Successive Jahn-Teller Phase Transitions in RbCuCl3

By means of X-ray diffraction measurements, it was found that RbCuCl 3 undergoes successive structural phase transitions at -10°C and 66°C. Superlattice reflections are observed at ( h , k ±1/2, l ) in Phase II (66°C> T >-10°C) and at ( h , k , l ±1/2) in Phase III ( T <-10°C), respectively. Phase I ( T >66°C) is hexagonal with one of following space groups; P 6 3 / m m c , P 62 c and P 6 3 m c ( Z =2), and Phase II is orthorhombic with space group P b c n ( Z =4).