Bismuth Substitution for Rare Earth and Charge/Orbital Ordering Related Structural Effects in Some Half Hole-Doped Manganites

The crystal and magnetic structures of the manganese oxide family Bi0.25RE0.25A0.5MnO3 (RE = La, Nd, Ho, Tm; A = Sr, Ca) were investigated by high resolution neutron diffraction. The half bismuth substitution for rare earth entails unusual structural distortions that make the manganese octahedra rather different from that in the non-substituted compounds. The findings for Ca-Bi manganites indicate an anisotropic expansion of the manganese octahedra and that the 6s2 lone electronic pair of Bi3+ cations is rather constrained than dominant. The CE-type antiferromagnetic ordering takes place in the Bi-Ca series while a part of the low temperature evidence for Bi-Sr members is in support to the phase separation conception.