Crystal structure of piezoelectric nonlinear-optic AgGaS2

Silver thiogallate, AgGaS2, is a representative member of the AIBIIIC 2VI family with chalcopyrite structure. AgGaS2 is strongly piezoelectric and is phase matchable for second harmonic generation. The lattice constants of this tetragonal crystal are a = 5.75722 ± 0.00003 and c = 10.3036 ± 0.0002 Å at 298 °K. The space group is I 42d, with four formulas per unit cell. The integrated intensities of 1978 reflections were measured within a hemisphere of reciprocal space having radius (sin θ)/λ = 1.02 Å−1 using PEXRAD, resulting in 268 symmetry-independent structure factors. The x coordinate of sulfur (0.2908 ± 0.0004) is 0.088 Å less than the value calculated on the assumption of a geometrically regular tetrahedral bond distribution about the B atom. By contrast, four AIIBIVC2V compounds previously reported have x coordinates for the Cv atom either slightly greater than (for ZnSiP2, CdSiP2, and ZnSiAs2), or not significantly different from (for ZnGeP2) that calculated. The experimental Ag–S distance is 2.556 ± 0.001 Å, and Ga–S is 2.276 ± 0.001 Å: the S–Ga–S angle bisected by the c axis is 111.1 ± 0.1°.