Tailoring Thermal Expansion of (LiFe) 0.5 x Cu 2- x P 2 O 7 via Codoping LiFe Diatoms in Cu 2 P 2 O 7 Oxide.

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 Cu 2 P 2 O 7 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) 0.5 x Cu 2- x P 2 O 7 , new Raman bands corresponding to LiFeP 2 O 7 appear and the NTE coefficient decreases gradually to near-zero thermal expansion at x = 1 (α v = -0.90 × 10 -6 °C -1 , -100 to 55 °C). Comparing (LiFe) 0.5 CuP 2 O 7 with Cu 2 P 2 O 7 and LiFeP 2 O 7 , 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 PO 3 and P-O-P, resulting in the obvious red shift of Raman bands. Ceramic (LiFe) 0.5 CuP 2 O 7 presents a lower difference in grain size and a higher relative density than Cu 2 P 2 O 7 and LiFeP 2 O 7 .