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The crystal structure of a strontium europium aluminate, Sr0.864Eu0.136Al2O4, with a novel hexagonal form was investigated by a combination of Rietveld analysis and the maximum-entropy method (MEM) with synchrotron X-ray powder diffraction data. The electron density image calculated by the MEM/Rietveld method revealed that the apical oxygen ion in the AlO4 tetrahedron has a broad distribution corresponding to an extraordinarily large atomic displacement parameter. This structure could be expressed by a split-atom model, with which the Rietveld refinement gave Rwp = 2.99% and RB = 4.16%. Subsequently, MEM-based pattern fitting (MPF) decreased the R factors to Rwp = 2.81% and RB = 2.34% and the electron density image clearly showed that the apical oxygen ions of the AlO4 tetrahedra are split over three sites around a threefold axis involving an elongated distribution of the residual O ions along the c axis. These results suggest that AlO4 tetrahedra in Sr0.864Eu0.136Al2O4 are orientationally disordered.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S002188980401430X/pd5014sup1.cif
Contains datablocks global, SEAO

Computing details top

Cell refinement: PowderX (Dong, 1999) developed by C. Dong; program(s) used to refine structure: RIETAN-2000 (Izumi et al., 2000) developed by F. Izumi; molecular graphics: VENUS (Izumi & Dilanian, 2002) developed by F. Izumi et al..

Figures top
[Figure 1]
[Figure 2]
[Figure 3]
[Figure 4]
[Figure 5]
strontium europium aluminate top
Crystal data top
Al2Eu0.136O4Sr0.864Dx = 3.73 Mg m3
Mr = 214.33? radiation, λ = 0.77571 Å
Hexagonal, P6322µ = 4.8 mm1
Hall symbol: P6c 2cT = 297 K
a = 5.11635 (10) ÅParticle morphology: spherical particle
c = 8.3673 (2) Åwhite
V = 189.69 (1) Å3cylinder, ? × ? × ? mm
Z = 2Specimen preparation: Prepared at 1523 K
F(000) = 198
Data collection top
SPring-8 BL02B2
diffractometer
Data collection mode: transmission
Radiation source: synchrotron radiation, synchrotoron radiationScan method: step
Si(111) double-crystal monochrometor2θmin = 2.50°, 2θmax = 70.00°, 2θstep = 0.01°
Specimen mounting: Sample was installed into Lindeman glass capillary.
Refinement top
Refinement on Inet7700 data points
Rp = 0.020Profile function: split psudo-Voigt of Toraya
Rwp = 0.03028 parameters
Rexp = 0.0171 constraint
RBragg = 0.041
χ2 = 3.240Background function: an 6th-order Legendre polynomial multiplied by a set of numerical values
Crystal data top
Al2Eu0.136O4Sr0.864Z = 2
Mr = 214.33? radiation, λ = 0.77571 Å
Hexagonal, P6322µ = 4.8 mm1
a = 5.11635 (10) ÅT = 297 K
c = 8.3673 (2) Åcylinder, ? × ? × ? mm
V = 189.69 (1) Å3
Data collection top
SPring-8 BL02B2
diffractometer
Scan method: step
Specimen mounting: Sample was installed into Lindeman glass capillary.2θmin = 2.50°, 2θmax = 70.00°, 2θstep = 0.01°
Data collection mode: transmission
Refinement top
Rp = 0.020χ2 = 3.240
Rwp = 0.0307700 data points
Rexp = 0.01728 parameters
RBragg = 0.041
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzBiso*/BeqOcc. (<1)
Sr000.252.06 (2)*0.864 (3)
Eu000.252.06*0.136
Al0.333330.666670.947311.49 (3)*
O10.4074 (6)0.814770.755.8 (2)*0.333
O20.36026 (6)0.0012 (9)0.0435 (4)2.12 (7)*0.500
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
???????

Experimental details

Crystal data
Chemical formulaAl2Eu0.136O4Sr0.864
Mr214.33
Crystal system, space groupHexagonal, P6322
Temperature (K)297
a, c (Å)5.11635 (10), 8.3673 (2)
V3)189.69 (1)
Z2
Radiation type?, λ = 0.77571 Å
µ (mm1)4.8
Specimen shape, size (mm)Cylinder, ? × ? × ?
Data collection
Data collection methodSPring-8 BL02B2
Specimen mountingSample was installed into Lindeman glass capillary.
Data collection modeTransmission
Scan methodStep
2θ values (°)2θmin = 2.50 2θmax = 70.00 2θstep = 0.01
Refinement
R factors and goodness of fitRp = 0.020, Rwp = 0.030, Rexp = 0.017, RBragg = 0.041, χ2 = 3.240
No. of data points7700
No. of parameters28
No. of restraints?

Computer programs: PowderX (Dong, 1999) developed by C. Dong, RIETAN-2000 (Izumi et al., 2000) developed by F. Izumi, VENUS (Izumi & Dilanian, 2002) developed by F. Izumi et al..

 

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