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The formation enthalpy, -3752.3 ± 4.7 kJomol-', of Hf-zirconolite, CaHfTi 2 0 7 , was obtained using high temperature oxide-melt solution calorimetry. Combined with heat capacity data obtained using low temperature adiabatic calorimetry we report the heat capacity (Cp) and the standard molar formation energetics (AH.E .... t, ASO, and AG6, elements) for Hf-zirconolite from T = 298.15 K to T = 1500 K. Comparison of Hf-zirconolite with Zr-zirconolite is made.

The specific heat of a polycrystalline sample of MnO was measured from TϷ1 K to TϷ400 K using two different experimental apparatuses at zero applied pressure. Features revealed by the data include a hyperfine contribution due to the Mn nuclei, a T 2 temperature dependence at low temperatures due to the type-II antiferromagnetic magnon contribution, and a sharp but well defined antiferromagnetic transition (T N ϭ117.7095 K) that is clearly second order in nature. The critical exponent ␣ deduced from the transition is consistent with a two-dimensional Ising model. The specific heat of MnO is also compared with recent results on the type-A antiferromagnet LaMnO 3 . ͓S0163-1829͑99͒08533-1͔

The specific heat of a polycrystalline sample of MnO was measured from T ≈ 1 K to T ≈ 400 K using two different experimental apparatuses at zero applied pressure. Features revealed by the data include a hyperfine contribution due to the Mn nuclei, a T2 temperature dependence at low temperatures due to the type-II antiferromagnetic magnon contribution, and a sharp but well defined antiferromagnetic transition (TN = 117.7095 K) that is clearly second order in nature. The critical exponent, α, deduced from the transition is consistent with a two dimensional Ising model. The specific heat of MnO is also compared with recent results on the type-A antiferromagnet LaMnO3.