*2.3.4 Conclusions: important points concerning complex perovskites*


**23**

provided the original work is properly cited.

*Dielectric Losses of Microwave Ceramics Based on Crystal Structure*

The microwave dielectrics are the perfect, ideal and well-proportional crystal structures for low dielectric losses. Most of them belong to paraelectrics with inversion symmetry *i* and showing high symmetry and nondefects. In this chapter, the effects of ordering and symmetry were presented as follows: there are two types of ordering conditions. One is a case of nonphase transition such as pseudo tungstenbronze solid solutions. These compounds show compositional ordering at a unique point of *x* = 2/3 on the Ba6−<sup>3</sup>*xR*8+2*x*Ti18O54 system, which shows the highest *Qf* without degradation of crystal symmetry. The other is a case of order-disorder phase transition such as indialite/cordierite. Indialite with a disordered structure and a high symmetry of 6/*mmm* point group has a higher *Qf* than cordierite with an ordered structure and low symmetry of *mmm* point group. It is clarified that the effect of high symmetry is predominant for high *Qf*. In the case of complex perovskite, a long sintering time of more than 80 h brings a high *Qf* accompanying ordering. It was clarified that the ordering is not necessary for high *Qf* and only a barometer of sintering in the solid-state reaction. Moreover, compositions deviated from stoichiometric complex perovskite showed higher *Qf* than the stoichiometric composition which has substituted Ta-ions for Mg/Zn-ions. The substitution brings a high density that is the compositional density. It was clarified that high compositional density brings high *Qf*.

The authors are grateful to Professors and graduate students of NIT, Meijo University and Hoseo University, and Doctors and researchers in the many companies, which collaborated with NIT. Visiting Professor Hitoshi Ohsato is grateful to the following projects: (1) support industries of Japan by Ministry of Economy, Trade and Industry (METI), Japan, (2) JSPS KAKENHI Grant Number 22560673, 25420721, JP16K06735 and (3) Nokia Foundation 2016 for Nokia Visiting Professors Project 201700003. Professor Heli Jantunen and Dr. Jobin Varghese are grateful to European Research Council Project No. 24001893 for financial assistance. The authors would also like to thank Honorary Research Professor Arthur E Hill of Salford University for valuable discussion and improving English during the preparation of this manuscript.

*DOI: http://dx.doi.org/10.5772/intechopen.82483*

**3. Conclusions**

**Acknowledgements**

**Author details**

Nagoya, Japan

Hitoshi Ohsato1,2\*, Jobin Varghese1

Engineering, University of Oulu, Oulu, Finland

\*Address all correspondence to: ohsato.hitoshi@gmail.com

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

and Heli Jantunen1

1 Microelectronics Research Unit, Faculty of Information Technology and Electrical

2 Department of Research, Nagoya Industrial Science Research Institute,
