Effect of Pd for Rh substitution on thermoelectric power in the semimetallic compound URhGa5

•The calculated number of doped electrons predicting an increase of the thermopower.•A synthesing of the URh0.97Pd0.03Ga5 single crystals.•A giant peak in the S(T) dependence at low-T is reduced drastically with time.•An increase in values of S, γ, and χ in URh0.97Pd0.03Ga5 compared to URhGa5.•Calculated values of S agree with those of experimental ones. Single crystals of URhGa5 and URh0.97Pd0.03Ga5 grown by the self-flux method were examined by X-ray diffraction, thermoelectric power, thermal and electrical conductivity, magnetization, and specific heat measurements. The giant thermoelectric peak exceeding 250μV/K at 15K observed for just grown URh0.97Pd0.03Ga5 crystals decreased drastically with ageing. Three percent palladium for Ru substitution in URhGa5 weakly changes the thermoelectric power beyond the peak area but substantially increases the electronic specific heat and magnetic susceptibility. The results of the diffusion thermoelectric power calculation, based on the electron structure and the Fermi surface literature data, are consistent with the determined data for URhGa5 crystal and its URh0.97Pd0.03Ga5 derivative.