Effects of Structural Characteristics on Dielectric Properties of Mg4Nb2O9–based Ceramics at Microwave Frequencies.

Reference Presenter Authors
(Institution)
Abstract
08-075 Eung Soo Kim Kim, E.(Kyonggi University); With the great demand for 5G wireless communication systems, much attention has been paid to the microwave dielectric materials with high quality factor (Qf). Several types of dielectric materials have been investigated and one of good candidate is Mg4Nb2O9 with corundum structure and there have been various attempts to improve Qf value of Mg4Nb2O9 ceramics by substituting divalent cations for Mg2+ or pentavalent cations for Nb5+. Most of these studies have been discussed for the relationships between the dielectric properties of Mg4Nb2O9-based ceramics and extrinsic factors, such as a secondary phase, density, and microstructure. However, fundamental studies should be carried out to understand the dependence of the microwave dielectric properties on the structural characteristics, which enables control and improvements in the microwave dielectric properties of Mg4Nb2O9-based ceramics. Mg4Nb2O9-based ceramics with corundum structure consists of three types of oxygen octahedral: Mg(1)O6, Mg(2)O6, and NbO6. The NbO6 octahedra are linked by face sharing. The bond lengths between the cation and oxygen ions in oxygen octahedra are affected by the ionic characteristics of the central ion. Therefore, the substitution of other cations at Nb-sites may change the bond length and bond strength, which affects the dielectric properties of Mg4Nb2O9-based ceramics as well as the characteristics of the corundum crystal structure. By several types of isovalent substitutions at Nb-sites, the characteristics of the bond between the cations and oxygen ions in oxygen octahedra can be modified to affect the dielectric properties of Mg4Nb2O9-based ceramics. Typically, two types of isovalent substitutions, (BxW6+1-x)5+ (B=Li1+, Mg2+, Al3+, Ti4+) and (M4+1/2W6+1/2)5+ (M=Ti4+, Sn4+, Zr4+) at Nb-sites of Mg4Nb2O9 will be discussed based on the relationships between the structural characteristics and microwave dielectric properties of Mg4Nb2O9-based ceramics.
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