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Competing structural phase transition scenarios in the giant tetragonality ferroelectric BiFeO3-PbTiO3: Isostructural vs multiphase transition
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Image of FIG. 1.
FIG. 1.

Rietveld plot of X-ray powder diffraction patterns of (1−x)BiFeO3-(x) PbTiO3 at room temperature for x = 0.28, x = 0.30, and x = 0.35. The plots on the left column correspond to specimens exhibiting pure tetragonal (T1) phase at room temperature and on the right to specimens exhibiting coexistence of T1 and rhombohedral (R) phases. The subscripts T and R with the indices of the Bragg peaks represent the tetragonal and rhombohedral peaks. The rhombohedral peaks are indexed with respect to the R3c cell.

Image of FIG. 2.
FIG. 2.

Scanning electron micrograph of a thermally etched sintered disc of x = 0. 35.

Image of FIG. 3.
FIG. 3.

Temperature evolution of the x-ray powder diffraction pattern of x = 0.30, 0.31, and 0.35. For sake of clarity only a very limited 2θ range is plotted. All the three compositions show formation of the intermediate tetragonal T2 phase whose prominent Bragg peak positions (101 and 110) are marked with vertical bars. The arrows in right panel shows extra hump on the left of the 101 peak of the T1 phase which cannot be accounted for by tetragonal or rhombohedral phase. The weak rhombohedral peaks are marked with “R” in x = 0.31 and x = 0.35.

Image of FIG. 4.
FIG. 4.

Temperature evolution of the neutron powder diffraction pattern of the x = 0.35 in the range 27–650 °C. Inset shows the rhombohedral superlattice reflection of the R3c phase (rhombohedral index 113R) at 27 and 500 °C. The up and down arrows indicate the peak of the T2 and R phases, respectively. The peaks corresponding to the different phases (T1, T2, R) can be identified by the corresponding subscripts of the indices.

Image of FIG. 5.
FIG. 5.

Portion of the Rietveld plots of the neutron powder diffraction pattern of x = 0.35 at (a) 25 °C (T1 + R), (b) 350 °C (T1 + T2 + R), (c) 550 °C (T1 + T2 + R) (d) 600 °C (T1 + T2), and (e) 700 °C (cubic). The vertical bars represent the Bragg positions corresponding to the different phases. The inset shows the R peak as a hump in a magnified plot. The Nb peak from the container is also labeled.

Image of FIG. 6.
FIG. 6.

Temperature variation of the lattice parameter, cell volume and volume fraction of T1, T2 and R phases obtained from Rietveld refinement. For sake of direct comparison, the rhombohedral parameter is shown after scaling (dividing) by √2.

Image of FIG. 7.
FIG. 7.

(a) Variation of Pb/Bi-O and Ti/Fe-O bond lengths with temperature. (b) Schematic of the unit cell of tetragonal (T1) structure. The bond distances shown correspond to the room temperature values.


Generic image for table
Table I.

Refined structural parameters of rhombohedral (R) and tetragonal (T1) phases at room temperature (27 °C) and 550 °C for x = 0.35


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Competing structural phase transition scenarios in the giant tetragonality ferroelectric BiFeO3-PbTiO3: Isostructural vs multiphase transition