Strain relaxation and the ferroelectric critical temperature were investigated in a series of epitaxial Pb͑Zr 0.20 Ti 0.80 ͒O 3 thin films of different thicknesses grown on metallic 0.5% Nb-doped SrTiO 3 substrates. Detailed x-ray diffraction studies reveal that strain relaxation progressively occurs via misfit dislocations as the film thickness is increased from fully coherent films ͑for films below 150 Å͒ to essentially relaxed films ͑for thicknesses above typically 800 Å͒. It is found that this change in the strain state does not modify the ferroelectric critical temperature which is found for all the samples to be around 680°C, a value much higher than the bulk.

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The specific heat Cp (1-330 K) and magnetic susceptibility χ (5-250 K) of a CuO sample sintered and annealed in oxygen are presented. In contrast with some earlier results, we find: (i) an essentially zero linear term in the low-temperature specific heat (γ* < 0.05 mJ mol-1 K-1);(ii) a minor change in slope in the susceptibility curve and a critical point in Cp at the antiferromagnetic transition (TN = 229.5 ± 0.5 K);(iii) a first-order peak in Cp at the commensurate-incommensurate transition (TM = 212.6 ± 0.5 K, ΔH = 4.5 ± 0.3 J mol-1);(iv) a smooth variation of the susceptibility below TM.The phonon density-of-states is determined by inelastic neutron scattering on a single crystal at room temperature, thus enabling a separation of the lattice and magnetic contributions to Cp. A large contribution due to short-range order is observed above TN, and it is concluded that CuO behaves as a 1D or 2D Heisenberg antiferromagnet.Thermodynamic functions are tabulated up to room temperature.