Study of partially stabilized Ce doped ZrO<sub>2</sub> crystals by electron paramagnetic resonance
The study of crystals of ZrO<sub>2</sub> solid solutions (PSZ) stabilized with yttrium and cerium oxides was carried out by electron paramagnetic resonance (EPR) in the X and Q range. The presence of Zr<sup>3+</sup> centers in annealed ZrO<sub>2</sub> crystals stabilized only by yttrium oxide (2.8 mol.% Y<sub>2</sub>O<sub>3</sub>) is established. Another kind of paramagnetic O-centers appear when CeO<sub>2</sub> is added to ZrO<sub>2</sub> crystals in addition to yttrium oxide. To estimate the concentration of Ce<sup>3+</sup> ions in PZS crystals, EPR spectra were recorded in the presence of a reference specimen at 7 K. Paramagnetic Ce<sup>3+</sup> ions have been identified and their relative amounts in PSZ crystals before and after high-temperature heat treatment has been measured. The annealing in air leads to a decrease in the concentration of Ce<sup>3+</sup> ions for all compositions and changes the color of the crystals from red to white. After annealing in the 2.0Y0.8Ce3Zr sample, the amount of paramagnetic Ce<sup>3+</sup> ions decreased approximately twice. Paramagnetic centers from Ce<sup>3+</sup> are not detected in a the sample with a low cerium content of 0.1 mol.% after annealing which indicates the complete transition of Ce<sup>3+</sup> to the Ce<sup>4+</sup> state. It is shown that the formed paramagnetic centers of cerium are bound by strong exchange interactions. No angular dependence of the EPR lines for the paramagnetic Ce<sup>3+</sup> cations on the applied external magnetic field was observed. The probable reason for the absence of such angular dependence is that impurity rare-earth ions are located next to each other, forming impurity clusters with effective spin Seff = 1/2.