Studies Of Dielectric Tunability Effect In Electronic Ferroelectric

Ferroelectric materials with a high dielectric tunability, i.e., a strong dependence of their dielectric permittivity on the applied dc bias electric field, have great application potential for many devices. Recently, a giant dielectric tunability effect in bulk LuFe2O4 is discovered, and the dielectric permittivity is extremely sensitive to applied dc bias electric field, in strong contrast to conventional ferroelectric materials. The physical origin of the giant dielectric tunability effect in bulk LuFe2O4 could be intrinsically related to electronic ferroelectricity due to the charge ordering of Fe2+ and Fe3+ ions.The dielectric characteristics and magnetodielectric effects of bulk La2NiMnO6 are found to resemble those of the electronic ferroelectric LuFe2O4. In addition, the activation energy for La2NiMnO6 (0.17 eV) is comparable to that of charge ordered LuFe2O4 (0.29 eV). This activation energy is close to the energy required to transfer an electron from Ni2+ to Mn4+, and is adequate to switch the direction of the polar regions. In charge ordered perovskites, both theoretical and experimental investigations have been carried out to reveal the existence of ferroelectricity. Therefore, we have prepared La2NiMnO6 ceramics by a solid state reaction method and measured their dielectric response. The extreme sensitivity of dielectric permittivity to applied dc bias electric field in bulk La2NiMnO6 is discovered. A small bias field of 40 V/cm can greatly reduce the dielectric permittivity in the vicinity of room temperature. This giant dielectric tunability effect is found to resemble those of the electronic ferroelectric LuFe2O4 and could be related to charge ordering of Ni2+ and Mn4+ ions, further confirming the existence of electronic ferroelectricity in La2NiMnO6.As compared to La2NiMnO6, investigations of other R2NiMnO6 oxides are relatively sparse. R = La, Nd and Y members have been shown to possess ordered (monoclinic, P21/n) double perovskite structures. Therefore, Y2NiMnO6 ceramics were well prepared by a solid state reaction method and were measured for their dielectric response. The extreme sensitivity of dielectric permittivity to an applied dc bias electric field in bulk Y2NiMnO6 was discovered. A small bias field of 40 V/cm can greatly reduce the dielectric permittivity in the vicinity of room temperature. This giant dielectric tunability effect is found to resemble those of the electronic ferroelectric LuFe2O4 and La2NiMnO6 and could be attributed to the charge ordering of Ni2+ and Mn4+ ions,further confirming the existence of electronic ferroelectricity in R2NiMnO6.