Structure and Physical Properties and Charge Ordering in La_2-xSr_xMnO₄ (1.125 ≤ x ≤ 2.0)

Structural measurements have revealed nonlinear changes of lattice parameters in the layered-perovskite manganites La_2-xSr_xMnO₄ with increasing Sr content; these changes can be well understood by means of interactions among the charge, crystal lattice and the orbital degree of freedom in this strongly correlated system. A probably spin-glass transition was detected for the first time in the x = 1.75 sample at the temperature of around 44 K. Fundamental properties of charge ordering appearing in the range of 1.5 ≤ x ≤ 1.75 have been observed at low-temperatures and are interpreted in terms of the Mn³⁺-dz² orbital ordering.