We
investigated the Sr2‑xPb
x
GeSe4 series from 0 ≤ x ≤
2 to study the impact of Pb on structure and properties. While the
noncentrosymmetric (NCS) compounds γ-Sr2GeSe4 and α-Pb2GeSe4 have already been
reported previously, the substitution variants Sr1.31Pb0.69GeSe4 (space group Ama2, a = 10.31220(1) Å, b = 10.39320(1)
Å, c = 7.42140(1) Å) and Sr0.19Pb1.81GeSe4 (I4̅3d, a = 14.6177(3) Å) are introduced
here for the first time. The experimentally determined optical band
gaps decrease as predicted with increasing Pb content from γ-Sr2GeSe4 to Sr1.31Pb0.69GeSe4, Sr0.25Pb1.75GeSe4, and
α-Pb2GeSe4 from 2.00, to 1.65, 1.45 and
1.42 eV, respectively. The nonlinear optical (NLO) properties of the
orthorhombic compounds γ-Sr2GeSe4 and
Sr1.3Pb0.7GeSe4 (approximated with
the supercell “Sr3PbGe2Se8”) were studied both theoretically, using first-principle
calculations, and experimentally. The calculations found the effective
nonlinear susceptibility, d
eff, of γ-Sr2GeSe4 and “Sr3PbGe2Se8” at the static limit to be 10.8 and 8.8 pm
V–1, respectively. The experimental d
eff values of γ-Sr2GeSe4,
Sr1.31Pb0.69GeSe4, Sr0.25Pb1.75GeSe4, and α-Pb2GeSe4 were 2.6, 2.3, 0.68, and 0.79 pm V–1, respectively.