Microscopic structures of Laves phases and structurally related compounds: a transmission electron microscopy study
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Tadahiro Yokosawa
Abstract
We present microstructural investigations of Laves phases AB2 and structurally related compounds using transmission electron microscopy. Convergent-beam electron diffration in combination with selected-area diffraction has been used to determine uniquely the space group symmetry of the respective phases from very small illuminated regions. In addition stacking faults, domain boundaries, and intergrowth have been studied by HREM images. By electron beam irradiation intermetallic phases have been transformed in-situ into phases of different compositions. Polar intermetallic phases in the systems Ca—Al—Zn, Ba—Al and Ba—Al—Zn, as well as transition metal based Nb-Co phases have been chosen for this case study. In the Ca—Al—Zn system, the C15- and C36-type crystals did not show orderliness but a randomly mixed occupation of the B-net by Al and Zn atoms. Starting from C36, a C15 phase of constant Ca and lower Zn content as well as a new C36 phase with higher Ca content could be synthesized by means of electron beam irradiation. In the case of CaAlZn no ordering of Al and Zn were observed, i.e., Al and Zn randomly mixed occupy the Cu-site in the CeCu2 structure type. By electron beam irradiation of CaAlZn, a novel hexagonal phase with a hitherto unknown crystal structure is formed. The crystal structures of Ba21Al40 and Ba14Al22+xZn5–x are derived from Laves-type structures by omitting and modifying some of the triangular and Kagom, layers. In the case of Ba21Al40, intergrowth of motifs from the crystal structures of Ba3Al5 and Ba4Al5 were observed, whereas for Ba14Al22+xZn5–x the bulk phase displays a domain structure. Adjacent domains are misoriented by ∼120°, the specific angle resulting from the pseudo-trigonal symmetry of the Ba-net. Therefore, only the (Al,Zn)-net is disordered. No superstructure formation were detected for the three polytypes C36, C15 and C14 in the Nb—Co system. However, TEM images of C36-Nb1–xCo2+x reveal a high stacking fault density with intergrowth of stacks of C36 and C15 sequence. When the C15 phase is rich in Nb, stacking faults seem to be more important than for Co-rich C15 phases, whereas stacking faults have seldom been observed for the Co-rich C14 phase.
© by Oldenbourg Wissenschaftsverlag, München
Articles in the same Issue
- Editorial: Crystal Chemistry of Intermetallic Compounds
- Fritz H. Laves – 100 years young
- Fritz H. Laves – an ideal for generations
- Gustav E. R. Schulze's pioneering work on Laves phases
- Preparation, phase stability and structure of the C36 Laves phase Nb1–xCo2+x
- Atom order and thermodynamic properties of the ternary Laves phase Ti(TiyNixAl1–x–y)2
- Atomic ordering in the Laves phases L1 V(Co1–xSix)2 (x = 0.43 and 0.56)
- Microscopic structures of Laves phases and structurally related compounds: a transmission electron microscopy study
- Binary rare earth Laves phases — an overview
- Binary intermetallic phases formed by Ca, Sr, Ba, Eu and Yb: similarities and differences
- Complexity of hexagonal approximants in the RE13Zn~58 system (RE = Ce, Pr, Nd, Sm, Gd, Tb and Dy)
- Reflections on symmetry and formation of axial quasicrystals
- Mosaic-like tilings derivated from o-Co4Al13 and m-Co4Al13 crystal structures
- High-pressure crystal chemistry of binary intermetallic compounds
- Re3B type intermetallics — crystal chemistry, bonding and properties
- Ti2Rh6B – a new boride with a double perovskite-like structure containing octahedral Rh6 clusters
- On the formation and crystal structure of the Pd6B phase
- Crystal growth and magnetic properties of rare earth borosilicides
- The effect of transition metal doping on thermal conductivity of YB66
- Structure refinements of iron borides Fe2B and FeB
- Cubic structure types of rare-earth intermetallics and related compounds
- Structural variations in Gd5Si4-xSnx: size vs. electronic effects
- Tin flux synthesis of rare-earth metal silicide compounds RESi1.7 (RE = Dy, Ho): a novel ordered structure derived from the AlB2 type
- Filling the CoSn host-cell: the HfFe6Ge6-type and the related structures
- Synthesis and characterization of Na2Ba4Ga2Sb6 and Li13Ba8GaSb12
- Ge40.0Te5.3I8: synthesis, crystal structure, and properties of a new clathrate-I compound
- Ag6GeS4X2 (X: Cl, Br): surprisingly no filled Laves phases but the first representatives of a new structure type
- Low- and high-temperature structures of YbCuBi
- (La3Zx)Al and (Ce3Zx)Al with Z = C, N, O: preparation, physical properties and chemical bonding of metal-rich perovskites
- Geometric variations and electron localizations in intermetallics: PbFCl type compounds
- A novel series of sphere packings with arbitrarily low density
- Books Received
Articles in the same Issue
- Editorial: Crystal Chemistry of Intermetallic Compounds
- Fritz H. Laves – 100 years young
- Fritz H. Laves – an ideal for generations
- Gustav E. R. Schulze's pioneering work on Laves phases
- Preparation, phase stability and structure of the C36 Laves phase Nb1–xCo2+x
- Atom order and thermodynamic properties of the ternary Laves phase Ti(TiyNixAl1–x–y)2
- Atomic ordering in the Laves phases L1 V(Co1–xSix)2 (x = 0.43 and 0.56)
- Microscopic structures of Laves phases and structurally related compounds: a transmission electron microscopy study
- Binary rare earth Laves phases — an overview
- Binary intermetallic phases formed by Ca, Sr, Ba, Eu and Yb: similarities and differences
- Complexity of hexagonal approximants in the RE13Zn~58 system (RE = Ce, Pr, Nd, Sm, Gd, Tb and Dy)
- Reflections on symmetry and formation of axial quasicrystals
- Mosaic-like tilings derivated from o-Co4Al13 and m-Co4Al13 crystal structures
- High-pressure crystal chemistry of binary intermetallic compounds
- Re3B type intermetallics — crystal chemistry, bonding and properties
- Ti2Rh6B – a new boride with a double perovskite-like structure containing octahedral Rh6 clusters
- On the formation and crystal structure of the Pd6B phase
- Crystal growth and magnetic properties of rare earth borosilicides
- The effect of transition metal doping on thermal conductivity of YB66
- Structure refinements of iron borides Fe2B and FeB
- Cubic structure types of rare-earth intermetallics and related compounds
- Structural variations in Gd5Si4-xSnx: size vs. electronic effects
- Tin flux synthesis of rare-earth metal silicide compounds RESi1.7 (RE = Dy, Ho): a novel ordered structure derived from the AlB2 type
- Filling the CoSn host-cell: the HfFe6Ge6-type and the related structures
- Synthesis and characterization of Na2Ba4Ga2Sb6 and Li13Ba8GaSb12
- Ge40.0Te5.3I8: synthesis, crystal structure, and properties of a new clathrate-I compound
- Ag6GeS4X2 (X: Cl, Br): surprisingly no filled Laves phases but the first representatives of a new structure type
- Low- and high-temperature structures of YbCuBi
- (La3Zx)Al and (Ce3Zx)Al with Z = C, N, O: preparation, physical properties and chemical bonding of metal-rich perovskites
- Geometric variations and electron localizations in intermetallics: PbFCl type compounds
- A novel series of sphere packings with arbitrarily low density
- Books Received
