Realizing isotropic negative thermal expansion covering room temperature by breaking the superstructure of ZrV2O7

Abstract

ZrV2O7 is a well-known isotropic negative thermal expansion (NTE) material. However, the NTE property of ZrV2O7 can only be observed in high temperatures above 375 K. In this paper, we report a facile method to break the superstructure of ZrV2O7 for realizing the NTE property of ZrV2O7 to room temperature by partial substitution of Mo for V atoms. The detailed structure information and the phase transition process are revealed by high-resolution synchrotron x-ray diffraction, neutron powder diffraction, and high pressure Raman spectral analyses. It is found that the incorporation of Mo prompts the V-O2-V/Mo angles to expand from 160° to 180°, which enables the NTE property at room temperature. Different from most open framework structures where NTE is dominated by low energy phonons, here several high energy phonon modes are found to have negative Grüneisen parameters and contribute to the negative thermal expansion.