Scientists from the Frank Laboratory of Neutron Physics at JINR, Osimi Tajik Technical University, and Lusofona University (Portugal) summarised the results of structural stability, electronic properties, and phonon dispersion studies of biocompatible zirconium dioxide, one of the most common materials for dental crowns and dentures, in its cubic (c-ZrO₂), tetragonal (t-ZrO₂), and monoclinic (m-ZrO₂) phases.

Figure 1. Crystal lattice models: a) cubic, b) tetragonal, and c) monoclinic phase of ZrO₂

The authors found that the monoclinic phase of zirconium dioxide is the most stable among the three phases in terms of total energy, lowest enthalpy, highest entropy, and other thermodynamic properties. In addition, the presence of rather weak frequencies in m-ZrO₂ confirms that the monoclinic phase is a stable conformation of zirconia.

The analysis of the electronic properties showed that during the m-t phase transformation of ZrO₂, the Fermi level first shifts by 0.125 eV toward higher energies and then decreases by 0.08 eV in the t-c cross-section. The band gaps for c-ZrO₂, t-ZrO₂, and m-ZrO₂ are 5.140 eV, 5.898 eV, and 5.288 eV respectively. Calculations to study the effect of 3.23, 6.67, 10.35, and 16.15 mol%Y₂O₃ on the structure and properties of m-ZrO₂ showed that the enthalpy of m-YSZ (zirconium dioxide stabilised with yttrium oxide) decreases linearly and accompanies further stabilisation of zirconium dioxide. Doping-induced phase transitions of ZrO₂ were discovered under the influence of Y₂O₃ doping, due to which the position of the Fermi level changes, and the band gap decreases.

It was established that the main contribution to the formation of the conduction band is made by the p-states of electrons, not only in pure systems, but also in those doped with Y₂O₃.

Biocompatible zirconium dioxide is one of the most common materials for dental crowns and dental implants. In addition, it is used for the production of joint endoprostheses. The material has high strength and low thermal conductivity, i.e. it causes no painful sensations when in contact with hot and cold food. Biocompatibility is a property of high-quality zirconium dioxide, whereby it does not provoke allergic reactions and does not irritate body tissues.

An article Study on Structural Stability of ZrO₂ and YSZ: Doping-Induced Phase Transitions and Fermi Level Shift is published in Advanced Energy Conversion Materials. A FLNP leading researcher Kholmirzo Kholmurodov is among the authors.