Birefringence above Tc in single crystals of barium titanate

• Published in: Journal of physics. Condensed matter Vol. 20; no. 14; pp. 142202 - 142202 (5)
• Main Authors: Ziębińska, A, Rytz, D, Szot, K, Górny, M, Roleder, K
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 09.04.2008; Institute of Physics
• Subjects: Birefringence (including stress birefringence, flow birefringence, etc.); Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of bulk materials and thin films; Physics; Monocrystals; Ferroelectric materials; Temperature effects; Thermal hysteresis; Birefringence; Barium titanates; Crystal symmetry; Heat treatments; Symmetry breaking; Soft modes
• ISSN: 0953-8984; 1361-648X
• DOI: 10.1088/0953-8984/20/14/142202

The temperature dependence of the birefringence above Tc in high quality BaTiO3 single crystals has been measured with very high accuracy. On the basis of literature data, the behaviour of the anomalous birefringence can be explained by the existence of polar clusters (microregions/nanoregions) connected with correlated jumps between the off-centre positions of Ti ions inside the oxygen octahedra. The underlying origin of the polar clusters is an intrinsic effect connected with the interdependence of the structural and polar soft modes (Bussmann-Holder et al 2007 Phys. Rev. Lett. 99 167603). These clusters locally break the intrinsic cubic symmetry and the phase above Tc becomes birefringent. A birefringence Deltan of the order of 10-5 has been found up to about 30 deg above Tc. In this temperature range Tc < T < Tc+30 K, the function Deltan(T) exhibits a thermal hysteresis: the values of Deltan were higher on heating than on cooling. A characteristic feature is the existence of a local Deltan(T) maximum at a temperature close to Tc on the high temperature side that appears due to a specific cluster-cluster interaction. Since the values of Deltan(T) runs were not dependent on the crystal thickness, one can conclude that in this limited temperature range above Tc the birefringence is an inherent feature of the crystal.