Exceptional Negative Thermal Expansion and Phase-Transition in Cu2-xMnxP0.5V1.5O7 Compounds

Negative thermal expansion (NTE) materials are unusual substances that shrink when heated and expand when cooled, garnering considerable attention due to their potential applications. Recently, Cu2P2O7 has garnered recognition for its excellent NTE performance (αv ~ -26.5×10-6 K-1 from 5 to 373 K) and facile synthesis. Interestingly, the NTE temperature range of this material can be expanded by substituting P with V, particularly with a P substitution value of 0.5. Therefore, starting with Cu2P0.5V1.5O7, we discovered that substituting Mn for Cu resulted in a structural phase transition in the Cu2-xMnxP0.5V1.5O7 system (x<=0.2), leading to extraordinary NTE properties: during the phase transition, the maximum volume reduction reached -1.6%, marking the most significant shrinkage recorded within the same temperature range to date. By employing EXAFS spectroscopy, we expect to gain a better understanding of the mechanism underlying this exceptional contraction.