Preparation and Formation Mechanism of ZrW2O8 by Sol–Gel Process

Abstract

ZrW2O8 is known as a material that shows negative thermal expansion. Amorphous ZrW2O8 with a particle size of 50–300 nm was prepared by a sol–gel process at a lower temperature of 723 K for 12 h. X‐ray diffraction analysis showed that the amorphous ZrW2O8 started to crystallize at 833 K and remained kinetically stable up to 953 K. We investigated the formation mechanism in a sol–gel process of ZrW2O8 by Fourier transform‐infrared spectroscopy, thermogravimetry‐differential thermal analysis, and X‐ray diffraction analysis. The precursor solution changed into an amorphous precursor sol at room temperature, and this changed into a crystalline precursor gel between 351 and 358 K. The precursor ZrW2O7(OH)2(H2O)2 was obtained by drying this gel at 343 K. These results indicate that the crystallization of the amorphous precursor depends on the heat‐treatment temperatures under low pH conditions because the residual −OH or −OR groups are removed by polycondensation reactions.