Understanding the thermally stimulated relaxation and defect behavior of Ti-containing microwave dielectrics: A case study of BaTi4O9

Relaxation phenomena in dielectrics are well known to be closely related to their defect chemistry. However, the relaxation behavior of microwave dielectrics has seldom been considered, despite these materials being an important member of the electroceramic family. Here, the relaxation behavior of the typical microwave dielectric ceramic barium tetratitanate (BaTi 4 O 9 ) was investigated. Significant thermally stimulated relaxation was observed in both dielectric spectroscopy and thermally stimulated depolarization current (TSDC) measurements, and the correlation between relaxation and defect behavior was addressed. TSDC characterization revealed that defect dipoles [(Ti Ti ' )−(V O •• )] with activation energies ( E a ) of 0.32–0.36   eV appeared at low temperature, while in-grain and across-grain boundary oxygen vacancies (V O •• ) appeared at higher temperature, yielding E a of 0.30–0.48   eV and 0.65–1.01   eV, respectively. It was further believed that these two types of defects, (Ti Ti ' )−(V O •• ) and V O •• , were correspondingly responsible for the dielectric relaxation observed at low and high temperature. The relaxation behavior of several typical Ti-containing microwave dielectrics, such as BaTi 4 O 9 , TiO 2 , MgTiO 3 and Ca 0.8 Sr 0.2 TiO 3 , was compared, which suggests that microwave dielectric performance and defect behavior are closely related to the connections of TiO 6 octahedra in the materials.