Negative thermal expansion and electrical properties of α-Cu2V2O7

The orthorhombic copper(II) vanadate (α-Cu2V2O7) was synthesized using a solid state method, and its negative thermal expansion (NTE) and electrical properties were systematically studied. The results show that the α-Cu2V2O7 exhibits NTE property linearly from room temperature (RT) to 470 K with the coefficient of thermal expansion (CTE) −5.8 × 10−6 K−1. The coupling rotation of rigid unit modes (RUMs) caused by transverse vibrations of bridge oxygen atoms is attributed to the NTE behavior. Moreover, NTE property performs nonlinearity in 470-610 K, and the average CTE is about −2.4 × 10−6 K−1 which is caused by the synthetic action of d9 Jahn-Teller effect of Cu2+ and small amount of micro-pores. The material exhibits low thermal expansion between 610 and 720 K with CTE 0.43 × 10−6 K−1. The distortion effect was confirmed by UV-vis absorption spectroscopy. The impedance spectroscopy analysis shows that the α-Cu2V2O7 has a certain semiconductor property, which is consistent with the results of ab-initio calculation. The NTE property and pyroconductivity bring a good potential application in composite conductive ceramic and high temperature conductive materials.