表面缺陷对电荷有序钙钛矿锰氧化物纳米颗粒自旋玻璃态行为的影响

Recently, the spin-glass characteristic and the suppression of charge ordering have been observed in the nanosized perovskite manganites of charge ordering. The surface defects (likely the oxygen deficiency) and the unideal coordination number of the terminal ions become considerable factors in the discussion about origination of spin glass. However, a systematic experimental study about the influence of surface defects is still rare. In this program, the Sol-Gel synthesis method will be used to prepare the precursors of charge-ordering manganite oxides,.and then the precursors will be annealed at different temperatures in different atmospheres to obtain nanoparticles with different sizes and surface defect contents. The influence of surface defects on the crystal structure of the nanoparticle system will be studied by characterizing the crystal structure and the morphology of the samples, and the elemental composition and oxygen content will be checked and analyzed. The study of the spin glass dynamic and magnetic properties will be carried out by measuring the magnetic dynamics, the exchange bias effect and the magnetoresistance effect, and the changes of those effects with the surface defect content will be provided. The research aims at . demonstrating the origin of the spin glass behavior and the intrinsic mechanism of the molten charge ordering in the perovskite manganite nanoparticles. Meanwhile, it will be expected to give the changes of the magnetic property and the magnetic response with the surface defect concentration. All these studies will be helpful and meaningful to understand the inherent mechanism of the magnetic properties of charge-ordering perovskite manganites at the nanoscale, and pave the way for its potential applications in magnetic fluid, biomedicine and spin valve devices.

近来，人们在电荷有序钙钛矿锰氧化物纳米颗粒中发现了自旋玻璃态和被压制的电荷有序态，普遍认为与表面缺陷（可能是氧缺陷）、表面化学配比等因素相关，但目前仍缺少与之相关的系统的实验验证。本项目拟用溶胶-凝胶法在不同退火温度和不同气氛下制备不同尺寸的电荷有序钙钛矿锰氧化物纳米颗粒，获得不同浓度的表面缺陷，利用各种形貌结构表征手段和元素分析方法研究表面缺陷对体系晶格结构的影响；通过磁动力学、交换偏置效应和磁阻效应的测量，研究体系自旋玻璃态动力学特征和磁性质，并总结这些效应随表面缺陷浓度的变化规律。以此澄清体系自旋玻璃态行为的真正起源，阐明电荷有序态被压制的内在原因，揭示体系磁性质和磁响应随表面缺陷浓度的变化规律。这对深入理解电荷有序钙钛矿锰氧化物纳米颗粒磁行为的内在机制有重要科学意义，并为其在磁流体、生物医学和自旋阀器件上的潜在应用提供新的调控途径。

钙钛矿型铁电材料因其内在的自发极化现象，在电介质储能陶瓷电容器上有着潜在的应用价值，因而受到人们的广泛关注。这种天然存在的内建电场又有利于抑制光催化过程中光生电子-空穴对的复合，提高光生载流子的分离率和迁移率，因此铁电材料在光催化领域也显示出了其独特的优势。本项目基于钙钛矿型铁电材料，首先研究了Nd掺杂和氧缺陷对BiFeO3微米颗粒磁性的影响，发现氧缺陷削弱了材料中的铁磁相互作用并破坏其反铁磁结构，减弱了其交换偏置效应；对Bi1-xNdxFeO3 (0.10 ≤ x ≤ 0.30)陶瓷阻抗谱的研究表明，该体系表现出非德拜型介电弛豫特征，晶粒内部的氧空位、铁电相互作用以及存在的准同型相界是影响其短程电导行为的可能因素；Bi1-xNdxFeO3 (0.10 ≤ x ≤ 0.30)的电滞回线存在着漏电现象以及击穿场强较低的情况，这表明陶瓷的致密程度不够，需要在工艺上加以改进。AgNbO3基粉末材料对罗丹明B（RhB）溶液的光催化实验研究显示，水热法制备的针尖形状的纯相AgNbO3纳米粉末相较立方形状的样品具有更高的光催化效率；固相法制备的元素掺杂AgNbO3粉末在可见光照射下其光催化降解RhB溶液的最高效率为纯相样品的2.78倍，光催化的一级反应速率最大值为纯相的9.87倍，极大地提升了AgNbO3基材料的光催化能力。这表明元素掺杂的AgNbO3基粉末材料在光催化领域具有潜在的实际应用前景。元素掺杂的AgNbO3陶瓷在室温下仍表现为铁电性，因致密度不够使其电滞回线仍存在漏电现象。具有较高比电容和电化学稳定性的MnMoO4•H2O/Ni3S2纳米复合结构的超级电容器电极则有望为提高电介质陶瓷储能性能提供一个新的调节方法。对窄带隙的MoS2单层膜的理论研究表明，衬底可以有效调节MoS2激子束缚能，从而改变电子-空穴的分离率，这为更高效的利用可见光和分离光生电子-空穴提供了新材料和新启示。

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