Sodium bismuth titanate (NBT) ceramics are among the most promising lead-free materials for piezoelectric applications. This work reports the crystal structure and phase evolution of NBT and Fe-modified NBT (from 0-2 at.% Fe) using synchrotron x-ray diffraction and Raman spectroscopy, at both ambient and elevated temperatures. The crystallographic results are discussed with reference to permittivity and piezoelectric thermal depolarization measurements of the same compositions. Changes in the depolarization temperature due to Fe substitution were detected by Raman spectroscopy and were found to correlate closely with depolarization temperatures obtained from converse piezoelectric coefficient and permittivity measured in situ. The depolarization temperatures obtained from direct piezoelectric coefficient measured ex situ as well as the phase transition temperatures obtained from synchrotron x-ray diffraction were found to be at higher temperatures. The mechanisms underlying the relationship between permittivity and piezoelectric depolarization to structural transitions observed in Raman spectroscopy and x-ray diffraction are discussed.