research papers
The structure of calcium europium orthoborate, Ca3Eu2(BO3)4, was determined using high-resolution powder X-ray diffraction data collected at the ID22 beamline (ESRF) under ambient conditions, as well as at high temperature. Rietveld refinement allowed determination of the lattice constants and structural details, including the Ca/Eu ratios at the three cationic sites and their evolution with temperature. Clear thermal expansion anisotropy was found, and slope changes of lattice-constant dependencies on temperature were observed at 923 K. Above this temperature the changes in occupation of the Ca/Eu sites occur, exhibiting a tendency towards a more uniform Eu distribution over the three Ca/Eu sites. Possible structural origins of the observed thermal expansion anisotropy are discussed.
Keywords: calcium borates; rare earths; thermal expansion anisotropy; site occupation; disordered structure.
Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S2052520620006757/ra5073sup1.cif | |
Rietveld powder data file (CIF format) https://doi.org/10.1107/S2052520620006757/ra5073Isup2.rtv | |
Text file https://doi.org/10.1107/S2052520620006757/ra5073sup3.txt | |
Text file https://doi.org/10.1107/S2052520620006757/ra5073sup4.txt | |
Text file https://doi.org/10.1107/S2052520620006757/ra5073sup5.txt | |
Portable Document Format (PDF) file https://doi.org/10.1107/S2052520620006757/ra5073sup6.pdf |
CCDC reference: 2004755
Computing details top
Dieuropium tricalcium tetraborate top
Crystal data top
Ca3·Eu2·(BO3)4 | V = 968.73 (1) Å3 |
Mr = 659.40 | Z = 4 |
Orthorhombic, Pnma | Synchrotron radiation, λ = 0.400218 Å |
Hall symbol: -P 2ac 2n | T = 295 K |
a = 7.20378 (2) Å | white |
b = 15.57492 (5) Å | cylinder, 1 × 0.7 mm |
c = 8.63406 (3) Å |
Data collection top
ID22 diffractometer, transmission geometry | Data collection mode: transmission |
Radiation source: synchrotron radiation, ESRF, beamline ID22 | Scan method: continuous |
Channel cut Si 111 monochromator | 2θmin = 2.500°, 2θmax = 33.00°, 2θstep = 0.002° |
Specimen mounting: packed into borosilicate capillary |
Refinement top
Rp = 6.04 | 19750 data points |
Rwp = 9.11 | Profile function: Voigt |
Rexp = 1.89 | Background function: manually determined, fitted at the last stage of refinement |
RBragg = 6.735 |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
x | y | z | Biso*/Beq | Occ. (<1) | |
Ca1 | 0.51946 (14) | 0.08348 (6) | 0.82354 (12) | 1.69 (2) | 0.5309 (12) |
Eu1 | 0.51946 (14) | 0.08348 (6) | 0.82354 (12) | 1.69 (2) | 0.4691 (12) |
Ca2 | 0.69687 (19) | 0.12768 (8) | 0.34419 (16) | 1.69 (2) | 0.7403 (10) |
Eu2 | 0.69687 (19) | 0.12768 (8) | 0.34419 (16) | 1.69 (2) | 0.2597 (10) |
Ca3 | 0.32762 (18) | 0.25 | 0.53358 (15) | 1.69 (2) | 0.4575 (16) |
Eu3 | 0.32762 (18) | 0.25 | 0.53358 (15) | 1.69 (2) | 0.5425 (16) |
B1 | 0.333 (3) | 0.4488 (11) | 0.447 (2) | 6.0 (4) | |
B2 | 0.710 (3) | 0.25 | 0.655 (3) | 6.0 (4) | |
B3 | 0.490 (4) | 0.25 | 0.134 (3) | 6.0 (4) | |
O1 | 0.5542 (10) | 0.1752 (4) | 0.0660 (9) | 4.54 (10) | |
O2 | 0.7541 (11) | 0.3240 (4) | 0.7248 (8) | 4.54 (10) | |
O3 | 0.4074 (12) | 0.4068 (5) | 0.5674 (10) | 4.54 (10) | |
O4 | 0.2036 (11) | 0.5085 (5) | 0.4873 (9) | 4.54 (10) | |
O5 | 0.3946 (11) | 0.4619 (5) | 0.3005 (10) | 4.54 (10) | |
O6 | 0.3950 (15) | 0.25 | 0.2692 (13) | 4.54 (10) | |
O7 | 0.6619 (15) | 0.25 | 0.5035 (12) | 4.54 (10) |
Geometric parameters (Å, º) top
Ca1—Eu1 | 0.00000 | Ca3—Eu3 | 0.00000 |
Ca1—O5i | 2.261 (8) | Ca3—O6 | 2.33 (1) |
Ca1—O3ii | 2.359 (8) | Ca3—O7 | 2.42 (1) |
Ca1—O2ii | 2.379 (8) | Ca3—O2iii | 2.442 (7) |
Ca1—O2iii | 2.430 (8) | Ca3—O2ix | 2.442 (7) |
Ca1—O4iv | 2.438 (8) | Ca3—O1x | 2.445 (7) |
Ca1—O4v | 2.546 (8) | Ca3—O1xi | 2.445 (7) |
Ca1—O1vi | 2.547 (7) | Ca3—O3ii | 2.525 (8) |
Ca1—O3v | 2.953 (8) | Ca3—O3 | 2.525 (8) |
Ca2—Eu2 | 0.00000 | B1—O3 | 1.34 (2) |
Ca2—O5vii | 2.353 (8) | B1—O5 | 1.35 (2) |
Ca2—O7 | 2.363 (7) | B1—O4 | 1.37 (2) |
Ca2—O4i | 2.465 (8) | B2—O2ii | 1.34 (1) |
Ca2—O6vii | 2.574 (8) | B2—O2 | 1.34 (1) |
Ca2—O5ii | 2.614 (8) | B2—O7 | 1.35 (3) |
Ca2—O1 | 2.715 (7) | B3—O6 | 1.36 (3) |
Ca2—O1viii | 2.788 (8) | B3—O1ii | 1.38 (2) |
Ca2—O3ii | 2.890 (8) | B3—O1 | 1.38 (2) |
Ca2—O6 | 2.963 (8) | ||
O5—B1—O3 | 132.1 (16) | O7—B2—O2ii | 119.7 (11) |
O4—B1—O5 | 111.1 (13) | O1ii—B3—O6 | 122.2 (9) |
O4—B1—O3 | 113.9 (14) | O1—B3—O1ii | 114.8 (18) |
O2—B2—O2ii | 119 (2) | O1—B3—O6 | 122.2 (9) |
O7—B2—O2 | 119.7 (11) |
Symmetry codes: (i) −x+1, y−1/2, −z+1; (ii) x, −y+1/2, z; (iii) x−1/2, −y+1/2, −z+3/2; (iv) −x+1/2, y−1/2, z+1/2; (v) x+1/2, −y+1/2, −z+3/2; (vi) x, y, z+1; (vii) x+1/2, −y+1/2, −z+1/2; (viii) x+1/2, y, −z+1/2; (ix) x−1/2, y, −z+3/2; (x) x−1/2, −y+1/2, −z+1/2; (xi) x−1/2, y, −z+1/2. |