Monolithic t‐ZrO2 Nanopowder through a ZrO(OH)2·xH2O Polymer Precursor

Abstract

Monolithic t‐ZrO2 (tetragonal structure) nanopowder is synthesized with an amorphous ZrO(OH)2·xH2O polymer precursor. The H2O molecules impart the structure and promote reconstructive thermal decomposition of the structure to t‐ZrO2 nanoparticles on heating at temperatures as low as 200°C. A prevalent endothermic heat output in the dissociation process controls the local temperature in exothermic nucleation and growth of various groups of the reaction species so that it is self‐controlled in high‐energy nanoparticles. Crystallites are, on average, d= 8 nm diameter, and they have a high value of Gibbs free energy or lattice volume Vo= 0.06770 nm3. The excess volume decreases to Vo= 0.06705 nm3 if the reaction temperature is increased to >200°C, i.e., approximately the bulk value of 0.06681 nm3; there is a minor increase to d= 12 nm at 600°C. Many oxygen vacancies in the thin surface space‐charge layers seem to support the stability of small particles in this particular polymorph. A pure m‐ZrO2 (monoclinic structure) appears with d= 22 nm at temperature as low as 800°C. The results are analyzed using X‐ray diffractometry, microstructure, infrared spectroscopy, and thermal studies of the polymer precursor and derivative t‐ZrO2 nanoparticles.