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| - Gd1.33Pt3(Al,Si)8 and Gd0.67Pt2(Al,Si)5: Two Structures Containing aDisordered Gd/Al Layer Grown in Liquid Aluminum
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| - Gd1.33Pt3Al8 was synthesized by the combination of Gd and Pt in excess liquid aluminum. Addition of silicon resultedin the incorporation of a small amount of this element into the material to form the isostructural Gd1.33Pt3Al7Si. Bothcompounds grow as rodlike crystals with hexagonal cross section. The structures were refined in the rhombohedralspace group R3̄m, with cell parameters a = 4.3359(6) Å and c = 38.702(8) Å for the ternary and a = 4.3280(8)Å and c = 38.62(1) Å for the quaternary compound. The structure is comprised of stuffed arsenic-like PtAl2 layersand disordered Gd/Al layers. Analysis of the hk0 zone reflections indicate the presence of an a* = √3a supercell,but the structure is not ordered along c, as revealed by the highly diffuse reflections in the 0kl zone photos.Therefore, the compounds are disordered variants of the Gd4Pt9Al24 type. Magnetic susceptibility studies revealantiferromagnetic transitions at 15 K for the ternary and 7 K for the quaternary compound. Variation of the reactantratio produces a different structure comprised of the same structural blocks, including the disordered Gd/Al layer.Gd0.67Pt2Al5 and its quaternary analogue Gd0.67Pt2Al4Si form in the hexagonal system P63/mmc with cell parametersa = 4.2907(3) Å and c = 16.388(2) Å for the ternary and a = 4.2485(6) Å and c = 16.156(3) Å for the quaternarycompound.
- The solvent of choice to synthesize Gd1.33Pt3(Al,Si)8 and Gd0.67Pt2(Al,Si)5 is liquid aluminum. Both of these intermetallic structures contain similar disordered monatomic layers of Gd3+ ions and triangles of aluminum. The extensive stacking disorder of these layers is apparent in the highly diffuse reflections in the 0kl zone photos and is likely due to the low-temperature growth of the compounds in liquid aluminum. The effect of adding silicon into the structures was explored; it lowers the antiferromagnetic ordering temperature.
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