Tuning Thermal Expansion From Strong Negative to Zero to Positive in Cu 2- x Zn x P 2 O 7 Solid Solutions

Chemical substitution is an effective method to control the thermal expansion properties in solid solutions. In this work, a series of solid solutions Cu2-xZnxP2O7(0 ≤ x ≤ 2) were synthesized by solid state methods. The thermal expansion in Cu2-xZnxP2O7 is tuned from strong negative thermal expansion (αv ~ -33.5×10-6 K-1, 100 - 375K) to near zero thermal expansion (αv ~ -2.78×10-6 K-1, 100 - 225K), and then to positive thermal expansion gradually with increasing content of Zn2+ substitution. The direct experiment results reveal that the Zn2+ substitution diminishes the rigidity of Cu/Zn-O and P-O bonds and the transverse vibrations of O atoms arousing negative thermal expansion. The present work realizes the control of thermal expansion from negative to near zero, and then to positive in the Cu2P2O7 system.