Phase evolution in the mechanochemical synthesis of stabilized nanocrystalline (ZrO2)0.97(Y2O3)0.03 solid solution by PAC technique

The mechanochemical activation process has proved to be an effective technique to enhance a solid-state reaction at relatively low temperatures. In such a process, the mechanical effects of milling, such as reduction of particle size and mixture homogenization, are accompanied by chemical effects. The actual chemical phases during the mechanical treatments are sometimes difficult to identify and quantify at an atomic level. In the present paper the XRD and PAC techniques are used to study the phase content evolution during the milling process to obtain the tetragonal stabilize (ZrO2)0.97(Y2O3)0.03 solid solution. It has been determined that 10 min of milling time are enough to start the solid solution formation. Both techniques allowed establishing that the obtained crystalline phase was tetragonal. PAC results showed that the stabilized solid solution occurs via the formation of distorted monoclinic ZrO2 form not distinguished by XRD. The time evolution of the phase contents could be modeled as a consecutive first order solid state reaction m-ZrO2→m′-ZrO2→t-SS. The values of the kinetic constants indicate that the process was controlled by the second reaction.