Control of Thermal Expansion in TaVO₅ by Double Chemical Substitution

The control of thermal expansion is an important and challenging issue. Focusing attention on the class of AMO₅ negative thermal expansion (NTE) materials, an approach to control their thermal expansion is still missing. In this work, the thermal expansion of TaVO₅ has been controlled from strong negative to zero to positive by double chemical substitution, i.e., Ti and Mo replace Ta and V elements, respectively. A joint study of temperature-dependent X-ray diffraction, X-ray photoelectron spectroscopy, and first-principles calculations has been performed to investigate the thermal expansion mechanism. With the increasing substitution of Ti and Mo atoms, the valence state always remains balanced, and the volume decreases together with a lattice distortion, which leads to the suppression of the NTE. Lattice dynamics calculations confirm that the negative Grüneisen parameters of the low-frequency modes weaken and the thermal vibrations of the polyhedral units diminish after the substitution of Ti and Mo atoms. The present work successfully achieves a tailored thermal expansion in TaVO₅ and draws a possible way to control the thermal expansion of other NTE materials.