Electron paramagnetic resonance study of ZnO varistor material.

Matsuoka-type zinc oxide (ZnO) varistor material was synthesized using a conventional solid-state reaction method. X-band electron paramagnetic resonance (EPR) data revealed that Mn ions substitute in the ZnO lattice with a 2+ paramagnetic state. Co ions with either 3+ or 2+ oxidation states are only detectable at cryogenic temperatures. A Cr3+ EPR signal was strongly suppressed or masked by a Mn2+ signal. Photoluminescence and electrical results indicated that the varistor sample has fewer intrinsic defects and much higher resistivity as compared to undoped and metal-ion doped ZnO.