Non-ambient X-ray Diffraction Research Articles

Studying phase transitions of different materials with novel non-ambient X-ray diffraction equipment

Studying phase transitions of different materials with novel non-ambient X-ray diffraction equipment

Non-ambient X-ray diffraction – a further dimension in crystallography

Non-ambient X-ray diffraction – a further dimension in crystallography

Mechanism of Solid-State Amorphization in the Fe-Si-Cu-Mg-O System

Solid-state amorphization process occurring at 600-1060 °C continuous annealing was observed by non-ambient x-ray diffraction on Fe-3%Si-0.5%Cu alloy surface with MgO as thermostable coating. The phenomenon was occurred at α→γ transformation temperatures (920-960 °C) in a layer consisting of Si solid solution in α-Fe and oxides (MgFe)2SiO4, (MgFe)O, SiO2. Amorphous state remained both during heating and cooling to 20 °C. Simulation for diffusion amorphization of Fe (Si) solid solution was proposed. Mg2Si complexes are reduced from oxides by hydrogen then transfer to solid solution and solid-state amorphization is occurred.

Thermo-Physical Parameters Determination of Nano-Crystalline Fe72.5Cu1Nb2Mo1.5Si14B9 Alloy for Twisted Magnetic Cores Heat Treatment Optimization

Thermophysical parameters of Finemet-type initially amorphous alloy produced using rapid quenching technique were determined. The temperature intervals of phase and structure changes have been obtained using calorimetry and non-ambient X-ray diffraction methods. The electric resistance data were recalculated to alloy electrical conductivity which it was recalculated to heat conductivity using the Wiedemann–Franz law. Resulting parameters were used for heat processes simulation that occurs in amorphous material of built-up transformer core during annealing in nanocrystallization temperature interval. Heat treatment of different sizes twisted magnetic cores was optimized.

Determination of critical points of amorphous Fe – Si – Nb – Cu – Mo – B alloy using non-ambient X-Ray diffraction method

Critical points of amorphous alloy of Fe – Si – Nb – Cu – Mo – B system was determined using the non-ambient x-ray diffraction method. The sample with amorphous structure was produced by planar flow casting process. Temperature range of alloy nanocrystalline state was established

The Effect of Copper and Manganese on the Amorphization Process in a Thin Fe–Si–Mg–O Film

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Experimental characterization and physics-based modeling of the temperature-dependent diffuse reflectance of plasma-sprayed Nd2Zr2O7 in the near to short-wave infrared.

Supercontinuum-laser illumination in conjunction with CO2-laser heating has been implemented to measure the near to short-wave infrared (970-1660nm) diffuse reflectance of plasma-sprayed Nd2Zr2O7 as a function of temperature. Owing to the broadband nature of this experimental technique, the diffuse reflectance of plasma-sprayed Nd2Zr2O7 has been measured at many wavelengths and has been shown to decrease with increasing temperature. A physics-based model for diffuse reflectance predicated on the crystal/electronic band structure of highly scattering semiconductor materials has been constructed to interpret the results of these measurements. Baseline materials characterization has also been performed to assist in the development of crystal/electronic band structure-optical property relationships that could be useful for the design of next-generation environmental barrier coatings. This characterization has included ambient and non-ambient x-ray diffraction as well as room-temperature, integrating-sphere diffuse reflectance spectroscopy.

In-Situ Kinetic Investigation of Calcium Aluminate Formation

Rapid in-situ non-ambient X-ray diffraction represents a powerful tool for characterizing the evolution of crystalline materials in real time. The calcium aluminate system and formation of Ca12Al14O33 (C12A7) is particularly sensitive to processing conditions. This report characterizes the kinetic pathways to thermodynamic equilibrium as a function of atmosphere (ambient, dry, and vacuum) and reactant heterogeneity (as-received, milled, and sol-gel reactants). When reactants are heterogenous (as-received and milled), intermediary phases of Ca3Al2O6 (C3A) and CaAl2O4 (CA) are observed as the route to C12A7 formation and Ca5Al6O14 (C5A3) is only observed as a decomposition product of C12A7. When reactants are heterogenous, C12A7 is only thermodynamically favorable under ambient conditions due to the stability provided by hydration. When reactants are homogenous (sol-gel), direct crystallization of C12A7 from an amorphous precursor is observed at low temperature regardless of atmosphere defining C12A7 as the kinetic equilibrium. These findings accurately define the heterogenous formation pathways and report for the first time the formation of C12A7 under a carbon-free vacuum environment.

Analysis of the Secondary Phases Formed by Corrosion of U₃Si₂-Al Research Reactor Fuel Elements in the Presence of Chloride Rich Brines.

Corrosion experiments with non-irradiated U3Si2-Al research reactor fuel samples were carried out in synthetic MgCl2-rich brine to identify and quantify the secondary phases because depending on their composition and on their amount, such compounds can act as a sink for the radionuclide release in final repositories. Within the experimental period of 100 days at 90 °C and anoxic conditions the U3Si2-Al fuel sample was completely disintegrated. The obtained solids were subdivided into different grain size fractions and non-ambient X-ray diffraction (XRD) was applied for their qualitative and quantitative phase analysis. The secondary phases consist of lesukite (aluminum chloro hydrate) and layered double hydroxides (LDH) with varying chemical compositions. Furthermore, iron, residues of non-corroded nuclear fuel (U3Si2), iron oxy hydroxides and chlorides were also observed. In addition to high amorphous contents (>45 wt %) hosting the uranium, the quantitative phase analysis showed, that LDH compounds and lesukite were the major crystalline phases. Scanning electron microscopy (SEM) and energy dispersive -Xray spectroscopy (EDS) confirmed the results of the XRD analysis. Elemental analysis revealed that U and Al were concentrated in the solids. However, most of the iron, added as Fe(II) aqueous species, remained in solution.

Corrosion of non-irradiated UAlx–Al fuel in the presence of clay pore solution: a quantitative XRD secondary phase analysis applying the DDM method

Abstract Corrosion experiments with non-irradiated metallic UAlx–Al research reactor fuel elements were carried out in autoclaves to identify and quantify the corrosion products. Such compounds, considering the long-term safety assessment of final repositories, can interact with the released inventory and this constitutes a sink for radionuclide migration in formation waters. Therefore, the metallic fuel sample was subjected to clay pore solution to investigate its process of disintegration by analyzing the resulting products and the remnants, i.e. the secondary phases. Due to the fast corrosion rate a full sample disintegration was observed within the experimental period of 1 year at 90°C. The obtained solids were subdivided into different grain size fractions and prepared for analysis. The elemental analysis of the suspension showed that, uranium and aluminum are concentrated in the solids, whereas iron was mainly dissolved. Non-ambient X-ray diffraction (XRD) combined with the derivative difference minimization (DDM) method was applied for the qualitative and quantitative phase analysis (QPA) of the secondary phases. Gypsum and hemihydrate (bassanite), residues of non-corroded nuclear fuel, hematite, and goethite were identified. The quantitative phase analysis showed that goethite is the major crystalline phase. The amorphous content exceeded 80 wt% and hosted the uranium. All other compounds were present to a minor content. The obtained results by XRD were well supported by complementary scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analysis.

On the Thermal and Thermodynamic (In)Stability of Methylammonium Lead Halide Perovskites.

The interest of the scientific community on methylammonium lead halide perovskites (MAPbX3, X = Cl, Br, I) for hybrid organic-inorganic solar cells has grown exponentially since the first report in 2009. This fact is clearly justified by the very high efficiencies attainable (reaching 20% in lab scale devices) at a fraction of the cost of conventional photovoltaics. However, many problems must be solved before a market introduction of these devices can be envisaged. Perhaps the most important to be addressed is the lack of information regarding the thermal and thermodynamic stability of the materials towards decomposition, which are intrinsic properties of them and which can seriously limit or even exclude their use in real devices. In this work we present and discuss the results we obtained using non-ambient X-ray diffraction, Knudsen effusion-mass spectrometry (KEMS) and Knudsen effusion mass loss (KEML) techniques on MAPbCl3, MAPbBr3 and MAPbI3. The measurements demonstrate that all the materials decompose to the corresponding solid lead (II) halide and gaseous methylamine and hydrogen halide, and the decomposition is well detectable even at moderate temperatures (~60 °C). Our results suggest that these materials may be problematic for long term operation of solar devices.

Structural properties of Pt/TiO2/Pt heterostructure grown on sapphire substrate—Influence of annealing processes

Simple gas sensors based on resistivity change of TiO2 thin films using combined top and bottom metallic contacts are very promising. In this work influence of ex situ annealing in ambient air on structure of TiO2 thin film stacked between two platinum contact layers has been studied. The layers were deposited using DC magnetron sputtering on unheated c-cut sapphire substrates. For lowering of the Schottky barrier at the Pt–TiO2 interfaces and for improved crystalline stability, ex situ annealing at 600 °C in air was carried out. In order to study separately influence of top and bottom platinum layers on crystal structure, also reference samples Pt/TiO2/Al2O3 and TiO2/Pt/Al2O3 have been prepared. Non-ambient X-ray diffraction measurement during annealing process and X-ray pole figures after annealing has been measured. Near epitaxial relationship was observed for bottom Pt layer grown on c-cut sapphire substrate: Pt(1 1 1)[11¯0]||Al2O3(0 0 0 1)[11¯00]. Inner titania layer shows randomly oriented both TiO2-rutile (R) and anatase (A) phases with the volumetric ratio of R/A ∼ 2.7. If prepared without top Pt contact layer, the TiO2 transforms during annealing to random single anatase phase. The TiO2 layer overgrown with only single Pt top contact layer shows randomly oriented both rutile and anatase phases with volumetric ratio R/A ∼ 2.3. The top Pt layer on TiO2 shows filamentary uniaxial orientation Pt(1 1 1)||Al2O3(0 0 0 1). The interdiffusion at the Pt–TiO2 interfaces extends to several nm.

In-situ non-ambient X-ray diffraction studies of indium tungstate

In situ variable temperature and high pressure X-ray diffraction studies were carried out on indium tungstate (In2W3O12). This material displays positive volume expansion in both its low temperature monoclinic and high temperature orthorhombic phases, with negative thermal expansion along the a axis and positive thermal expansion along the b and c axes. Upon hydrostatic compression in a diamond anvil cell, one crystalline to crystalline phase transition is observed in the range 1.9 to 2.7GPa, and progressive irreversible amorphization occurs at pressures above 4.3GPa. The crystalline high pressure phase appears to be isostructural to previously observed high pressure phases in other A2M3O12 compounds.

Anomalous phase transitions of lead-free piezoelectricxNa0.5Bi0.5TiO3−(1−x)BaTiO3solid solutions with enhanced phase transition temperatures

Temperature-dependent structural phase transitions and dielectric properties for a series of xNa(0.5)Bi(0.5)TiO(3)-(1-x)BaTiO(3) (NBT-BT) samples where x ranges from 0.05 to 0.30 have been investigated. Non-ambient x-ray diffraction together with dielectric data as a function of temperature have demonstrated an enhancement in the ferroelectric to paraelectric phase transition temperature with the increase in NBT content, including inhibition of two well-known low-temperature polymorphic phase transitions of BaTiO(3). Anomalous dielectric response has been observed for samples with x >= 0.20 suggesting a crossover from a first-order to a second-order phase transition. The critical point lies between x=0.15 and x=0.20. Deviation from the classical Curie-Weiss law has been seen for samples having x >= 0.10. A modified Curie-Weiss law was employed to model the dielectric response in the paraelectric phase and the maximum value of the critical exponent gamma was found to be 1.45 for x=0.30. It is suggested that the dielectric properties are heavily influenced by the induced strain upon doping rather than chemical inhomogeneities and structural disorder, which are common occurrences in doped ferroelectrics.

Structural investigation of a novel perovskite-based lead-free ceramics: xBiScO3−(1−x)BaTiO3

A full structural investigation was carried out on novel lead-free piezoelectric solid solutions of xBiScO3−(1−x)BaTiO3 (BS-BT) between x=0.0 and 0.35 utilizing x-ray and neutron powder diffraction. This particular system demonstrated an extended tetragonal-pseudocubic phase boundary at room temperature in the region 0.05≤x≤0.20. Rietveld refinements were performed on the neutron powder diffraction data to obtain detailed crystallographic information across the phase diagram of this binary system. The best model to describe the phase boundary was found to be a mixture of tetragonal (P4mm) and strongly pseudocubic rhombohedral (R3m) phases. Non-ambient x-ray diffraction patterns were collected in the temperature range of −253 to 325 °C to elucidate the effect of incorporation of BiScO3 on the temperature-dependent structural phase transitions of BaTiO3. Interestingly, the BS-BT system for x≥0.05 demonstrated only one structural phase transition, which is the ferroelectric to paraelectric phase transition, suppressing the other two low temperature phase transitions. High-temperature dielectric properties were also studied in order to examine the physical properties of the ceramics.

Grain growth in nanocrystalline copper thin films investigated by non-ambient X-ray diffraction measurements

The microstructure evolution (crystallite size and microstrain) as well as the residual stress of Cu thin films of various thicknesses (250 nm, 500 nm, and 1 μm) on passivated Si substrates during isochronal annealing was investigated by in situ X-ray diffraction measurements in the temperature range between 25 °C and 250 °C. Before annealing, the thermoelastic behavior was investigated excluding the occurrence of thermally activated relaxation processes occurring above ambient temperature by in situ stress measurements below ambient temperature. On this basis, above ambient temperature, effects of stress relaxation and emerging secondary stresses (due to grain growth and annihilation of crystal defects, giving rise to a considerable tensile stress contribution development) could be identified for all three layers in the temperature regime between ambient temperature and 250 °C. Grain growth in the nanocrystalline thin films started at much lower temperatures as compared to coarse-grained materials. The results were discussed in terms of the effects of different driving forces and grain-boundary mobilities acting in nanocrystalline materials.

Crystal structures and chemistry of double perovskites Ba 2M(II) M′(VI)O 6 ( M=Ca, Sr, M′=Te, W, U)

Structures of the double perovskites Ba 2 M(II) M ′(VI)O 6 ( M=Ca, Sr, M′=Te, W, U) at room temperature have been investigated by the Rietveld method using X-ray and neutron powder diffraction data. For double perovskites with M=Sr, the observed space groups are I2/ m ( M′ =W) and R 3 ¯ ( M′=Te), respectively. In the case of M=Ca, the space groups are either monoclinic P2 1/ n ( M′=U) or cubic Fm 3 ¯ m ( M′=W and Te). The tetragonal and orthorhombic symmetry reported earlier for Ba 2SrTeO 6 and Ba 2CaUO 6, respectively, were not observed. In addition, non-ambient X-ray diffraction data were collected and analyzed for Ba 2SrWO 6 and Ba 2CaWO 6 in the temperature range between 80 and 723 K. It was found that the rhombohedral R 3 ¯ structure exists in Ba 2SrWO 6 above room temperature between the monoclinic and the cubic structure, whereas the cubic Ba 2CaWO 6 undergoes a structural phase transition at low temperature to the tetragonal I4/ m structure.

D-36 Grain Growth and Texture Sharpening in Copper, Nickel and Palladium Thin Films, Investigated by Non-Ambient X-ray Diffraction Measurements

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Non-ambient X-ray diffraction residual stress analysis of thin films: tracing nanosize-related effects on thermoelastic constants and identifying sources of residual stresses

The stress evolutions at non-ambient temperatures in Ni and Pd layers (the thickness of each metal layer was 50 nm) were investigated employingin-situX-ray diffraction measurements in a temperature range between 173 and 523 K. Stress determinations were performed by analysing the X-ray diffraction data according to the sin2ψmethod on the basis of the crystallite group variant. The stress evolution in the Ni layer was correlated with the change of its coherently diffracting domain size and its microstrain with temperature. The advantage of measurements at temperatures below ambient to distinguish the thermal stresses from the effects of stress relaxation and emerging secondary stresses, arising from thermally activated processes (such as grain growth), is highlighted in this work for the first time. The possibility of using thein-situX-ray diffraction stress measurement to obtain coefficients of thermal expansion and thermoelastic slopes of thin films (with nanosized grains) is discussed in detail.

Coefficients of thermal expansion of thin metal films investigated by non-ambient X-ray diffraction stress analysis

Cu, Ni and Pd layers were deposited by DC-magnetron sputtering on Si wafer substrates. The mechanical stresses and the coefficients of linear thermal expansion (CTEs) were investigated by non-ambient (in-situ) X-ray diffraction measurements employing the sin 2 ψ crystallite group method. It was found that, in the as-produced state, the CTEs were larger than expected on the basis of literature values for the Cu and Ni layers, but not for the Pd layer. Upon annealing of the layers grain growth and decrease of the crystalline imperfection, monitored by in-situ X-ray diffraction measurements of the diffraction line broadening, occurred. The increase of the crystallite size was paralleled by a decrease of the CTE values for the Cu and Ni films. The grain-size dependence of the CTE is discussed in terms of the coordination (state of bonding) of atoms at grain boundaries and surfaces.