High-temperature Phase Transition Research Articles

<i>In Situ</i> XRD Study of Zirconia Phase Transformation Produced from Chemical and Mineral Processes

The high temperature phase transition of zirconia produced from commercial zirconyl chloride chemical was compared with that produced from a Malaysian zircon mineral. Zirconyl chloride was produced from zircon by using the hydrothermal fusion method. Initial XRD diffractogram of these samples at room temperature show that they are of amorphous structure. High temperature XRD studies was then performed on these samples; heated up to 1500°C. The XRD diffractograms shows that the crystalline structure of tetragonal zirconia was first observed and the monoclinic zirconia becomes more visible at higher heating temperature.

Correction: Spin-phonon coupling and high-temperature phase transition in multiferroic material YMnO3

Correction for ‘Spin-phonon coupling and high-temperature phase transition in multiferroic material YMnO3’ by Mayanak Kumar Gupta et al., J. Mater. Chem. C, 2015, 3, 11717–11728.

Phosphate bioisostere containing amphiphiles: a novel class of squaramide-based lipids.

We describe a novel class of amphiphiles with squaramide moiety as a phosphate bioisostere. Most synthesized squaramide-based amphiphiles have the favorable physicochemical properties of lipids, such as: formation of stable liposomes or giant unilamellar vesicles in aqueous solution, high phase-transition temperature, low vesicle leakage and phospholipase resistance properties.

Phase transition and thermal depolarization of double perovskite modified low sintering temperature PbTiO3 piezoelectric ceramics

Phase transition and thermal depolarization of PbTiO3 piezoelectric ceramics with Double Perovskite modified were investigated. With 5mol% Double Perovskite (BFM, BNM, YNM, SNM), the PbTiO3 has a possibility to change the crystal structure to a large extent, and the sintering temperature can be controlled below 960°C. With increasing ionic radius difference between addition and PbTiO3, the crystal structure of modified PbTiO3, measured by synchrotron radiation changed from Tetragonal (P4mm) to Orthorhombic (Pmm2) and became more ordered (from 2×2×1 super cell to 6×2×2 super cell). The ordered Orthorhombic structure PT has higher phase transition temperature (496–540°C) than the Tetragonal PT (481°C). All modified PbTiO3 ceramics show high depolarization temperature. The depolarization temperatures of PT-BFM, PT-BNM, PT-YNM, and PT-SNM are 470°C, 480°C, 495°C, and 505°C, respectively.

Thermal-Driven Fluorite–Pyrochlore–Fluorite Phase Transitions of Gd2Zr2O7 Ceramics Probed in Large Range of Sintering Temperature

Fluorite (F)–pyrochlore (P)–fluorite (F) phase transitions of Gd2Zr2O7 were investigated from 573 K to 1873 K (300 °C to 1600 °C), by means of X-ray diffraction, infrared spectra (IR), and Raman spectra. The low-temperature F phase can stably exist below 1523 K (1250 °C) and the F–P transition occurs at 1523 K to 1573 K (1250 °C to 1300 °C). The ordering process of P phase forms at 1573 K to 1773 K (1300 °C to 1500 °C) and the ordering degree increases with increasing sintering temperature and heat preservation period. High-temperature phase transition from P to F occurs between 1773 K and 1823 K (1300 °C and 1550 °C). IR spectra of samples with different ordering degrees show an interesting shift at 510 cm−1. Raman spectra show that only the A1g mode displays a significant change between F and P phases. This ordering degree and phase transition temperature studies would allow a more targeted experimental optimization of Gd2Zr2O7 to use in nuclear waste host, thermal barrier coatings, and solid oxide fuel cells.

The structures and dielectric properties of high temperature phase transition compounds with 4-(dimethylamino)pyridinium

The reactions of 4-(dimethylamino)pyridine (DMAP) and metal chloride in dilute hydrochloric acid yield two four-coordinate complexes, 1 (DMAP+)(FeCl4−) and 2 (DMAP+)2(CoCl42−). The differential scanning calorimetry (DSC) measurements, temperature-dependent dielectric properties and variable-temperature single-crystal X-ray diffraction analyses of compound 1 confirmed the reversible isostructural phase transition with the same space group P21/n (No. 14) at 298K and 373K. The temperature-dependent single crystal structural analyses of compound 1 reveal the distinct and synchronous molecular motions of both the cationic and anionic moieties, where the orientational changes of organic cations and the order–disorder transformations of FeCl4− anions are mainly responsible for dielectric properties of compound 1. The variable-temperature structure analyses and the variable-temperature PXRD measurements reveal that compound 2 undergoes a reversible structural phase transition at around 381K. The space groups of compound 2 change from triclinic P-1 in room temperature phase (RTP) to monoclinic C2/c in high temperature phase (HTP), accompanied by thermal and dielectric anomalies.

High-temperature phase transition and local structure of a hydrous anorthoclase

The in situ Raman spectra of a hydrous anorthoclase at temperatures of 20–800 °C have been measured using a LABRAM-HR spectrometer and Linkam TS 1500 heating stage. The frequencies of modes at 54, 99, 130 and 162 cm−1 related to M–O vibrations decrease sharply and then increase drastically or keep steady at temperatures above 200 °C. A knee point can be clearly seen at about 200 °C for those modes. The frequency of the mode at 282 cm−1 shows little temperature dependence. However, for the two strongest modes at 471 and 512 cm−1, the frequencies decrease linearly with increasing temperature. From evolution of the frequencies of modes at 54, 99, 130 and 162 cm−1 with temperature, the following conclusions can be drawn: (1) The distance of the local M–O bond shortens rather than lengthens at temperatures above 200 °C; (2) The abrupt changes of the local structure of M site induce a collapse of the framework structure and displacive phase transition at 200 °C; and (3) The H atoms incorporated in anorthoclase are located at the M site. These results are indicative for the structure and properties of anorthoclase at deep earth conditions.

Thickness Effect on Thermal Stability by Phase Transition of Single Crystal Hematite Nanorings

Single-crystal hematite (α- Fe 2 O 3) nanorings with three different thicknesses were synthesized by a hydrothermal method. The results of X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) show that the nanorings are single-crystal and have relatively uniform outer diameters of 160nm, and heights of about 100nm. Magnetic measurements up to 920K have been performed on hydrothermally synthesized α- Fe 2 O 3 nanorings and nanoparticles using a quantum design vibrating sample magnetometer. A high temperature phase transition of thermal stability (α- Fe 2 O 3 to Fe 3 O 4) occurs when magnetic measurement was performed under high vacuum (< 9.5 × 10-5 Torr). The phase transition temperature is 670K for nanorings with thickness of ∼30nm, 718K for nanorings with thickness of ∼50nm, 678K for nanorings with thickness of ∼65nm, and 640K for ∼35nm nanoparticles. This data show better thermal stability of nanorings with the thickness of ∼50nm than the other two kinds of nanoring samples The Néel temperature (T N ) of α- Fe 2 O 3 nanorings with the thickness of ∼50nm is determined to be 937.2K by magnetic measurement for the first time, about 22.8K below the bulk value. The small reduction of the T N of the α- Fe 2 O 3 nanorings is consistent with the finite-size scaling theory.

Order–disorder phase transition in the antiperovskite-type structure of synthetic kogarkoite, Na3SO4F

High-temperature phase transition of synthetic kogarkoite, Na3SO4F, has been studied by high-temperature X-ray powder and single-crystal diffraction. The temperature of the phase transition can be estimated as 112.5±12.5°C. The low-temperature phase, α-Na3SO4F, at 293K, is monoclinic, P21/m, a=18.065(3), b=6.958(1), c=11.446(1)Å, β=107.711(1)°, Z=12. The structure contains thirteen symmetrically independent Na sites with coordination numbers varying from 6 to 8, and six independent S sites. The high-temperature β-phase at 423K is rhombohedral, R-3m, a=6.94(1), c=24.58(4)Å, Z=9. The crystal structure of both polymorphs of Na3SO4F can be described as a 9R antiperovskite polytype based upon triplets of face-sharing [FNa6] octahedra linked into a three-dimensional framework by sharing corners. In the α-modification, the SO4 tetrahedra are completely ordered and located in the framework cavities. In the β-modification, there are only two symmetrically independent Na atoms in the structure. The main difference between the structures of the α- and β-phases is the degree of ordering of the SO4 tetrahedra: in the α-modification, they are completely ordered, whereas, in the β-modification, the complete disorder is observed, which is manifested in a number of low-occupied O sites around fully occupied S sites. The phase transition is therefore has an order–disorder character and is associated with the decrease of structural complexity measured as an information content per unit cell [577.528 bits for the low- (α) and 154.830 bits for the high- (β) temperature modifications].

High temperature and composition induced phase transitions in LiZnV1−xAsxO4 phenacites: Crystal structure and Raman spectroscopy studies

In this work, using techniques of X-ray diffraction and Raman spectroscopy, we report the composition and high-temperature induced phase transition in the system LiZnV1−xAsxO4 (0⩽x⩽1). Both techniques showed that the increase of arsenic amount induced a structural transition from R-3 LiZnVO4 type to LiZnAsO4 type belonging to R3 space group, the transition occurring between x=0.7 and x=0.8. Furthermore, increasing temperature for the compositions (0.8⩽x⩽1) manifests a transition from the LiZnAsO4 structural type with R3 space group to the R-3 LiZnVO4 structural type. For this series, the transition from the space group R3 to the centro-symmetric space group R-3 shows considerable changes in the compositional and temperature dependencies of the bands: spectral positions of all the observed Raman bands exhibit shifts linearly proportional to the temperature increase, with points of shift-rate changes revealing a symmetry change. The Raman-spectra based temperature-composition phase diagram confirms the results obtained using the method of Rietveld refinements, thus showing the R-3 to R3 transition occurring between x=0.7 and 0.8.

Effect of the texture of Langmuir copolymer films on structural phase transitions

An atomic-force microscopy study has surprisingly revealed that ultrathin copolymer films fabricated according to Langmuir technology constitute a network of tangled filaments. A long-range order is absent in the samples. The observed filaments consist of several parallel-packed copolymer chains. The shape of ferroelectric domains in a film is independent of the direction of copolymer chains. Each domain includes a large number of filaments. The nature of high-temperature (ferroelectric) and low-temperature phase transitions has been discussed in terms of structural data.

Amide as Terminal Groups: Synthesis and Properties as New Tolane‐Type Liquid Crystals

AbstractA series of novel tolane‐type liquid crystals with amide group as terminal group have been prepared. The terminal amide groups were modified, and the influence of these structural parameters on liquid crystal phases was investigated by polarizing optical microscope (POM) and differential scanning calorimetry (DSC). Three of these new compounds exhibit nematic phase, good thermal stabilities. In general, these liquid crystals with amide as end groups have high melting points and phase transition temperatures, which result from the hydrogen bonds. Based on theoretical calculations, these new molecules with strong electron donating amide as end group have narrower HOMO‐LUMO energy gap and higher dipole moment than tolane.

A first-order phase transition in zektzerite, NaLiZrSi6O15: high-temperature single-crystal X-ray diffraction study

The crystal structure of zektzerite, NaLiZrSi6O15, orthorhombic (space group Cmca), consists of six-tetrahedral-repeat corrugated double silicate chains connected into a three-dimensional framework by edge-sharing Li tetrahedral–Zr octahedral chains. At room temperature, the Na+ ions occur at the Na(1) site located within the cylindrical channels created by the corrugation of the silicate double chains. The second sodium site, Na(2), occurs above and below the Zr octahedron and is nominally vacant at room temperature. Above 773 K, vacancies are created at the Na(1) site due to the migration of Na+ ions from the Na(1) to the Na(2) site. Crystal structure refinements at 300, 773, 973, 1223 and 1323 K indicate a progressive increase in the sodium occupancy at the Na(2) site from 0.04 at 773 K to 0.35 at 1323 K. Induced by increasing Na+-ion migration, a first-order high-temperature phase transition occurs above 1123 K as evidenced by a break in the slopes of the thermal expansion curves of the unit cell dimensions and a substantial increase in the electrical conductivity. The unit cell measurements as a function of temperature show marked hysteresis effects during the heating and cooling cycles.

Development and application of an apparatus for high-temperature measurement of magnetic susceptibility.

An apparatus for high-temperature measurement of magnetic susceptibility using the modified Gouy method was developed. It can be used at temperatures of up to 1200 °C. The apparatus consists of the heating system, weighing system, and temperature-programming controller. The sample should be placed at a position of relatively constant B(dB/dz) in a gradient magnetic field. Each crucible is used only once for a single measurement to reduce the error. The reliable accuracy and good repeatability of the apparatus are demonstrated by measuring the magnetic susceptibilities of a DD483 superalloy, Ni-based solid solution alloy, and Ni3Al-based solid solution alloy at various temperatures. The results also successfully explain the change in the γ' precipitation in DD483 superalloys. Therefore, the apparatus provides a convenient and powerful tool for investigating high-temperature phase transitions in the presence of a magnetic field.

One-step scalable preparation method for non-cationic liposomes with high siRNA content

Cationic liposomes (LPs) have been utilized for short interfering RNA (siRNA) delivery in vitro and in vivo owing to their high affinity for siRNA via electrostatic binding. However, both cytotoxicity and non-specific adsorption of cationic LPs in the body have prevented clinical siRNA applications. These situations have led to siRNA encapsulation in non-cationic LPs. We found that the instillation of neutral phospholipids dissolved in ethanol into aqueous solutions containing siRNA and CaCl2 resulted in high siRNA encapsulation (siRNA encapsulation efficiency: ∼80%; siRNA weight ratio: ∼10wt% of LPs). The products were monodispersed, ∼200nm, and negatively charged. Furthermore, when phospholipids with a high-phase transition temperature or cholesterol were used, the encapsulation efficiency and siRNA content remained high. Although anionic LPs could not encapsulate siRNAs using this method, the use of cholesterol-conjugated siRNA helped achieve substantial siRNA encapsulation in anionic LPs. These non-cationic siRNA-containing LPs did not show cytotoxicity in vitro, and could be formed with polyethylene glycol-conjugated phospholipids. When conjugated with targeting ligand, the non-cationic siRNA-containing LPs could suppress the expression of target gene in vitro. These data demonstrate that our preparation method would be suitable for large-scale LP production for systemic siRNA delivery.

Temperature dependence of crystal structure of CaGeO3high-pressure perovskite phase and experimental determination of its Debye temperatures studied by low- and high-temperature single-crystal X-ray diffraction

Single-crystal X-ray diffraction study of CaGeO 3 perovskite has been conducted over the temperature range of 98 to 1048 K. The crystal begins to deteriorate at a temperature above about 900 K and completely amorphizes by 980 K. The diffraction-intensity distribution and the structure refinements indicate that the Pbnm structure is kept until the occurrence of amorphization. The obtained unit-cell parameters, unit-cell volumes, bond lengths, and displacement parameters increase monotonously with increasing temperature. Thus, no evidence for the existence of the Cmcm high-temperature phase, previously suggested above 520 K, is observed. The Ge-O bond lengths show much smaller thermal expansions than the Ca-O bond lengths; the former ranges between 0.42(2) × 10 −5 K −1 and 0.57(2) × 10 −5 K −1 , and the latter between 1.58(4) × 10 −5 K −1 and 3.96(6) × 10 −5 K −1 . The Debye temperatures and static disorder components for each constituent atom were determined by applying the Debye model to the temperature dependence of mean square displacements (MSDs) of the atoms. Consequently, no significant static disorder components can be detected in each atom. The Debye temperatures averaged over all directions, obtained from the Debye model fitting to U eq , yield the harmonic one particle potential coefficients of 4.76(2) eVÅ −2 for Ca, 11.0(1) eVÅ −2 for Ge, 5.02(2) eVÅ −2 for O1, and 5.33(5) eVÅ −2 for O2. These values become larger in order of Ca < O1 < O2 << Ge, which shows that the one particle potential of Ge is much narrower than that of Ca. This relationship between Ca and Ge is consistent reasonably with bonding stiffness expected from the thermal expansion coefficients of the bond lengths. The anisotropies of MSDs are remarkable in O1 and O2 atoms as a consequence of the strong interaction with adjacent Ge atoms, forming the rigid bonds with these O atoms. In comparison of the three Pbnm orthorhombic perovskites of CaGeO 3 , CaTiO 3 , and MgSiO 3 , all of these have the BO 6 octahedra more rigid than the AO 12 polyhedra (A = Ca or Mg; B = Ge, Ti, or Si) and the tilt angles of BO 6 octahedra are the largest in MgSiO 3 perovskite. These observations indicate that if MgSiO 3 perovskite under high pressures undergoes the same sequence of the high-temperature phase transitions as CaTiO 3 perovskite, the phase boundaries have positive Clapeyron slopes and the phase transition temperatures should become further much higher than those (1512 K for the Pbnm to I4/mcm transition and 1635 K for the I4/mcm to Pm3̅m transition) observed in CaTiO 3 perovskite at ambient pressure. This leads to the conclusion that the high-temperature phase transition to a perovskite phase with different symmetry under high pressures previously suggested in MgSiO 3 perovskite is unlikely.

Phase transitions in non-centrosymmetric pyridinium trifluoromethanesulfonate crystal: Vibrational studies

Infrared spectroscopy (4000–400cm−1) in the wide temperature range, from 11 to 473K, has been used to investigate the non-centrosymmetric pyridinium trifluoromethanesulfonate crystal, exhibiting several phase transitions. The assignments of the bands observed in the studied spectra have been proposed. The temperature dependence of the wavenumbers and the full width at half maximum (FWHM) of the bands arising from some internal vibrations of the pyridinium cation and the triflate anion have been analyzed in order to achieve a knowledge of whether these both ions are involved in the phase transitions and what is the role of these both ions in these phase transitions. The infrared measurements showed that the both ions, pyridinium cation and triflate anion are involved in the high temperature phase transitions of the order–disorder type, previously reported at 305.1 and 396.7K. They also revealed that these transitions are governed by a rotational mobility (changes in dynamical states) of both the pyridinium and triflate ions. Our results show that the multiple structures of the νNH and νND bands observed in the studied infrared spectra is due to the Fermi resonance interaction between the stretching vibration of the N–H⋯O hydrogen bond and the overtones and combinations of the internal vibrations of the pyridinium cation.

Dinuclear Face-Sharing Bi-octahedral Tungsten(VI) Core and Unusual Thermal Behavior in Complex Th Tungstates.

Two new thorium tungstates A6 Th6 (WO4 )14 O (A=K and Rb) were synthesized by high-temperature solid-state reactions. The structures of both phases are based on a rare dinuclear confacial bi-octahedral [W2 O9 ](6-) core, encapsulated in a [Th6 W7 O46 (W2 O9 )](32-) cage showing a cross-section geometry similar to a six-leafed lily. The adjacent cages are connected in two dimensional layers by WO4 tetrahedral linkers. Due to the dissimilarities in mutual orientations of adjacent layers in these two structures, K6 Th6 (WO4 )14 O crystallizes in space group of R32 while Rb6 Th6 (WO4 )14 O stabilizes in P$\bar 6$2c. The high-temperature phase transition was observed in Rb6 Th6 (WO4 )14 O and investigated using high-temperature PXRD technique. The results demonstrate a very unusual thermal behavior of this compound. The Raman and IR spectra of both phases were analyzed with respect to their complex structures.

Control of the metal-insulator transition in VO₂ epitaxial film by modifying carrier density.

External controlling the phase transition behavior of vanadium dioxide is important to realize its practical applications as energy-efficient electronic devices. Because of its relatively high phase transition temperature of 68 °C, the central challenge for VO2-based electronics, lies in finding an energy efficient way, to modulate the phase transition in a reversible and reproducible manner. In this work, we report an experimental realization of p-n heterojunctions by growing VO2 film on p-type GaN substrate. By adding the bias voltage on the p-n junction, the metal-insulator transition behavior of VO2 film can be changed continuously. It is demonstrated that the phase transition of VO2 film is closely associated with the carrier distribution within the space charge region, which can be directly controlled by the bias voltage. Our findings offer novel opportunities for modulating the phase transition of VO2 film in a reversible way as well as extending the concept of electric-field modulation on other phase transition materials.

Low-temperature phase transitions in [Cd(DMSO)6](BF4)2 studied by differential scanning calorimetry, X-ray single crystal diffraction and infrared absorption spectroscopy

The differential scanning calorimetry (DSC) measurements made for [Cd(DMSO)6](BF4)2, in the temperature range of 113–298K revealed existence of two low-temperature solid–solid phase transitions: phase Cr 3↔phase Cr 2 at Tc2c=218K and phase Cr 2↔phase Cr 1 at Tc1c=246K. X-ray single crystal diffraction studies of [Cd(DMSO)6](BF4)2 have shown that these transitions are related to a crystal symmetry reduction from an orthorhombic crystallographic system (Fdd2, No. 43) to a monoclinic one (Cc, No. 9). The [Cd(DMSO)6](BF4)2 compound undergoes also series of reversible high temperature phase transitions but they are not a subject of this work and will be presented in our next paper. The characteristic changes of the FT-FIR, FT-MIR and FT-RS spectra of [Cd(DMSO)6](BF4)2 at the phase transitions’ temperatures confirmed that phase transitions phase Cr 3↔phase Cr 2↔phase Cr 1 are related to the crystal structure change. It was also found that the reorientation of the BF4− anions and DMSO ligands freezes below 218K.