Structure and optical properties of LixAg1–xAlSe2.

The complete solid solution Li x Ag 1– x AlSe 2 was prepared at 850 °C in the form of phase-pure powder samples as well as single crystals. They adopt noncentrosymmetric crystal structures belonging to the tetragonal CuFeS 2 -type (space group I 4 ‾ 2 d) for x = 0–0.5 and orthorhombic β-NaFeO 2 -type (space group Pna 2 1) for x = 0.6–1, both being built up from corner-sharing metal-centred tetrahedra and exhibiting complete disorder of Li and Ag atoms. Solid-state 7Li NMR spectra support the presence of unique Li sites. The substitution of Li for Ag atoms allows control of optical band gaps, which increase linearly from 2.7 eV to 3.6 eV. Second harmonic generation responses were measured to evaluate the potential of these compounds as infrared nonlinear optical materials. Li x Ag 1– x AlSe 2 undergoes a transformation from tetragonal to orthorhombic structures with increasing Li substitution, which also widens the band gap. [Display omitted] • The solid solution Li x Ag 1– x AlSe 2 was prepared at 850 °C. • A tetragonal-to-orthorhombic transformation takes place as Li content increases. • The band gap increases from 2.7 eV for AgAlSe 2 to 3.6 eV for LiAlSe 2. • Solid state 7Li NMR spectra reveal unique Li sites. [ABSTRACT FROM AUTHOR]