点缺陷调控的PSN-PMN-PT弛豫铁电单晶晶格结构、电畴与极性疲劳研究

A good fatigue resistance of piezoelectric device plays a significant role in improving its performances (such as reliability, stability and even prolonging lifetime). In our previous research, a new Pb(Sc1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PSN-PMN-PT) relaxor ferroelectric single crystal was fabricated, which exhibits an excellent piezoelectric property and thermal stability. The influence of point defect, lattice structure and domain on polarity fatigue is the key to enhance the fatigue resistance. Therefore, a targeted control of inner point defects in PSN-PMN-PT crystal induced by acceptor/donor doping in different sites, especially Mn2+/Co3+ substitutional Ti4+, K+ substitutional Pb2+, V5+ substitutional Ti4+, and La3+ substitutional Pb2+, can be carried out for the high-quality material. Meanwhile, the type of point defects and their concentrations are characterized and identified by photoelectron spectroscopy (XPS) combined with electrical measurements. The effects of the type, concentration, migration and recombination of point defects on lattice structure and domain morphology are thorough investigated. Finally, the relationships of polarity fatigue with point defect, lattice structure, and domain are explored on the basis of the experimental and theoretical analyses. As a consequence, it is possible to realize the effective control of improving anti-fatigue and then to reveal the nature of fatigue with the corresponding mechanism.

良好的抗极性疲劳能力对于提高压电元器件可靠性、稳定性、延长其寿命至关重要。前期我们生长了压电性和热稳定性优异的三元Pb(Sc1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3（PSN-PMN-PT）新型弛豫铁电单晶。明确点缺陷、晶格结构、电畴对极性疲劳的影响规律是改善该体系抗极性疲劳能力的关键。本申请拟以PSN-PMN-PT为研究对象，通过不同原子占位受主（Mn2+、Co3+取代Ti4+;K+取代Pb2+）和施主（V5+取代Ti4+;La3+取代Pb2+）掺杂调控材料内部点缺陷。结合光电子能谱(XPS)与电性能测量技术对点缺陷种类和浓度进行鉴别与半定量计算；系统研究点缺陷种类、浓度、迁移与复合对晶格结构、电畴形貌的微观调控；在实验基础上，结合理论分析，探索“点缺陷---晶格结构---电畴---极性疲劳”之间的关联规律，寻求提高抗极性疲劳能力的调控方法，理解极性疲劳的起源

本项目主要针对循环交变电场下弛豫铁电单晶极性疲劳的机理问题展开研究，拟通过间接探测晶体中点缺陷及其在外场作用下的演化行为，理解点缺陷对电畴结构和极性疲劳的影响。基于此目的，首先研究了三元PSN-PMN-PT弛豫铁电单晶中点缺陷的类型、外场作用下的演化行为以及对晶体极性疲劳的影响，并与二元PMN-PT铁电单晶作了对比。结果表明：PT基铁电单晶中存在多种点缺陷，如电子/空穴、氧空位、铅空位、空间电荷以及复合缺陷偶极子；随循环电场次数增大，点电荷缺陷逐渐迁移到能量上有利的方向，形成偶极子对畴壁钉扎，导致矫顽场增大，极化强度下降；PMN-PT晶体中，缺陷偶极子对铁电性的贡献表现出[111]方向选择性，相反[001]方向内偏场更强；相比于PSN-PMN-PT晶体， PMN-PT具有更小的极性疲劳特性。其次，研究了疲劳过程中电畴结构和形貌的变化以及退火后晶体点缺陷变化情况。结果发现：疲劳电场大于矫顽场，晶体容易产生微裂纹，导致不可逆疲劳；在微裂纹产生之前，仅仅发生缺陷迁移及畴钉扎，但退火后畴钉扎减弱或消失，晶体的压电性能可以回复到原来的90%。研究了施主和受主掺杂点缺陷的类型、疲劳过程中电荷缺陷对晶体结构和电畴结构的影响。结果显示：施主掺杂Mn元素以多个价态存在，缺陷种类和浓度大大增强，导致晶体在退火态下具有大的内偏场，钉扎畴壁迁移，晶体表现大的矫顽场。在此研究基础上用光场替代电场，探索了光激励作用下电畴的对结构和性能的研究。