Substitution for Pb2+ and/or Sn2+ in the tetragonal PbSnF4 by aliovalent cations has been examined using a solid-state reaction under streaming gaseous HF. Three types of defect formation were found: anion-excess solid solutions for the PbSnF4/MF4 and PbSnF4/M′F3 systems (M=Zr;M′ = In), an anion-deficient solid solution for the PbSnF4/NaF system, and anion-excess phases for the PbSnF4/M″F3 systems (M″=Al, Ga). The structures and electrical properties have been characterized by X-ray diffraction and ac conductivity measurements. The anion-excess solid solution Pb1−xSn1−xZr2xF4+4x was obtained for the compositional range 0≤x≤0.15. The sample with x = 0.02 showed higher conductivities than the tetragonal PbSnF4 for T < 300 K. The anion-excess ordered phase Pn0.9Sn0.9Al0.2F4.2 has tetragonal symmetry; the cell constants in relation to that for the tetragonal PbSnF4 are a∼√5a (PbSnF4), c∼c((PbSnF4). The supercell is caused by an ordered Al3+ arrangement on the cationic sites. The anion-excess ordered phases showed lower ionic conductivities than PbSnF4.