Ba4AgGa5Pn8 (Pn = P, As): new pnictide-based compounds with nonlinear optical potential

Abstract

Two new quaternary pnictide-based multinary compounds, Ba₄AgGa₅P₈ and Ba₄AgGa₅As₈, were synthesized from Pb-flux reactions. By using the single crystal X-ray diffraction technique the structures were determined to crystallize with the noncentrosymmetric (NCS) space group Iba2 (No. 45) (cell parameters: a = 7.294(9)/7.4769(8) Å, b = 18.03(2)/18.5766(19) Å, c = 6.557(8)/6.7590(7) Å for the P- and As-containing compounds, respectively). Theoretical calculations indicate strong SHG responses for both compounds, which are approximately two times larger than that of AgGaSe₂. Based on the calculated cutoff-energy-dependent static SHG coefficients, the large NLO coefficients of these compounds should originate from the distorted GaPn₄ tetrahedra, which construct various layers and chains giving rise to a large polarization. Both compounds have moderate birefringence (Δn), 0.157 and 0.206 for Ba₄AgGa₅P₈ and Ba₄AgGa₅As₈, respectively, suitable to meet the phase-matching condition in the SHG process.