After a comparison of the β‐, ϵ‐, γ‐, and δ‐type GaSe crystal structures, the different interlayer interactions are discussed. New values for the intralayer interatomic distances Se–Ga = 2.463 (15) Å, Ga–Ga = 2.457 (18) Å, and the interlayer distance Se–Se = 3.880 (15) Å are proposed. These are mean values for the δ‐type determined with a higher accuracy than the previous ones, relevant to the ϵ‐ and γ‐type structure. The influence of the growth method on crystal type and dislocation density are discussed.

GaS p, hexagonal, space group P63/mmc, a = 3.587 (3), c = 15"492 (7) A, Z= 4. The mean atomic distances in the layers are: Ga-Ga=2"447 (9), Ga-S=2-334 (4) and S-S=4-599 (18) A. The mean atomic distances between the layers are" S-S=3"768 (11) and A. The interlayer S-S distance is more than twice the van der Waals radius.

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GaSe 3, hexagonal, space group P63mc, a=3.755 (3), c=31.990 (10) A, Z=8. The mean atomic distances in the layers are: Ga-Ga= 2.457 (10), Ga-Se= 2.463 (10) and Se-Se= 4.784 (15) A. The mean atomic distances between the layers are: Se-Se= 3"880 (15), Ga-Se=4.392 (16) A. The interlayer Se-Se distance is less than twice the van der Waals radius.

The electron density in the A "'sv' crystal Gas vms experimentaHy determined by x-ray diffraction. The 1esult1ng dens1ty distribut1on varies markedly from the d1stribut1on predicted by the pseudopotential model proposed by Schluter et al, The real bonds observed in the x-ray difFraction determined distribution are curved and are located not only between Ga-Ga and Ga-S nearest neighbors as predicted by the pseudopotential model, but also between Ga and S next-nearest neighbors in the same elementary cell, between Ga and S atoms in adjoining elementary cells, and between S-S interlayer neighbors in the same elementary cell. The taro atoms Ga and S are highly polarized. These findings allow a better understanding of the bondlngs and the discrepancies bete'een our experimental 6ndings, and the present pseudopotential model should permit an improvement in a future theoretical model for bonding in the A"'Bv' crystals.Z"=0 -0.2625 in steps of AZ"=0.0125. Order by PAPS number and journal reference from American