High-temperature X-ray Diffraction Analysis Research Articles

Features of Phase Transformations of Low-activation 12%-Chromium Ferritic-Martensitic Steel Ek-181

An investigation of the features of structural-phase transformations during heating and cooling of the lowactivation 12%-chromium ferritic-martensitic steel EK-181 (Fe–12Cr–2W–V–Ta–B) is performed in the range of temperatures from 30 to 1100°C by the methods of high-temperature X-ray diffraction analysis (XRD) in situ. The critical points of an (α →γ) - transformation (Ас1 ≈ 850°С, Ас3 ≈ 950°С) in the course of steel heating and the temperature interval (910–890°C) of the diffusion-induced transformation of the austenite →α-ferrite type under cooling are determined. It is shown that the position of these points changes depending on the method (XRD or differential scanning calorimetry) of their identification, which is attributed to the differences in their heating-cooling rates. During heating in the range of temperatures of 830–875°C, a significant increase in the volume fraction of М23С6 carbides is observed. Further temperature increase up to 1000–1100°C leads to their complete dissolution. In the course of cooling of the steel specimens from 1100 to 30°C, there is no carbide particle precipitation.

Effect of Gd addition on phase composition, structure, and properties of beta-solidifying TiAl-based alloy with Zr and Cr content variability

The aim of the present work was to study the influence of Gd microaddition on the sequence and temperatures of phase transformations as well as on the microstructural evolution and properties of a new six-component TiAl-based alloy Ti-44.5Al-2V-1Nb-xZr/yCr-(0 … 0.1)Gd (at.%) with variable Zr (x = 0.5–1.5 at.%; eq. 1.2–3.5 wt%) and Cr (y = 1.5–2.5 at.%; eq. 2.0–3.5 wt%) content in the as-cast condition using thermodynamic calculations in Thermo-Calc software and experimental methods including differential scanning calorimetry, in-situ high-temperature X-ray diffraction analysis, optical, scanning, and high-resolution transmission microscopy. It was demonstrated that in all compositions of the studied alloy the sequence of phase transformations at high temperature interval includes L→β, β→α, and α→γ transformations, passing through the single-phase β and α fields. These are then followed by a three-phase eutectoid reaction α→α2+γ in Zr-containing compositions and further by a four-phase α→α2+γ+β reaction in Cr- and (Zr+Сr)-containing compositions. It has been revealed that the addition of 0.1 at.% Gd does not change the sequence and temperatures of these phase transformations. Nevertheless, the formation of nano-particles, identified as base-centered monoclinic Gd2O3 oxide located in Zr-containing compositions inside the γ lamellae and in Cr- and (Zr + Cr)-containing compositions on the boundaries of the γ lamellae and inside the β phase interlayers and being coherent with the β0 phase, results in reduction of (α2+γ) colony size in the as-cast condition (VAR + VAR + VIM) down to 100 ± 10 μm. It has been also found that ultimate tensile strength and plastic elongation in Zr- and Cr-containing compositions of the studied alloy in the as-cast condition measured at room temperature are 473 ± 8 MPa, 1.1 ± 0.1% and 513 ± 10 MPa, 1.4 ± 0.1%, respectively. The addition of 0.1 at.% Gd results in plastic elongation increasing to (1.3–1.6)±0.1%, while remaining the strength unaffected.

Environmentally sustainable facile synthesis of nanocrystalline holmium hafnate (Ho2Hf2O7): Promising new oxide-ion conducting solid electrolyte

A2B2O7 oxides with defect-fluorite structure are one of the potential candidates for solid oxide fuel cell electrolyte material due to their excessive thermodynamic stability in oxygen potential gradient at elevated temperature between 500 and 900 °C. Holmium hafnate nanoparticles have been synthesised through the Leeds Alginate Process (LAP) using inorganic salts of holmium and hafnium as starting materials immobilized in alginate beads. Ion exchange with sodium alginate and its subsequent thermal treatment have been used to prepare the nanopowder of Ho2Hf2O7. Thermal decomposition of dried beads is carried out at 700 °C for 2 h and 6 h to obtain the nanoparticles of Ho2Hf2O7. This calcination temperature was determined after carrying out simultaneous thermogravimetric analysis and differential scanning calorimetry (TGA/DSC). High Temperature X-ray Diffraction (HT-XRD) was carried out to gain further insight into the thermal decomposition process in static ambient environment. HT-XRD analysis corroborated with the results obtained from TGA/DSC. Nano-crystalline powder of single phase Ho2Hf2O7 has been obtained by calcination of oven dried ion-exchanged alginate beads in relatively low temperature range of 500–700 °C. Rietveld refinement of X-ray diffraction (XRD) data confirmed the formation of single phase defect fluorite structure of Ho2Hf2O7. The crystallographic parameters calculated from TEM and XRD analysis are in excellent agreement with each other. Furthermore, TEM–EDX analysis confirms that the Ho2Hf2O7 synthesised by the facile alginate process is nearly stoichiometric. Raman spectroscopy gives evidence of the presence of oxide-ion vacancy in holmium hafnate which is supported with ac-impedance spectroscopy measurement at selected three temperatures. The present study suggests that the LAP has the capability of yielding on a large scale single phase defect-fluorite nanoparticles of electrolyte materials for solid oxide fuel cells in environmentally sustainable, economical and energy efficiently manner.

Mechanism of stress relaxation and phase transformation in additively manufactured Ti-6Al-4V via in situ high temperature XRD and TEM analyses

Additive manufacturing is being increasingly used in the fabrication of Ti-6Al-4V parts to combine excellent mechanical properties and biocompatibility with high precision. Unfortunately, due to the build-up of thermal residual stresses and the formation of martensitic structure across a wide range of typical processing conditions, it is generally necessary to use a post-thermal treatment to achieve superior mechanical performance. This investigation aims to obtain a deeper understanding of the micro/nanostructural evolution (α′ martensite phase decomposition), accounting for the kinetics of phase transformation during the heat treatment of 3D-printed Ti-6Al-4V alloy. As the mechanism of phase transformation and stress relaxation is still ambiguous, in this study the changes in crystal lattice, phase, composition and lattice strain were investigated up to 1000°C using both in situ high temperature X-ray diffraction (XRD) and transmission electron microscopy (TEM). Based on the result a mechanism of phase transformation is proposed, via the accommodation/substitution of Al, V and Ti atoms in the crystal lattice. The proposed mechanism is supported based on elemental concentration changes during heat treatment, in combination with changes in crystal structure observed using the high temperature XRD and TEM measurements. This study provides a deeper understanding on the mechanism of phase transformation through martensitic decomposition, as well as a deeper understanding of the influence of post-thermal treatment conditions on the alloy's crystal structure.

Novel approach to thermal degradation kinetics of gypsum: application of peak deconvolution and Model-Free isoconversional method

In this work, we have reinvestigated the thermal degradation kinetics of synthetic gypsum (CaSO4·2H2O) using a novel approach based on peak deconvolution followed by the application of Model-Free isoconversional method. Gypsum was prepared using wet chemical route and characterized by conventional X-ray diffraction, in situ high-temperature X-ray diffraction (HT-XRD), infrared spectroscopy (IRTF-ATR), simultaneous thermal gravimetry, and differential thermal technique (TG/DTA). The physicochemical analysis showed that gypsum thermally degrades into calcium sulfate anhydrite (γ-CaSO4; anhydrite III) via an intermediate phase formed by calcium hemihydrate (CaSO4·0.5H2O; bassanite). HT-XRD analyses revealed the difference between the bassanite and anhydrite III phases, although they have a similar structure. The thermal kinetics of gypsum indicated a complex behavior of overall process mechanism consisting of overlapping contributions, which were separated into two individual ones using a mathematical deconvolution of Fraser Suzuki function. The separate thermal processes were analyzed using Model-Free isoconversional and Malek’s methodology. The kinetic results showed that both processes may be represented by Johnson–Mehl–Avrami [JMA(n)] equation which corresponds to nucleation and growth mechanisms, with n > 1. The first process corresponding to the partial dehydration of gypsum into bassanite was carried out by a two-dimensional JMA mechanism, while the second process, attributed to the complete dehydration of gypsum, was performed according to a three-dimensional JMA. Calculations of thermodynamic parameters have shown that the dehydration process of gypsum is accompanied by endothermic effects and requires heat, in agreement with the thermal analysis data.

Electrochemical- and Crystallographic Operando Characterization of La0.75Sr0.25Cr0.5Mn0.3Ni0.2O3 -δ Anode Infiltrated into Sc0.2Ce0.01Zr0.79O2 -δ Electrolyte Scaffold

An operando measurement cell has been used in this work for simultaneous monitoring of electrochemical (EC) properties using electrochemical impedance spectroscopy and crystallographic structure using high temperature (HT) X-ray diffraction analysis (XRD) of La0.75Sr0.25Cr0.5Mn0.3Ni0.2O3−δ (LSCMN) anode at working conditions, i.e. redox conditions. Gradual reversible increase of Sc0.2Ce0.01Zr0.79O2−δ (ScCeSZ) lattice parameter in reducing atmosphere and oxide ion flux through the membrane has been demonstrated. Reversible changes in LSCMN lattice parameters due to reducing gas atmosphere has been observed. Finally, partially reversible degradation of LSCMN electrode has been demonstrated.

Reaction Rate Enhancement for Cu(In,Ga)Se2 Absorber Materials Using Ag-Alloying

The addition of Ag to Cu-Ga-In precursors for synthesizing (Ag,Cu)(In,Ga)Se2 (ACIGS) thin films has shown benefits including improved adhesion, greater process tolerance, and potential for improved device performance. In this study, reaction pathways to form Cu(In,Ga)Se2 (CIGS) and ACIGS were studied by time-progressive reactions at 450 °C in a 5% Ar/H2Se atmosphere followed by ex situ characterization. Results indicated that the addition of 25% Ag/(Ag+Cu) to the CIGS film reduces the reaction time by 50%. X-ray diffraction (XRD) analysis of CIGS films showed that the CuInSe2 phase initially formed after 3.5 min. The slow reaction of the stable γ-Cu9(In,Ga)4 phase, however, required more than 20 min to complete. Importantly, the addition of Ag to the CIGS film accelerated the reaction. Energy-dispersive X-ray spectroscopy shows that Ga/(Ga+In) grading occurs in the first 10 min of the reaction. XRD analysis showed that the chalcopyrite phase fully forms after 10 min and no significant changes were observed in samples selenized from 10–45 min. Reaction pathways of Ag-alloyed films were further characterized using in situ high temperature XRD analysis. The onset temperature of Se reaction was detected at 230 °C and a AgIn2 phase transformation to (Ag,Cu)In2 occurred during the early stage of the reaction.

Insight into the Thermal Behavior of Tourmaline Mineral

The thermal behavior of tourmaline mineral during the whole process from solid state at room temperature to molten salt at high temperature and back to solid state at room temperature has been systematically investigated. Surface characterization based on observation of the sintering point, thermogravimetry-differential scanning calorimetry, high-temperature x-ray diffraction analysis, field-emission transmission electron microscopy, and high-temperature Raman spectrometry did not reveal any significant changes in the crystal structure of tourmaline except for a slight decrease in grain size during the heating process from room temperature to 890°C. Further increase in the temperature to 1050°C resulted in a phase transformation into cordierite along with a sharp decrease in grain size; the phase transformation was complete at 1200°C. When the temperature was decreased to 890°C, the tourmaline phase was observed to precipitate in the molten salt, and the grain size was found to grow gradually. A continuous decrease in temperature resulted in more tourmaline with slightly smaller grain size due to the pinning effect at second-phase grain boundaries.

Understanding the effect of Ce and Zr on chemical expansion in yttrium doped strontium cerate and zirconate by high temperature X-ray analysis and density functional theory

Aliovalent cation-doped perovskite-type oxides (ABO3) exhibit proton conductivity originating from the hydration of oxide ion vacancies, which is accompanied by structural deformation, i.e. chemical expansion. The chemical expansion may lead to failure in electrochemical devices, and thus it is necessary to understand the causes of this process at the atomic scale. In this study, the chemical expansion behaviors of Y-doped strontium cerate and zirconate were comparatively investigated. High-temperature X-ray diffraction (HT-XRD) and thermogravimetric analysis (TGA) revealed that the cerate exhibits larger chemical expansion. Density Functional Theory (DFT) calculations revealed that this tendency can be accounted for by the different atomic distribution of the Y dopant between the cerate and zirconate, which results in differences in the size of the oxide ion vacancies to be hydrated as well as different elastic character.

Change of phase composition during isothermal treatment of steels aluminium and silicon alloyed

Abstract The change in the volume and composition of phases during of isothermal treatment of Cr-Ni-Mo steels was investigated by methods of high-temperature X-ray diffraction analysis. Redistribution of carbon between phases is investigated. It is shown the influence of silicon and aluminium on these processes. The research made it possible to recommend steel compositions and isothermal treatment to obtain a large volume of retained austenite with a high carbon content to provide TRIP effect.

Non stoichiometry and lattice expansion of BaZr0.9Dy0.1O3-δ in oxidizing atmospheres

The changes in lattice parameter and oxygen non-stoichiometry in BaZr0.9Dy0.1O3-δ (BZDy10) were studied by high temperature X-ray diffraction (HT-XRD) and thermogravimetric analysis (TGA) as a function of temperature at three oxygen partial pressures. The experiments were performed under dry conditions to prevent the competition with the hydration reaction. The decrease of the lattice parameter with increasing oxygen partial pressure confirms the oxidation from Dy3+ to Dy4+ with the consumption of oxygen vacancies. The change in oxygen non-stoichiometry (∆δ) measured by TGA showed similar trends: δ decreases with increasing oxygen partial pressure, in agreement with the oxidation of the dysprosium cations. The changes in Dy3+ concentration were estimated from the lattice strain, and in combination with the TGA data, were found to be consistent with a defect model where changes in oxygen non-stoichiometry are compensated fully by Dy valence changes rather than by oxygen-site polarons. Comparison of XRD and TGA data also enabled determination of isostoichiometric coefficients of thermal expansion (6.68–7.44·10−6/°C, below 450 °C, depending on gas atmosphere) and isothermal coefficients of chemical expansion (~0.06) for dry BZDy10.

Structural Changes in Ytterbium Ferrite YbFe2O4 in the Temperature Range From–150 °C TO 300 °C

Structural changes and thermal expansion of the iron ferrite sample YbFe2O4 of a rhombohedral modification are studied by high-temperature X-ray diffraction and differential thermal analysis. It is demonstrated that no phase transitions are observed in the temperature range from–150 °C to 300 °С. There are only anisotropic changes in unit cell parameters due to changes in Yb–O and Fe–O bond lengths.

The effect of process parameters on the amorphous citrate sol-gel synthesis of Cu-doped Ca12Al14O33

Ca12Al14O33 (C12A7) is a highly functional material due to its ability to act as an anionic source and its conversion from a wide band-gap insulator to a conductive oxide material as a function of processing. Cationic doping, on the order of 1 mol%, of C12A7 has been shown to have profound effects on the physical properties of the material. One such cation, Cu, increases the catalytic efficiency and drastically alters the electronic landscape. The amorphous citrate sol-gel synthesis technique is widely used to synthesize doped C12A7 materials as it promises homogeneous cationic dispersion and a fine and controlled grain size. This promise relies on the formation of a homogeneous citrate resin of cationic citrate species, homogeneous decomposition of cation citrate species, and homogeneous crystallization of the desired phase. In this report, theoretical complex diagrams are calculated to determine the optimal pH for citrate resin formation in the Cu-C12A7 system. The resin decomposition and crystallization kinetics are characterized through high-temperature X-ray diffraction and thermogravimetric analysis. The optimal pH range for the citrate resin homogeneity was theoretically determined to be a range from 3 to 6, and experimental characterization shows that raising the pH from < 1 to 4 leads to Cu-C12A7 phase purity, reduces grain size by 30%, and inhibits CaCO3 formation to lower the synthesis temperature from ∼900 °C to 840 °C. This report highlights the importance of sol-gel solution chemistry and the corroboration of XRD analysis with microstructural analysis

In situ high-temperature X-ray diffraction, FT-IR and thermal analysis studies of the reaction between natural hydroxyapatite and aluminum powder

The present work focuses on the study of the effects of mechanical activation on the reaction between hydroxyapatite (HAp) and aluminum metal powder using Algerian phosphate (natural HAp) as a starting raw material. Aluminum metal powder was used to obtain reinforced (HAp) composites materials with alumina. The alumina phases result from the oxidation of aluminum powder at high temperature. The reactions and phase transformations between HAp and aluminum powder were studied using thermal techniques (DTA/TG), X-ray diffraction (in situ HTXRD and standard), infrared spectroscopy (FT-IR) and SEM analysis. After mechanical treatment for different milling time, no new phases were formed from HAp and Al after 40 h of milling at room temperature. However, all mixture powders were milled for different time showing the formation of several alumina transitions during heat treatment. The oxidation of Al powder, the formation of alumina transitions (χ and κ-Al2O3), α-alumina, HAp crystallization and tricalcium phosphate (β-TCP and α-TCP) formation were affected by ball milling time. After 40 h of ball milling, the aluminum was not detected at 673 K, which confirms the solid-state oxidation of aluminum at low temperatures. The results showed the formation of high amount of α-TCP at 1173 K in the samples milled for 40 h.

Low-Temperature Spark Plasma Sintering of ZrW2−xMoxO8 Exhibiting Controllable Negative Thermal Expansion

Molybdenum-doped zirconium tungstate (ZrW2−xMoxO8) has been widely studied because of its large isotropic coefficient of negative thermal expansion (NTE). However, low density and poor sinterability limit its production and application. In this study, relative density greater than 90% single-phase ZrW2−xMoxO8 (0.0 ≤ x ≤ 1.0) sintered bodies were fabricated by spark plasma sintering (500–600 °C for 10 min) using ZrW2−xMoxO7(OH)2·2H2O precursor powders as the starting material. High-temperature X-ray diffraction and thermomechanical analysis were used to investigate the change in the order–disorder phase transition temperature of the sintered materials; it gradually dropped from 170 °C at x = 0.0 to 78 °C at x = 0.5, and then to below room temperature at x ≥ 0.7. In addition, all sintered bodies exhibited NTE behavior. The NTE coefficient was controllable by changing the x value as follows: from −7.85 × 10−6 °C−1 (x = 0) to −9.01 × 10−6 °C−1 (x = 0.6) and from −3.22 × 10−6 °C−1 (x = 0) to −2.50 × 10−6 °C−1 (x = 1.0) before and after the phase transition, respectively. Rietveld structure refinement results indicate that the change in the NTE coefficient can be straightforwardly traced to the thermodynamic instability of the terminal oxygen atoms, which only have one coordination.

High-Temperature Investigations of Ytterbium Manganite YbMnO3

Samples of mechanically activated ytterbium manganite with a hexagonal crystal structure have been investigated for the first time by the methods of high-temperature X-ray diffraction and thermal analysis in the temperature range from room temperature to 1200°С. Structural transitions have been revealed from the space group P63сm into P63/mmс in the temperature range of 1100–1180°С. Structural analysis of the two modifications of the ytterbium manganite—high-temperature, with the space group P63/mmс, and low-temperature, with the space group P63сm,—has been performed. The specific features of the oxidation–reduction processes in the initial and mechanoactivated samples of the ytterbium manganite have been studied. The data obtained made it possible to refine the limits of the stability of the low-temperature modification, which possesses ferroelectric properties.

In-Situ Synthesis of Carbon-Coated Porous Silicon for Li-Ion Batteries Via Inorganic CO2 Reduction Route with Magnesium Silicide

Carbon coating step in silicon (Si) anode research has been considered as a necessity in order to enhance cycling performance by increasing electronic conductivity and bolstering stable Solid-Electrolyte Interphase (SEI) layer between Si host and liquid electrolytes1-5. Many strategies have been employed to deposit carbon layer on the surface of Si, including chemical vapor deposition (CVD), sol-gel/carbonization method, etc. Although those processes can offer uniform coating on diverse types of Si nanostructures (nanowires, nanotubes, and nanoparticles) with improved battery performance, they require costly procedures; sophisticated equipment and, oftentimes, toxic precursors, that make the overall fabrication process unsuitable to scale up and advance towards commercialization. In this work, we demonstrate a novel strategy that can abridge the additional carbon coating step and yet simultaneously obtain carbon coating and porous structure on Si host via simple/one-pot thermal treatment where CO2 is reduced down to carbon by inorganic magnesium silicide (Mg2Si). Based on the Ellingham diagram which describes oxidative nature of pure metallic elements, Mg has a strong tendency of reducing other oxygen-containing molecules, such as CO2 or silica (SiO2). The Gibbs free energy of the CO2 reduction reaction with Mg2Si is estimated to be -519 kJ/mol at 700 oC, indicating a thermodynamically feasible process. During the thermal treatment, CO2 gas and Mg2Si powder undergo spontaneous redox reaction and result in composite of MgO, Si, and C, confirmed by in-situ high temperature X-ray diffraction analysis. In this redox reaction, element Mg act as a reductant that takes O atoms away from CO2 molecules, leaving elemental carbon layer between MgO and Si. After the MgO removal (sacrificing template for porous structure) via acid leaching, microstructural characterization reveals porous structures in Si host and uniform carbon layers (thickness: 20 ~ 40 nm) on the Si surface. Most importantly, obtaining micron-sized Si with macro-porous structures, the tap density of the material is 3~4 times higher than commercially available nano Si powder, which is greatly beneficial to develop Li-ion batteries with high volumetric densities. Cycling performance tests with CR2032-type coin cell (vs. Li/Li+) also show high initial coulombic efficiency (85~88%), good rate capability (>1000 mAh/g at 1.0 C-rate), and excellent long-term cycling performance (~1300 mAh/g after 300 cycles at 0.5 C-rate & ~1000 mAh/g after 500 cycles at 1.0 C-rate). 1 Lu, Z. et al. Nonfilling Carbon Coating of Porous Silicon Micrometer-Sized Particles for High-Performance Lithium Battery Anodes. ACS Nano 9, 2540-2547, doi:10.1021/nn505410q (2015). 2 de Guzman, R. C., Yang, J., Cheng, M. M.-C., Salley, S. O. & Simon Ng, K. Y. Effects of graphene and carbon coating modifications on electrochemical performance of silicon nanoparticle/graphene composite anode. Journal of Power Sources 246, 335-345, doi:http://dx.doi.org/10.1016/j.jpowsour.2013.07.100 (2014). 3 Shen, L., Wang, Z. & Chen, L. Carbon-coated hierarchically porous silicon as anode material for lithium ion batteries. RSC Advances 4, 15314-15318, doi:10.1039/C4RA01255K (2014). 4 Yi, R., Dai, F., Gordin, M. L., Sohn, H. & Wang, D. Influence of Silicon Nanoscale Building Blocks Size and Carbon Coating on the Performance of Micro-Sized Si–C Composite Li-Ion Anodes. Advanced Energy Materials 3, 1507-1515, doi:10.1002/aenm.201300496 (2013). 5 Gao, P., Tang, H., Xing, A. & Bao, Z. Porous silicon from the magnesiothermic reaction as a high-performance anode material for lithium ion battery applications. Electrochimica Acta 228, 545-552, doi:http://dx.doi.org/10.1016/j.electacta.2017.01.119 (2017).

Synthesis and Characterization of Yttria-Stabilized Zirconia Nanoparticles Doped with Ytterbium and Gadolinium: ZrO2 9.5Y2O3 5.6Yb2O3 5.2Gd2O3

Defect cluster thermal barrier coatings (TBCs) are attractive alternatives to Yttria-stabilized zirconia (YSZ) in advanced applications. In this study, YSZ nanoparticles doped with ytterbium and gadolinium (ZrO2 9.5Y2O3 5.6Yb2O3 5.2Gd2O3 (ZGYbY)) were synthesized through a chemical co-precipitation and calcination method, and characterized by in situ high-temperature X-ray diffraction analysis in the temperature range of 25 °C to 1000 °C (HTK-XRD), thermogravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy, Raman spectroscopy, and field emission scanning electron microscopy (FE-SEM). Precise cell parameters of t-prime phase and the best zirconia phase for TBC applications were calculated by Cohen’s and Rietveld refinement methods. Optimum crystallization temperature of the precursor powder was found to be 1000 °C. Furthermore, FE-SEM results for the calcined ZGYbY powders indicated orderly particles of uniform shape and size with a small tendency toward agglomeration. Average lattice thermal expansion coefficient in the temperature range of 25 °C to 1000 °C was determined to be 31.71 × 10−6 K−1.

In situ high-temperature X-ray diffraction analysis of Mg2Si formation kinetics via reaction of Mg films with Si single crystal substrates

Conformal compact Mg2Si films can be formed on Si substrates (for battery, photovoltaic, thermoelectric, or other applications) via the direct reaction of Mg films with such substrates at modest temperatures (≥280 °C). In this work, in situ high-temperature X-ray diffraction (HTXRD) analyses have been used to track the reactive conversion of Mg films on Si single crystal (wafer) substrates into Mg2Si at 280–400 °C in a flowing He atmosphere. Prior reported complications associated with the evaporation or oxidation of magnesium films during heating were avoided by applying a thin (15 nm) titanium capping layer on the 1 μm thick magnesium films. The reaction of Mg films with <100> oriented and <111> oriented Si single crystals proceeded at parabolic rates with time. Similar values were obtained for the parabolic rate constants and activation energies for Mg reaction with both Si substrate orientations. These observations were consistent with solid-state diffusion through the thickening Mg2Si product as the rate-limiting step. The activation energy values obtained for Mg2Si formation were consistent with a previously reported correlation between the activation energies and melting points of other M2Si-type silicides formed by solid-state-diffusion-limited reaction with Si substrates.

Structural and magnetic studies of mechanically activated ErMnO3

The polycrystalline ErMnO3 with a hexagonal structure, synthesized by ceramic technology, and its derivative samples obtained by mechanical activation were studied by high-temperature X-ray diffraction analysis and magnetometry. It has been found that the phase transition from the polar P63cm structural modification to the centrosymmetric P63/mmc proceeds in ErMnO3 in two stages (at 650 °С and 1150 °С). Grain growth kinetics in mechanically activated ErMnO3 samples was studied; the activation energy values were determined. The magnetic phase transitions, corresponding to the antiferromagnetic ordering, were detected for all samples. The Neel point was found to decrease from 75 to 62 K with decreasing grain size from ∼300 to ∼50 nm. It was found that the electronic structure of the materials does not change noticeably upon mechanical activation. The observed lowering of the Neel temperatures in the mechanically activated samples was accounted for by multiple lattice distortions.