Tuning thermal expansion from strong negative to zero to positive in Cu_2-xZn_xP₂O₇ 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 Cu_2-xZn_xP₂O₇ (0 ≤ x ≤ 2) were synthesized by solid state reaction methods. The thermal expansion in Cu_2-xZn_xP₂O₇ is tuned from strong negative thermal expansion (α_v ∼ -33.5×10⁻⁶ K⁻¹, 100 - 375K) to near zero thermal expansion (α_v ∼ -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.