We report the results of a Seebeck effect study carried out on the single crystals of Eu 1 À x Ca x B 6 (0 x 1) at temperatures 1.8-300 K. The Seebeck coefficient is shown to be determined by the sum of the linear term S ¼ AT and a phonon-drag contribution, which is induced by the local phonon mode of europium (calcium) with the characteristic frequency 7.3 meV (9.1 meV). The crossover from negative (A % À0.23 mV K À2 for x ¼ 0) to positive (A % þ1.2 mV K À2 for x ¼ 0.244) values of the diffusion thermopower indicates the smooth change of the band structure when approaching the hole-like conductivity found in Eu 1 À x Ca x B 6 at x > x C % 0.2.

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