【作者】 马妍；

【导师】 陈湘明；

【作者基本信息】 浙江大学 ， 材料学， 2009， 博士

【摘要】 多铁性材料是指具有铁电、（反）铁磁与铁弹三种有序中两种或两种以上的铁性材料。由于其丰富的物理内涵与诱人的应用前景,多铁性材料正成为凝聚态物理与材料科学的热点研究领域。本文系统地研究了BiFeO₃、YFeO₃与YMnO₃基陶瓷的微结构、介电弛豫与多铁性,并讨论了其物理本质,得到以下主要结论:采用固相反应法制备了(Bi_1-xNa_x)(Fe_1-xNb_x)O₃ （x=0.1,0.3和0.5）陶瓷,并评价了其介电、铁电和磁学性能。在BiFeO₃中引入NaNbO₃后,随着后者含量的增加将依次形成菱方结构的BiFeO₃基固溶体与赝立方结构的(Bi_1-xNa_x)(Fe_1-xNb_x)O₃固溶体钙钛矿相。由于漏导的明显降低,在所研究的(Bi_1-xNa_x)(Fe_1-xNb_x)O₃陶瓷的所有成分中都测得了更加规则的电滞回线,且随着NaNbO₃含量的增加,自发极化强度P_r增大。在550 K-600 K和650 K-710 K温度区间,(Bi_0.9Na_0.1)(Fe_0.9Nb_0.1)O₃陶瓷中存在着两个介电弛豫。低温介电弛豫和点缺陷相关;而高温介电弛豫和反铁磁转变相关。同时(Bi_0.9Na_0.1)(Fe_0.9Nb_0.1)O₃陶瓷在室温存在弱铁磁性。采用固相反应法制备了YFeO₃陶瓷,并评价了其介电和磁学性能。在123-350K和400-623 K温度区间,YFeO₃陶瓷中存在两个介电弛豫,并在二者之间存在一个介电常数平台。低温介电弛豫是一个本征的热激活过程,符合Arrhenius定律,其激活能和电子铁电体的激活能非常接近;而高温介电弛豫和点缺陷相关。同时YFeO₃陶瓷在室温具有弱铁磁性。用放电等离子体烧结（SPS）方法在较低温度和非常短的时间内成功制备了YFe_1-xMn_xO₃（x=0.1,0.2和0.4）致密陶瓷,并评价了其介电、铁电和磁学性能。所研究的YFe_1-xMn_xO₃陶瓷的所有成分中都存在一个明显的介电弛豫,它是一个热激活的过程,遵循Arrhenius定律,且随着Mn含量的增加,激活能降低。对于不同成分分别在123 K和153 K测得了规则的电滞回线。同时,所研究的YFe_1-xMn_xO₃陶瓷的所有成分在室温都具有弱铁磁性。这说明,通过Mn替代Fe,可在维持YFeO₃较好室温铁磁性的基础上,得到良好的铁电性。用SPS原位合成结合热处理的方法成功制备了致密单相的YMnO₃陶瓷,并评价了其介电、铁电和磁学性能。和固相反应法相比,制备过程大为简化。YMnO₃陶瓷在低温区（160-300 K）存在一个明显的介电弛豫,它是一个热激活的过程;在较高的温区（300-420 K）存在一个介电常数台阶。YMnO₃陶瓷在反铁磁转变温度以下具有弱铁磁性。此外,本研究还采用SPS原位合成结合热处理的方法成功制备了YMn_0.8Fe_0.2O₃致密陶瓷,并评价了其介电、铁电和磁学性能。YMn_0.8Fe_0.2O₃陶瓷的介电温谱与YMnO₃陶瓷非常类似,在低温区（150-390 K）存在一个明显的介电弛豫,它是一个热激活的过程;在较高的温区（300-450 K）存在一个介电常数台阶。YMn_0.8Fe_0.2O₃陶瓷在153 K测得了明显的电滞回线,并且在室温和低温都存在弱铁磁性。通过Fe取代YMnO₃中的Mn,可以得到增强的室温铁磁性和良好的铁电性。更多还原

【Abstract】 Multiferroics are a class of materials possessing at least two ferroic propertiesamong ferroelectricity, ferromagnetism （antiferromagnetism）, and ferroelasticity.Because of its rich connotation in condense matter physics and attracing potentialapplications, multiferroic materials have become the hot research topic in condensematter physics and material science. In the present work, the microstructure, dielectricrelaxation, and multiferroic properties in BiFeO₃, YFeO₃ and YMnO₃-based ceramicswere systematically investigated, and the physical nature was discussed. Thefollowing conclusions were obtained:(Bi_1-xNa_x)(Fe_1-xNb_x)O₃ （x=0.1, 0.3, and 0.5） ceramics were prepared by a solidstate reaction method, and the dielectric, ferroelectric and magnetic properties wereevaluated. By introducing NaNbO₃ into BiFeO₃, BiFeO₃-based solid solution withrhombohedral perovskite structure and (Bi_1-xNa_x)(Fe_1-xNb_x)O₃ solid solution ofperovskite phase with pseudocubic structure were formed subsequently withincreasing NaNbO₃ content. Due to the significantly reduced leakage, allcompositions of (Bi_1-xNa_x)(Fe_1-xNb_x)O₃ ceramics investigated here showed moreregular P-E hysteresis loops, and P_r was enhanced with increasing NaNbO₃ content.Two dielectric relaxations were observed in the temperature ranges of 550-600 K and650-710 K in (Bi_0.9Na_0.1)(Fe_0.9Nb_0.1)O₃ ceramics. The lower-temperature dielectricrelaxation was related to the point defect, and the higher-temperature dielectricrelaxation was related to the antiferromagnetism transition. Meanwhile, weakferromagnetic characteristic was observed in (Bi_0.9Na_0.1)(Fe_0.9Nb_0.1)O₃ ceramics.YFeO₃ ceramics were prepared by solid state reaction method, and the dielectricand magnetic properties were evaluated. Two dielectric relaxations were observed inthe temperature ranges of 123-350 K and 400-623 K in YFeO₃ ceramics and adielectric constant step was detected between them. The low-temperature dielectricrelaxation was an intrinsic thermal activated process following the Arrhenius law withthe activation energy very close to that for electronic ferroelectrics, while thehigh-temperature dielectric relaxation was related to the point defect. Meanwhile, weak ferromagnetic characteristic was detected in YFeO₃ ceramics at roomtemperature.YFe_1-xMn_xO₃ （x=0.1, 0.2, and 0.4） dense ceramics were successfully prepared bySPS （Spark Plasma Sintering） in a very short time at relatively low temperature, andthe dielectric, ferroelectric and magnetic properties were evaluated. An obviousdielectric relaxation was observed for all compositions of YFe_1-xMn_xO₃ ceramicsinvestigated here. It was a thermal activated process following the Arrhenius law, andthe activated energy decreased with increasing Mn content. Regular ferroelectrichysteresis loops were detected at 123 K and 153 K for different compositions, andweak ferromagnetic characteristic was observed at room temperature for allcompositions of YFe_1-xMn_xO₃ ceramics invstigated here. That is, throughMn-substituting for Fe, good ferroelectric properties could be achieved together withthe good room-temperature ferromagnetism of YFeO₃.YMnO₃ dense ceramics with single phase were successfully prepared in-situ bySPS followed by annealing, and the dielectric, ferroelectric and magnetic propertieswere evaluated. Compared with solid state reation method, the synthesis process wasgreatly simplified. An obvious dielectric relaxation was observed in the lowtemperature range （160-300 K）, which is a thermally activated process, and adielectric step was detected in the higher temperature range （300-420 K）. Weakferromagnetic characteristic was observed in the temperature lower than theantiferromagnetic transition temperature in YMnO₃ ceramics.In addition, YMn_0.8Fe_0.2O₃ dense ceramics were successfully prepared in-situ bySPS followed by annealing, and the dielectric, ferroelectric and magnetic propertieswere evaluated. The temperature dependence of dielectric properties in YMn_0.8Fe_0.2O₃ceramics was very similar to those in YMnO₃ ceramics. An obvious dielectricrelaxation was observed in the low temperature range （150-390 K） in YMn_0.8Fe_0.2O₃ceramics, which was a thermally activated process, and a dielectric constant step wasdetected in the higher temperature range （300-450 K）. Obvious ferroelectric hysteresisloops were detected at 153 K, and a weak ferromagnetic characteristic was observedat room temperature and low tempreture. Through Fe-substituting for Mn in YMnO₃, the enhanced room temperature ferromagnetic properties were achieved together withthe good ferroelectric properties.更多还原