Phase transitions and dielectric properties of NaNbO3-based solid solutions
Prof. Igor Raevski
Southern Federal University,
Faculty of Physics and Research Institute of Physics
地点： 4 号楼 14楼第二会议室
联系人： 曾江涛 副研究员
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 Tm 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 Tm 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.