A normal to relaxor ferroelectric transition was induced by the substitution of BaZrO3 for LiTaO3 in a typical lead-free (K,Na)(Nb,Sb)O3-LiTaO3-BaZrO3 system and this was found to accompany a tetragonal to rhombohedral phase structural transformation. The typical relaxor behavior characterized by diffuse phase transition and frequency dispersion was identified by the measurement of frequency-dependent dielectric permittivity. The transmission electron microscopy studies demonstrated that the above phenomenon would be closely related to the domain morphology evolution from normal micron-sized lamellar domains, to tweed-like domains and finally to polar nanodomains. Selected area and convergent beam electron diffraction patterns further confirmed that the composition (2.5 mol% BaZrO3) exhibited rhombohedral and tetragonal phase coexistence. The evolution of domain morphology with temperature also disclosed the diffuseness of ferroelectric phase transition.