Tuning the electrocaloric effect in 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 ceramics by relaxor phase blending

The pseudo-first-order phase transition in 0.94Bi(0.5)Na(0.5)TiO(3)-0.06BaTiO(3) ceramics leads to a sharp increase in temperature change (AT) in the vicinity of the ferroelectric-to-relaxor transition temperature T-FR (similar to 100 degrees C) [Appl. Phys. Lett. 110 (2017) 182904]. In this study, we add the 0,78Bi(0.5)Na(0.5)TiO(3)-0.06BaTiO(3-)0.16(Sr0.7Bi0.2)TiO3 relaxor phase to the 0.94Bi(0.5)Na(0.5)TiO(3)-0.06BaTiO(3) ferroelectric matrix to tune its electrocaloric effect. The results show that the addition of the relaxor phase plays a vital role in phase and localstructure evolution. A transition occurs between the ferroelectric and ergodic relaxor phases when the mass fraction of the latter increases to 30% (x = 0.3), as verified by X-ray diffraction analysis, Raman spectroscopy, and polarization-electric field (P-E) hysteresis loops. Furthermore, addition of the relaxor phase reduces the TFR from 76 degrees C at x = 0.1-55 degrees C at x = 0.2; however, this transition disappears at x = 0.3 and 0.4 composite. In-situ piezo-force microscopy (PFM) images illustrate that domains can be written into x = 0.1 and 0.2 ceramics with a valley in the piezoresponse curves. Increasing the temperature agitates the domain arrangement and decreases the contrast for PFM images; this indicates a gradual phase transition in the composite. The temperature corresponding to maximum Delta T exhibits a downward shift (0.58 K at 80 degrees C for x = 0.1 and 0.5 K at 65 degrees C for x = 0.2), while the temperature-Delta T curves are flat when x = 0.3 and 0.4. Moreover, the maximum Delta T shows a decrease with an increase in the relaxor phase content; this is believed to be related to a decrease in the latent heat due to a pseudo-first-order to second-order transition. Thus, we suggest that the incorporation of a relaxor phase into ferroelectric matrices is an effective technique to tune their electrocaloric effect and improve the thermal stability of ceramic composites.