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Detailed Program
Paper Number : EL-O03
Time Frame : 18:09~18:21
Presentation Date : Thurseday, 27, November
Session Name : Electronic Ceramics
Session Chair 1# : Chae Il Cheon
Session Chair 2# : Hitoshi Ohsato
Effects of Mg and/or Ti-site substitution on Microwave Dielectric Properties of MgTiO3-based Ceramics
Hyun Jin JO
Kyonggi University
With the rapid development of wireless communication systems, the high quality factor (Qf) of microwave dielectrics is important factor to meet the needs for low dielectric loss. Although MgTiO3-based ceramics are well-known for dielectric materials with high Qf value, the dependence of dielectric properties on structural characteristics should be investigated to improve the Qf value of MgTiO3-based ceramics. These investigations could be applied to develop the enhanced dielectric properties of materials at microwave frequencies effectively.
In this study, dependence of the microwave dielectric properties on divalent and/or tetravalent cation substitution for Mg and/or Ti-sites of MgTiO3-based ceramics were investigated (MgTiO3 (MT), (Mg0.95Zn0.05)TiO3 (MZT), Mg(Ti0.95Sn0.05)O3 (MTS), (Mg0.95Zn0.05)(Ti0.95Sn0.05)O3 (MZTS)). Crystal structural characteristics of MgTiO3-based ceramics were quantitatively evaluated by the Rietveld refinement method from the X-ray diffraction (XRD) data.
Single phase of ilmenite structure was obtained for the MgTiO3-based ceramics sintered at 1400oC for 4h. For the MgTiO3-based ceramics in this study, MZTS ceramics showed the largest unit-cell volume due to the larger ionic radius of Zn2+ (0.74 Å) and Sn4+ (0.69 Å) than that of Mg2+ (0.72 Å) and Ti4+ (0.609 Å) at a coordination number of 6, respectively. For the microstructure of MZTS ceramics with substitution of Zn2+ and Sn4+ for Mg and Ti-sites of MgTiO3 ceramics showed more uniform grain size than that of pure MgTiO3 ceramics, which improved the Qf value of MZTS ceramics.
Qf value of MgTiO3-based ceramics significantly depended on the B-site bond valence as well as the average covalency of ABO3 ilmenite structure. It has been reported that strong bond valence means high bond strength between cation and oxygen ions in oxygen octahedra, which decreased the lattice anharmonicity. MZTS ceramics showed higher Qf value than those of other MgTiO3-based ceramics due to both the largest B-site bond valence and average covalency, which was affected by low electronegativity difference. Temperature coefficients of resonant frequency (TCF) of MgTiO3-based ceramics were affected by the average oxygen octahedral distortion of ilmenite structure. The TCF value of MZTS ceramics was lower than that of other MgTiO3-based ceramics because of lower average oxygen octahedral distortion. Also, the dielectric constants (K) of MgTiO3-based ceramics were dependent on the dielectric polarizability of composing ions obtained from the additivity rule. The K value of MTS ceramics was lower than that of other MgTiO3-based ceramics due to lower polarizability of Sn4+ (2.83 Å3) than that of Ti4+ (2.93 Å3).


References:

[1] J. Li, Y. Han, T. Qiu, C. Jin, Mater. Res. Bull. 47 (2012) 2375.
Acknowledgements : This research was supported by Basic Science Research Program throuth the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology.