Local structure anomaly around Ge dopants in Mn3Cu0.7Ge0.3N with negative thermal expansion

Local structure analysis of Cu and Ge atoms in the negative thermal expansion material Mn3Cu0.7Ge0.3N was conducted using x-ray absorption fine structure measurements. The temperature dependence of the interatomic distance was found to reflect the macroscopic negative thermal expansion both for Cu–Mn and Ge–Mn shells, although the magnitude of the relative change was much larger for Ge–Mn than Cu–Mn. An enhanced anomaly of the Debye–Waller factor was observed for the Ge–Mn shell in the temperature region of the negative expansion, indicating the presence of static local disorder around Ge impurities. These local structure anomalies strongly suggest that the local and inhomogeneous strain around Ge is essential in broadening the discontinuous volume contraction.