Giant tunability of sol-gel derived BaFe12-xZrxO19 ceramics under extremely low electric bias

Reference	Presenter	Authors (Institution)	Abstract
08-017	Piyi Du	Du, P.(State key Lab of Silicon Materials);	Tunable materials have been extensively studied due to their potential applications in many electrical devices, such as phase shifters, tunable oscillators, filters and wireless communications. High tunability has been practically achieved in a number of ferroelectric materials such as Sr1-xBaxTiO3, Cd2Nd2O7 and KTa1-xNbxO3. However, in these case for the bias to modulate conventional dipoles, high dc electric field of 10-100kV/cm are usually required to control the permittivity obtained, which obviously limits their applications. In this study, single phased M-type barium ferrite ceramics with colossal permittivity contributed by defect pair dipoles is obtained and giant tunability appears simultaneously under super low dc bias. In this system based on charge balance, Fe3+ will most probably transform into Fe2+ due to substitution of Zr4+ for Fe3+. Electric charges will be localized between the two ions of Fe3+ and Fe2+ and Fe2+/Fe3+ pair dipoles will be formed. The electron hopping between Fe2+ and Fe3+ contributes high permittivity to be above 20k in ceramics with Zr4+ content of 0.1-0.3 and the pair dipoles could be easily aligned along the super low dc electric field to decrease the permittivity. As a result, giant dielectric tunability of more than 80% with only low dc electric field of 23V/cm is obtained in BaFe12-xZrxO19 ceramics, which is in strong contrast to conventional ferroelectrics where a high electric bias of dozens of kV/cm is required. Such a giant tunability contributed by extremely low bias field in Zr4+-doped ferrite ceramics may be promised for novel applications in tunable devices.
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