Structural transformations in ferroelastic TlNO3

The structures of high-temperature phases (phase II (79 degrees C < T < 144 degrees C) and phase I (144 degrees C < T < 206 degrees C)) of TINO3 are refined by the Rietveld technique using neutron powder diffraction data. The structure of phase II (trigonal; P3(1); Z = 9) is ordered and that of phase I (cubic; Pm3m; Z = 1) is disordered. The transition from room-temperature (RT) phase III to phase II involves the flipping of one of the eight nitrate ions in the RT unit cell about an in-plane axis and small but significant displacements of the other atoms from their phase III locations. Phase I is characterized by twelvefold orientational disorder of the nitrate ions. A new glassy-type phase is observed on quenching the Sample from phase I to RT.