High Temperature X-ray Diffraction Studies Research Articles

In situ high-temperature X-Ray diffraction study of tantalum metal

An in-situ thermal behavior study was conducted on the metallic tantalum under two conditions. The experimentation was carried out on tantalum pellets which were heated progressively “underwent reaction and under continuous pumping or under controlled monoxide pressure” in a graphite resistance high temperature X-ray diffractometer up to 2300 K. Through the in-situ study, a thermodynamic analysis showed that this involved the formation of Ta2O, Ta2O5 (low temperature modification) and Ta2C likely to be formed between 293 and 2300 K, in agreement with a reaction mechanism that we established to occur in four stages.

FTIR, Raman spectroscopy and HT-XRD in compatibility study between naproxen and excipients

Detection of incompatibility between an active pharmaceutical ingredient (API) and excipients, including the selection of the most biopharmaceutical advantageous excipients is extremely important in the pre-formulation process of developing a solid dosage form technology. Therefore, having fast and reliable methods for identifying incompatibility is fundamental in pharmaceutical technology. For this purpose, combined Fourier transform infrared (FTIR) and Raman spectroscopy as well as high-temperature X-ray diffraction (HT-XRD) were used as a new approach for incompatibility detection, whereas differential scanning calorimetry (DSC) was applied as a reference method. In addition, to facilitate the interpretation of FTIR and Raman data, a multivariate analysis was used – hierarchical cluster analysis (HCA). The tests were carried out in mixtures of naproxen (NPX) with eight selected polymer excipients, mixed at a 1:1 ratio. The results of spectroscopic analyses have shown the physical incompatibility of NPX with methylcellulose (MC), hydroxypropylmethylcellulose (HPMC), hydroxyethylcellulose (HEC), sodium starch glycolate (SSG) and sodium carboxymethylcellulose (CMC). HT-XRD studies performed when these mixtures were heated to 156 °C and then cooled to 25 °C showed a decrease in naproxen crystallinity in these mixtures. Furthermore, the results obtained with spectroscopic methods were confirmed by DSC tests and an intrinsic dissolution rate study.

Re-investigation of ‘minasgeraisite-(Y)’ from the Jaguaraçu pegmatite, Brazil and high-temperature crystal chemistry of gadolinite-supergroup minerals

AbstractThe chemical composition (including B, Be and Li), the Raman spectrum and the crystal-structure evolution (at the temperature range 27–1000°C) of a Mn-bearing, Bi-rich gadolinite-subgroup mineral from the Jaguaraçu Pegmatite, Brazil (type-locality of minasgeraisite-(Y)) was studied. Elemental mapping revealed that the crystal investigated has complex chemical zonation with various Bi (~8–24 wt.% Bi2O3), Ca (~8–10 wt.% CaO) and Y (~11–17 wt.% Y2O3) content. The sample investigated has all the specific features of the chemical composition of minasgeraisite-(Y), except Ca excess and, thus, should be considered as hingganite-(Y). The Raman spectrum of the sample under study has bands at 140, 179, 243, 350, 446, 519, 559, 625, 902, 973, 3224, 3353, 3532 and 3763 cm–1, and is similar to that of hingganite-(Y) / -(Nd). Crystal-structure refinement confirmed that the crystal in question should be considered as hingganite-(Y) and is in line with the previously obtained data on gadolinite-subgroup minerals from the Jaguaraçu Pegmatite. High-temperature single-crystal X-ray diffraction studies revealed that the mineral starts to decompose above 800°C. We can conclude that beryllosilicates are most stable at high-temperature conditions within the gadolinite supergroup and that species with a higher M-site occupancy have higher stability upon heating.

High-temperature X-ray diffraction study of anorthite-tialite materials

ABSTRACT The structure of two mixtures of anorthite and tialite (10 mol-% tialite + 90 mol-% anorthite, 15 mol-% tialite +85 mol-% of anorthite) has been investigated using XRD at different temperatures in solid and liquid states. Such mixtures are used as refractory materials in the lining furnaces for metals with a high melting point. All measurements were carried out using a high-temperature vacuum chamber under a purified helium atmosphere. It has been found that the XRD patterns of the solid samples show reflections of various modifications of tialite and anorthite. Weak reflections of mullite can be identified at temperatures above 1000°C. A structural model of the investigated melts has been proposed based on nanocrystal clusters located in a disordered diffuse matrix. The environment of the disordered part of the matrix is formed by particles (atoms, atomic clusters) that do not participate in nanocrystal clusters.

Phase diagrams guide synthesis of highly ordered intermetallic electrocatalysts: separating alloying and ordering stages.

Supported platinum intermetallic compound catalysts have attracted considerable attention owing to their remarkable activities and durability for the oxygen reduction reaction in proton-exchange membrane fuel cells. However, the synthesis of highly ordered intermetallic compound catalysts remains a challenge owing to the limited understanding of their formation mechanism under high-temperature conditions. In this study, we perform in-situ high-temperature X-ray diffraction studies to investigate the structural evolution in the impregnation synthesis of carbon-supported intermetallic catalysts. We identify the phase-transition-temperature (TPT)-dependent evolution process that involve concurrent (for alloys with high TPT) or separate (for alloys with low TPT) alloying/ordering stages. Accordingly, we realize the synthesis of highly ordered intermetallic catalysts by adopting a separate annealing protocol with a high-temperature alloying stage and a low-temperature ordering stage, which display a high mass activity of 0.96 A mgPt-1 at 0.9 V in H2-O2 fuel cells and a remarkable durability.

Thermal expansion and microstructure evolution of atmospheric plasma sprayed NiCrAlY bond coat using in-situ high temperature X-ray diffraction

The paper focuses on in-situ high-temperature X-ray diffraction (HT-XRD) study on atmospheric plasma sprayed NiCrAlY coating. The sample was in-situ heated from 25 °C to 1150 °C in a controlled atmosphere (3 × 10−4 bar), and the corresponding X-ray diffraction patterns for different temperatures were recorded. The effect of temperature on crystallite size, lattice strain, and coefficient of linear thermal expansion was studied. Major phases identified are γ-Ni, γ’-Ni3Al, β-NiAl, and α-Cr. The formation of stable α-Al2O3 and spinel was found above 1000 °C. The transformation of β to γ’ and γ phase was observed as a function of temperature. The equilibrium phases and the thermal expansion of disordered Face Centered Cubic (FCC) and Body Centered Cubic (BCC) phases were predicted and supported by Thermo-Calc prediction for the stable temperature range. Results showed that the non-equilibrium microstructure produced by thermal spray process did not alter the thermal expansion behaviour. In-situ treatment resulted in microstructure and elemental homogenization. The thermal expansion and mechanism of phase evolution were discussed.

Evolution of microstructure, magneto-structural transformation, and magnetocaloric effect in (Fe72-0.9xNi8-0.1xCo8)Zr7B4Cu1Gax (0 ≤ x ≤ 6 at.%) alloys

We report the evolution of microstructure, magnetic properties, and magnetocaloric effects in a series of (Fe72-0.9xNi8-0.1xCo8)Zr7B4Cu1Gax (0 ≤ x ≤ 6 at.%) alloys. The high temperature X-ray diffraction, calorimetric, and thermomagnetic studies revealed that the α-Fe → γ-Fe transformation occurred in the range of 691–733 K in arc-melted ingots (AMIs), whereas the same occurred at 660–723 K in as-spun ribbons (ASRs). The Curie temperature of γ phase lies in the range of 1126–1140 K and 1106–1126 K for AMIs and ASRs, respectively. Addition of Ga reduces the saturation magnetization and induce nanocrystallization in ASRs. A second-order magnetic transition has been identified in x = 0 ASR using Arrott plot exhibiting magnetic entropy change (|ΔSM|) of 0.973 J/kg.K at TCγ under magnetic field of 0.976 T. The refrigeration capacity of x = 0 and x = 6 ASRs has been estimated to be 12.78 J/kg and 22.98 J/kg, respectively, at 0.976 T.

Magnesium-Doped Sr2(Fe,Mo)O6-δ Double Perovskites with Excellent Redox Stability as Stable Electrode Materials for Symmetrical Solid Oxide Fuel Cells.

In this work, magnesium-doped Sr2Fe1.2Mg0.2Mo0.6O6−δ and Sr2Fe0.9Mg0.4Mo0.7O6−δ double perovskites with excellent redox stability have been successfully obtained. The physicochemical properties including: crystal structure properties, redox stability, thermal expansion properties in oxidizing and reducing conditions, oxygen content as a function of temperature and transport properties, as well as the chemical compatibility with typical electrolytes have been systematically investigated. The in situ oxidation of reduced samples using high-temperature XRD studies shows the crystal structure of materials stable at up to a high-temperature range. The in situ reduction and oxidation of sinters with dilatometer measurements prove the excellent redox stability of materials, with the thermal expansion coefficients measured comparable with electrolytes. The oxygen nonstoichiometry δ of compounds was determined and recorded in air and argon up to 900 °C. Sr2Fe1.2Mg0.2Mo0.6O6−δ oxide presents satisfactory values of electrical conductivity in air (56.2 S·cm−1 at 600 °C) and reducing conditions (10.3 S·cm−1 at 800 °C), relatively high coefficients D and k, and good ionic conductivity (cal. 0.005 S·cm−1 at 800 °C). The stability studies show that both compounds are compatible with Ce0.8Gd0.2O1.9 but react with the La0.8Sr0.2Ga0.8Mg0.2O3−d electrolyte. Therefore, the magnesium-doped double perovskites with excellent redox stability can be potentially qualified as electrode materials for symmetrical SOFCs and are of great interest for further investigations.

Evidence of structural and two magnetic phase transitions in Cu doped La2FeMnO6 double perovskites

In this report, we have addressed a comprehensive study on the structural phase transitions with the help of a combination of high temperature x-ray diffraction and temperature dependence Raman spectroscopy. We also report the magnetic ground state of all the samples at room temperature and 5 K. The combined high temperature x-ray diffraction and temperature dependence Raman study suggests that the samples undergo structural phase transitions from orthorhombic to tetragonal to cubic dominated mixed phase. With the help of x-ray photoelectron spectroscopy, we confirmed the presence of multi-oxidation states of Fe and Mn ions. The temperature evolution of magnetization data has been recorded at a field of 100 Oe and temperature range between 2 K and 300 K, and reveals the presence of two magnetic phase transitions for pristine, 10% and 20% doping of Cu in the composition La 2 FeMn 1−x Cu x O 6 . The magnetic study of all the samples reveal that the magnetic ground state of all the samples shows paramagnetic nature at room temperature, whereas at lower temperature all the samples are ferromagnetic except the highest doped sample which is purely paramagnetic. The law of approach to saturation method is imposed in the saturation region of M-H curve observed at 5 K. The transition temperature decreases with the amount of Cu doping, due to the substitution of Cu in Mn-site resulting in destroy of the Mn 3+ -O 2- - Mn 4+ bridges which is responsible for weakening of double exchange interaction between Mn 3+ and Mn 4+ . • Temperature dependent XRD has shown a structural phase transition from orthorhombic to tetragonal to cubic space group. • Temperature evolution of the phononic modes predominantly influenced by the lattice degrees of freedom. • Magnetic studies have shown two phase transitions confirming low temperature FM phase with different ordering mechanisms.

Nb-doping effect on microstructure, thermal and dielectric properties of bismuth nickel tantalate pyrochlore

Mixed nickel pyrochlore of the Bi2NiTaNbO9 composition (sp. gr. Fd-3m:2, a = 10.53242(3) Å, Z = 8) in which half of the tantalum(V) ions are replaced with Nb(V) was synthesized by solid-phase reaction for the first time. X-ray diffraction (XRD) data indicate the formation of a disordered pyrochlore structure with nickel, tantalum and niobium ions distributed in the same system of crystallographic positions. Doping with Nb(V) ions affects the microstructure of the sample. A dense, low-porous ceramic with fuzzy grain boundaries is formed. High-temperature XRD study shows that Bi2NiTaNbO9 is thermally stable up to 1050 °C. The thermal expansion coefficient increases uniformly and weakly from 3.3 to 8.6 × 10−6 °C−1 in the interval 30–960 °C, and its average value is 6.0 × 10−6 °C−1. Bi2NiTaNbO9 pyrochlore can be classified as a weakly expanding compound with isotropic thermal expansion. Doping with niobium had no significant effect on its thermal behavior and stability. By impedance spectroscopy the electrical properties of the samples are investigated. It was found that Bi2NiTaNbO9 exhibits dielectric properties. At room temperature and 1 MHz the sample exhibits dielectric permittivity with the value equals to 40–41 (dielectric loss tangent is 0.01). The sample capacitance weakly depends on temperature and frequency. The conduction activation energy is 1.34 eV. Doping with Nb(V) ions improves the sample dielectric characteristics.

Phase-transition kinetics of calcium-doped TiO2: A high-temperature XRD study

Controlling titanium dioxide crystallinity is crucial in view of the possible oxide applications. In this study, we examined the effects of calcium doping on the anatase-rutile phase transition via in-situ high-temperature X-ray diffraction. The phase transition temperature of calcium-doped TiO2 was approximately 900 °C, specifically 900 °C, 875 °C, and 900 °C for the 2%, 4%, and 6% calcium-doped TiO2, respectively. The larger radius of the calcium ion compared to that of the titanium ion hindered the calcium incorporation into the TiO2 lattice. Moreover, the hampered titanium-oxygen bond rotation during the phase transition led to an increase in the phase-transformation temperature. Furthermore, at higher calcium concentrations, the corresponding activation energies increased first and then decreased. This may have been controlled by the decreasing nucleation rate during the reaction.

Oxygen-Deficient (Ln,Sr)2NiO4- δ Nickelates for Oxygen Electrodes of Solid Oxide Fuel and Electrolysis Cells: Anisotropic Thermochemical Expansion and Thermomechanical Constraints

Perovskite-like and perovskite-related oxides based on variable-valence transition metals may exhibit substantial changes in oxygen content in the course of temperature cycling or under variation of oxygen chemical potential at elevated temperatures. This gives rise to a chemical contribution to the thermal expansion (chemical expansion/contraction or chemical strain) originating mainly from the accompanying changes in the average oxidation state of transition metal cations and, consequently, their ionic radii. Excessive dimensional changes caused by the chemical expansion impose constraints on the applicability of functional oxides at elevated temperatures and under variable redox conditions (due to thermomechanical instability or incompatibility with other materials) and complicate the processing of oxide ceramics at high temperatures. Another unfavorable phenomenon is microcracking caused by a strongly anisotropic expansion of crystal lattice, with effects on the microstructural and mechanical integrity and electrical and electrochemical properties. The present work is a representative study case that focuses on layered Ln2NiO4-based ceramic materials for oxygen electrodes of solid oxide fuel/electrolysis cells (SOFC/SOEC).Ln2NiO4+δ–based oxides (Ln = La, Pr, Nd) with perovskite-related K2NiF4-type structure demonstrate high oxygen diffusivity and surface exchange kinetics in combination with comparatively high electronic conductivity and are considered, therefore, as attractive mixed ionic-electronic conductors for oxygen electrodes of high-temperature SOFC/SOEC [1]. Acceptor-type substitution of Ln3+ by Sr2+ in Ln2NiO4+ δ is compensated by comparatively high oxygen deficiency in Sr-rich Ln2-xSrxNiO4-δ phases at elevated temperatures [2,3]. The transition from oxygen excess to oxygen deficiency is expected to be accompanied by a change in the ionic transport mechanism from prevailing interstitial oxygen diffusion in rock-salt layers to oxygen vacancy diffusion in perovskite-type layers.Ceramic powders of Ln2-xSrxNiO4-δ (Ln = La, Nd, Pr, x = 1.0-1.6) were prepared by the Pechini method with final calcination steps at 1150-1200°C in oxygen. Thermogravimetric studies confirmed that acceptor-type substitution by strontium is compensated by the formation of oxygen vacancies and electron-holes and progressively increases high-temperature oxygen nonstoichiometry (Fig.1A), which reaches as high as δ = 0.36-0.40 for x = 1.6 at 900°C in air. High-temperature XRD studies demonstrated that Ln2-xSrxNiO4-δ nickelates exhibit strongly anisotropic lattice expansion interrelated with oxygen deficiency changes on heating (Fig.1B). Highly anisotropic expansion induces microcracking phenomenon, which, in turn, results in a strong hysteresis in dimensional changes (Fig.1C) and also in variations of electrical conductivity (Fig.1D) on cycling in air for the ceramic samples sintered at 1200-1300°C.An appropriate approach to minimize or neglect the undesirable effects of anisotropic expansion and microcracking is to preserve the grain size in Ln2-xSrxNiO4-δ ceramics or porous electrodes at ~1 micron or submicron level. In particular, spark plasma sintering with subsequent careful oxidation treatment was adopted to avoid grain growth and to produce mechanically stable ceramics with smooth reversible thermochemical expansion and enhanced electrical properties. Acknowledgments: This work was supported by the FCT/MCTES/FEDER (projects CARBOSTEAM (POCI-01-0145-FEDER-032295) and CICECO-Aveiro Institute of Materials (UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020), and PhD grant SFRH/BD/138773/2018).

Tempering of an additively manufactured microsegregated hot-work tool steel: A high-temperature synchrotron X-ray diffraction study

Rapidly solidified microstructures, produced by concentrated heat sources, have gained increasing attention due to the widespread expansion of additive manufacturing techniques. In laser powder bed fusion of tool steels, the as-built microstructure consists of a microsegregated network of cell-like walls decorated with retained austenite (RA). This inhomogeneous elemental distribution leads to phase transformation sequences dictated by local – instead of global – equilibrium. This work uses synchrotron X-ray diffraction to study the kinetics of retained austenite decomposition during tempering of a microsegregated as-built AISI H13 tool steel. The RA decomposition products are also characterized by hardness tests, scanning electron microscopy, and atom probe tomography. Present results evidence the formation of high temperature para-equilibrium (T < 650 °C) or equilibrium (T ≥ 650 °C) microstructures. The para-equilibrium microstructural path evidences isothermally stable RA, which transforms into fresh martensite upon cooling due to carbon depletion. However, the cell-like microsegregation arrangement is retained due to insufficient homogenization of substitutional elements. The equilibrium microstructural path results in isothermal transformation of RA into ferrite + carbides, as well as dissolution of the cell-like microsegregation structure. These results provide insights towards the understanding and development of optimized heat treatment cycles appropriate for such increasingly common inhomogeneous microstructures. The results are relevant not only to laser powder bed fusion, but also to other localized melting/remelting processes with associated high cooling rates.

Electrical conductivity studies on LAMOX based electrolyte materials for solid oxide fuel cells

In this study, the electrical conductivity of the LAMOX based electrolytes (La1.8Dy0.2Mo2-xWxO9 (x = 0, 0.1, 0.2, 0.5, and 1), and La1.8Dy0.2Mo2-xGaxO9 (x = 0.1)) synthesized by the citrate complexion method has been studied using DC four-probe method. The electrical conductivity of the electrolytes is measured in the temperature range of 800–400 °C in the air (∼100 ml min−1). The effect of W and Ga substitution at the Mo site on the electrical conductivity is evaluated. The long-term electrical conductivity stability test (time on stream) (5 h) is conducted at 650, 580, and 520 °C to study the effect of possible phase transition on electrical conductivity. A high-temperature XRD study is also conducted in the temperature range of 500–650 °C (during heating and cooling) on selected electrolyte materials (La1.8Dy0.2Mo2-xWxO9 (x = 0 and 0.1) and La1.8Dy0.2Mo2-xGaxO9 (x = 0.1)) to study the α↔β phase transition. The electrical conductivity of these electrolytes in the air at 800 °C is in the range of 5.3 × 10−2 – 14 × 10−2 S cm−1. The activation energy (EA) of these electrolytes is in the range of 1.11–1.62 eV. The VTF parameters σo, B, and To are in the range of 67.46–395.88 S cm−1 K0.5, 0.122–0.254 eV, and 247–347 °C, respectively. The La1.8Dy0.2Mo2-xWxO9 (x = 0.1) shows highest electrical conductivity (14 × 10−2 S cm−1, EA = 1.54 eV) among all electrolytes in air at 800 °C and for this material the VTF parameters σo, B, and To are 170.32 S cm−1 K0.5, 0.153 eV, and 302 °C, respectively.

Effect of rare earth on structural, morphological, vibrational, magnetic and dielectric properties of RFe0.5Cr0.5O3 (R = Nd, Eu) perovskites

RFe0.5Cr0.5O3 (R = Nd,Eu) perovskites were synthesized through solid-state reaction. The structural analysis evidences the orthorhombic symmetry of these materials in accordance with their tolerance factor. The lattice parameters, bond lengths, and bond angles, as obtained by Rietveld refinement, vary systematically with the size of R3+ cations. The structural stability and thermally activated expansion of the crystal lattice are affirmed by means of a high-temperature X-ray diffraction (HT-XRD) study. The microstructure of the prepared powders is investigated using scanning electron microscopy (SEM), as well as X-ray diffraction (XRD) through the calculation of the crystallite size. Diffuse reflectance spectra indicate that these materials behave as semiconductors, and the gap energies are calculated. Room-temperature Mössbauer spectroscopy highlights the presence of magnetic frustration phenomenon in both materials. The frequency-dependent dielectric study reveals a colossal dielectric constant in agreement with the Maxwell-Wagner relaxation mechanism resulting from intergrain boundaries, as asserted by impedance spectroscopy. The conductivity mechanism is provided by the correlated barrier hopping model for EuFe0.5Cr0.5O3 perovskite, and the non-overlapping small polaron tunneling mechanism for NdFe0.5Cr0.5O3 material. High-temperature dielectric measurements reveal two anomalous features attributed to the magnetodielectric effect and the onset of ferroelectric-paraelectric transition, respectively. Metallic behavior is identified at higher temperatures for both materials.

Synthesis of β-Bi2O3 nanoparticles via the oxidation of Bi nanoparticles: Size, shape and polymorph control, anisotropic thermal expansion, and visible-light photocatalytic activity

Bismuth trioxide (Bi2O3) is known for its simple composition but rich polymorphism that allows a number of phase-dependent physicochemical properties and technical applications. We here report our controllable synthesis of highly discrete β-Bi2O3 (tetragonal) nanoparticles (NPs) via the thermal oxidation of nearly-monodisperse Bi NPs. The size and shape (spherical and tear- or rod-like) of β-Bi2O3 NPs are tunable by the size of parent Bi NPs whereas β and α (monoclinic) polymorphs can be selectively achieved by tailoring the oxidation temperature. The phase stability of β polymorph from room temperature to 450 °C enables us to perform an in situ high-temperature XRD study on the temperature dependence of its lattice parameters, which reveals a marked thermal expansion anisotropy in β-Bi2O3 with a linear thermal expansion coefficient of +35.1 × 10−6 °C−1 in the c axis, fifteen times higher than that in the a axis. Meanwhile, the narrow band gap (2.27 eV for β vs. 2.77 eV for α) and strong visible-light absorption endow β-Bi2O3 NPs with a good photocatalytic activity for the visible-light Rhodamine B dye degradation. We expect that our work could be a valuable reference for the studies on the size, shape and polymorph control, thermal property, and photocatalytic application of Bi2O3.

Structure and properties of phases in the Cu2-ХSe-Sb2Se3 system. The Cu2-XSe-Sb2Se3 phase diagram

The phase diagram of the Cu2−XSe-Sb2Se3 system is revisited to clarify ambiguity/disagreement in previously reported data. Ternary Cu3SbSe3 and CuSbSe2 compounds were obtained. In order to confirm that the phases have been identified correctly, crystal structures were solved, and the energy band gaps measured. For the sample containing 75 mol% Sb2Se3 and 25 mol% Cu1.995Se the temperature range of the stability of the high-temperature CuSb3Se5 phase was determined for the first time. This phase is formed at 445 °С, decomposes following a peritectic reaction at 527 °С, and can be quenched. A high-temperature X-ray diffraction study of a sample containing 75 mol% Sb2Se3 and 25 mol% Cu2Se allowed us to measure the thermal expansion of the CuSbSe2 and Sb2Se3 phases present in the sample. The anisotropy of thermal expansion of CuSbSe2 is similar to that of As2S3 (orpiment); thermal expansion of Sb2Se3 is similar to that of AsS (realgar). The 6 balance equations of the invariant phase transformations involving all the ternary compounds existing in the Cu2−XSe-Sb2Se3 system were suggested for the first time. The temperature and the enthalpies of all these transformations were measured. A phase diagram of the Cu2−XSe-Sb2Se3 system was found for the first time in all the range of concentrations at temperatures from ambient to the complete melting. This diagram takes into consideration the phase equilibria that involve all the ternary compounds that are possible in this system. The liquidus of the Cu2−XSe-Sb2Se3 system was calculated according to Redlich-Kister equation; it agrees with the experimental data within 1–17 °С.

Thermal Expansion Behavior of the Alpo4- 5 Molecular Sieve- High Temperature XRD Studies

High temperature X-ray diffraction studies have been carried out on calcined AlPO4-5 molecular sieve in the temperature range 298-673K in order to study the thermal expansion behavior of this material.

In-situ high temperature XRD study on thermally induced phase changes of BiVO4: The formation of an iso-type heterojunction

Different crystal phases of BiVO4 were synthetized by co-precipitation method with ethylenediaminetetraacetic acid (EDTA). In-situ high-temperature XRD was used to study the thermal stability and (ir)reversibility of phase changes. The presence of EDTA yielded a tunable iso-type homojunction BiVO4 within 360 < T < 490 °C that is composed of two tetragonal phases.

High temperature X-ray diffraction study of the formation of Na2Ti3O7 from a mixture of sodium carbonate and titanium oxide

Na2Ti3O7 has attracted much attention in the field of anode materials for Na-ion batteries thanks to its non-toxicity and very low working potential of 0.3 V vs Na0/Na+. Building a clearer picture of its formation from cheap Na2CO3 and TiO2 starting materials is therefore of obvious interest. Here, we report new insights from an in-situ high temperature X-ray diffraction study conducted from room temperature to 800 °C, complemented by ex-situ characterizations. We were thereby able to position the previously reported Na4Ti5O12 and Na2Ti6O13 intermediate phases in a reaction scheme involving three successive steps and temperature ranges. Shifts and/or broadening of a subset of the Na2Ti6O13 reflections suggested a combination of intra-layer disorder with the well-established ordering of successive layers. This in-situ study was carried out on reproducible mixtures of Na2CO3 and TiO2 in 1:3 molar ratio prepared by spray-drying of mixed aqueous suspensions. Single-phase Na2Ti3O7 was obtained after only 8 h at 800 °C in air, instead of a minimum of 20 h for a conventional solid-state route using the same precursors. Microstructure analysis revealed ~ 15 µm diameter granules made up from rectangular rods of a few-µm length presenting electrochemical properties in line with expectations. In the absence of grinding or formation of intimate composites with conductive carbon, the specific capacity of 137 mAh/g at C/5 decreased at higher rates.