Determination of the thermal stability and isothermal bulk modulus of the ZrO 2 polymorphs at room temperature by molecular dynamics with a semi-empirical quantum-chemical model

Abstract

We evaluated the thermal stability and isothermal bulk modulus of the cubic (c), tetragonal (t), and monoclinic (m) ZrO 2 polymorphs at room temperature by molecular dynamics with a semi-empirical quantum-chemical model. The procedure used was based on the semi-empirical calculation of the lattice energy of the different polymorphs as a function of the lattice volume, followed by fitting the Murnaghan equation of state to these lattice energy–volume curves. This yields directly the equilibrium lattice energy ( E 0), the equilibrium lattice volume ( V 0), and the bulk modulus ( B 0). The monoclinic form ( E 0 m = − 119.41 eV / Zr O 2 ) was found to be more stable than the tetragonal form ( E 0 t = − 119.29 eV / Zr O 2 ), which in turn was more stable than the cubic form ( E 0 c = − 119.21 eV / Zr O 2 ). We thence deduced the existence of the cubic–monoclinic and tetragonal–monoclinic phase transformations, and calculated the volume changes associated with these phase transformations (∼3.9–4.5%) from V 0 c , V 0 t , and V 0 m . Also, we found that the bulk moduli of the ZrO 2 polymorphs are close to 200 GPa, and are in the sequence B 0 t > B 0 c > B 0 m . All these results were in clear agreement with the literature data, obtained by complex ab initio molecular dynamics and/or sophisticated experimental techniques. This suggests that applications of molecular dynamics with semi-empirical quantum-chemical models may have an important role to play in the theoretical design of ceramic materials.