Ferroelectric Properties and Electrocaloric Effect in Dy2O3 Substitution on Lead-Free (Na0.5 Bi0.5)0.94 Ba0.06TiO3 Ceramic

We report the impact of dysprosium (Dy, with y = 0.01, 0.02, 0.05 and 0.08) substitution in (Na0.5 Bi0.5)0.94 Ba0.06TiO3 (NBT-6BT) lead-free ceramics. The structural, vibrational dielectric, ferroelectric and electrocaloric (EC) properties of all samples were systematically investigated. X-ray diffraction analysis revealed the coexistence of tetragonal (P4mm) and rhombohedral (R3c) structural phases at low content of Dy (y = 0.01, 0.02 and 0.05). The structural changes with the introduction of Dy were confirmed by Raman spectroscopy at room temperature. The evolution of the Raman spectra with temperature was found to be strongly correlated with the dielectric measurements. Higher stability of the ferroelectric (FE) phase was obtained at room temperature for the compositions y = 0.01, 0.02 and 0.05, with optimum values for y = 0.02 as remanent polarization Pr = 32µC/cm2, as well as piezoelectric coefficients d33 = 137 pC/N, kp = 0.27 and kt = 0.16, whereas a higher content of Dy (y = 0.08) induced a remarkable decrease of the ferroelectric and piezoelectric properties. Using the direct EC measurement, the ceramic corresponding to y = 0.02 exhibited a significant EC response, where ΔT = 1.2 K under 5 kV/mm. The incorporation of Dy was found to enhance the EC responsivity coefficient ζ = iT/ΔE), with a best value of ζ = 0.24 K.mm/kV for y = 0.02.