High-temperature Phase Transition Research Articles

Melting behavior of waste glass cullet briquettes in soda‐lime‐silica container glass batch

AbstractThe melting behavior of representative container glass batch with and without the addition of 15wt% briquettes produced from waste cullet fine particles was investigated in the context of reducing both waste and glass melting energies. Carbonate raw material decomposition and reactions during melting were studied by DTA‐TGA‐MS. The decomposition kinetics of two batches, representing typical container glass batches with 0% and 15% briquette additions, were calculated by transformation degree based on the Ginstling‐Brounstein and Arrhenius equations. High temperature phase transitions and fractions of silica reaction in each batch were obtained from X‐ray diffractometry (XRD). The briquette additions accelerated the decomposition reactions and the silicate reaction kinetics by decreasing the activation energy for carbonate decomposition. Silica sand in the batch was shown to melt at lower temperatures with the addition of briquettes. Batch melting processes at different temperatures and briquette melting on top of the molten glass at high temperatures were investigated by macroscopic investigations of sample cross sections postmelting. The positive effects of briquette additions to container glass batches, in terms of increased melting rate and reduced batch reaction and decomposition temperatures, are supported by the results of this study.

Poly(ethylene-co-1-tetradecylacrylate) and poly(ethylene-co-1-octadecylacrylate) copolymers as novel solid–solid phase change materials for thermal energy storage

Poly(ethylene-co-1-tetradecylacrylate) (EcoTDA) and poly(ethylene-co-1-octadecylacrylate) (EcoODA) copolymers were synthesized using poly(ethylene-co-acrylic acid) (EcoA) copolymers with 5 and 20% acrylic acid contents, respectively, and fatty alcohols (1-tetradecanol and 1-octadecanol) as novel polymeric solid–solid phase change materials. Chemical structure, thermal property, and crystalline morphology of the copolymers were characterized by using Fourier transform infrared spectroscopy, differential scanning calorimetry (DSC), and polarized optical microscopy, respectively. Poly(ethylene-co-1-tetradecylacrylate) and poly(ethylene-co-1-octadecylacrylate) copolymers have two reversible phase transitions in DSC thermograms, that is, they have two morphologically different phases to transform from solid to amorphous connected each other. The change in surface morphology is only by color tone after the low-temperature phase transition as it was discrete to single color amorphous after the high-temperature phase transition according to microscopy. This property makes them resistant to flow above the first transition where thermal energy is stored for utility. Microindentation test proved that the hardness and reduced modulus values are considerably low after the solid–solid phase transition, but it is still measurable as a solid material.

Fabrication and release of silicon nitride micro string array by convection freeze sublimation method at atmospheric pressure

A convection freeze sublimation (CFS) method was developed to release silicon nitride strings with a high aspect ratio and high tensile stress, which are widely applied as electromechanical resonators. This method is cost-efficient and easy to operate for its implementation at atmospheric pressure and no vacuum or cryogenic equipment is needed. The CFS system is composed of cyclohexane, nitrogen gas, a freezer and a drying chamber. Cyclohexane with low surface tension (24.38 mN m−1) and high phase transition temperature (6.5 °C) was chosen as the medium in the CFS method. Nitrogen gas was introduced into the drying chamber to facilitate the sublimation of solid cyclohexane by enhancing heat convection at the solid–air interface. A convective mass transfer model was calculated to quantitatively analyze the influence of convective parameters on the sublimation rate. The silicon nitride string array were successfully released with the aid of 3 ml min−1 flow of nitrogen gas. However, when the nitrogen flow rate exceeded 6 ml min−1, the strings adhered in some points because solid cyclohexane is prone to melt instead of sublimating under excessive heat introduced by nitrogen gas. Furthermore, a finite element model was built to explore the influence of different outlet parameters on the magnitude and uniformity of flow field on the surface of solid cyclohexane. To evaluate the mechanical property of the released string, we measured the natural frequency of a single string and confirmed the influence of tensile stress on its natural frequency. The results showed that the CFS method is able to serve as a general tool for ultra-weak structure releasing, which makes this method applicable in fields such as optomechanics and metamaterials.

Synthesis, structure and properties of printable W-doped thermochromic VO2 with a low phase transition temperature

Vanadium dioxide (VO2) could be a good candidate for thermochromic materials due to the characteristic features of phase transition and discoloration. However, the high phase transition temperature (Tc) of 68 °C becomes the limitation of its practical application. In this work, a cost-effective fabrication method was developed to prepare W-doped thermochromic VO2 with a low phase transition temperature. Herein, tungsten (W) was introduced into an O-V-O system via a simple hydrothermal method, followed by annealing in an argon atmosphere to reduce the Tc of VO2. The results show that the micromorphology of VO2 changed significantly from rectangular to continuous sheet-like and that the particle size was increased after W-doping. Annealing could decrease the size of undoped VO2, and the morphology became an inhomogeneous and disordered cusp-like shape. In addition, annealing made the W-doped VO2 particles with a larger size exhibit crimps, shrinkage and collapse. The Tc of VO2 (M phase to R phase) was reduced to 34.3 °C, 18.6 °C and 10.6 °C with W-doping levels of 1.5 at%, 2.0 at% and 3.0 at% at annealing temperatures of 500 °C, 550 °C and 500 °C, respectively. Infrared spectra indicate that the largest integrated infrared transmittance was increased from 51.78% to 81.91% (sample of S-22). Therefore, W-doped thermochromic VO2 could be a promising candidate for applications in printing, sensors and optical devices as functional materials.

Metal-free three-dimensional perovskite ferroelectrics.

Inorganic perovskite ferroelectrics are widely used in nonvolatile memory elements, capacitors, and sensors because of their excellent ferroelectric and other properties. Organic ferroelectrics are desirable for their mechanical flexibility, low weight, environmentally friendly processing, and low processing temperatures. Although almost a century has passed since the first ferroelectric, Rochelle salt, was discovered, examples of highly desirable organic perovskite ferroelectrics are lacking. We found a family of metal-free organic perovskite ferroelectrics with the characteristic three-dimensional structure, among which MDABCO (N-methyl-N'-diazabicyclo[2.2.2]octonium)-ammonium triiodide has a spontaneous polarization of 22 microcoulombs per square centimeter [close to that of barium titanate (BTO)], a high phase transition temperature of 448 kelvins (above that of BTO), and eight possible polarization directions. These attributes make it attractive for use in flexible devices, soft robotics, biomedical devices, and other applications.

High-temperature superconductivity and quantum Griffith singularity in two-dimensional crystal

Superconductors have become one of the most important directions in condensed matter physics and materials science due to their unique properties incuding zero-resistance and perfect diamagnetism. With the development of the fabrication technique of two-dimensional (2D) single crystals, 2D superconductors have recently come to be a new research frontier, in which novel physics phenomena, such as high-temperature superconductivity and quantum phase transitions, have emerged and received wide attention. In this artcle, we first briefly review the research background and basic properties of 2D superconductors. Then, focusing on two important classes of phenomena—high-temperature superconductivity and quantum phase transitions, the article is organized into two parts. In the first part, we introduce a typical example of high-temperature superconductivity in 2D systems, the ultrathin FeSe films grown on SrTiO3 (STO) substrate, including the experimental properties and mechanism discussions. In the second part, as an example of quantum phase transitions in 2D systems, an overview of the theories and experiments of the newly-discovered quantum Griffiths singularity in 2D crystalline superconductors is given. In the end, we summary the high-temperature superconductivity and quantum Griffiths singularity in 2D crystals and provide an outlook of the future development in the relevant frontiers.

Mn doped ternary relaxor single crystal with high shear piezoelectricity and improved stability

The complete set of elastic, piezoelectric and dielectric constants of [011]C poled rhombohedral 0.27Pb(In0.5Nb0.5)O3 − 0.46Pb(Mg1/3Nb2/3)O3 − 0.27PbTiO3:Mn single crystal with "2 R" engineered domain structure have been measured. These special domain structure possesses high shear piezoelectric properties with d15 = 1642 pC/N and k15 = 0.862. Meanwhile, the crystal exhibits high phase transition temperature (TR-M = 126 °C) and relative high mechanical quality factors (Q33 = 870, Q15 = 220). This "2R" domain structure has a much easier poling procedure and improved stability against external field, which give the possibility for applications in shear mode transducers. Finally, the physical mechanism of high shear piezoelectricity was explored, which shows that both intrinsic (crystalline orientation) and extrinsic factors (domain structure) favors high shear piezoelectricity in "2R" domain structure.

Discovery of an Antiperovskite Ferroelectric in [(CH3)3NH]3(MnBr3)(MnBr4).

It is known that perovskites with the general chemical formula of ABX3 (A, B = cations, X = anion) have been intensively studied over the last half century because of their diverse functional properties, such as ferroelectricity in BaTiO3, piezoelectricity in PZT (lead zirconate titanate), and recently developed photovoltaic properties in CH3NH3PbI3. However, rather less attention has been paid to their "inverse" analogs, antiperovskites, which have a chemical formula X3BA, where A and B are anions and X is a cation. Although most of important ferroelectrics are perovskites, no antiperovskite ferroelectrics have been found since the discovery of antiperovskites in 1930. Here, for the first time, we report a X3BA antiperovskite ferroelectric [(CH3)3NH]3(MnBr3)(MnBr4) (where (CH3)3NH is X, MnBr3 is B, and MnBr4 is A), which shows outstanding ferroelectricity with a significantly high phase transition temperature of 458 K as well as fascinating photoluminescence properties with two intense emissions. This finding opens a new avenue to explore the golden area of antiperovskites for high-performance functional materials.

High-Pressure Phase Relations and Crystal Structures of Postspinel Phases in MgV2O4, FeV2O4, and MnCr2O4: Crystal Chemistry of AB2O4 Postspinel Compounds.

We have investigated high-pressure, high-temperature phase transitions of spinel (Sp)-type MgV2O4, FeV2O4, and MnCr2O4. At 1200-1800 °C, MgV2O4 Sp decomposes at 4-7 GPa into a phase assemblage of MgO periclase + corundum (Cor)-type V2O3, and they react at 10-15 GPa to form a phase with a calcium titanite (CT)-type structure. FeV2O4 Sp transforms to CT-type FeV2O4 at 12 GPa via decomposition phases of FeO wüstite + Cor-type V2O3. MnCr2O4 Sp directly transforms to the calcium ferrite (CF)-structured phase at 10 GPa and 1000-1400 °C. Rietveld refinements of CT-type MgV2O4 and FeV2O4 and CF-type MnCr2O4 confirm that both the CT- and CF-type structures have frameworks formed by double chains of edge-shared B3+O6 octahedra (B3+ = V3+ and Cr3+) running parallel to one of orthorhombic cell axes. A relatively large A2+ cation (A2+ = Mg2+, Fe2+, and Mn2+) occupies a tunnel-shaped space formed by corner-sharing of four double chains. Effective coordination numbers calculated from eight neighboring oxygen-A2+ cation distances of CT-type MgV2O4 and FeV2O4 and CF-type MnCr2O4 are 5.50, 5.16, and 7.52, respectively. This implies that the CT- and CF-type structures practically have trigonal prism (six-coordinated) and bicapped trigonal prism (eight-coordinated) sites for the A2+ cations, respectively. A relationship between cation sizes of VIIIA2+ and VIB3+ and crystal structures (CF- and CT-types) of A2+B23+O4 is discussed using the above new data and available previous data of the postspinel phases. We found that CF-type A2+B23+O4 crystallize in wide ionic radius ranges of 0.9-1.4 Å for VIIIA2+ and 0.55-1.1 Å for VIB3+, whereas CT-type phases crystallize in very narrow ionic radius ranges of ∼0.9 Å for VIIIA2+ and 0.6-0.65 Å for VIB3+. This would be attributed to the fact that the tunnel space of CT-type structure is geometrically less flexible due to the smaller coordination number for A2+ cation than that of CF-type.

Crystal packing, high-temperature phase transition, second-order nonlinear optical and biological activities in a hybrid material: [(S)[sbnd]C7H16N2][CuBr4

The directed synthesis of non-centrosymmetric copper (II) bromo-complex has been achieved through the use of homochiral organic molecule. Reaction containing (S)-(−)-3-aminoquinuclidine, CuBr2, HBr and H2O were subjected to mild hydrothermal conditions, resulting in the growth of single crystals of [(S)C7H16N2][CuBr4]. The compound crystallizes in the non polar space group P212121(No. 19), which exhibits the enantiomorphic crystal class 222 (D2). In the crystal structure, the tetrabromocuprate(II) anion is connected to three organic cations through NH…Br hydrogen bonds to form cation-anion-cation molecular units, which are held together by means of offset face-to-face interactions to give one-dimensional chains. DSC measurements indicated that the compound [(S)C7H16N2][CuBr4] underwent a reversible phase transition at 80 °C. [(S)C7H16N2][CuBr4] is more than 1.2 times as efficient as KDP in second harmonic generation; making it a potentially attractive material for non-linear optical applications. The synthesized product was also screened for in vitro antioxidant and antimicrobial activities, while showing favorable antioxidant activities against DPPH as well as the discoloration of β-carotene.

High-Pressure Synthesis, Structures, and Properties of Trivalent A-Site-Ordered Quadruple Perovskites RMn7O12 (R = Sm, Eu, Gd, and Tb).

A-site-ordered quadruple perovskites RMn7O12 with R = Sm, Eu, Gd, and Tb were synthesized at high pressure and high temperature (6 GPa and ∼1570 K), and their structural, magnetic, and dielectric properties are reported. They crystallize in space group I2/ m at room temperature. All four compounds exhibit a high-temperature phase transition to the cubic Im3̅ structure at ∼664 K (Sm), 663 K (Eu), 657 K (Gd), and 630 K (Tb). They all show one magnetic transition at TN1 ≈ 82-87 K at zero magnetic field, but additional magnetic transitions below TN2 ≈ 12 K were observed in SmMn7O12 and EuMn7O12 at high magnetic fields. Very weak kinklike dielectric anomalies were observed at TN1 in all compounds. We also observed pyroelectric current peaks near 14 K and frequency-dependent sharp steps in dielectric constant (near 18-35 K)-these anomalies are probably caused by dielectric relaxation, and they are not related to any ferroelectric transitions. TbMn7O12 shows signs of nonstoichiometry expressed as (Tb1- xMn x)Mn7O12, and these samples exhibit negative magnetization or magnetization reversal effects of an extrinsic origin on zero-field-cooled curves in intermediate temperature ranges. The crystal structures of SmMn7O12 and EuMn7O12 were refined from neutron powder diffraction data at 100 K, and the crystal structures of GdMn7O12 and (Tb0.88Mn0.12)Mn7O12 were studied by synchrotron X-ray powder diffraction at 295 K.

Phase transitions in huddling emperor penguins

Emperor penguins (Aptenodytes forsteri) are highly adapted to the harsh conditions of the Antarctic winter: they are able to fast for up to 134 days during breeding. To conserve energy, emperor penguins form tight groups (huddles), which is key for their reproductive success. The effect of different meteorological factors on the huddling behaviour, however, is not well understood. Using time-lapse image recordings of an emperor penguin colony, we show that huddling can be described as a phase transition from a fluid to a solid state. We use the colony density as order parameter, and an apparent temperature that is perceived by the penguins as the thermodynamic variable. We approximate the apparent temperature as a linear combination of four meteorological parameters: ambient temperature, wind speed, global radiation and relative humidity. We find a wind chill factor of −2.9 , a humidity chill factor of −0.5 rel. humidity, and a solar radiation heating factor of 0.3 . In the absence of wind, humidity and solar radiation, the phase transition temperature (50% huddling probability) is −48.2 °C for the investigated time period (May 2014). We propose that higher phase transition temperatures indicate a shrinking thermal insulation and thus can serve as a proxy for lower energy reserves of the colony, integrating pre-breeding foraging success at sea and energy expenditure at land due to environmental conditions. As current global change is predicted to have strong detrimental effects on emperor penguins within the next decades, our approach may thus contribute towards an urgently needed long-term monitoring system for assessing colony health.

Exploring the work function variability and structural stability of VO2(1 1 0) surface upon noble metal (Ag, Au, Pt) adsorption and incorporation

Vanadium dioxide (VO2) has attracted great attention, with scientific and technological advances over the past few decades due to its reversible metal-insulator transition at 340 K. However, the high phase transition temperature (Tc) of VO2 limits its practical applications. Our first-principles calculations show that VO2(1 1 0) surfaces with adsorbed noble metals (Ag, Au, Pt) exhibit a lower work function compared with the clean surface and further induces a lower Tc due to charge transfer from the noble metals to the VO2(1 1 0) surface. However, the work functions of the VO2(1 1 0) surfaces after the incorporation of noble metals are higher than that of the clean surface. In addition, the results of formation energies of various configurations show that the VO2(1 1 0) surface with the adsorption and incorporation of Ag is energetically more favorable than those with Au and Pt. Therefore, it may be concluded that the adsorption and incorporation of noble metals can not only tailor the work function of VO2, in turn realizing the rational tuning of Tc of VO2, but also stabilize the structures of VO2 thin films. These results provide guidance for further exploration of VO2-based optical switching devices and smart windows.

High-temperature order-disorder phase transition in Fe-18Ga alloy evaluated by internal friction method

The structure, internal friction (IF) behavior, resistivity and magnetostriction property of Fe-18Ga alloy were systematically analyzed in this investigation. In the IF spectra of Fe-18Ga alloy covered from room temperature (RT) to 800 °C, a prominent IF peak (labeled as Ptr peak) was observed in the high temperature range 530 °C–690 °C besides the reported IF peak related with grain boundary relaxation in the moderate temperature range 400 °C–530 °C. The peak position of Ptr peak hardly changes with measuring frequency, implying that its mechanism is most possibly related with phase transition. Considering from the wide peak shape, Ptr peak can be decomposed into two components: the lower temperature Ptr1 peak located around 530 °C–605 °C and the higher temperature Ptr2 peak located around 605 °C–690 °C. Combined with calculated phase diagram, resistivity and magnetostriction analysis, the mechanism of Ptr peak was suggested to originate from the order-disorder phase transition related with Ga atom distribution in Fe-18Ga alloy: Ptr1 peak was ascribed to D03→B2 transition and Ptr2 peak was ascribed to B2→A2 transition, respectively.

Role of vacancies in the high-temperature pseudodisplacive phase transition in GeTe

To date, the high-temperature phase transition R3m$\text{\ensuremath{-}}Fm\phantom{\rule{0.83328pt}{0ex}}\overline{3}\phantom{\rule{0.83328pt}{0ex}}m$ in GeTe is commonly believed to be second-order displacive with an anomalous volume contraction at the phase transition temperature, ${T}_{PT}$, from diffraction measurements. Three main results are here reported: (i) the phase transition is accompanied by latent heat absorption, (ii) in the high-resolution x-ray-diffraction powder pattern the cubic phase appears before the merging of the rhombohedral peaks, and (iii) the cubic phase possesses a larger amount of germanium vacancies than the rhombohedral phase. From results (i)--(iii) we conclude that the phase transition is not purely second-order displacive and that the volume contraction observed at ${T}_{PT}$ can be explained with the formation of vacancies in the cubic phase.

Aqueous sol–gel synthesis, thermoanalytical study and electrical properties of La2Mo2O9

Nano- and micro-sized La2Mo2O9 ceramics have been successfully synthesized by an aqueous sol–gel synthesis method using a tartaric acid as a ligand. Thermal analysis of both as-prepared La–Mo–O tartrate gel precursor and La2Mo2O9 double oxide heat-treated at different temperatures was performed. The high-temperature phase transition from α to β-phases was additionally investigated by broadband high-temperature impedance spectroscopy techniques. The α ↔ β phase transition was characterized by monitoring the conductivity and a transfer of heat with respect to temperature. The crystalline phase stability of monoclinic La2Mo2O9 compound was confirmed by x-ray diffraction measurements, while the dense nanoscale surface composed of the particles, ranging from 50 to 100 μm, was confirmed by scanning electron microscopy.

Phase formation kinetics, hardness and magnetocaloric effect of sub-rapidly solidified LaFe11.6Si1.4 plates during isothermal annealing

High-temperature phase transition behavior and intrinsic brittleness of NaZn13-type τ1 phase in La–Fe–Si magnetocaloric materials are two key problems from the viewpoint of materials production and practical applications. In the present work, the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation was introduced to quantitatively characterize the formation kinetics of τ1 phase in sub-rapidly solidified LaFe11.6Si1.4 plates during the isothermal annealing process. Avrami index was estimated to be 0.43 (∼0.5), which suggests that the formation of τ1 phase is in a diffusion-controlled one-dimensional growth mode. Meanwhile, it is found that the Vickers hardness as a function of annealing time for sub-rapidly solidified plates also agrees well with the JMAK equation. The Vickers hardness of τ1 phase was estimated to be about 754. Under a magnetic field change of 30 kOe, the maximum magnetic entropy change was about 22.31 J/(kg·K) for plates annealed at 1323 K for 48 h, and the effective magnetic refrigeration capacity reached 191 J/kg.

Review on thermochromic vanadium dioxide based smart coatings: from lab to commercial application

With an urgent demand of energy efficient coatings for building fenestrations, vanadium dioxide (VO2)-based thermochromic smart coatings have been widely investigated due to the reversible phase transition of VO2 at a critical transition temperature of 68 °C, which is accompanied by the modulation of solar irradiation, especially in the near-infrared region. As for commercial applications in our daily life, there are still some obstacles for VO2-based smart coatings, such as the high phase transition temperature, optical properties (luminous transmittance and solar modulation ability), environmental stability in a long-time period, as well as mass production. In this review, recent progress of thermochromic smart coatings to solve above obstacles has been surveyed. Meanwhile, future development trends have also been given to promote the goal of commercial production of VO2 smart coatings.

A high-temperature molecular ferroelastic phase transition and switchable dielectric response in the trimethylbromomethylammonium salt [C4H11NBr] [PF6

A new molecular ferroelastic compound [TMBMA] [PF6] was successfully synthesized, wherein the origin of the phase transition and dielectric anomalies is related to the order–disorder processes of the TMBMA cations.

High-temperature reversible phase transitions and exceptional dielectric anomalies in cobalt(ii) based ionic crystals: [Me3NCH2X]2[CoX4] (X = Cl and Br).

Two isostructural ionic cobalt(ii) halides, trimethylchloromethyl ammonium tetrachlorocobalt(ii) (1, [Me3NCH2Cl]2[CoCl4]) and trimethylbromomethyl ammonium tetrabromocobalt(ii) (2, [Me3NCH2Br]2[CoBr4]), have been discovered as new high-temperature phase transition materials. 1 exhibits two successive structural phase transitions from P212121 to P21/c at 252 K and then to Pnma at 335 K, accompanied by step-like dielectric anomalies. The two-step sequential reversible phase transitions of 1 derive from the order-disorder transformation of CoCl4 anions and organic Me3NCH2Cl cations, respectively. Its analogue 2 also crystallizes in P21/c at 293 K by changing the halogen atoms of both cations and anions of 1. Unlike 1, 2 displays only one structural phase transition with a much higher transition temperature at 387 K, which is mainly influenced by intermolecular interactions and more energy is required to provide the freedom of the motion. All the findings in the present work indicate that the phase transition temperature and properties of materials can be tuned by using halogens in this series of compounds, which could open a new way to design and assemble novel high-temperature phase transition materials.