A low-temperature topotactic route is used to assemble metal-anion arrays within a perovskite host. Ion exchange between RbLaNb 2 O 7 and CuX 2 (X ) Cl, Br) results in a new set of layered copperoxyhalide perovskites, (CuX)LaNb 2 O 7 . Rietveld structural analysis of X-ray powder diffraction data confirms the formation of a two-dimensional copper-halide network in the double-layered perovskite interlayer. This new structure type contains unusual CuO 2 X 4 octahedra that corner-share with NbO 6 octahedra from the perovskite slab and edge-share with each other along all four equatorial edges. Magnetic susceptibility measurements show that both products exhibit antiferromagnetic transitions below 40 K. Additionally, these materials are found to be low-temperature phases, decomposing completely by 700°C. The synthetic approach described in this work is significant in that it demonstrates how host structures can be used as templates in the directed low-temperature assembly of extended metal-anion arrays.
A bismuth-silver alloy (Bi-11wt.%Ag) has been identified as a viable Pb-free power die-attach solder. The alloy has a solidus at 262.5°C and a liquidus at 360°C. It has a shear modulus of 13.28 GPa and an ultimate tensile strength (UTS) of 59 MPa. Bismuth-silver alloys oxidize in air but will solder to nickel, silver, and gold under reducing atmospheres. Germanium may be added in small amounts (Յ500 ppm) to improve the wetting. Wire, ribbon, and preform shapes of the alloy have been fabricated by conventional metalworking techniques.
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