  The effects of lithium absorption on the crystal structure and electronic
properties of IrSi3, a binary silicide with a noncentrosymmetric crystal
structure, were studied. X-ray and neutron diffraction experiments revealed
that hexagonal IrSi3 (space group P6_3mc) transforms into trigonal Li2IrSi3
(space group P31c) upon lithium absorption. The structure of Li2IrSi3 is found
to consist of a planar kagome network of silicon atoms with Li and Ir spaced at
unequal distances between the kagome layers, resulting in a polar structure
along the c-axis. Li2IrSi3 exhibited type-II superconductivity with a
transition temperature Tc of 3.8 K, displaying a structure type that no
previous superconductors have been reported to have.
