- The molar heat capacity of spark plasma sintering-processed YAG and Nd:YAG (1 at.% Nd) and of single crystal Nd:YAG (1.1 at.% Nd) was evaluated by differential scanning calorimetry from between 298 K and 1623 K. The heat capacity data were fitted to an a + bT + CT - 1 relation. As-sintered SPS samples exhibited lower heat capacity values than did the single crystal. To examine the influence of possible defects created within the SPS apparatus on heat capacity, post-sintering heat treatment at 1673 K in 101.3 kPa of oxygen was applied to the SPS samples. Such treatment resulted in a heat capacity increment close to that obtained for the single crystal, probably due to annealing of the above-mentioned defects. The measured heat capacities of the studied materials were in good agreement with values calculated according to the Neumann–Kopp relation for mixed oxides.