Ordering phenomena and transport properties of Bi1/2Sr1/2MnO3 single crystals

Measurements of the electrical and thermal conductivities, thermopower, and paramagnetic susceptibility have been performed on single-crystal samples of Bi1/2Sr1/2MnO3, complemented with the x-ray powder diffraction data. A pronounced hysteretic behavior, observed below the cubic-to-orthorhombic transition at T-crit=535 K, is related to the onset of long-range charge order (CO) at T-CO=450 K and its further evolution down to about 330 K. The diffraction data suggest that the charge-ordered state is formed by Zener pairs, represented by Mn4+ dimers linked by one extra e(g) electron, and is possibly stabilized by cooperative Bi,Sr displacements. An extremely low thermal conductivity is observed down to the lowest temperatures, without any recovery at the antiferromagnetic ordering temperature T-N=150 K. Such behavior points to a presence of strong scatterers of phonons. Their possible origin can be linked to "optical-like" oscillations that are associated with fluctuating charges within the Zener pairs. (C) 2003 American Institute of Physics.