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Recently, tricritical ferroelectrics have been drawn tremendous attention, owing to their ultrahigh dielectric permittivities of up to <i>&#949;_r</i> &gt; 5 &#215; 10⁴, and their consideration for prototype materials in the development of high-performance energy storage devices. Nevertheless, such a materials system suffers from the disadvantage of low breakdown strength, which makes its energy density far from the satisfactory level for practical application. In this paper, a material-modification approach has been reported, for improving the dielectric strength for tricritical ferroelectric materials Ba(Ti_{1&#8722;<i>x</i>}Sn<i>_x</i>)O₃ (BTS) through doping with Bi_1.5ZnNb_1.5O₇ (BZN) additives. The results suggest that the electric strength has been largely improved in the modified tricritical ferroelectric material (BTS<i>_x</i>-<i>y</i>BZN), and the associated energy density reaches <i>U</i>_e = 1.15 J/cm³. Further microstructure investigation indicates that the modified tricritical ferroelectric material exhibits homogenous fine grains with perovskite structure in crystal symmetry, and the BZN may help to form a special structure that could enhance the breakdown strength. The findings may advance the material design and development of high-energy storage materials.