Significant enhancement of negative thermal expansion in LiYO2 induced by microstructure effect

The limited volume shrinkage rate poses a barrier to the application of negative thermal expansion (NTE) materials, and there are rare methods to significantly enhance NTE. Microstructure effect is an effective method to realize enhancement of NTE in bulk samples. However, there are a few reported materials exhibiting this effect. Herein, we achieved a significant enhancement of NTE in the phase-transition-type NTE material LiYO2. LiYO2 possesses a smaller unit cell volume in its high temperature phase than that in the low temperature phase, resulting in the intrinsic volume contraction (0.88%) before the phase transition completed. The volume contraction of the bulk sample reaches 3.66% from −100 to 50 °C, which is 4.16 times that of the powder sample. The results show that LiYO2 is sensitive to pressure, and the internal stress in the bulk sample facilitates the phase transition process. The anisotropy of LiYO2 and the pores in the bulk sample induce a microstructural effect. This work makes LiYO2 a promising material for NTE applications.