We studied surface structure and lattice parameters of surfaces with r
egular steps (which are present because the planar surface is tilted b
y 7 degrees to crystallographic plane (100) of SrTiO3) using the RHEED
technique at temperatures T from 5 to 300 K. The lattice parameters a
(parallel to) and a(perpendicular to), measured in plane parallel and
normal to the edges of the regular steps, from 300 K down to 150 K alm
ost coincide, then bifurcate, and a(perpendicular to) bends downward;
the relative deviation saturates at roughly 6%. Thus, our measurements
show at least one strong transition at T about 105 K and weaker ones
at lower temperatures. We think that these transitions are surface-pro
moted transformations closely related to the weak transitions in bulk
strontium titanate, which are ascribed to changes in the electrical su
bsystem. The emerging electrical polarization is directed mainly norma
l to the step edges.