【作者】 侯建伟；

【导师】 唐明华；

【作者基本信息】 湘潭大学 ， 微电子学与固体电子学， 2010， 硕士

【摘要】 高介电调谐性是指介电常数对直流偏置电场的强烈依赖关系,在许多器件中都有潜在的应用价值。不过,在传统的铁电材料中,每厘米几十千伏的强电场才能使它的介电常数发生明显的变化。对于陶瓷或晶体形式的块体材料而言,高直流偏置电场意味着几千伏高的直流电压才能够实现有效的介电调谐,这明显地限制了块体材料在可调性器件中的应用。近年来,发现了电子型铁电体LuFe2O4的巨介电调谐效应,它的介电常数对所施加的直流偏置电场具有极度灵敏性,这与传统的铁电材料形成了鲜明的对比。LuFe2O4的巨介电调谐效应本质上是同电子铁电性相关联的,而电子铁电性归因于Fe2+和Fe3+离子之间的电荷有序。块体La2NiMnO6的介电特性和磁介电效应同电子铁电体LuFe2O4非常相似,而且La2NiMnO6的激活能(0.17 eV)比LuFe2O4(0.29 eV)还要低,接近Ni2+与Mn4+之间的电子跃迁所需的能量大小,刚好可以使极化子微区发生翻转。在电荷有序型的钙钛矿氧化物中,已经进行了理论和实验研究来证实其铁电性的存在。于是,用固相反应烧结法制备了La2NiMnO6陶瓷并对其进行了介电测试,发现了La2NiMnO6的介电常数对所施加的直流偏置电场的极度灵敏性。在常温下,一个40 V/cm的小偏置电场就可以极大程度地减少它的介电常数。这种常温下的巨介电调谐效应与电子铁电体LuFe2O4非常相似,同Ni2+与Mn4+的电荷有序密切相关,从而进一步证明了La2NiMnO6的电子铁电性的存在。与La2NiMnO6相比,对其它R2NiMnO6型的氧化物的研究相对较少。R = La, Nd和Y的氧化物都具有有序的双钙钛矿型结构(P21/n),因此,Y2NiMnO6也应该同La2NiMnO6一样存在Ni2+与Mn4+的电荷有序。于是,用固相反应烧结法制备了Y2NiMnO6陶瓷并对其进行了介电测试,研究了Y2NiMnO6的介电常数对所施加的直流偏置电场的极度灵敏性。在常温下,一个40 V/cm的小偏置电场就可以极大程度地减少它的介电常数。这种常温下的巨介电调谐效应与电子铁电体LuFe2O4和La2NiMnO6均非常相似,同Ni2+与Mn4+的电荷有序密切相关,从而进一步证明了R2NiMnO6的电子铁电性的存在。更多还原

【Abstract】 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.更多还原