Effective Infrared Response of Inhomogeneous Ferroelectrics

Dielectric inhomogeneities may have rather pronounced effect on the measured effective permittivity and dielectric function in high-permittivity dielectrics including the polar phonon response. We address the effect of grain boundaries in SrTiO₃ and BaTiO₃ ceramics and nanograin ceramics and estimate the dead-layer properties in the grain-boundary region using the generalized brick-wall model. Also we discuss the effective response due to the strong grain anisotropy in the ferroelectric BaTiO₃. A new interpretation of the infrared spectra of classical relaxors is suggested, based on the effective medium approach and rather strong polar cluster anisotropy.

Keywords:

• Relaxors
• effective medium approximation
• infrared dielectric response

Acknowledgments

Helpful discussions with C. Pecharroman from ICM Madrid are acknowledged. The authors thank Jing Liu (Stockholm University) for the ST nano-ceramics, V. Buscaglia (Genova University) for the BT ceramics and nano-ceramics and I. Bykov (IPMS Kiev) for the PMN crystal. The work was supported by the Czech Grant Agency (projects 202/04/0993 and 202/03/0551), Czech Academy of Sciences (projects A1010213 and AVOZ 10100520) and Czech Ministry of Education (project OC 525.20).

Paper originally presented at IMF-11, Iguassu Falls, Brazil, September 5–9, 2005