钙钛矿铁电材料中化学计量失配对铁电性和磁性的影响

The investigation on the modulation of the long-range ferroelectric order in competition with quantum fluctuations in ABO3-type perovskite ferroelectric materials has been always a hot topic in the fields of quantum manipulation. Incipient ferroelectrics SrTiO3(STO)is in the quantum critical regime, thus its FE instability hidden in the cloud of quantum fluctuations can occur against even weak intrinsic or external stimulus, which has been receiving great research attention due to rich physical phenomena. In this research project, we start with an alternative approach(nonstoichiometry)to modulate the ferroelectric instability in STO, and emphatically study the influence of nonstoichiometry on ferroelectricity and magnetism in ABO3-type perovskite ferroelectric materials. The primary contents are as follows:(1)thoroughly study and perfect the connection of the antisite-like defects and the ferroelectricity and magnetism in STO;(2)a further study on the influence of nonstoichiometry on ferroelectricity and magnetism in ABO3-type perovskite ferroelectric materials and the involved physical mechanism;(3)To further explore the various possible factors which may affect the magnetism, including the effect of oxygen vacancies on magnetism;(4)design high-performance materials exhibiting both spin and ferroelectric orders. In this project, combining with the theoretical model and the first-principles calculations, many experimental measurements are performed to study the physical mechanism for explaining the ferroelectricity and magnetism in nonstoichiometric ABO3-type perovskite ferroelectric materials. This research project will perfect and enrich the research in the fields of ferroelectric and magnetic physics.

调控钙钛矿铁电材料中铁电序与量子涨落的竞争一直是量子调控研究领域中的热点。先兆型铁电材料SrTiO3(STO)因其处于量子临界区域，故其中的铁电不稳定性对于内部或外部的微小扰动非常敏感，展现出了十分丰富的物理现象。本项目从一种调控STO铁电序的新方法-化学计量失配入手，着重研究化学计量失配对ABO3钙钛矿铁电材料中铁电性和磁性的影响。主要研究内容包括：(1)通过多重实验手段，深刻理解和完善与化学计量失配的STO中铁电性和磁性相关的反位缺陷理论；(2)拓展研究化学计量失配对非边缘型ABO3量子顺电体材料和传统ABO3铁电材料的影响及其中的物理机制；(3)探索影响磁性的各种可能因素，包括氧空位的影响；(4)设计同时具有良好铁电性和磁性的材料。本项目以实验探索为重点，结合理论计算，深入研究化学计量失配影响钙钛矿铁电材料铁电性和磁性的物理机制。本课题将完善和丰富铁电、磁性物理领域的研究。

本项目以实验探索为重点，结合理论计算，深入研究了对钙钛矿铁电材料铁电性和磁性的调控及背后隐含的物理机制。本项目实施三年以来，主要研究内容以及成果如下：(1) 首次对放置一段时间前后的铁电材料进行了X射线衍射图谱和拉曼光谱的表征，揭示了时效处理对铁电材料晶格结构的影响。随后深入研究了不同铁电相下和不同外加电场下电极化曲线的变化，搞清了影响氧空位分布对称性的诸多因素，及其对钙钛矿铁电材料铁电性的影响机制—氧空位只能记忆和稳定原始的电畴构型，而对其他铁电相的铁电畴没有影响。(2) 通过微量Zn掺杂，在Sr0.9Ba0.1TiO3 中获得了成分依赖的多重极化态，完全不同于我们熟知的Ca掺杂的情况。随着Zn含量的增加，体系的极化态先减弱后增强最后保持不变，实现了对材料内禀极化序的调控，揭示了材料中量子涨落、各种铁电相互作用和反铁扭曲这几种相互作用之间的竞争与耦合。(3) 项目将研究延伸到Cr掺杂的钙钛矿磁电材料TbMnO3的铁电性和磁性上，揭示了eg电子在Mn的磁有序形成中起到了很大的作用，而3d电子和4f电子的耦合主要来源于t2g电子，基本不涉及eg电子。本项目共发表相关SCI论文11篇（标记本项目基金资助）。