research papers
A new metric is proposed to improve the fidelity of structures refined against precession electron diffraction data. The inherent dynamical nature of electron diffraction ensures that direct refinement of recorded intensities against structure-factor amplitudes can be prone to systematic errors. Here it is shown that the relative intensity of precessed reflections, their rank, can be used as an alternative metric for refinement. Experimental data from erbium pyrogermanate show that applying precession reduces the dynamical transfer of intensity between reflections and hence stabilizes their rank, enabling accurate and reliable structural refinements. This approach is then applied successfully to an unknown structure of an oxygen-deficient bismuth manganite resulting in a refined structural model that is similar to a calcium analogue.
Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108767312007234/td5007sup1.cif |
Computing details top
Tribismuth dimanganate(IV) top
Crystal data top
Bi3Mn2O7 | β = 90° |
Mr = ? | γ = 90° |
?, Cmc21 | V = 504.50 Å3 |
a = 16.8 (1) Å | Z = 4.0 |
b = 5.51 (1) Å | ? radiation, λ = ? Å |
c = 5.45 (1) Å | × × mm |
α = 90° |
Crystal data top
Bi3Mn2O7 | β = 90° |
Mr = ? | γ = 90° |
?, Cmc21 | V = 504.50 Å3 |
a = 16.8 (1) Å | Z = 4.0 |
b = 5.51 (1) Å | ? radiation, λ = ? Å |
c = 5.45 (1) Å | × × mm |
α = 90° |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
x | y | z | Biso*/Beq | ||
Bi1 | 0.00 | 0.22 | 0.03 | ||
Bi2 | 0.18 | 0.74 | 0.48 | ||
Mn1 | 0.10 | 0.24 | 0.50 | ||
O1 | 0.00 | 0.76 | 0.98 | ||
O2 | 0.21 | 0.78 | 0.03 | ||
O3 | 0.10 | 0.50 | 0.27 | ||
O4 | 0.09 | 0.05 | 0.23 |
Experimental details
Crystal data | |
Chemical formula | Bi3Mn2O7 |
Mr | ? |
Crystal system, space group | ?, Cmc21 |
Temperature (K) | ? |
a, b, c (Å) | 16.8 (1), 5.51 (1), 5.45 (1) |
α, β, γ (°) | 90, 90, 90 |
V (Å3) | 504.50 |
Z | 4.0 |
Radiation type | ?, λ = ? Å |
µ (mm−1) | ? |
Crystal size (mm) | × × |
Data collection | |
Diffractometer | ? |
Absorption correction | ? |
No. of measured, independent and observed (?) reflections | ?, ?, ? |
Rint | ? |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | ?, ?, ? |
No. of reflections | ? |
No. of parameters | ? |
No. of restraints | ? |
Δρmax, Δρmin (e Å−3) | ?, ? |