Specific heat (1-330 K), Meissner effect and magnetic susceptibility of Tl₂Ba₂Ca₂Cu₃O₁₀, Tl₂Ba₂CaCu₂O₈ and Tl₂Ba₂CuO₆ ceramic samples

Abstract

The specific heat (T≤330 K), magnetic susceptibility (T≤250 K) and Meissner effect of three samples of the series Tl2Ba2Can-1CunO4+2n+x with n=1, n=2 and n=3 are reported. The critical temperatures measured by AC susceptibility are Tc(onset)≈10 K for n=1, Tc(midpoint)=99.5 K for n=2 and Tc(midpoint)=121.4 K for n=3, with transition widths (10%-90%) smaller than 10 K. The Meissner field expulsion at 4 K in 20 G amounts to 8%, 51% and 24%, respectively. The constant component of the susceptibility increases with the number of Cu layers and with Tc. The linear term in the low-temperature specific heat is lower than 7 mJK-2mol-1 and scales with the impurity Curie term of the magnetic susceptibility. Small anomalies are observed in the specific heat at Tc; their shape and their amplitude are consistent with those of the Meissner transitions. The origin of smearing is discussed in relation with the small coherence length. Thermochemical data are tabulated. © 1989.