Magneto-structural coupling in [Formula: see text]

[Formula: see text] compound is well Known to show the frustration of the spin structure. At 12 K, [Formula: see text] distorts to break symmetry of the degenerated frustrated spin states by the spin-Peierls-like phase transition, accompanying with the antiferromagnetic ordering. On the other hand, [Formula: see text] undergoes a Jahn-Teller phase transition at a temperature of 310 K, differing from the low temperature ferrimagnetic transition temperature [Formula: see text] of about 60 K. It is also reported that [Formula: see text] shows another magnetic phase transition at about 30 K. These two phase transitions accompanying with the lattice change can be understood by the magneto-elastic interactions. Two interactions, the Jahn-Teller interaction and the spin-Peierls-like interaction are co-exist in [Formula: see text] system. In this report the [Formula: see text] compounds with x = 0.8, 0.6 and 1 are investigated by the X-ray diffraction measurements. From these measurements the crystal structures are determined. The full width at half maximum and integrated intensity give the fruitful information for magnetic elastic interactions.