Synthesis, conductivity behaviour and second-order nonlinear optics of partially substituted double KDP containing As5+ and Na+

A new solid solution K0.95Na0.05H2(PO4)0.5(AsO4)0.5 abbreviated (KNDAP) has been prepared by slow evaporation of an aqueous solution at room temperature. Its crystal structure which was solved by the direct method from single crystal X-ray diffraction data can give birth to two kinds of disorder. The first one is statistical or dynamical in the shortest OH…O hydrogen bond that can facilitate the migration of proton. As for the second kind, it is related to the effect of the substitution of Na+ and As5+ in the same site occupancy as that of the K+ and P5+, respectively. This disorder could promote hard defects in the structure, which can enhance the physical properties, especially, the conductivity.