Stabilization of LnB12 (Ln = Gd, Sm, Nd, and Pr) in Zr1-xLnxB12 under Ambient Pressure

We report ambient pressure stabilization of a previously synthesized high-pressure (6.5 GPa) phase, GdB12, in a Zr1-xGdB12 solid solution (with similar to 54 at. % Gd solubility, as determined by both powder X-ray diffraction and energy dispersive spectroscopy). Limited solubilities of Sm (similar to 15 at. % Sm), Nd (similar to 7 at. % Nd), and Pr (similar to 4 at. % Pr), in ZrB12 were also achieved. Previous attempts at preparing these rare-earth borides were unsuccessful even under high pressure. On the basis of insights provided from the unit cell sizes observed via solid solutions, at least 6.5 GPa of pressure would be needed to synthesize these rare-earth borides since Sm, Nd, and Pr atomic radii are larger than that of Gd. The solid-solution formation for Zr1-xGdxB12 and Zr1-xSmxB12 can be seen in the change of the unit cell of each of the solid solutions relative to their pure parent compounds as well as in the change of color of the respective alloys. For Zr0.45Gd0.55B12 and Zr0.70Sm0.30B12, the cubic unit cell parameter (a) reached a value of 7.453 and 7.428 angstrom, respectively, compared to 7.412 angstrom for pure ZrB12.