The higher hardness along with the excellent dielectric and ferroelectric properties of the ferroelectric material is always required for its direct application. In spite of that, in comparison to the ferroelectric and piezoelectric properties, the study of the hardness property of the ferroelectric materials is almost deprived. Herein, we had showed the improvement in the hardness and relaxor property of the Rb substituted Na0.5Bi0.5TiO3 (NBT) with the variation of the grain size. The emergence of the polar nano region, which is responsible for the relaxor behavior, was verified with the addition of Rb (or with the reduction of the grain size). This interesting behavior was explained through the temperature dependent "order parameter" of all compositions. The reduced coercive field helped to enhance the discharge energy storage density up to 0.71 J/cm(3) for the 4 mole % Rb substituted NBT. The same composition had the hardness of 11.75 GPa, which showed its excellent resistance to the abrasion. These outcomes showed the possibility of the current material to replace the lead based piezoceramics. Moreover, to utilize this material as an orthopedic implant, its biocompatibility was assessed in vitro. As an advantage, by using the current lead free piezoelectric material as an implant, the failure of the implant can be evaluated noninvasively.