Complex Structures of Intermetallic Compounds Interpreted as Intergrowth of Segments of Simple Structures
By the end of 1982 more than 2000 structure types were known for intermetallic compounds (elements, binary and multicomponent alloys) according to «Pearson’s Handbook of Crystallographic Data for Intermetallic Phases». Restricting ourselves to the ternary lanthanoid-transition metal-silicides, germ...
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| Main Authors: | , , |
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| Format: | Article |
| Language: | deu |
| Published: |
Swiss Chemical Society
1985-06-01
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| Series: | CHIMIA |
| Online Access: | https://www.chimia.ch/chimia/article/view/9662 |
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| Summary: | By the end of 1982 more than 2000 structure types were known for intermetallic compounds (elements, binary and multicomponent alloys) according to «Pearson’s Handbook of Crystallographic Data for Intermetallic Phases». Restricting ourselves to the ternary lanthanoid-transition metal-silicides, germanides, stannides, borides, aluminides, and gallides, we are still confronted with about 150 types, of which at least two thirds form new atom arrangements which cannot be considered ternary ordered derivatives of binary structure types. – There is always arbitrariness in attempting to describe any crystal structure for the reason that one should take into account the chemistry of the compound, its physical properties, and its geometrical relationships to other structures. This challenge is particularly difficult to overcome with intermetallic compounds because in this case the lack of information on the nature of the chemical bonding does not allow an easy understanding of their physical properties and leaves also a (too) large degree of freedom in their crystal-chemical interpretation. If, with particularly well-chosen compounds, we can improve our vision by wearing, for example, «von Schnering’s spectacles» which allow to discover clusters in any structure..., belonging to the category of cluster compounds, these do not provide a satisfactory view of the structures of pure intermetallics. For this class of compounds we need another kind of spectacles! – One of the most successful approaches to the problem consists in interpreting complex structures of intermetallic compounds as being built up from «building units», such as slabs, columns, or blocks, characteristic of simple structure types. As an example we shall show that some 30 of the structure types found with ternary lanthanoid alloys can be described as linear combinations of slabs derived from 6 simple structure types. On the whole, more than one third of all 150 structure types can be interpreted as an intergrowth of various simple structure segments. Structure series, which group structures containing segments derived from the same parent structures, can then be considered, and new structure types can be predicted, by imagining different combinations of segments. This provides a useful guideline for material scientists who are searching for new compounds with interesting physical properties such as superconductivity or magnetism.
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| ISSN: | 0009-4293 2673-2424 |