Synthesis and characterisation of Ga-doped hexagonal BaTiO3

The hexagonal polymorph of BaTiO3 (P6(3)/mmc) has been stablished at room temperature by partial replacement of Ti by Ga, where BaTi1-yGayO3-y/2 and 0.06less than or equal toyless than or equal to0.125 for samples prepared at 1300degreesC. The unit cell expands with increasing y and Rietveld Refinement of Neutron diffraction data shows that oxygen vacancies occur only in the hexagonal close packed layers between the face-sharing Ti2O9 dimers. Exaggerated grain growth (> 100 mum) Occurs for ceramics processed at greater than or equal to1400degreesC and/or for sintering periods 2 hours. Electrical measurements show the materials to be electrically insulating with room temperature permittivity values of similar to70-80. Dense ceramics (94-97% of the theoretical X-ray density) resonate at microwave frequencies with Q.f values of similar to4000-8000 at similar to5.5 GHz.