Negative thermal expansion properties of Cu1.8Co0.2V2O7

Abstract

Cu1.8Co0.2V2O7 with negative thermal expansion (αl = −13.2 × 10−6 K−1, 153–773 K) was prepared by adopting the solid phase method. The crystal structure, microstructure, thermal expansion properties, and Raman spectra of Cu1.8Co0.2V2O7 were analyzed by using variable temperature X-Ray diffraction (XRD), dilatometer, and variable temperature Raman spectroscopy, respectively. In the crystal structure of Cu1.8Co0.2V2O7, one V5+ and four O2− form [VO4] tetrahedra, two [VO4] tetrahedra form [V2O7] structures by sharing top-angle oxygen atoms, one Cu2+ (Co2+) and five O2− are connected to form a [CuO5] tetragonal units, [CuO5] and [VO4] are connected by sharing O2 and O3 atoms to form a chain to produce a layered staggered structure.The results of variable temperature XRD indicated that with the gradual increase of temperature, the transverse vibration of O atoms shared by [CuO5] and [VO4] increases and the coupling effect between [CuO5] and [VO4] polyhedra is enhanced. Therefore, the angle between Cu–O2–V and Cu–O3–V and the unit cell parameters a and c gradually decrease, leading to a gradual decrease in the Cu1.8Co0.2V2O7 inner layer spacing. This work provides a new negative thermal expansion material.