An Sr doping 0.65(Bi0.5Na0.5) TiO3-0.35 (Sr0.7+x + Bi0.2) TiO3 ceramic with tunable crystal structures and energy storage performances

A group of 0.65(Bi0.5Na0.5)TiO3 -0.35(Sr0.7+x + Bi0.2)TiO3 (BNT-S0.7+xBT) composite ceramic pellets are synthesized using a traditional solid sintering method, where a tunable x, the changeable volume of Sr, is to tailor energy storage through the adjustments of the A-site stoichiometry in BNT-S0.7+xBT. We find that a small excess of Sr2+ ions will result in an extensively tuning on the crystal grain size and even contribute to the A-site disorder and charge fluctuation of BNT-S0.7+xBT. As such, the BNT-S0.7+xBT exhibits a minimum average grain size and a highly compact crystal morphology, and thus, BNT-S0.75BT ceramic exhibits a high dielectric constant (εr) of about 5100 at 110 °C. Meanwhile, a relatively thin polarization–electric field (P–E) loop with a high maximum polarization of 42 μC/cm2 and a low remnant electric polarization of 5 μC/cm2 are obtained in a BNT-S0.75BT pellet under 100 kV/cm, corresponding to an energy density of 0.98 J cm−3 and a good η of 70.7%. Attractively, the maximum polarization (Pm) of BNT-S0.75BT ceramic at 25–100 °C hardly decreases, implying excellent temperature stability of polarization performances under high electric field of 100 kV/cm, which favors the energy storage of relaxor ferroelectric ceramics and is valuable to a supercapacitor serving at evaluated high temperature.