In the present work, single-phase Ba4Sm2Fe0.5Ti3Nb6.5O30 ceramics with a tetragonal tungsten bronze structure (TTB) were synthesized. Pinched polarization–electric field (P–E) hysteresis loops are observed below the Curie temperature (Tc) in the as-synthesized ceramics. The origin of the loops was thoroughly studied using in situ TEM and XRD. The in situ selected area electron diffraction (SAED) patterns showed that the pinched loops originated from the coexistence of polar commensurate and nonpolar incommensurate superlattice reflections. In situ XRD results revealed increasing tetragonality with rising temperature, implying that the enhancement in octahedral tilting was closely related to the commensurate-incommensurate structural modulation.