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Reprint, avatlahle directly trrim the publisher Photuctipying prnnittrd hy liceme only 6 1999 OPA (Overseas Puhlibhers Awxialion) N.V. Published hy licenre under the Gordon and Breach Science Publirhm imprint.The B~,_3,Nd,+~,Til,0sP solid solution (BNT) is well established as a useful microwave resonator material due to its high dielectric constant ( E~) . high quality factor (Q = I/tan&), and tunable temperature coefficient of resonant frequency (Tf). Its crystal structure is similar to that of the tungsten bronzes, containing large pentagonal channels parallel to [Ool], which are only partly occupied by the divalent species. These pentagonal sites are separated by Nd+3 and Ti06 octahedra arranged in an essentially perovskite-like manner. Ceramics of this phase have been processed in this study by a mixed-oxide route, and the variation in properties caused by doping with either Ca, Sr, or Pb was investigated. Most samples showed a multiphase character, with Nd4TigOz4 (ss) being the main secondary phase. For x < 0.75, single-phase BNT was always obtained, while phase purity was only attained at 1400°C when x = 0.75. Doping with PbO was found to usefully reduce 'If whilst leaving both E, and Q at reasonable levels. Pb-doping lead to a moderately lower Q and, contrary to earlier reports, slightly lowered E,.

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The activities of EA Technology in microwave processing of oxide ceramics are reviewed. Comparative sintering rate measurement techniques have been used to demonstrate microwave enhanced densification of oxide ceramics. Temperature distributions within microwave and conventionally heated ceramics are simulated. Based on these simulations a method for firing large components has been developed which achieves uniform microstructures and low thermal stresses by careful control of temperature distribution.

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