Thermodynamic properties of the spin-Peierls transition in CuGeO3

We present an investigation of the spin-Peierls transition atTSP=14.5 K in polycrystalline CuGeO3 through specific-heat and thermal-expansion measurements. Clear second-order phase-transition anomalies are found in both properties atTSP, although only a small entropy of S≈0.1 Rln2 is released at the transition. Most of the entropy is released atTSPthermal expansion exhibit extrema atT*≈40 K. These are caused by one-dimensional antiferromagnetic fluctuations along the Cu chains, possibly accompanied by structural fluctuations. Using Ehrenfest's relation, a hydrostatic pressure coefficient (∂TSP/∂p)p→0 ≈ (0.45±0.06) K/kbar is derived.