Key Laboratory of Inorganic Functional Material and Device, CAS, Shanghai Institute of Ceramics, Chinese Academy of Sciences

中国科学院无机功能材料与器件重点实验室

　　Phase transitions and dielectric properties of NaNbO₃-based solid solutions

　　Prof. Igor Raevski

　　Southern Federal University,

　　Faculty of Physics and Research Institute of Physics

　　Rostov-on-Don, Russia

　　时间：2016年11月23日（星期三）上午09:45

　　　　地点： 4 号楼 14楼第二会议室

　　联系人： 曾江涛 副研究员

　　 李国荣 研究员

　　欢迎各位老师同学光临!

　　NaNbO₃, is an end member of several alkaline niobate-based solid solutions, such as (Na,K)NbO₃ or (Na,Li)NbO₃, which represent an important group of environmental-friendly, lead-free piezoceramics. Moreover, the NaNbO3-based antiferroelectric (AFE) materials were recently proposed for energy storage, high-strain actuators, and electrocaloric applications.

　　On heating from liquid helium temperature NaNbO₃ exhibits a series of seven phase transitions from low temperature ferroelectric (FE) phase N (R3C) to high temperature paraelectric cubic phase U (Pm3m). In addition one more FE phase Q (Pmc2₁) can be induced in by application of electric field. Q phase can also appear due to size effects. The e(T) maximum is observed at 370 ⁰C and corresponds to the transition between two AFE phases: P(Pbma) and R(Pmnm).

　　NaNbO₃ -based solid solutions are usually divided into two groups. In solid solutions of the group I high temperature FE phase appears at small (a few mol.%) content x of the second component, the e(T) maximum temperature T_m dependence on x is rather smooth and the e(T) maxima are sharp. In solid solutions of the group II the AFE phase remains stable up to the comparatively high ( ?10-50 mol.%) critical x=x₀ value while at x>x₀ the FE phase becomes stable which is accompanied by an abrupt drop in T_m values and dramatic increase of the e(T) maxima diffusion. Compositions with x>x₀ exhibit a relaxor-like behavior. Relaxor-like behavior is also observed in some ternary NaNbO₃ -based solid solution systems.

　　The effect of technological factors on phase transitions’ temperatures and diffusion as well as on dielectric properties of nominally pure NaNbO₃ and NaNbO₃ -based solid solutions will be discussed.