Crystal structure of yttrium sesquicarbide

The yttrium sesquicarbide Y2C3, which is synthesized at ultra-high pressure of 1.5–5.0GPa and at high temperature of 1200–1600°C, exhibits superconductivity around 6–18K. The superconducting transition temperature, Tc, is strongly dependent on the synthesizing conditions. We have performed neutron powder diffraction measurements for two samples with different Tc values of 14.9K and 9.1K to investigate the structural difference. The analyses of the diffraction patterns revealed that there was no deficiency and no anomaly in the atomic displacement parameters of the Y and C sites in both samples. We found alternatively the delicate difference of the interatomic distances between the two samples, which have possibility to cause the change of the Tc value.