Tristate ferroelectric memory effect attained by tailoring the ferroelectric behavior in Bi 1/2 (Na 0.8 K 0.2 ) 1/2 TiO 3 with Eu doping.

The ferroelectric behavior of Bi 1/2 (Na 0.8 K 0.2 ) 1/2 TiO 3 has been tailored by Eu 3+ doping and the intermediate relaxor state is utilized for tristate ferroelectric memory effect. As Eu 3+ content increases, the local structural disorder tends to get enhanced and the stability of ferroelectric order gets weakened. The disruption effect of Eu 3+ is manifested structurally in XRD and PL spectra, and electrically in the ferroelectric, dielectric and piezoelectric properties. We found that the BNKT:3.0%Eu which owns a relaxor state under electrical cycle would be suitable for tristate ferroelectric memory, where two ferroelectric states and the relaxor state are respectively served as the "±1" and "0" memory states. We designed the verification experiments, and the results show good feasibility and stability. Moreover, it is innovative using PL spectra of Eu 3+ to understand the structural changes related to different memory states, owning to its sensitivity to local structural symmetry. It also implies the possibility for non-destructive optical readout.