Crystal structure of yttrium sesquicarbide

The yttrium sesquicarbide Y2C3, which is synthesized at ultra-high pressure of 1.5-5.0 GPa and at high temperature of 1200-1600 °C, exhibits superconductivity around 6-18 K. 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 14.9 K and 9.1 K 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.