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DF: Fachverband Dielektrische Festkörper

DF 17: Nano- and microstructured dielectrics

DF 17.4: Vortrag

Donnerstag, 25. März 2010, 16:30–16:50, H11

Size Effects in Fine Barium Titanate Particles — •Pavel Sedykh¹, Dieter Michel¹, Elena V. Charnaya², and Jürgen Haase¹ — ¹University of Leipzig, Faculty of Physics and Earth Sciences, Linnéstraße 5, 04103 Leipzig, Germany — ²St.Petersburg State University, Faculty of Physics, Ul’yanovskaya street 1, 198504 St.Petersburg, Russia

¹³⁷Ba NMR spectroscopy is very suitable to study size effects in very fine particles of barium titanate where particle sizes varied between 155 and 15 nm. The NMR measurements were carried out within the temperature range of the ferroelectric tetragonal phase and allowed us to deduce information about the spontaneous electric polarization. The fine particles are composed of an “ordered” part showing a tetragonal structure and a so called “disordered” part. The “ordered” part reveals a first order phase transition and a temperature dependence of the spontaneous polarization which may be described by a power law similar as predicted by the Landau theory but the phase transition temperature becomes slightly lower with decreasing particle diameter and the exponent changes from 1/2 to about 1/3. The applicability of the core-shell model is discussed and the thickness of the shell is estimated. The shell thickness was shown to strongly decrease with decreasing particle size below 50 nm. Therefore, the applicability of other structural models is also discussed.