ABSTRACT
Tailoring the thermal expansion coefficient of negative thermal expansion (NTE) materials to achieve near-zero thermal expansion has attracted great attention recently. Here, LiFe diatoms are adopted to substitute Cu in Cu2P2O7 oxide to design Li-O-P and Fe-O-P linkages, with the stronger bond strength of Li-O and Fe-O compared to Cu-O and hence lowering the bond strength of P-O. With increasing the diatomic LiFe in (LiFe)0.5xCu2-xP2O7, new Raman bands corresponding to LiFeP2O7 appear and the NTE coefficient decreases gradually to near-zero thermal expansion at x = 1 (αv = -0.90 × 10-6 °C-1, -100 to 55 °C). Comparing (LiFe)0.5CuP2O7 with Cu2P2O7 and LiFeP2O7, the average bond length of P-O increases while the bond angle of P-O-P decreases, and this is verified by some weakened vibrational energies of terminal PO3 and P-O-P, resulting in the obvious red shift of Raman bands. Ceramic (LiFe)0.5CuP2O7 presents a lower difference in grain size and a higher relative density than Cu2P2O7 and LiFeP2O7.
