Observation of a low-symmetry crystal structure for superconducting (formula presented) by Ni K-edge x-ray absorption measurements

The local atomic structure of (formula presented) has been determined over the temperature range of 3 to 300 K by Ni K-edge x-ray absorption fine structure measurements. No anomalies were observed near (formula presented) However, below (formula presented) the symmetry of (formula presented) octahedra is lower than the cubic (formula presented) determined by conventional diffraction measurements. We suggest that the onset of local distortions could be closely related with removal of the degeneracy in the electronic states dominated by the Ni d bands. The results are discussed in relation to nuclear magnetic resonance, x-ray photoemission measurements, and the superconductivity.