Abstract
We report the detailed study on the low temperature dielectric dynamics of the epitaxial BiFeO3 thin films grown on Nb-doped SrTiO3 substrate. The results indicate that the contributions from the thin film dominate the dielectric response, although it comes from both the thin film and the electrode interface. Furthermore, the origins of the low temperature dielectric anomalies are investigated with electric circuit fittings. A possible phase transition at 210 K is revealed from analysis with dielectric loss tangent. The dielectric constants obtained from the constant phase elements (CPEs) are more than 400 even at low temperatures. Finally, the physical significances of the CPE model are discussed.
Highlights
Multiferroic BiFeO3 (BFO) has attracted much attention because of the coexistence of ferroelectricity and antiferromagnetism at room temperature
The dielectric properties of a In/BFO/LSMO capacitor showed obvious effects from the electrode interface.[3]. This is similar with many other large dielectric materials like CaCu3Ti4O12, LuFe2O4, LaMnO3 et al In literatures and our previous results, it was shown that both giant dielectric constant and magnetocapacitance can be attributed to the interfacial effects in leaky oxide.[4,5,6,7]
The insulating BFO thin films are necessary in the dielectric measurements because the interfacial effects may dominate in the leaky samples.[3]
Summary
Multiferroic BiFeO3 (BFO) has attracted much attention because of the coexistence of ferroelectricity and antiferromagnetism at room temperature. The giant dielectric constant (as large as 104) was observed in BFO ceramics in which the large values are attributed to hopping electrons at the electrode interface and grain boundaries.[1,2] The dielectric properties of a In/BFO/LSMO capacitor showed obvious effects from the electrode interface.[3] This is similar with many other large dielectric materials like CaCu3Ti4O12, LuFe2O4, LaMnO3 et al In literatures and our previous results, it was shown that both giant dielectric constant and magnetocapacitance can be attributed to the interfacial effects in leaky oxide.[4,5,6,7] the leakage current can be suppressed in fabricated BFO thin films dramatically,[8,9,10] one should still be careful about the conclusions deduced from the dielectric results It is proposed in a few recent papers that there may be several phase transitions at low temperatures for BFO.[11,12,13,14,15] The dielectric measurements based on BFO bulk materials revealed that the elastic and dielectric anomalies at low temperature may be related to these transitions.[16] The electrical equivalent circuit fitting was utilized to investigated the impedance spectroscopy (IS) of epitaxial BFO thin films above room temperature.[6] In this paper, we present the dielectric property of epitaxial BFO below room temperature.
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