Specific heat of Nd1-xCaxB6 single crystals.

We measured the heat capacity on random alloys of Nd1-xCaxB6 (x < 0.4) in the 0.4 to 300 K temperature range. We calculated the lattice contribution to the specific heat, arising from the Debye-type phonons of the boron framework and Einstein-type oscillators of the cation sublattice. Subtracting lattice and Schottky-type contributions from the measured heat capacity, we find that the electronic portion, linear in temperature, decreases sharply upon doping with Ca.