Abstract
The specific heat of the superconductors La1.85Sr0.15CuO4 and YBa2Cu3O7 was measured from 1 to 350 K. A maximum in C/T3 near 22 K indicates enhanced phonon density of states at energies ω∼11 meV. A lattice specific heat still below 3R at room temperature implies the existence of high energy phonon states at ∼50 meV or beyond. The initial Debye temperature lies in the 380–400 K range. At low temperatures, abnormal electronic contributions are seen, mainly in YBa2Cu3O7. The specific heat jumps are resolved in six samples: ΔC/Tc≃14 mJ·K-2·mole–Cu-1 in La1.85Sr0.15CuO4 and ΔC/Tc≃13 mJ·K-2·mole–Cu-1 in YBa2Cu3O7.