Crystal Structure of High-Temperature Paraelectric Phase in Bi-Layered Perovskite Sr_0.85Bi_2.1Ta₂O₉

Abstract

The crystal structure of Bi-layered perovskite Sr0.85Bi2.1Ta2O9 was determined at 750 K by X-ray Rietveld analysis. Sr0.85Bi2.1Ta2O9 with space group A21am at room temperature transforms to the paraelectric phase above 670 K, passing through a probable intermediate state at 510 K. Assuming two possible orthorhombic Fmmm and tetragonal I4/mmm space groups, analysis of the crystal structure of the paraelectric phase gave the final discrepancy factors R w p of 11.3% and 9.9%, respectively. Examination of possible reflections and peak positions at high-angles proved that the true space group is I4/mmm for the high temperature paraelectric phase. The lattice constants are a=3.927 (1), c=25.142 (1) Å at 750 K. The TaO6 octahedron is not perfect and is slightly distorted along the c-axis, having the dipole moment of 0.478 debye.

Effect of non-stoichiometry on ferroelectricity and piezoelectricity in strontium bismuth tantalate ceramics

“…The enhancement of the spontaneous polarization P s and enlargement of the E c value in the SBT(x) was favorably explained from the results of X-ray and/or neutron crystal structure analysis. [2][3][4] Fig . 4 shows the frequency dependence of the impedance, |Z|, and the phase, θ, in the k 33 mode for the SBT(x = 0.2) ceramics.…”

“…[2][3][4] These reports focused on the relationship between the ferroelectric properties and the crystal structure of SBT. However, there are a few reports regarding the piezoelectric properties of SBT.…”

Ferroelastic phase in SrBi2Ta2O9 and study of the ferroelectric phase-transition dynamics

“…9 Recently, an intermediate phase between the FE and PE phases has been suggested on the basis of structural and specific heat measurements, however, its space group was not determined. 10,11 Very recently, Hervoches et al 12 published powder neutron diffraction data of Sr 0.85 Bi 2.1 Ta 2 O 9 and suggested the Amam space group for this phase is between 550 and ϳ820 K. On the other hand, Kim et al 9 proposed a polar symmetry B2cb for this phase, but their structure remains polar up to 1273 K, which seems very unlikely.…”

Lattice strain driven dielectric insulation response of Sr1−xCaxBi2Nb2O9 ceramics

“…1 8 therefore possibly x ¼ 0:1 substitution of calcium modified perovskite phase to the maximum after this substitution phase is distorted comparatively. All diffraction peaks are indexed in tetragonal space group I4/mmm, popularly known 9 for lattice parameters calculations in these ceramics. Lattice parameters are calculated using observed d-values from diffractograms and listed in Table 1.…”