Syntheses, structures and characterization of noncentrosymmetric MZnPO4 (M = K, NH4)

Abstract

Two phosphates, KZnPO₄ and NH₄ZnPO₄, were successfully synthesized using a solid-state reaction method and characterized via single-crystal X-ray diffraction. Both of their structures feature a three-way skeleton composed of isolated PO₄ and ZnO₄ tetrahedra, with K⁺/NH₄⁺ cations occupying the spaces within the frameworks to balance charges. These compounds are isostructural and crystallize in the noncentrosymmetric P6₃ space group. Their structures were compared, revealing that non-centrosymmetric (NCS) KZnPO₄ and NH₄ZnPO₄ exhibit second harmonic generation (SHG) responses of 0.4 × KDP and 1 × KDP, respectively. Furthermore, by combining the electronic structure and SHG density calculations, we examined the effects of ZnO₄ tetrahedra on the SHG response of KZnPO₄ and NH₄ZnPO₄.