Mn掺杂对KNbO3和(K0.5Na0.5)NbO3无铅钙钛矿陶瓷铁电压电性能的影响

Effect of manganese doping on ferroelectric and piezoelectric properties of KNbO3 and(K0.5Na0.5)NbO3 lead-free ceramics

(K0.5Na0.5)NbO3基无铅压电陶瓷具有出色的综合铁电压电性能,已经初步满足了部分实际应用场景的需求.近期的研究发现,某些元素的掺杂对优化(K0.5Na0.5)NbO3基陶瓷的机电耦合性能起着至关重要的作用.本文将MnO2添加到KNbO3和(K0.5Na0.5)NbO3两种压电陶瓷中,对比研究了Mn掺杂对两种陶瓷微观结构和宏观电学性能的不同影响,分析了造成这些差异的微观物理机理.实验结果表明,掺杂后的两种陶瓷中均存在Mn2+.Mn掺杂会使KNbO3陶瓷的铁电畴尺寸减小、居里温度降低、拉曼光谱中的振动峰宽化、相变过程变得弥散,并呈现出束腰电滞回线和可回复的双极场致应变曲线;在(K0.5Na0.5)NbO3陶瓷中掺杂Mn后,其性能变化却显著不同,陶瓷的铁电畴尺寸无明显变化、居里温度未发生变化、拉曼光谱中的振动峰未发生宽化,呈现出饱和的矩形电滞回线和不可回复的双极场致应变曲线.这可能是因为,(K0.5Na0.5)NbO3陶瓷相比KNbO3陶瓷具有更大的离子无序度和晶格畸变,从而使得Mn掺杂所产生的影响相对减小.

Potassium sodium niobate(K0.5Na0.5)NbO3-based lead-free piezoelectric ceramics are excellent ferroelectric materials and have been demonstrated to have many practical applications.Recent studies have revealed that chemical doping plays a crucial role in optimizing the electromechanical coupling properties of(K0.5Na0.5)NbO3-based piezoelectric ceramics.In this paper,MnO+2 is doped into potassium niobate(KNbO3)and(K0.5Na0.5)NbO3 piezoelectric ceramics prepared by the conventional solid-state reaction method.The influences of doped Mn cation on KNbO3 and(K0.5Na0.5)NbO3 piezoelectric ceramics including microstructure and macroscopic electrical properties are systematically investigated.The doping effects of Mn cation on the KNbO3 and(K0.5Na0.5)NbO3piezoelectric ceramics are significantly different from each other.For the Mn-doped KNbO3 piezoelectric ceramics,the sizes of ferroelectric domains are reduced.Meanwhile,the diffused orthorhombic-tetragonal phase transition is observed,which is accompanied by reducing dielectric loss and Curie temperature,and broadening vibration peaks in Raman spectrum.It is known that the oxygen vacancy can be formed to compensate for the charges created by the acceptor doping of Mn into the B site of perovskite,and thus forming a defect dipole with the acceptor center.From the ferroelectric measurement,a double hysteresis loop(P-E curve)and a recoverable electric-field-induced strain due to the formation of defect dipole are observed.On the contrary,for the Mn-doped(K0.5Na0.5)NbO3 piezoelectric ceramics,the sizes of ferroelectric domains are not reduced.Meanwhile,the Curie temperature and vibration peaks in Raman spectrum are not changed.A rectangular hysteresis loop(P-E curve)and an unrecoverable electric-field-induced strain are observed in the ferroelectric measurement.The difference between these systems might originate from the greater ionic disorder and lattice distortion in(K0.5Na0.5)NbO3 piezoelectric ceramics.The difference in ionic radius between Na+and K+can affect the migration and distribution of oxygen vacancies,which makes it difficult to form stable defect dipoles in the Mn-doped(K0.5Na0.5)NbO3 piezoelectric ceramics.The results will serve as an important reference for preparing high-performance(K0.5Na0.5)NbO3-based piezoelectric ceramics via chemical doping.