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要旨:
The XYZ half-Heusler crystal structure can conveniently be described as
a tetrahedral zinc blende YZ structure which is stuffed by a slightly
ionic X species. This description is well suited to understanding the
electronic structure of semiconducting 8-electron compounds such as
LiAlSi (formulated Li+[AlSi](-)) or semiconducting 18-electron compounds
such as TiCoSb (formulated Ti4(+)[CoSb](4-)). The basis for this is that
[AlSi](-) (with the same electron count as Si-2) and [CoSb](4-) (the
same electron count as GaSb) are both, structurally and electronically,
zinc blende semiconductors. The electronic structure of half-metallic
ferromagnets in this structure type can then be described as
semiconductors with stuffing magnetic ions which have a local moment:
for example, 22-electron MnNiSb can be written Mn3+[NiSb](3-). The
tendency in the 18-electron compound for a semiconducting gap -believed
to arise from strong covalency-is carried over in MnNiSb to a tendency
for a gap in one-spin direction. Here we similarly propose the
systematic examination of 18-electron hexagonal compounds for
semiconducting gaps; these would be the 'stuffed wurtzite' analogues of
the 'stuffed zinc blende' half-Heusler compounds. These semiconductors
could then serve as the basis for possibly new families of half-metallic
compounds, attained through appropriate replacement of non-magnetic ions
by magnetic ones. These semiconductors and semimetals with tunable
charge carrier concentrations could also be interesting in the context
of magnetoresistive and thermoelectric materials.
