**Acknowledgements**

This work was financed by the Slovenian Research Agency in the frame of the program group P2-0105, projects J2-5483 and J2-9253, and PhD program of Maja Makarovic. I would like to thank Prof. Dragan Damjanovic for immense and fruitful discussions on domain walls and defect-related pinning effects as well as Maxwell-Wagner piezoelectric relaxation phenomena and modeling. Most of this chapter was written based on my knowledge that I received by working with Dragan. Further thanks go to the team at the Electronic Ceramics Department of the Jozef Stefan Institute for the constant support and never-ending interactive discussions. The research team is also acknowledged for extensive (micro)structural analyses and electric characterization of the carefully prepared samples over multiple scales of the material, without which complex mechanisms, such as those discussed in this chapter, cannot be seriously studied and thus explained.
