Strong Negative Thermal Expansion of Cu2PVO7 in a Wide Temperature Range

Negative thermal expansion (NTE) is an abnormal thermophysical phenomenon. Although NTE has been discovered in a growing number of materials, it is difficult to achieve both strong NTE and a wide operating temperature range in one material. In this work, the strong NTE of the oxide Cu2PVO7 is reported in a wide temperature range (αv ∼ −26.01 × 10–6 K–1, 100–648 K), where the thermal expansion is highly anisotropic. The NTE capacity of Cu2PVO7 is outstanding among the NTE framework structure oxides. Joint methods of high-resolution synchrotron X-ray diffraction, extended X-ray absorption fine structure, pair distribution function of synchrotron X-ray total scattering, density functional theory calculations, and maximum entropy model calculations were carried out to reveal the NTE mechanism of Cu2PVO7. Transverse vibrations of O atoms together with deformations of CuO5 and P/VO4 polyhedral units account for the rotation and twist among the polyhedra, leading to the NTE. The present work pushes forward progress in research regarding strong NTE oxides.