Changes of the crystal structure at the relaxor ferroelectric phase transition of strontium barium niobate (SBN53)

Abstract

The average crystal structures of the ferroelectric and the intermediate paraelectric phases of SBN53 were refined at various temperatures up to 200 °C from single crystal X‐ray diffraction data. Shifts of the atoms reduce the microscopic spontaneous electric polarization which, however, does not entirely vanish on heating at the ferroelectric (FE) phase transition near 95 °C. Most atoms show an unusual temperature dependence of the atomic displacement parameters (adp). At the FE transition, a very large anisotropic increase of the U33 adp of part of the niobium atoms indicates enhanced structural disorder in the intermediate high temperature phase. A similarly high anisotropic U11 adp of the large Me2 site can be assigned to static disorder caused by incomplete occupation by Ba2+ and Sr2+ which is not affected by the FE phase transition.

Long-Range and Local Structure of SrxBa1–xNb2O6 (x = 0.33 and 0.67) across the Ferroelectric–Relaxor Transition

“…The change in Nb ADPs is clearly associated with the paraelectric (PE) phase transition. Graetsch investigated the room-temperature structure of SBN with a wide composition range ( x = 0.32–0.82) and reported an U 33 increase of ∼0.03 Å 2 when comparing the structures of the FE and the RE compositions ( x = 0.69 and 0.81, respectively, the latter composition is PE at 300 K). The author also reported a gradual decrease of oxygen ADPs from 300 to 427 K for SBN53, similar to the current study.…”

“…Graetsch investigated the room-temperature structure of SBN with a wide composition range ( x = 0.32–0.82) and reported an U 33 increase of ∼0.03 Å 2 when comparing the structures of the FE and the RE compositions ( x = 0.69 and 0.81, respectively, the latter composition is PE at 300 K). The author also reported a gradual decrease of oxygen ADPs from 300 to 427 K for SBN53, similar to the current study. When heating CBN28 (Ca doped analogues) above the T c , U 33 of the respective Nb1 sites adapts a similar value (∼0.04 Å 2 ) .…”

“…Indeed, there is a missing link between the local atomic configuration, which is often key in interpreting the varied dielectric response, − and the RE to FE transition in TTB phases. In contrast to the well-established room-temperature structure, ,,,, the high-temperature phase has rarely been investigated. Experimental data on the local structure across the phase transition temperature are scarce, although density functional calculations and group theory , have suggested an intriguing tilting pattern for SBN.…”

Structural changes of relaxor ferroelectric Sr0.52Ba0.48Nb2O6(SBN52) on quenching and reheating

“…Sr 0.52 Ba 0.48 Nb 2 O 6 crystals were grown according to the procedure of Whipps (1972) from a barium strontium tetraborate flux. A mixture of strontium carbonate, barium carbonate, niobium oxide and boric acid was melted in a Pt crucible at 1350 C and slowly cooled to 700 C at a rate of 5 C per hour followed by further cooling at a rate of 50 C h À1 to room temperature (Graetsch, 2014). The crystals were removed from the solidified flux by etching in hot dilute nitric acid.…”

Local structure of relaxor ferroelectric Sr$_x$Ba$_{1-x}$Nb$_2$O$_6$ from pair distribution function analysis

“…12 Recent structure refinement of a flux grown SBN53 (T C ≈ 368 K) has shown that at 600 K it can be still described in terms of a polar space group P4bm. 24 These uncertainties can be rationalized taking into account the fact that clusters of polarized NbO 6 chains have been shown to exist above the T C . 25 The chains produce strong diffuse scattering in the form of planes perpendicular to c * .…”