Valence electron structure and properties of the ZrO2

To reveal the properties of ZrO₂ at the atom and electron levels, the valence electron structures of three ZrO₂ phases were analyzed on the basis of the empirical electron theory of solids and molecules. The results showed that the hybridization levels of Zr and O atoms in the m-ZrO₂ were the same as those in the t-ZrO₂, while those in the c-ZrO₂ rose markedly. The electron numbers and bond energies on the strongest covalent bonds in the m-ZrO₂ phase were the greatest, the values were 0.901106 and 157.5933 kJ/mol, respectively. Those in the t-ZrO₂ phase took second place, which were 0.722182 and 123.9304 kJ/mol, and those in the c-ZrO₂ phase were the smallest, which were 0.469323 and 79.0289 kJ/mol. According to the product of the bond energy on the strongest covalent bond and equivalent bond number (this value reflected the crystal cohesive energy), the order from the greatness to smallness was the c-ZrO₂> t-ZrO₂ > m-ZrO₂. This showed that the m-phase bonds were the tightest, their energy was the smallest, the crystal cohesive energy of the m-phase was the largest, and the m-phase existed most stably at room temperature. So it must need energy or higher temperature to take apart the stronger covalent bonds to form a new phase. Supported by the Major Project of the National Natural Science Foundation of China (Grant No. 90505015)