phase transitions have been identified in the perovskite-structured phase SrSnO 3 using differential scanning calorimetry and dilatometry, and have subsequently been structurally characterised using high-resolution neutron powder diffraction. Between 298 and 905 K, SrSnO 3 is orthorhombic, space group Pmcn before undergoing a continuous phase transition to a second orthorhombic phase in space group Incn. At 1062 K there is a first order phase transition to a tetragonal phase in space group I4/ mcm before finally transforming to the aristotype phase at 1295 K. Using the magnitude of the anti-phase tilt as a measure of the order parameter for the transition from I4/ mcm to P m 3 ¯ m suggests this transition is tricritical in nature. Crystal structures are reported for the three hettotype phases.

Epitaxially induced high temperature (>900K) cubic-tetragonal structural phase transition in BaTiO3 thin films

For (001)c oriented BaTiO3 thin films, it has been found that epitaxial constraint can result in a dramatic increase in the temperature of a tetragonal (T) structural phase transition. For 2000-Å-thick films grown directly on SrTiO3 substrates, a T→cubic (C) phase transition was found on heating at >950K, where the lattice constant changed smoothly with temperature. It was also found for films of the same thickness that the T→C transition is nearly restored to that of bulk crystals by the use of a buffer layer, which relaxes the epitaxial constraint. These results provide evidence of an epitaxially induced high temperature structural phase transition in BaTiO3 thin films, where the ferroelectric (internal) and structural (external) aspects of the phase transition are decoupled.

Dielectric and AC ionic conductivity investigations in K3H(SeO4)2 single crystal

Optical observation under the polarizing microscope and DSC measurements on K3H(SeO4)2 single crystal have been carried out in the temperature range 25–200°C. It reveals a high-temperature structural phase transition at around 110°C. The crystal system transformed from monoclinic to trigonal. Electrical impedance measurements of K3H(SeO4)2 were performed as a function of both temperature and frequency. The electrical conduction and dielectric relaxation have been studied. The temperature dependence of electrical conductivity indicates that the sample crystal became a fast ionic conductor in the high-temperature phase. The frequency dependence of conductivity follows the Jonscher's universal dynamic law with the relation σ(ω)=σ(0)+Aωn, where ω is the frequency of the AC field, and n is the exponent. The obtained n values decrease from 1.2 to 0.1 from the room temperature phase to fast ionic phase. The high ionic conductivity in the high-temperature phase is explained by the dynamical disordering of protons between the neighboring SeO4 groups, which provide more vacant sites in the crystal.