Phase formation of sodium bismuth titanate (Na(0.5)Bi(0.5)TiO(3) or NBT) during the calcination process is investigated using in situ high-temperature diffraction. Reactant oxide and carbonate powders were heated from room temperature to 700 degrees C and diffraction patterns were measured sequentially and continuously in 60 s intervals during heating using a laboratory X-ray powder diffractometer with a curved position-sensitive detector. A small fraction of a transient phase was observed in the range of 500 degrees-650 degrees C and attributed to a reaction between Bi(2)O(3) and TiO(2). A diffusion-dependent particle conversion mechanism is proposed for the formation of NBT in which the Bi(2)O(3) particle and structure transforms into the perovskite phase.