文摘
Two new phases in the Ag–Cd–P–S system containing two second-order Jahn–Teller (SOJT) distorted d<sup>10sup> cations (Cd<sup>2+sup> and Ag<sup>+sup>), namely, Ag<sub>2sub>Cd(P<sub>2sub>S<sub>6sub>) (1) and AgCd<sub>3sub>(PS<sub>4sub>)S<sub>2sub> (2), are obtained via medium-temperature solid-state synthesis. Compound 1 exhibits a two-dimensional layered structure and undergoes a first-order structural phase transition at approximately 280 °C. This outcome can be ascribed to the significant mismatch in the expansion coefficients between Cd–S (Ag–S) and P–P (P–S) bonds evaluated through bond valence theory. The three-dimensional non-centrosymmetric (NCS) framework of 2 is constructed by two types of tetrahedral layers consisting of corner-shared CdS<sub>4sub>, AgS<sub>4sub>, and PS<sub>4sub> tetrahedra. Compound 2 exhibits second harmonic generation (SHG) intensity of 0.45 times that of commercial AgGaS<sub>2sub> (AGS) at a laser irradiation of 1.85 μm and an optical band gap of 2.56 eV, and no intrinsic vibrational absorption of chemical bonds is observed in the range of 2.5–18.2 μm. Both phase transition in 1 and SHG properties in 2 are closely related to the SOJT distorted d<sup>10sup> cations and diverse phosphorus–sulfur polyanions (P<sub>asub>S<sub>bsub>)<sup>n−sup>, which together can easily result in NCS distorted structures and interesting properties.