The changes of signal intensity oF Zr~(3+) centers of ZrO_2 nanopowder in various gases (He, H_2, O_2, air and wet air) and at different annealing temperatures have been studied by means of ESR. On the surface of ZrO_2, about 1 * 10~(-7) mol·g of Zr~(3+) centers were detected, which are the oxygen coordinatively unsaturated Zr ions. It is found that the concentration of Zr~(3+) center changes reversibly and quickly with O_2 partial pressure in various gases. This result reveals that the Zr~(3+) centers are mainly on the surface of ZrO_2 and their concentration is related to O_2 adsorption equilibrium. Based on the quantitative ESR analysis and particle size data of ZrO_2, the present authors propose that the oxygen coordinatively unsaturated Zr~(3+) centers should be located at the crystal corners of ZrO_2 initial particles.

Key words: ZIRCONIUM OXIDE, ADSORPTION, ESR, OXYGEN