Abstract
We have measured the low-temperature specific heat (1.3≤T≤20 K) and the dc magnetic susceptibility (100≤T≤250 K) of eight samples of the high-T c superconductor Y x Ba3−x Cu3O7−δ (x=0.9, 1.0, 1.1) and of two samples of nonsuperconducting YBa2Cu3O6+δ. We have also performed specific heat measurements on the possible impurity phases: YBa3Cu2O7, Y2BaCuO5, CuO, and BaCuO2+x . The superconducting samples all have a nonzero, sample-dependent linear term γ* and an upturn inC/T at very low temperature. We show that this anomalous behavior is at least partly due to the presence of a small amount (≈1%) of BaCuO2+x impurity phase in the measured samples. This is evidenced by the correlation between γ* and the Curie component of the susceptibility, which is proportional to the amount of paramagnetic impurities.
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Eckert, D., Junod, A., Bezinge, A. et al. Low-temperature specific heat of YBa2Cu3O7, YBa2Cu3O6, Y2BaCuO5, YBa3Cu2O7, BaCuO2, and CuO. J Low Temp Phys 73, 241–254 (1988). https://doi.org/10.1007/BF00681980
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DOI: https://doi.org/10.1007/BF00681980