本研究中探討混相鐵酸鉍的介電色散行為。同時具有長方晶與菱長晶的鐵電材料─混相鐵酸鉍，與弛豫體─鈮鎂酸鉛((1-x)PbMg1/3Nb2/3O3 - xPbTiO3 (PMN - PT))有以下類似性質；(1)具有單斜晶的型態相邊界(Morphotropic phase boundary, MPB)構造，(2)量測介電對溫度的頻譜(ε´-T)時，呈現了頻率色散現象，(3)具奈米尺度的電域結構，顯示了類弛豫體(relaxor-like)的現象。本研究中發現ε´-T介電譜是由介電色散與相變2個部分所貢獻。其中，混相鐵酸鉍的介電色散是由於介電弛豫機制所造成的，相變則與發生在150℃附近的單斜晶(monoclinic)M_C⟶M_A轉變有關。
利用介電頻譜術，可以將混相鐵酸鉍大致歸納出，由低頻導電弛豫、中頻介電弛豫、高頻弛豫3個不同機制所組成的，推測機制分別由漏電流、偶極的極化轉向以及微區的相界效應所貢獻。並藉由等效電路模型的分析方式，得到內部的弛豫時間以及位能分布，算出介電、導電弛豫的活化能為0.11 eV、0.23 eV，認為較小活化能是造成介電色散的原因。
基於微觀下的導電量測，了解到混相鐵酸鉍導電行為與不同相間的相邊界有關聯，並利用改變歷史偏壓的方式翻轉內部極化，達到不同的導電操控。

In this study, the dielectric dispersion of mixed-phase BiFeO3 is investigated. Mixed-phase BiFeO3, which has tetragonal (T) and rhombohedral (R) phases, is similar to the relaxor system, such as (1-x)PbMg1/3Nb2/3O3 - xPbTiO3 (PMN - PT) in several aspects: (1) They both possess monoclinic phases of the morphotropic phase boundary (MPB). (2) Their dielectric constant-temperature dependence (ε´-T) show the frequency dispersion behaviors. (3) They both consist of nanodomain structures. Therefore, mixed–phase BiFeO3 exhibits the relaxor-like behavior. In this study, we observed ε´-T spectrum include the dielectric dispersion and phase transition parts. The former is contributed to dielectric relaxation, and the latter is associated with monoclinic phase transformation from M_C to M_A.
We also discovered three main mechanisms in dielectric spectrum. There are low frequency conductive relaxation, middle frequency dielectric relaxation, and high frequency relaxation. They come from leakage current, dipolar reorientation polarization, and interfaces of micro-regions, respectively. Further, we use equivalent lumped circuit to analyze the relaxation time and the distribution of potential energy. Calculation results indicated 0.11 eV and 0.23 eV for activation energy of dielectric relaxation and conductive relaxation, respectively, and we inferred the dielectric dispersion is due to the small activation energy.
Based on the nano-scale conductive mapping, we can conclude the conductive phenomenon comes from the phase boundaries of mixed-phase. The conductive state can be controllable by switching polarization with applying DC bias.

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