scholarly journals A Mechanistic Understanding of Non-Classical Crystal Growth in Hydrothermally Synthesized Sodium Yttrium Fluoride Nanowires

2020 ◽  
Author(s):  
Alex Bard ◽  
Xuezhe Zhou ◽  
Xiaojing Xia ◽  
Guomin Zhu ◽  
Matthew Lim ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Crystal Growth ◽  
Materials Science ◽  
Atom Probe ◽  
Oriented Attachment ◽  
Yttrium Fluoride ◽  
X Ray ◽  
Transmission Electron ◽  
Classical Crystal

Sodium yttrium fluoride (NaYF<sub>4</sub>) is an upconverting material with many potential uses in chemistry, materials science, and biology that can be synthesized hydrothermally in both cubic (α) and hexagonal (β) crystallographic polymorphs. Understanding the mechanisms underlying the phase conversion between the cubic and hexagonal polymorphs is of great interest to help inform future efforts to synthesize atomically-precise quantum materials with well-defined sizes and morphologies. In this work, we use a combination of analytical transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), powder X-ray diffraction (XRD), in situ liquid cell TEM, atom probe tomography (APT), and extended x-ray absorption fine structure (EXAFS) measurements to show evidence suggesting that the hexagonal NaYF<sub>4</sub> nanowires form through a non-classical crystal growth mechanism involving the formation and subsequent oriented attachment of mesocrystals consisting of cubic (α) plase units. EXAFS spectroscopy also suggests that substitutional Yb<sup>3+</sup> point defects within NaYF<sub>4</sub> are distributed evenly throughout the crystal lattice without clustering, and also that they may exhibit selective substitution into one of the two possible trivalent yttrium sites in the unit cell for hydrothermally synthesized NaYF<sub>4</sub>.

scholarly journals A Mechanistic Understanding of Non-Classical Crystal Growth in Hydrothermally Synthesized Sodium Yttrium Fluoride Nanowires

2020 ◽  
Author(s):  
Alex Bard ◽  
Xuezhe Zhou ◽  
Xiaojing Xia ◽  
Guomin Zhu ◽  
Matthew Lim ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Crystal Growth ◽  
Materials Science ◽  
Atom Probe ◽  
Oriented Attachment ◽  
Yttrium Fluoride ◽  
X Ray ◽  
Transmission Electron ◽  
Classical Crystal

Sodium yttrium fluoride (NaYF<sub>4</sub>) is an upconverting material with many potential uses in chemistry, materials science, and biology that can be synthesized hydrothermally in both cubic (α) and hexagonal (β) crystallographic polymorphs. Understanding the mechanisms underlying the phase conversion between the cubic and hexagonal polymorphs is of great interest to help inform future efforts to synthesize atomically-precise quantum materials with well-defined sizes and morphologies. In this work, we use a combination of analytical transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), powder X-ray diffraction (XRD), in situ liquid cell TEM, atom probe tomography (APT), and extended x-ray absorption fine structure (EXAFS) measurements to show evidence suggesting that the hexagonal NaYF<sub>4</sub> nanowires form through a non-classical crystal growth mechanism involving the formation and subsequent oriented attachment of mesocrystals consisting of cubic (α) plase units. EXAFS spectroscopy also suggests that substitutional Yb<sup>3+</sup> point defects within NaYF<sub>4</sub> are distributed evenly throughout the crystal lattice without clustering, and also that they may exhibit selective substitution into one of the two possible trivalent yttrium sites in the unit cell for hydrothermally synthesized NaYF<sub>4</sub>.

Non-Classical Hydrothermal Synthesis of Hexagonal Sodium Yttrium Fluoride Nanowires

2019 ◽  
Author(s):  
Alex Bard ◽  
Xuezhe Zhou ◽  
Xiaojing Xia ◽  
Guomin Zhu ◽  
Matthew Lim ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Materials Science ◽  
Atom Probe ◽  
Oriented Attachment ◽  
Yttrium Fluoride ◽  
X Ray ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Show Evidence

Sodium yttrium fluoride (NaYF<sub>4</sub>) is an upconverting material with many potential uses in chemistry, materials science, and biology that can be synthesized hydrothermally in both cubic (α) and hexagonal (β) crystallographic polymorphs. Understanding the mechanisms underlying the phase conversion between the cubic and hexagonal polymorphs is of great interest to help inform future efforts to synthesize atomically-precise quantum materials with well-defined sizes and morphologies. In this work, we use a combination of analytical and cryogenic transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), powder X-ray diffraction (XRD), in situ liquid cell TEM, atom probe tomography (APT), and extended x-ray absorption fine structure (EXAFS) measurements to show evidence suggesting that the hexagonal NaYF<sub>4</sub> nanowires form through a non-classical crystal growth mechanism involving oriented attachment of grains of the cubic (α) phase. EXAFS spectroscopy also suggests that substitutional Yb<sup>3+</sup> point defects within NaYF<sub>4</sub> are distributed evenly throughout the crystal lattice without clustering, and also that they selectively substitute into one of the two possible trivalent yttrium sites in the unit cell.

scholarly journals Revisiting the Bøggild Intergrowth in Iridescent Labradorite Feldspars: Ordering, Kinetics, and Phase Equilibria

Minerals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 727
Author(s):  
Shiyun Jin ◽  
Huifang Xu ◽  
Seungyeol Lee
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Atom Probe ◽  
Phase Region ◽  
Two Phase ◽  
Subsolidus Phase ◽  
Plagioclase Feldspar ◽  
X Ray ◽  
Transmission Electron ◽  
Scanning Transmission

The enigmatic Bøggild intergrowth in iridescent labradorite crystals was revisited in light of recent work on the incommensurately modulated structures in the intermediated plagioclase. Five igneous samples and one metamorphic labradorite sample with various compositions and lamellar thicknesses were studied in this paper. The lamellar textures were characterized with conventional transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The compositions of individual lamellae were analyzed with high-resolution energy-dispersive X-ray spectroscopy (EDS) mapping and atom probe tomography (APT). The average structure states of the studied samples were also compared with single-crystal X-ray diffraction data (SC-XRD). The Na-rich lamellae have a composition of An44–48, and the Ca-rich lamellae range from An56 to An63. Significant differences between the lamellar compositions of different samples were observed. The compositions of the Bøggild intergrowth do not only depend on the bulk compositions, but also on the thermal history of the host rock. The implications on the subsolidus phase relationships of the plagioclase feldspar solid solution are discussed. The results cannot be explained by a regular symmetrical solvus such as the Bøggild gap, but they support an inclined two-phase region that closes at low temperature.

Phase Transformations in Ti-7w/oMo-3w/oMe Alloy

1974 ◽  
Vol 32 ◽  
pp. 514-515
Author(s):  
S. Fujishiro
Keyword(s):  
Electron Microscopy ◽  
Mechanical Properties ◽  
Transmission Electron Microscopy ◽  
Tensile Strength ◽  
Mechanical Processing ◽  
Ray Method ◽  
X Ray ◽  
Transmission Electron ◽  
Water Quench ◽  
Alpha Beta

The mechanical properties of three titanium alloys (Ti-7Mo-3Al, Ti-7Mo- 3Cu and Ti-7Mo-3Ta) were evaluated as function of: 1) Solutionizing in the beta field and aging, 2) Thermal Mechanical Processing in the beta field and aging, 3) Solutionizing in the alpha + beta field and aging. The samples were isothermally aged in the temperature range 300° to 700*C for 4 to 24 hours, followed by a water quench. Transmission electron microscopy and X-ray method were used to identify the phase formed. All three alloys solutionized at 1050°C (beta field) transformed to martensitic alpha (alpha prime) upon being water quenched. Despite this heavily strained alpha prime, which is characterized by microtwins the tensile strength of the as-quenched alloys is relatively low and the elongation is as high as 30%.

A High Resolution Study of G.P. Zones in Aluminum - 4.2 at % Silver

1982 ◽  
Vol 40 ◽  
pp. 722-723 ◽  
Author(s):  
R. Gronsky
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Computer Simulations ◽  
Structural Characteristics ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Resolution Study

The phenomenon of clustering in Al-Ag alloys has been extensively studied since the early work of Guinierl, wherein the pre-precipitation state was characterized as an assembly of spherical, ordered, silver-rich G.P. zones. Subsequent x-ray and TEM investigations yielded results in general agreement with this model. However, serious discrepancies were later revealed by the detailed x-ray diffraction - based computer simulations of Gragg and Cohen, i.e., the silver-rich clusters were instead octahedral in shape and fully disordered, atleast below 170°C. The object of the present investigation is to examine directly the structural characteristics of G.P. zones in Al-Ag by high resolution transmission electron microscopy.

Electron holography in materials science

1991 ◽  
Vol 49 ◽  
pp. 670-671
Author(s):  
Hannes Lichte ◽  
Edgar Voelkl
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Materials Science ◽  
Fourier Spectrum ◽  
Object Wave ◽  
Electron Holography ◽  
Reconstruction Procedure ◽  
Numerical Reconstruction ◽  
Transmission Electron ◽  
Unique Interpretation

The object wave o(x,y) = a(x,y)exp(iφ(x,y)) at the exit face of the specimen is described by two real functions, i.e. amplitude a(x,y) and phase φ(x,y). In stead of o(x,y), however, in conventional transmission electron microscopy one records only the real intensity I(x,y) of the image wave b(x,y) loosing the image phase. In addition, referred to the object wave, b(x,y) is heavily distorted by the aberrations of the microscope giving rise to loss of resolution. Dealing with strong objects, a unique interpretation of the micrograph in terms of amplitude and phase of the object is not possible. According to Gabor, holography helps in that it records the image wave completely by both amplitude and phase. Subsequently, by means of a numerical reconstruction procedure, b(x,y) is deconvoluted from aberrations to retrieve o(x,y). Likewise, the Fourier spectrum of the object wave is at hand. Without the restrictions sketched above, the investigation of the object can be performed by different reconstruction procedures on one hologram. The holograms were taken by means of a Philips EM420-FEG with an electron biprism at 100 kV.

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