Cd7SiAs6, a Nonchalcopyrite Arsenide with a Strong Nonlinear-Optical Response

A new arsenide, Cd7SiAs6, has been successfully synthesized and characterized. It is the first arsenide that adopts a nonchalcopyrite structure and possesses a strong nonlinear-optical (NLO) response. In the structure, the CdAs3 trigonal planar unit, a kind of π-conjugated planar NLO-active group, was identified for the first time. Furthermore, theoretical calculations reveal that the CdAs3 planar unit contributes more to the NLO effect than the CdAs4 tetrahedron does. The result may provide valuable insights for the future exploration of IR NLO materials, especially for application above 10 μm.