  Measurements of the electrical and thermal conductivities, thermopower and
paramagnetic susceptibility have been performed on single crystal samples of
Bi1/2Sr1/2MnO3 and complemented with the X-ray powder diffraction data. A
pronounced hysteretic behavior, observed below the cubic-to- orthorhombic
transition at Tcrit = 535 K, is related to the onset of long-range charge order
at TCO = 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 eg 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 anti- ferromagnetic ordering temperature TN = 150 K. Such be- havior
points to a presence of strong scatterers of phonons. Their possible origin can
be linked to "optical-like" oscilla- tions which are associated with
fluctuating charges within the Zener pairs.
