The CirPAD, a circular 1.4 M hybrid pixel detector dedicated to X-ray diffraction measurements at Synchrotron SOLEIL

Desjardins, Kewin; Mocuta, Cristian; Dawiec, A.; Réguer, Solenn; Joly, Philippe; Dubuisson, Jean Michel; Alves, F. Caseiro; Noureddine, Arafat; Bompard, F.; Thiaudière, Dominique

doi:10.1107/s1600577521012492

Cited by 12 publications

(8 citation statements)

References 25 publications

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“…The diffracted signals were acquired through the acquisition of two CirPAD detector frames at two different angular positions, in order to fill the gap between detector modules. 29 One single XRD profile was acquired every 30 s. Quantitative information was extracted from the XRD profiles by Rietveld refinement. Scanning transmission electron microscopy (STEM) using high angle annular dark field imaging (HAADF) was used to check material inhomogeneity through Zcontrast imaging in a probe corrected JEOL JEM ARM 200F.…”

Section: Samples and Experimental Methodsmentioning

confidence: 99%

“…The incidence angle of the X-ray beam on the specimen was adjusted to 10°, corresponding to the value at which the diffracted signal was optimized and free from artifacts. The diffracted signals were acquired through the acquisition of two CirPAD detector frames at two different angular positions, in order to fill the gap between detector modules . One single XRD profile was acquired every 30 s. Quantitative information was extracted from the XRD profiles by Rietveld refinement.…”

Section: Samples and Experimental Methodsmentioning

confidence: 99%

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Crystallization of Ge-Rich GeSbTe Alloys: The Riddle Is Solved

Rahier

Ran

Ramond

et al. 2022

ACS Appl. Electron. Mater.

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Among the phase-change materials, Ge-rich GeSbTe (GST) alloys are of considerable interest as they offer a much higher thermal stability than their congruent contenders, a desirable characteristic for embedded digital memories and neuromorphic devices. Up to now, the mechanisms by which such alloys crystallize and progressively switch from one resistivity state to the other remain unclear and very controversial. Using in situ synchrotron X-ray diffraction during isothermal annealing and advanced transmission electron microscopy techniques, we solve this riddle and unveil the mechanisms leading to the overall crystallization of such alloys. During annealing at 310 °C, the initially homogeneous and amorphous material undergoes a progressive phase separation, leading to the formation of Ge-rich regions of different compositions. During this decomposition, the first formed GeTe embryos crystallize and trigger the heterogeneous crystallization of the Ge cubic phase. As the phase separation proceeds, these embryos dissolve and the Ge phase gradually builds up through the nucleation of small grains. Only when this Ge cubic phase is largely formed, the remaining amorphous matrix may locally reach the Ge 2 Sb 2 Te 5 composition at which it can crystallize as large grains. Our density functional theory calculations confirm that the quite exotic Pnma GeTe structure we have experimentally identified is more stable than the regular R3m structure at nanometric sizes.

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Section: Samples and Experimental Methodsmentioning

confidence: 99%

Section: Samples and Experimental Methodsmentioning

confidence: 99%

Crystallization of Ge-Rich GeSbTe Alloys: The Riddle Is Solved

Rahier

Ran

Ramond

et al. 2022

ACS Appl. Electron. Mater.

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“…The energy selected was 8.3 keV, which was tuned using a double Si(111) crystal (3–23 keV) and two Rh-coated mirrors. A Circular Hybrid Pixel Array Detector 47 (CirPad) was used, which consists of 20 XPAD modules assembled together in a circular arch geometry, capable of covering angles up to 135° and an angular opening of 0.0115°. Due to the geometry of the CirPad, a gas blower (FMB Oxford, UK) was used to heat the capillary reactor.…”

Section: Experimental Methodsmentioning

confidence: 99%

Structural Changes of Ni and Ni–Pt Methane Steam Reforming Catalysts During Activation, Reaction, and Deactivation Under Dynamic Reaction Conditions

Tusini,

Casapu,

Zimina

et al. 2024

ACS Catal.

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Ni-based catalysts are the most widely used materials to produce H2 in large-scale methane steam reformers under stationary conditions. For domestic applications such as fuel cells, H2 production involves the exposure of the catalysts to more dynamic conditions due to the daily startup and shutdown operation mode, making Ni-based catalysts susceptible to oxidation and deactivation. In this context, we report a systematic investigation of the structural changes occurring for monometallic Ni/MgAlO x and bimetallic NiPt/MgAlO x catalysts during methane steam reforming under transient conditions, comprising catalyst activation, operation, and deactivation processes. Besides extensive catalytic tests, the samples prepared by incipient wetness impregnation were characterized by complementary methods, including N2-physisorption, X-ray diffraction, H2-temperature-programmed reduction, and electron microscopy. Next, the structure of the Ni and Pt species was monitored under reaction conditions using time and spatially resolved in situ/operando X-ray absorption spectroscopy. The results obtained show that before catalyst activation by H2-reduction, nickel diffuses into the support lattice and forms mixed oxides with magnesium. In the activated catalysts, Ni is present in the metallic state or alloyed with Pt. A clear beneficial effect of the noble metal addition was identified on both the activity and stability of the bimetallic NiPt/MgAlO x catalyst. In contrast, the pronounced oxidation and reincorporation of Ni into the support lattice were observed for the monometallic sample, and these catalyst deactivation effects are hindered in the bimetallic Ni–Pt catalyst. Overall, the outcome of our study not only helps in understanding the catalyst activation/deactivation processes at an atomic level but also provides the basis for the rational development of improved methane steam reforming catalysts.

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“…In brief, it enables performing X-ray diffraction in situ during controlled heating of the reaction mixture in a 1 mm-diameter quartz capillary opened under argon flow to mimic the conditions of ex situ lab synthesis. For these experiments, we used a circular 2D detector covering a 140° detection angle in a single acquisition . The powder was placed in a 1 mm diameter quartz capillary.…”

Section: Methodsmentioning

confidence: 99%

“…For these experiments, we used a circular 2D detector covering a 140°detection angle in a single acquisition. 25 The powder was placed in a 1 mm diameter quartz capillary. The capillary was introduced into a sample holder connected to an argon flux and placed in the center of the capillary oven.…”

Section: ■ Methodsmentioning

confidence: 99%

Galvanic Replacement and Etching of MAX-Related Phases in Molten Salts toward MXenes: An In Situ Study

Defoy,

Baron,

Séné

et al. 2023

Chem. Mater.

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Galvanic replacement in molten salts has recently been uncovered as a pathway to design new compositions of layered transition-metal carbides related to the family of MAX phases, M n+1 AlX n , where M is a transition metal, X is carbon for carbide phases, and A is mainly an element of the IIIA and IVA groups of the periodic table. These compounds can be further involved in etching processes by the removal of A elements to yield new 2D transition-metal carbides, M n+1 X n T z , the so-called MXenes, where T stands for surface groups. Although promising, the chemical modification of MAX-related materials in molten salts has been reported only for a few compounds, and little is known about the corresponding reaction mechanisms. In this work, we question the versatility of galvanic reactions in molten salts for MAX-related phases by combining for the first time in situ X-ray diffraction and in situ X-ray absorption spectroscopy during reactions in molten salts for two compounds, Ti 3 AlC 2 and Mo 2 Ga 2 C. The first one shows minute-scale transformation into molten ZnCl 2 toward Ti 3 ZnC 2 , followed by evolution into Ti 3 C 2 Cl 2 . On the contrary, we do not observe replacement but etching of Mo 2 Ga 2 C into Mo 2 GaC and then orthorhombic Mo 2 C, with a loss of the layered structure. We highlight the role of molten salt chemistry in this process and discuss the different behaviors of these two MAX-related phases versus galvanic reactivity in molten salts to open the way to new MAX compositions.

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The CirPAD, a circular 1.4 M hybrid pixel detector dedicated to X-ray diffraction measurements at Synchrotron SOLEIL

Cited by 12 publications

References 25 publications

Crystallization of Ge-Rich GeSbTe Alloys: The Riddle Is Solved

Crystallization of Ge-Rich GeSbTe Alloys: The Riddle Is Solved

Structural Changes of Ni and Ni–Pt Methane Steam Reforming Catalysts During Activation, Reaction, and Deactivation Under Dynamic Reaction Conditions

Galvanic Replacement and Etching of MAX-Related Phases in Molten Salts toward MXenes: An In Situ Study

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