  We combine the microcanonical formulation of lattice gauge theories (LGTs)
developed by Callaway and the microcanonical inflection point analysis (MIPA)
proposed by Bachmann et al. to achieve a systematic characterization of phase
transitions (PTs) in U(1) lattice electrodynamics. Besides identifying the
well-known deconfinement PT (DPT) due to the neutral pair dissolution, which we
classify as a first-order PT, we unequivocally detect three higher-order PTs.
According to MIPA, we observe two independent third-order PTs in the confined
phase; instead, in the deconfined (Coulomb) phase, we observe a dependent
third-order PT. For a deeper understanding of the physical meaning of these
PTs, we numerically compute the average number density of monopolar and pair
defects as a function of energy. Our analysis reveals that DPT is only one of
the major mechanisms observable in LGT. The independent third-order PTs are
associated, respectively, to the first occurrence of monopolar topological
defects and to the production of pairs.
