KJ Ceramics 31

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Detailed Program

Paper Number : EL-I02

Time Frame : 16:55~17:20

Presentation Date : Thurseday, 27, November

Session Name : Electronic Ceramics

Session Chair 1# : Chae Il Cheon

Session Chair 2# : Hitoshi Ohsato

Dielectric Relaxation in BiFeO3-based Ceramics

Chae Il CHEON

Hoseo University

Bismuth ferrite, BiFeO3 (BF) has attracted many researchers’ attention due to its very high Curie temperature (830oC), large polarization (~100 μC/cm2), and multiferroic properties. However, difficulty in preparation of a single phase by a ceramic process and a large coercive field of above 10 kV/mm restrict its applications. BF-based solid solutions have been proposed for solving these problems. BaTiO3 (BT) and (Bi,K)TiO3 (BKT) with a tetragonal structure (P4mm) could be the proper end-member which makes a solid solution with BF of rhombohedral structure (R3c). It has been reported that the crystal structure of a BF-based solid solution changes from a rhombohedral (R3c) to a pseudocubic with the increase in a BT or BKT content at around 0.3 BT and 0.4 BKT, respectively. BF-BT and BF-BKT ceramics around the phase boundary are known to show outstanding ferroelectric and piezoelectric properties such as a large remanent polarization of about 50 μC/cm2 and a moderate electro-mechanical coupling factor (k33) of 0.3 ~ 0.35 with temperature stability up to 300oC. However, there is a large variance among temperature-dependent dielectric properties reported in literatures. Relaxor-like dielectric properties, i.e., broad dielectric maximum with frequency dispersion, have been observed in the pseudocubic composition range and claimed to originate from nanosized polar domains. And a Maxwell-Wagner type dielectric relaxation was also observed in a BF-BKT ceramic. These dielectric relaxations due to relaxor ferroelectric phase transitions and extrinsic effects make a definite understanding on the temperature-dependent dielectric behavior difficult in BiFeO3–based ceramics. Therefore, the phase transitions and the related dielectric behaviors are not clearly revealed yet.
In this work, the relaxor-like dielectric behavior was investigated in BF-BKT ceramics with metrically cubic compositions ( 0.4 ~ 0.8 BKT). Dielectric constant and the corresponding loss factor were measured in the temperature range of RT to 650oC at various frequencies. Two kinds of dielectric relaxations were observed; one at 200 ~ 300oC and the other at 300 ~ 600oC. Impedance spectroscopy was utilized for understanding the origins of the relaxations. The temperature-dependent dielectric properties of BF-BKT ceramics will be compared with the reported results for BiFeO3-based ceramics in literatures.

Acknowledgements :

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