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A Mechanistic Understanding of Nonclassical Crystal Growth in Hydrothermally Synthesized Sodium Yttrium Fluoride Nanowires
journal contribution
posted on 2020-03-18, 18:04 authored by Alexander
B. Bard, Xuezhe Zhou, Xiaojing Xia, Guomin Zhu, Matthew B. Lim, Seung Min Kim, Matthew C. Johnson, Justin M. Kollman, Matthew A. Marcus, Steven R. Spurgeon, Daniel E. Perea, Arun Devaraj, Jaehun Chun, James J. De Yoreo, Peter J. PauzauskieSodium yttrium fluoride
(NaYF4) is an important upconverting
material with many potential uses in chemistry, materials science,
and biology, which 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 synthetic
efforts, for example in the design of 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 that the hexagonal NaYF4 nanowires form through a nonclassical crystal growth mechanism
involving the formation and subsequent oriented attachment of mesocrystals
consisting of cubic (α) phase units. EXAFS measurements also
suggest that substitutional Yb3+ point defects within NaYF4 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 β-NaYF4.
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EXAFSNaYF 4hydrothermallyNaYF 4 nanowires formmaterialatom probe tomographyβ- NaYF 4APTmeasurementpolymorphXRDX-raynonclassical crystal growth mechanismNonclassical Crystal GrowthTEMtransmission electron microscopytrivalent yttrium sitesHydrothermally Synthesized Sodium Yttrium Fluoride Nanowires Sodium yttrium fluoridephase
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