Large negative thermal expansion in GdFe(CN)6 driven by unusual low-frequency modes

Understanding the negative thermal expansion (NTE) mechanism is of great importance. In this work, we consider the new NTE compound GdFe(CN)6 (alpha v = -34.2 x10-6 K-1) as a case study to investigate the NTE mechanism from the perspective of the lattice vibrational dynamics. The atomic mean-square displace-ments suggest that the NTE of GdFe(CN)6 comes from the strong tension effect induced by the transverse vibrations of the atomic -Fe-C equivalent to N-Gd- linkages, with the largest contribution given by N atoms. Lattice dynamics calculations show that three low-frequency optical modes at about 50 cm-1 show the largest negative Gruneisen parameters thus providing the largest contribution to the NTE. The existence of these unusual low-frequency vibrational modes can be ascribed to the presence of GdN6 trigonal prisms in the framework structure of GdFe(CN)6.(c) 2023 Published by Elsevier B.V. on behalf of Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.