Identification of the impurity phase in high-purity CeB6 by convergent-beam electron diffraction

Research output: Contribution to journalArticleResearchpeer-review

Abstract

The rare earth hexaborides are known for their tendency towards very high crystal perfection. They can be grown into large single crystals of very high purity by inert gas arc floating zone refinement. The authors have found that single-crystal cerium hexaboride grown in this manner contains a significant number of inclusions of an impurity phase that interrupts the otherwise single crystallinity of this prominent cathode material. An iterative approach is used to unequivocally determine the space group and the lattice parameters of the impurity phase based on geometries of convergent-beam electron diffraction (CBED) patterns and the symmetry elements that they possess in their intensity distributions. It is found that the impurity phase has a tetragonal unit cell with space group P4/mbm and lattice parameters a = b = 7.23 ± 0.03 and c = 4.09 ± 0.02 Å. These agree very well with those of a known material, CeB4. Confirmation that this is indeed the identity of the impurity phase is provided by quantitative CBED (QCBED) where the very close match between experimental and calculated CBED patterns has confirmed the atomic structure. Further confirmation is provided by a density functional theory calculation and also by high-angle annular dark-field scanning transmission electron microscopy.

Original languageEnglish
Pages (from-to)489-500
Number of pages12
JournalActa Crystallographica Section A: Foundations and Advances
Volume75
Issue number3
DOIs
Publication statusPublished - 1 May 2019

Keywords

  • cerium hexaboride (CeB )
  • cerium tetraboride (CeB )
  • convergent-beam electron diffraction
  • Gjønnes–Moodie lines
  • impurity phases
  • quantitative convergent-beam electron diffraction
  • space groups

Cite this

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title = "Identification of the impurity phase in high-purity CeB6 by convergent-beam electron diffraction",
abstract = "The rare earth hexaborides are known for their tendency towards very high crystal perfection. They can be grown into large single crystals of very high purity by inert gas arc floating zone refinement. The authors have found that single-crystal cerium hexaboride grown in this manner contains a significant number of inclusions of an impurity phase that interrupts the otherwise single crystallinity of this prominent cathode material. An iterative approach is used to unequivocally determine the space group and the lattice parameters of the impurity phase based on geometries of convergent-beam electron diffraction (CBED) patterns and the symmetry elements that they possess in their intensity distributions. It is found that the impurity phase has a tetragonal unit cell with space group P4/mbm and lattice parameters a = b = 7.23 ± 0.03 and c = 4.09 ± 0.02 {\AA}. These agree very well with those of a known material, CeB4. Confirmation that this is indeed the identity of the impurity phase is provided by quantitative CBED (QCBED) where the very close match between experimental and calculated CBED patterns has confirmed the atomic structure. Further confirmation is provided by a density functional theory calculation and also by high-angle annular dark-field scanning transmission electron microscopy.",
keywords = "cerium hexaboride (CeB ), cerium tetraboride (CeB ), convergent-beam electron diffraction, Gj{\o}nnes–Moodie lines, impurity phases, quantitative convergent-beam electron diffraction, space groups",
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Identification of the impurity phase in high-purity CeB6 by convergent-beam electron diffraction. / Peng, Ding; Nakashima, Philip N.H.

In: Acta Crystallographica Section A: Foundations and Advances, Vol. 75, No. 3, 01.05.2019, p. 489-500.

Research output: Contribution to journalArticleResearchpeer-review

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