  We present a systematic study of the field and size dependencies of the
static fluxon lattice configuration in Bi-2212 intrinsic Josephson junctions
and investigate conditions needed for the formation of a rectangular fluxon
lattice required for a high power flux-flow oscillator. We fabricate junctions
of different sizes from Bi2Sr2CaCu2O8+x and Bi1.75Pb0.25Sr2CaCu2O8+x single
crystals using the mesa technique and study the Fraunhofer-like modulation of
the critical current with magnetic field. The modulation can be divided into
three regions depending on the formed fluxon lattice. At low field, no periodic
modulation and no ordered fluxon lattice is found. At intermediate fields,
modulation with half-flux quantum periodicity due to a triangular lattice is
seen. At high fields, the rectangular lattice gives integer flux quantum
periodicity. We present these fields in dependence on the sample size and
conclude that the transitions between the regions depend only on lambdaJ(Jc)
and occur at about 0.4 and 1.3 fluxons per lambdaJ, respectively. These numbers
are universal for the measured samples and are consistent with performed
numerical simulations.
