Molybdenum lowers negative thermal expansion of zirconium vanadate to room temperature

The phenomenon of negative thermal expansion (NTE) has attracted attention for its potential uses ranging from cooktops and dental fillings to mitigating the positive thermal expansion in composite materials. Zirconium vanadate, ZrV₂O₇, is one well-known such material, but its NTE properties are only observed at temperatures above water’s boiling point. New work provides a better understanding of this material’s unique behavior.

Wei et al. report a method for modifying the superstructure of ZrV₂O₇ to achieve NTE at room temperature. Using solid-state reactions to substitute molybdenum for some of the material’s vanadium atoms, the group found several high-energy phonon modes with negative Grüneisen parameters help drive the NTE phenomenon.

“The method to widen the isotropic NTE temperature range of zirconium vanadate covering room temperature will speed up the research into applications of this material and the design of novel materials with this structure with better properties, such as more broadened NTE range and enhanced NTE amplitude,” said author Erjun Liang. “The observation of high energy optical phonons contributing considerably to the NTE of this structure set up a stage for theoretical investigations on the mechanisms of NTE.”

Through a series of structural measurements including high-resolution synchrotron X-ray diffraction, neutron powder diffraction and high-pressure Raman spectroscopy, the group found the V-O₂-V/Mo angle expanded from 160 to 180 degrees when molybdenum was incorporated. This resulted in a reduction in the temperature of the transition from the superstructure to the parent cubic structure exhibiting NTE from 375 to 225 Kelvin.

Liang hopes to further investigate the theoretical underpinnings of zirconium vanadate’s NTE mechanism, as well as methods to extend the temperature range of the phenomenon and evaluate the effect of oxygen vacancies on NTE.

Source: “Realizing isotropic negative thermal expansion covering room temperature by breaking the superstructure of ZrV₂O₇,” by Wei Wei, Qilong Gao, Juan Guo, Mingju Chao, Lunhua He, Jun Chen, and Erjun Liang, Applied Physics Letters (2020). The article can be accessed at https://doi.org/10.1063/1.5143691 .