Tuning thermal expansion and phase transition temperature with Mg substitution in Zn2V2O7

Abstract

The thermal expansion coefficient of a material exhibiting negative thermal expansion above 400 °C, Zn${}_2$V${}_2$O${}_7$, was tuned using Mg as a substituent on the Zn site. Samples $x=0.0,0.1,0.2$ and 0.3 were prepared using high-temperature ceramic methods. Changes to the structure and properties with Mg substitution were analyzed using Rietveld refinement of ambient and variable-temperature X-ray diffraction data (VTXRD) using synchrotron radiation. The parent structure Zn${}_2$V${}_2$O${}_7$ transitions from the $\alpha$ phase ($C2/c$) to the $\beta$ phase ($C2/m$) near 650 °C, and Mg substitution lowers the temperature of this transition as corroborated by differential scanning calorimetry measurements. Mg substitution allows the volume thermal expansion coefficient to be tuned from –19.80 ppm K⁻¹ in $x=0.0$ to –13.46 ppm K⁻¹ in $x=0.3$.