Enhancement of relaxor behavior by La doping and its influence on the energy storage performance and electric breakdown strength of ferroelectric Pb(Zr0.52Ti0.48)O3 thin films

Abstract

La-doped Pb1-xLax(Zr0.52Ti0.48)O3 (PLZT) thin films with dopant concentrations of up to 12% were fabricated on (111)Pt/Ti/SiO2/Si substrates by a sol-gel spin-coating method to investigate the effects of La content on the phase transition, ferroelectric and energy-storage performance properties of PZT thin films. The compositional-induced relaxor behavior was increased with the doping of La, due to the presence of polar nano-regions (PNRs). The existence of PNRs in the relaxor ferroelectric, as opposed to the microscopic long-range ordered domains in the normal ferroelectric, induced the difference between the polarizations of the normal and relaxor ferroelectrics. The results indicated that the decrease in remanent polarization and coercive field in the PLZT thin films with increasing La content was associated with the phase transition from normal ferroelectric behavior in undoped PZT to relaxor behavior in PLZT thin films due to the substitution of Pb2+ ions by La3+ ions. The maximum recoverable energy-storage density (27.5 J/cm3) and efficiency (62.2%) were obtained for the 8% La-doped film due to the large electric breakdown strength (2200 kV/cm) and slimmer polarization hysteresis loop. Because of the thinner films (250 nm), the low driven voltage of 55 V can be used to charge the thin film capacitors to obtain the above energy-storage properties. Moreover, an excellent charge-discharge cycling life with fatigue-free performance up to 1010 cycles was also realized in the thin films. All of the excellent results indicated that the relaxor PLZT thin films with 8% La doping possess excellent potential for low voltage operation advanced capacitors with high energy-storage performance.