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Secondary electron emission from a protective layer in AC PDP is known to be dominated by potential emission mechanism, which is sensitive to its energy band structure. Therefore, the secondary electron emission property can be modified by a change in the energy band structure of the protective layer. The addition of controlled amount of titanium oxide into the conventional magnesium oxide protective material might affect the overall voltage characteristics of panels due to the fact that TiO2 has higher dielectric constant than MgO and that the ion radius of Ti is similar to that of Mg. The electrical properties of panels with protective layers evaporated from the starting materials with different [TiO2/(MgO + TiO2)] ratios were investigated. When the [TiO2/(MgO + TiO2)] ratios of 0.1 and 0.15 were used, the panel exhibited a sustaining voltage of 122 V, which was 16 V smaller than that of the pure MgO, without lowering its memory margin. The relative dielectric constant of Mg2−2xTixO2 films increased with addition of TiO2 to the pure MgO, however, it then suddenly decreased above the [TiO2/(MgO + TiO2)] ratio of 0.1. The surface roughness of Mg2−2xTixO2 had a minimum when the [TiO2/(MgO + TiO2)] ratio in the starting materials was 0.1. The variation trends of the relative dielectric constant and the surface roughness of Mg2−2xTixO2 films with increasing [TiO2/(MgO + TiO2)] ratio in the starting materials were found to be consistent with that of the voltage characteristics.