Structural, ferroelectric and energy-storage properties of lead-free Zr-doped Bi _0.5 (Na _0.80 K _0.20 ) _0.5 TiO ₃ films

Perovskite-type lead-free Bi0.5(Na0.80K0.20)0.5(Ti1-xZrx)O3 (BNKT-xZr) ferroelectric films (with x from 0.00 to 0.05) were synthesized on Pt/Ti/SiO2/Si substrates via chemical solution deposition. The influence of Zr4+ concentration on the microstructures, ferroelectric and energy-storage properties of the prepared films was investigated in detail. It showed that the BNKT-xZr films possessed rhombohedral and tetragonal symmetries in morphotropic phase boundary when a small amount of Zr4+ was added. Ferroelectric and energy-storage properties of the films investigated at an applied electric field of 600kV/cm were significantly enhanced with appropriate Zr4+ concentration. The remnant polarization (Pr), maximum polarization (Pmax) and Pmax-Pr values at x=0.02 reached the highest values of 18.1μC/cm2, 42.0μC/cm2 and 24.0μC/cm2, respectively. Thanks to the strong enhancement in Pmax and the large Pmax-Pr value, the highest recoverable energy-storage density gets the value of 4.6J/cm3 for the 2mol.% Zr4+-doped BNKT film. These obtained results indicate that the appropriate Zr4+-doped BNKT films have many application potentials in the advanced capacitors.