Specific heat of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="normal">Gd</mml:mi><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Ba</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Cu</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn>7</mml:mn><mml:mo>−</mml:mo><mml:mi>δ</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>in the normal and superconducting states

The specific heat $c$, resistance $R$, and magnetic susceptibility $\ensuremath{\chi}$ of the high-temperature superconductor $\mathrm{Gd}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ have been measured from 1.5 to 180 K and compared with those of $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ and ${\mathrm{La}}_{1.85}$${\mathrm{Ba}}_{0.15}$Cu${\mathrm{O}}_{4}$. For the Gd compound, an antiferromagnetic transition is seen in the specific-heat data at 2.24 K, and a Curie-Weiss dependence of $\ensuremath{\chi}$ is also seen, with $7.98{\ensuremath{\mu}}_{B}$ per Gd ion and $\frac{1}{\ensuremath{\chi}}$ extrapolating to zero at -5.89 K. The entropy associated with this peak in the specific heat is consistent with an assignment of $J=\frac{7}{2}$ to the total angular-momentum quantum number of the Gd ion, indicating that crystal-field effects are small. The specific heat of the Gd compound is larger than that of the Y compound at these temperatures; this is attributed to the larger mass of the Gd ion. A peak in $\frac{c}{{T}^{3}}$ near 20 K in the Gd compound indicates a sharply defined peak in the phonon density of states near 10 meV. The superconducting transition temperature ${T}_{c}$ of $\mathrm{Gd}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ indicated by the specific-heat data is 93.8 K, and the jump in the specific heat at ${T}_{c}$ is 301 mJ/K g-atom, in agreement with previous observations for $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$. Evidence is seen for a temperature-dependent phonon density of states in $\mathrm{Gd}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$, and it is pointed out that such a temperature dependence is also seen in previously published data for ${\mathrm{La}}_{1.85}$${\mathrm{Ba}}_{0.15}$Cu${\mathrm{O}}_{4}$ and ${\mathrm{La}}_{1.8}$${\mathrm{Sr}}_{0.2}$Cu${\mathrm{O}}_{4}$.

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