Ba3ZnTa2-x,NbxO9 and Ba3MgTa2-xNbxO9 (0 ≤ x ≤ 1):: synthesis, structure and dielectric properties

Oxides belonging to the families Ba3ZnTa2-xNbxO9 and Ba3MgTa2-xNbxO9 were synthesized by the solid state reaction route. Sintering temperatures of 1300degreesC led to oxides with disordered (cubic) perovskite structure. However, on sintering at 1425degreesC hexagonally ordered structures were obtained for Ba3MgTa2-xNbxO9 over the entire range (0 less than or equal to x less than or equal to 1) of composition, while for Ba3ZnTa2-xNbxO9 the ordered structure exists in a limited range (0 less than or equal to x less than or equal to 0.5). The dielectric constant is close to 30 for the Ba3ZnTa2-xNbxO9 family Of oxides while the Mg analogues have lower dielectric constant of similar to18 in the range 50 Hz to 500 kHz. At microwave frequencies (5-7 GHz) dielectric constant increases with increase in niobium concentration (22-26) for Ba3ZnTa2-xNbxO9; for Ba3MgTa2-xNbxO9 it varies between 12 and 14. The "Zn" compounds have much higher quality factors and lower temperature coefficient of resonant frequency compared to the "Mg" analogues. (C) 2002 Elsevier Science Ltd. All rights reserved.