Biaxial negative thermal expansion in Zn[N(CN)(2)](2)

Negative thermal expansion (NTE) has both scientific and application value as a novel physical behavior, but the types of NTE materials are still limited. In the present work, a framework structure material, metal dicyanamide ZnIN(CN)(2)](2), has been found to show biaxial negative thermal expansion in a wide temperature range (alpha(a) = -11.82 x 10(-6) K-1, alpha(b) = -11.75 x 10(-6) K-1. from 173 K-473 K). Through a joint study of variable temperature X-ray diffraction, extended X-ray absorption fine structure, Raman spectroscopy, and the maximum entropy method, the NTE mechanisms in ZnIN(CN)(2)](2) have been revealed. The pronounced transverse vibration of C atoms in the multiatomic bridge linkage -N C-N- and the rotation of ZnN4 tetrahedra play a key role in biaxial negative thermal expansion. This work provides a new class of potential framework structure NTE materials.