x O 3 (BNKT-xFSN) ceramics were studied. The FSN complex ions induce the phase transition from ferroelectric state to relaxor state. The coercive field and remanent polarization decrease rapidly with the increase of FSN content. With the increase of the external electric field, the energy storage density of BNKT-xFSN ceramics gradually increases and reaches the maximum value of 0.96 J/cm 3 (90 kV/cm) at x = 0.09, and the corresponding efficiency is 62%. Meanwhile, the field-induced strain of

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... T-0.07FSN ceramic increases from 0.13% at 50 kV/cm to 0.43% at 80 kV/cm, and the corresponding electrostrictive coefficient Q 33 reaches the maximum value of 0.0213 m 4 /C 2 . BNKT-xFSN relaxed ceramics with pseudo-cubic structure have large electrostrictive coefficients when T d is near room temperature. The local composition inhomogeneity by FSN complex ions at B-sites induces the relaxor characteristics of BNKT-xFSN ceramics.