Synthesis and characterisation of Ga-doped hexagonal BaTiO3

The hexagonal polymorph of BaTiO3 (P63/mmc) has been stablished at room temperature by partial replacement of Ti by Ga, where BaTi1-yGayO3-y/2 and <f>0.06≤y≤0.125</f> for samples prepared at 1300°C. 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 μm) occurs for ceramics processed at ≥1400°C and/or for sintering periods ≥2 hours. Electrical measurements show the materials to be electrically insulating with room temperature permittivity values of ~70–80. Dense ceramics (94–97% of the theoretical X-ray density) resonate at microwave frequencies with Q.f values of ~4000–8000 at ~5.5 GHz. [Copyright &y& Elsevier]