  We report x-ray scattering studies of nanoscale structural correlations in
the paramagnetic phases of the perovskite manganites
La$_{0.75}$(Ca$_{0.45}$Sr$_{0.55}$)$_{0.25}$MnO$_3$,
La$_{0.625}$Sr$_{0.375}$MnO$_3$, and Nd$_{0.45}$Sr$_{0.55}$MnO$_3$. We find
that these correlations are present in the orthorhombic $O$ phase in
La$_{0.75}$(Ca$_{0.45}$Sr$_{0.55}$)$_{0.25}$MnO$_3$, but they disappear
abruptly at the orthorhombic-to-rhombohedral transition in this compound. The
orthorhombic phase exhibits increased electrical resistivity and reduced
ferromagnetic coupling, in agreement with the association of the nanoscale
correlations with insulating regions. In contrast, the correlations were not
detected in the two other compounds, which exhibit rhombohedral and tetragonal
phases. Based on these results, as well as on previously published work, we
propose that the local structure of the paramagnetic phase correlates strongly
with the average lattice symmetry, and that the nanoscale correlations are an
important factor distinguishing the insulating and the metallic phases in these
compounds.
