Microstructural effects on negative thermal expansion extending over a wide temperature range in β-Cu_1.8Zn_0.2V₂O₇

We discuss that β-Cu_1.8Zn_0.2V₂O₇ exhibits a large negative thermal expansion (NTE) behavior with a wide operating temperature window. The crystallographic parameters obtained by synchrotron x-ray diffraction experiments indicate that the volume contraction of β-Cu_1.8Zn_0.2V₂O₇ remains at most Δv/v = 0.83%. In contrast, the dilatometry measurements show T-linear NTE behavior from 100 K to 700 K and a large volume contraction of ΔV/V = 2.16% on heating from 200 K to 700 K. This discrepancy indicates that NTE in β-Cu_1.8Zn_0.2V₂O₇ is enhanced by the microstructural effect, similar to that employed for explaining the colossal NTE behavior in layered ruthenates. We further discuss that β-Cu_1.8Zn_0.2V₂O₇ is free from expensive and toxic elements, making it a potential candidate for practical NTE materials.