Effect of calcining temperature on the tetragonal-to-monoclinic phase transition characteristics in 2 mol% yittria-doped zirconia ceramics

Two types of tetragonal-to-monoclinic (t-m) phase transitioncharacteristics were observed in the 2Y-TZP powder samples. In thesample calcined below 1200°C, the t-m phase transitionoccurred below 200°C, and the fraction of the monoclinic phaseincreased sigmoidally. At the beginning of the transition, thefraction of the monoclinic phase increased gradually, and the latticestrain remained unchanged. The abrupt increase in the monoclinicphase accompanying the increase in the lattice strain of thetetragonal phase followed this. Finally, the fraction of themonoclinic phase was saturated, and the lattice strain dropped to0%. The reaction between the adsorbed water and 2Y-TZP was essentialfor the t-m phase transition of 2Y-TZP to occur in air at around roomtemperature. The lattice strain stored in the tetragonal latticeassisted the phase transition. On the other hand, the fraction of themonoclinic phase increased, accompanied by a decrease in the latticestrain in the 1400°C calcined powder. After the fraction ofthe monoclinic phase was almost saturated, the lattice strain droppedto 0%. A gas-solid reaction between the water vapor in air and2Y-TZP and the diffusion of OH− ion into the 2Y-TZP lattice wereessential for this type of t-m phase transition.