Tuning thermal expansion from strong negative to zero to positive in Cu2-xZnxP2O7 solid solutions

Chemical substitution is an effective strategy 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 reaction 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 achieves the regulation of thermal expansion from negative to near zero and finally to positive in the Cu2P2O7 system.