Dielectric and microwave absorption properties of KNN/Al2O3 composite ceramics

Abstract Potassium sodium niobate (KNN) based ceramics are commonly used in piezoelectric applications. In this work, we paid attention to their dielectric properties in the frequency range of 8.2–12.4 GHz (x-band) to develop a microwave absorbing ceramic. (1-x)KNN-xAl 2 O 3 (x = 0.1, 0.2, 0.3) ceramics were prepared by the traditional ceramic processing. With the increase of Al 2 O 3 content, the ceramics exhibit smaller particle size and higher porosity. KNN and Al 2 O 3 as well as a small amount of Nb 2 O 5 can be detected in the ceramics. And the third phase is caused by the volatilization of K and Na elements and the diffusion effect of Al and Nb elements. The complex permittivity of the composite ceramics decreases with the increase of Al 2 O 3 , and this is attributed to the low permittivity of Al 2 O 3 as well as the increased porosity of the ceramics. Both the thickness d and Al 2 O 3 content have great influence on the microwave absorption properties of the ceramics. The reflection loss peaks shift to lower frequency with the increase of the thickness d . And when x = 0.3 and d = 0.95 mm, the ceramic has optimum microwave absorption property with the reflection loss peak is − 6.8 dB and the effective frequency range is 8.66–11.27 GHz.