Antiferroelectric orthorhombic P-to-R phase transition induced exotic electrocaloric effect in NaNbO3-based lead-free ceramics

Phase transition is expected in designing high-performance electrocaloric effect (ECE). However, hidden antiferroelectricity in NaNbO3-based ceramics complicates ECE evolution as compared to conventional ferroic materials. Therefore, a NaNbO3-xBi(0.5)Li(0.5)TiO(3) (x = 0.08, 0.10, and 0.12) system is introduced to explore ECE performance in P (Pbma), Q (P2(1)ma), and R (Pnma) phases since a Bi0.5Li0.5TiO3 dopant plays a Janus role in stabilizing ferroelectric Q (x = 0.08 and 0.10) and inducing the antiferroelectric (AFE) relaxor R phase (x = 0.12). Rietveld refinement reveals a phase structure change from the P/Q to R state. Bi0.5Li0.5TiO3 addition makes a downshift of P-to-R transition temperature accompanied by an increase in relaxation property, as certified by dielectric analysis/piezoelectric force images, in situ XRD/Raman spectra, and ferroelectric tests. Additionally, a square P-E loop evolves into less-sharp and finally changes into a slant one with increasing Bi0.5Li0.5TiO3 content. ECE is directly measured, and its peak value increases from 0.15 K for x = 0.08 and 0.21 K for x = 0.10 and finally to 0.11 K for x = 0.12 composition. Interestingly, dual ECE peaks appear in x = 0.10, and it is probably contributed by R relaxor polar nanodomains. This work not only clarifies actual ECE behavior in AFE orthorhombic (P/R) NaNbO3-based ceramics but also fulfills understandings of AFE P-to-R transitions in modulating ECE.

Automated summary

By introducing Bi0.5Li0.5TiO3 dopant, the electrocaloric effect (ECE) performance of NaNbO3-xBi(0.5)Li(0.5)TiO(3) (x = 0.08, 0.10, and 0.12) system in different phases (P, Q, and R) was studied. It was found that the addition of dopant changed the phase structure of the material and improved its ECE performance, especially in x = 0.10 where a dual peak ECE phenomenon occurred.