Effect of dopants on microwave dielectric properties of Ba(Zn1/3Nb2/3)O3 ceramics

Ba(Zn1/3Nb2/3)O3 (BZN) has been prepared with various amounts of different dopants such as oxides of monovalent, divalent, trivalent, tetravalent, pentavalent and hexavalent elements. Effect of these dopants on microwave dielectric properties of BZN is investigated. Some of the dopants are found to increase quality factor Q × f and slightly alter the temperature coefficient of resonant frequency (τf). Annealing undoped BZN increased the quality factor. Small amounts of dopants such as oxides of Ni, In, Al, Ga, Zr, Ce, Sn, Ti, Sb, and W increased the quality factor. The doped ions substitute for the ordered B ions decreasing the order parameter. Annealing increased the quality factor for all doped BZN samples. Doping BZN with In2O3, Al2O3, WO3 and SnO2 decreased the order parameter but at the same time increased the quality factor indicating that order parameter alone is a poor indicator of quality factor. The quality factor is found to depend on the dopant ionic radii and its concentration. The quality factor increased when the ionic radius of the dopant is close to the ionic radius of the B site ions Zn or Nb. Microstructure studies using SEM showed that the doped high Q ceramics contained large grains.