Patent 7276462 was granted and assigned to NGK Insulators on October, 2007 by the United States Patent and Trademark Office.
Provided is a dielectric composition which, when applied to an electron emitter, enables suppression of reduction of electron emission quantity with passage of time. The dielectric composition contains, as a primary component, a PMN-PZ-PT ternary solid solution composition represented by the following formula PbxBip(Mgy/3Nb2/3)aTib-zMzZrcO3 [wherein x, p, and y satisfy the following relations: 0.85≦x≦1.05, 0.02≦p≦0.1, and 0.8≦y≦1.0; a, b, and c are decimal numbers falling within a region formed by connecting the following five points (0.550, 0.425, 0.025), (0.550, 0.150, 0.300), (0.100, 0.150, 0.750), (0.100, 0.525, 0.375), and (0.375, 0.425, 0.200); z satisfies the following relation: 0.02≦z≦0.10; and M is at least one element selected from among Nb, Ta, Mo, and W], and contains Ni in an amount of 0.05 to 2.0 wt. % as reduced to NiO.