  The nature of charge stripe order and its relationship with structural phase
transitions were studied using synchrotron X-ray diffraction in
La$_{1.875}$Ba$_{0.125-x}$Sr$_{x}$CuO$_{4}$ ($0.05\leq x\leq 0.10$). For
$x=0.05$, as temperature increased, incommensurate superlattice peaks
associated with the charge order disappeared just at the structural phase
transition temperature, $T_{\rm d2}$. However, for $x=0.075$ and 0.09, the
superlattice peaks still existed as a short range correlation even above
$T_{\rm d2}$, indicating a precursor of charge ordering. Furthermore,
temperature dependences of the superlattice peak intensity, correlation length,
and incommensurability for $x=0.05$ are different from those for $x=0.075$ and
0.09. These results suggest that the transition process into the charge stripe
order strongly correlates with the order of the structural phase transitions. A
quantitative comparison of the structure factor associated with the charge
order have been also made for all the samples.
