Effect of NiO and Al₂O₃ on the Curie temperature, microstructure, and dielectric properties of Ba0.5Sr0.5TiO₃ ceramics

A series of new x ( y NiO/ z Al 2 O 3 )‐(1– x )Ba 0.5 Sr 0.5 TiO 3 ( x = 10, 30, and 50 wt.%, y = 1, 1.3, 1.5, z = 1, 1.3, and 1.5 mol) ceramics were prepared using the solid‐phase method. The effects of the spinel oxides on the microstructure, lattice vibrations, and dielectric properties of Ba 0.5 Sr 0.5 TiO 3 were assessed. When NiO and Al 2 O 3 were present in equal quantities, they reacted to form NiAl 2 O 4 . Under the recombination effect, the dielectric permittivity of Ba 0.5 Sr 0.5 TiO 3 was effectively reduced, the Curie temperature ( T c ) was increased, and tunability gradually increased. The T c value was not significantly altered when NiO was in excess. Impurity phases were generated, and the T c value decreased when Al 2 O 3 was in excess. This study elucidated the unique role of the spinel structure. The 50 wt.%(NiO/Al 2 O 3 )‐50 wt.%Ba 0.5 Sr 0.5 TiO 3 had excellent microwave dielectric properties, with dielectric permittivity, tunability, and Q values of 300, 18.7%, and 357, respectively.