A series of M3PS4 (M = Ag, Cu and Ag/Cu) thiophosphates with diamond-like structures exhibiting large second harmonic generation responses and moderate ion conductivities

Abstract

A series of thiophosphates with similar diamond-like structures, M₃PS₄ (M = Ag, Cu and Ag/Cu), were successfully synthesized. Among them, Ag₃PS₄ and Ag_1.5Cu_1.5PS₄ satisfy the phase-matching condition and display excellent second harmonic generation (SHG) responses about 1.3 and 0.8 times that of benchmark AgGaS₂. First-principles and dipole moment calculations indicate that their SHG effects originate from the combined action between MS₄ and PS₄ tetrahedra. Moreover, they also exhibit moderate ion conductivities (order of 10⁻⁷ to 10⁻⁵ S cm⁻¹) between 10 and 80 °C and relatively small activation energies (E_a = 0.28–0.34 eV).