Meaning
Non stoichiometric form of zirconium dioxide characterized by a deficiency in oxygen atoms relative to the standard crystal structure. The material zro2-x exhibits unique electronic and catalytic properties compared to the fully oxidized white zirconia. It often appears as a black or dark grey powder due to the presence of free electrons and structural defects.
Defect Chemistry
Creation of the sub oxide involves the removal of oxygen from the lattice under reducing conditions. In zro2-x, the missing atoms create vacancies that facilitate the movement of charge carriers. This modification transforms an insulating ceramic into a semiconductor with tunable electrical resistance.
Catalytic Activity
Surface defects provide active sites for the promotion of chemical reactions. The unsaturated bonds in zro2-x attract reactant molecules more strongly than the stoichiometric surface. This enhancement is used in the production of hydrogen and the synthesis of organic compounds where a reactive substrate is required.
Phase Transformation
Stability of the crystalline lattice depends on the concentration of vacancies and the temperature. While pure zirconia undergoes volume changes during cooling, zro2-x can be stabilized in the cubic or tetragonal phase at room temperature. This structural control prevents the cracking of ceramic coatings used in high temperature environments.
By adjusting the value of x, the lattice of zro2-x is tuned to match the thermal expansion of the underlying metal substrate. This compatibility is essential for the longevity of thermal barrier coatings and electrochemical sensors. The material remains mechanically stable even when cycled between extreme temperatures.
