Thermal energy harvesting has great potential for environment-friendly self-powered devices. Materials based on relaxor-ferroelectric single crystals such as PMN-PT (lead titanium-lead magnesium niobate) have gained significant interest for their outstanding properties. In this context, single crystals from (1-x)PbMg(1/3)Nb(2/3)O(3)xPbTiO(3) solid solution were grown using the modified Bridgman method in the composition range of x = 0.25, 0.35, and 0.40. This paper presents a systematic comparison between (1-x)PMN-xPT single crystals and ceramics involving the effect of composition and the crystal orientation on thermal properties assuming a one-dimensional heat-flow process. Results demonstrate that thermal and pyroelectrical properties are intimately coupled to the chemical composition, where the studied single crystals have a good performances compared to their corresponding ceramics, which make them very promising for efficient cooling systems, and IR devices applications.