  This work presents the most detailed and extensive theoretical study to date
of the structural configurations of Ruddlesden-Popper (RP) phases in
antiferrodistortive (AFD) perovskites and formulates a program of study which
can be pursued for RP phases of any AFD perovskite system. We systematically
investigate the effects of oxygen octahedral rotations on the energies of RP
phases in AFD perovskites (A_n+1 B_n O_3n+1) for n = 1...30, providing
asymptotic results for n --> infinity that give both the form of the
interaction between stacking faults and the behavior of such stacking faults in
isolation. We find an inverse-distance interaction between faults with a
strength which varies by as much as a factor of two depending on the
configuration of the octahedra. We find that the strength of this effect can be
sufficient to (a) stabilize or destabilize the RP phase with respect to
dissociation into the bulk perovskite and the bulk A-oxide and (b) affect the
energy scales of the RP phase sufficiently to constrain the rotational states
of the octahedra neighboring the stacking faults, even at temperatures where
the octahedra in the bulk regions librate freely. Finally, we present evidence
that the importance of the octahedral rotations can be understood in terms of
changes in the distances between oxygen ions on opposing sides of the RP
stacking faults.
