The New Laves Phase Na2Ba

After preliminary investigations o f the B a -N a N system, resulting in the discovery of the first sub-nitride NaBa3N [1], we decided to examine more closely the intermetallic phases formed by the two metals, leading to the discovery of the new Laves phase N a2Ba. The literature contains a variety o f conflicting reports concerning N a -B a intermetallic phases. The standard references for binary phase diagrams [2,3] show for N a -B a quite different liquidus curves and binary phases. The work of Remy [4], re­ produced in [2], contains three phases N a12Ba, N a6Ba, and NaBa, based on differential thermal analyses. The primary source of [3] is the work of Stevens and Kanda [5], who deduce from X-ray powder diffraction and thermal data that two phases NaBa and N a4Ba exist up to 197 °C and 65 °C, respectively. The structures are, however, not given but only observed X-ray powder reflec­ tions without intensities, and tentative lattice con­ stants. Addison [6] reproduced these results from resistivity measurements, with only slightly varied positions of the equilibrium lines. In an earlier work from the Kanda group [7], N a2Ba5 or (Na4Ba9), as well as N a2Ba forming peritectically at 175 °C, are described. The Laves phase N a2Ba that we report was observed only below 86 °C and its X-ray diagram conforms to 17 of the 28 report­ ed diffraction lines given for N a4Ba. Some of the remaining lines match well with the diffraction