Unveiling the key factor for the phase reconstruction and exsolved metallic particle distribution in perovskites

Abstract The exsolution of transition metals in perovskite oxides has been actively researched for intelligent catalyst design in energy-related applications. To significantly increase the amount of exsolved particles, the complete phase reconstruction from simple perovskite to Ruddlesden-Popper (R-P) perovskite is greatly desirable. However, a comprehensive understanding of key parameters affecting the phase reconstruction to R-P perovskite is still unexplored. Herein, the oxygen vacancy formation energies (Evf-O) from PrO and TO2 in Pr0.5(Ba/Sr)0.5TO3-δ (T = Mn, Fe, Co, and Ni) are proposed as the important factor in determining the type of phase reconstruction in perovskites. Furthermore, using in-situ temperature & environment-controlled X-ray diffraction measurements, we mapped out the phase diagram and found the optimum ‘x’ range required for the complete phase reconstruction to R-P perovskite (x ≥ 0.3) in Pr0.5Ba0.5-xSrxFeO3-δ (PBSF) system. Among PBSF, the (Pr0.5Ba0.2Sr0.3)2FeO4+δ – Fe metal (R-PBSF30) has the smallest size of exsolved Fe metal particles when the phase reconstruction occurs from simple perovskite under reducing condition. The exsolved nano-Fe metal particles exhibited high particle density and are well-distributed on the perovskite surface, showing great catalytic activity in fuel cell mode (1.23 W cm-2 at 800 oC) and high syngas production by co-electrolysis of CO2 and H2O (–1.62 A cm-2 at 1.5 V, 800 oC).

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Unveiling the key factor for the phase reconstruction and exsolved metallic particle distribution in perovskites

Nature Communications ◽

10.1038/s41467-021-26739-1 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Hyunmin Kim ◽

Chaesung Lim ◽

Ohhun Kwon ◽

Jinkyung Oh ◽

Matthew T. Curnan ◽

...

Keyword(s):

Particle Density ◽

Metal Particles ◽

Phase Reconstruction ◽

X Ray Diffraction ◽

X Ray ◽

Syngas Production ◽

High Particle ◽

Oxygen Vacancy Formation ◽

Key Factor

AbstractTo significantly increase the amount of exsolved particles, the complete phase reconstruction from simple perovskite to Ruddlesden-Popper (R-P) perovskite is greatly desirable. However, a comprehensive understanding of key parameters affecting the phase reconstruction to R-P perovskite is still unexplored. Herein, we propose the Gibbs free energy for oxygen vacancy formation in Pr0.5(Ba/Sr)0.5TO3-δ (T = Mn, Fe, Co, and Ni) as the important factor in determining the type of phase reconstruction. Furthermore, using in-situ temperature & environment-controlled X-ray diffraction measurements, we report the phase diagram and optimum ‘x’ range required for the complete phase reconstruction to R-P perovskite in Pr0.5Ba0.5-xSrxFeO3-δ system. Among the Pr0.5Ba0.5-xSrxFeO3-δ, (Pr0.5Ba0.2Sr0.3)2FeO4+δ – Fe metal demonstrates the smallest size of exsolved Fe metal particles when the phase reconstruction occurs under reducing condition. The exsolved nano-Fe metal particles exhibit high particle density and are well-distributed on the perovskite surface, showing great catalytic activity in fuel cell and syngas production.

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Internal Stresses in Metal Matrix Composites in Relation with Matrix Phase Transformations

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.996.944 ◽

2014 ◽

Vol 996 ◽

pp. 944-950

Author(s):

Lilian Vautrot ◽

Guillaume Geandier ◽

Mickael Mourot ◽

Moukrane Dehmas ◽

Elisabeth Aeby-Gautier ◽

...

Keyword(s):

Metal Matrix Composites ◽

Metal Matrix ◽

High Energy ◽

Internal Stresses ◽

Steel Matrix ◽

Matrix Composites ◽

X Ray Diffraction ◽

Cell Parameters ◽

Key Factor

For metal matrix composites, internal stresses are a key factor for understanding the interactions between matrix and reinforcements and the mechanical properties of the composite. From in situ high energy X-ray diffraction on a steel matrix composite reinforced with TiC, the evolutions of the phase fractions and mean cell parameters of each phase during thermal treatment have been determined. In addition, a methodology is developed in order to get more information on the stress state evolutions in each phase during the treatment.

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Activation of a Cu/ZnO catalyst for methanol synthesis

Journal of Applied Crystallography ◽

10.1107/s0021889806003098 ◽

2006 ◽

Vol 39 (2) ◽

pp. 209-221 ◽

Cited By ~ 26

Author(s):

Jens Wenzel Andreasen ◽

Frank Berg Rasmussen ◽

Stig Helveg ◽

Alfons Molenbroek ◽

Kenny Ståhl ◽

...

Keyword(s):

Solid Solution ◽

Methanol Synthesis ◽

Structural Changes ◽

Catalyst Design ◽

X Ray Diffraction ◽

Structural Behaviour ◽

Intimate Contact ◽

X Ray ◽

Zno Particles

The structural changes during activation by temperature-programmed reduction of a Cu/ZnO catalyst for methanol synthesis have been studied by severalin situtechniques. The catalyst is prepared by coprecipitation and contains 4.76 wt% Cu, which forms a substitutional solid solution with ZnO as determined by resonant X-ray diffraction.In situresonant X-ray diffraction reveals that the Cu atoms are extracted from the solid solution by the reduction procedure, forming metallic Cu crystallites. Cu is redispersed in bulk or surface Zn lattice sites upon oxidation by heating in air. The results are confirmed byin situelectron energy loss spectroscopy andin situresonant small-angle X-ray scattering. The average Cu particle size in the reduced catalyst as determined by the latter technique is ∼27 Å. The observed structural behaviour may have important implications for catalyst design and operation. More than one type of Cu particle with different origins may be present in Cu/ZnO catalysts with Cu loadings higher than the solubility limit of Cu in ZnO: particles formed by extraction of Cu from the (Zn,Cu)O solid solution and particles formed by reduction of CuO primary particles. The former type is highly dispersed and in intimate contact with the surface of the host ZnO particles. The possibility of re-forming the (Zn,Cu)O solid solution by oxidation may provide a means of redispersing Cu in a deactivated catalyst.

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Time-resolved in situ X-ray diffraction study of the liquid-phase reconstruction of Mg–Al–carbonate hydrotalcite-like compounds

Journal of Materials Chemistry ◽

10.1039/b002827o ◽

2000 ◽

Vol 10 (7) ◽

pp. 1713-1720 ◽

Cited By ~ 262

Author(s):

Franck Millange ◽

Richard I. Walton ◽

Dermot O'Hare

Keyword(s):

Liquid Phase ◽

Diffraction Study ◽

Phase Reconstruction ◽

X Ray Diffraction ◽

Time Resolved ◽

X Ray

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The Use of Advanced Analytical Techniques for Characterization of the Chemical, Physical, and Crystallographic Nature of a Surface

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100071107 ◽

1973 ◽

Vol 31 ◽

pp. 132-133 ◽

Cited By ~ 1

Author(s):

R. E. Herfert

Keyword(s):

Surface Characterization ◽

Analytical Techniques ◽

X Ray Diffraction ◽

Depth Of Penetration ◽

X Ray ◽

The Past ◽

Transmission Electron ◽

Scanning Electron

Studies of the nature of a surface, either metallic or nonmetallic, in the past, have been limited to the instrumentation available for these measurements. In the past, optical microscopy, replica transmission electron microscopy, electron or X-ray diffraction and optical or X-ray spectroscopy have provided the means of surface characterization. Actually, some of these techniques are not purely surface; the depth of penetration may be a few thousands of an inch. Within the last five years, instrumentation has been made available which now makes it practical for use to study the outer few 100A of layers and characterize it completely from a chemical, physical, and crystallographic standpoint. The scanning electron microscope (SEM) provides a means of viewing the surface of a material in situ to magnifications as high as 250,000X.

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Epitaxy and texture analysis of Bi-Sr-Ca-Cu-O thin films on (100) MgO using Transmission Electron Microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100173479 ◽

1990 ◽

Vol 48 (4) ◽

pp. 68-69

Author(s):

J. T. Sizemore ◽

D. G. Schlom ◽

Z. J. Chen ◽

J. N. Eckstein ◽

I. Bozovic ◽

...

Keyword(s):

Electron Microscopy ◽

Thin Films ◽

Transmission Electron Microscopy ◽

Critical Currents ◽

Unit Cell ◽

X Ray Diffraction ◽

Cell Axis ◽

Transmission Electron ◽

Synthesis Procedure

Investigators observe large critical currents for superconducting thin films deposited epitaxially on single crystal substrates. The orientation of these films is often characterized by specifying the unit cell axis that is perpendicular to the substrate. This omits specifying the orientation of the other unit cell axes and grain boundary angles between grains of the thin film. Misorientation between grains of YBa2Cu3O7−δ decreases the critical current, even in those films that are c axis oriented. We presume that these results are similar for bismuth based superconductors and report the epitaxial orientations and textures observed in such films.Thin films of nominally Bi2Sr2CaCu2Ox were deposited on MgO using molecular beam epitaxy (MBE). These films were in situ grown (during growth oxygen was incorporated and the films were not oxygen post-annealed) and shuttering was used to encourage c axis growth. Other papers report the details of the synthesis procedure. The films were characterized using x-ray diffraction (XRD) and transmission electron microscopy (TEM).

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Coherent electron nanodiffraction from clean silver nano particles in a UHV STEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010015112x ◽

1993 ◽

Vol 51 ◽

pp. 1058-1059

Author(s):

J. Liu ◽

M. Pan ◽

G. E. Spinnler

Keyword(s):

Supported Catalysts ◽

Imaging Techniques ◽

Nano Particles ◽

Metal Particles ◽

Shape Structure ◽

Dynamical Simulations ◽

Small Metal Particles ◽

Extract Information

Small metal particles have peculiar chemical and physical properties as compared to bulk materials. They are especially important in catalysis since metal particles are common constituents of supported catalysts. The structural characterization of small particles is of primary importance for the understanding of structure-catalytic activity relationships. The shape and size of metal particles larger than approximately 5 nm in diameter can be determined by several imaging techniques. It is difficult, however, to deduce the shape of smaller metal particles. Coherent electron nanodiffraction (CEND) patterns from nano particles contain information about the particle size, shape, structure and defects etc. As part of an on-going program of STEM characterization of supported catalysts we report some preliminary results of CEND study of Ag nano particles, deposited in situ in a UHV STEM instrument, and compare the experimental results with full dynamical simulations in order to extract information about the shape of Ag nano particles.

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Devitrification products of rapidly solidified Ni-Nb amorphous alloys.

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010017788x ◽

1990 ◽

Vol 48 (4) ◽

pp. 950-951

Author(s):

G. A. Bertero ◽

W.H. Hofmeister ◽

N.D. Evans ◽

J.E. Wittig ◽

R.J. Bayuzick

Keyword(s):

Electron Microscopy ◽

Amorphous Structure ◽

Sulphuric Acid Solution ◽

X Ray Diffraction ◽

High Fracture ◽

Transmission Electron ◽

Xrd Techniques ◽

Rapidly Solidified ◽

Electromagnetically Levitated

Rapid solidification of Ni-Nb alloys promotes the formation of amorphous structure. Preliminary results indicate promising elastic properties and high fracture strength for the metallic glass. Knowledge of the thermal stability of the amorphus alloy and the changes in properties with temperature is therefore of prime importance. In this work rapidly solidified Ni-Nb alloys were analyzed with transmission electron microscopy (TEM) during in-situ heating experiments and after isothermal annealing of bulk samples. Differential thermal analysis (DTA), scanning electron microscopy (SEM) and x-ray diffraction (XRD) techniques were also used to characterize both the solidification and devitrification sequences.Samples of Ni-44 at.% Nb were electromagnetically levitated, melted, and rapidly solidified by splatquenching between two copper chill plates. The resulting samples were 100 to 200 μm thick discs of 2 to 3 cm diameter. TEM specimens were either ion-milled or alternatively electropolished in a methanol-10% sulphuric acid solution at 20 V and −40°C.

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