In this article, we report our studies on the relaxor behavior of Ba(Ti1-x,Hf-x)O-3 ceramics, made with close compositions between 0.20 <= x <= 0.30, to locate the hafnium concentration boundary for the normal to relaxor crossover. X-ray diffraction followed by Rietveld refinement shows the occurrence of single-phase cubic structure for the synthesized Ba(Ti1-x,Hf-x)O-3 ceramics. Temperature and frequency dependence of the real (epsilon ') and imaginary (epsilon '') parts of the dielectric permittivity has been studied in the temperature range of 90-350 K at frequencies of 0.1, 1, 10, and 100 kHz. A diffuse phase transition accompanying frequency dispersion is observed in the permittivity versus temperature plots revealing the occurrence of relaxor ferroelectric behavior. The T-m verses Hf concentration plot shows a discontinuous jump and change in the slope at x = 0.23. Quantitative characterization based on phenomenological models has also been presented. The plausible mechanism of the relaxor behavior has been discussed, Substitution of Hf4+ for Ti4+ in BaTiO3 reduces the long-range polar ordering yielding a diffuse ferroelectric phase transition. (c) 2007 Elsevier Ltd. All rights reserved.