A New Superstructure for the BaAl4-Structure Type: An Experimental and Theoretical Study of La2NiAl7

Abstract

<p>A new ternary aluminide, La₂NiAl₇, has been synthesized from the elements in sealed silica tubes. The crystal structure of La₂NiAl₇ was determined by single-crystal X-ray diffraction and crystallizes in the tetragonal space group <em>I</em>4<em>mm</em> (No. 123) with <em>Z </em>= 4 and lattice parameters <em>a </em>= 6.221(3) and<em> c </em>= 21.403(2) Å. Refinement based on <em>F</em>₀² yielded <em>R</em>₁ = 0.0313 and <em>wR</em>₂ = 0.0392 [<em>I</em> > 2σ(<em>I</em>)]. It is a new structure type, which belongs to the family of BaAl₄-related structures. The La₂NiAl₇ structure corresponds to a 3D superstructure (√2<em>a</em> × √2<em>b</em> × 2<em>c</em>) of the BaAl₄-structure type, whereas La₃Al₁₁ is only a 1D superstructure (3<em>a</em> × <em>b</em> × <em>c</em>). Tight-binding band structure calculations using the density functional theory have been carried out to understand the structural stability of La₂NiAl₇ as well as La₃Al₁₁.</p>