Acta Cryst. (2008). E64, i65 [ doi:10.1107/S1600536808026421 ]
A natural sample of perovskite (calcium caesium sodium iron titanium oxide) from the Tapira Alkaline Complex in southeastern Brazil was found by electron microprobe analysis to have the chemical formula (Ca2+0.95 (1)Ce3+0.011 (2)Na+0.010 (4))(Fe3+0.022 (2)Ti4+0.98 (1))O2-3 and by IR spectroscopy to be an anhydrous mineral. Oxygen anions are arranged around Ti4+ in an almost perfect octahedron and around Ca2+ in a distorted 12-fold polyhedron.
Among crystals averaging 1-2 cm3 in size, some have carbonate incrustations and alterations due to intemperism. The cleanest crystals were separated and the biggest were chosen for polished sections for chemical analysis. Electron microprobe analyses were performed for four crystals on a JEOL JXA-8900 RL microscope, qualitatively with wavelength-dispersive mode and quantitatively with energy-dispersive mode. Standards used included rutile (TiO2) for Ti, anorthite (CaAl2Si2O8) for Ca, olivine [(Mg,Fe)2SiO4] for Fe, albite (NaAlSi3O8) for Na, and synthetic glasses for the lanthanide content. Infrared spectra were recorded for ground crystals on a Perkin Elmer GX spectrophotometer. Crystals were examined by polarizing microscope.
Initial refinements were performed using scattering factors for the neutral atoms of the major elements, with site occupancies based on the microprobe analyses (Ca0.96 (2)Ti0.98 (1)O3), giving R = 0.0436, wR = 0.1099, and S = 1.315. The minor elements were added next, with the cation distribution based on the loparite (Na and Ce at A site) and latrappite structures (Fe at B site), and with the constraints that the displacement parameters of atoms within each of these sites be equal. The site occupancies for Ca and Ti were refined whereas those for the Na, Ce, and Fe atoms (including their uncertainties) were taken from the chemical analysis. In the final model, scattering factors for the ions were used and electroneutrality was found to be maintained with a total cation charge of +5.89 (2), according to the chemical formula (Ca2+0.95 (1) Ce3+0.011 (2) Na+0.010 (4)) (Fe3+0.022 (2)Ti4+0.98 (1))O2-3.
Data collection: XSCANS (Siemens, 1991); cell refinement: XSCANS (Siemens, 1991); data reduction: XSCANS (Siemens, 1991); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: CrystalMaker (CrystalMaker, 2007); software used to prepare material for publication: WinGX (Farrugia, 1999).
![[Figure 1]](./mg2053fig1thm.gif)
| Fig. 1. Part of the unit cell with the A site represented in dark blue, the B site in dark grey, and the oxygen ions in dark red. The bonds of the AO12 are also all represented in blue. Displacement ellipsoids are drawn at the 70% probability level [symmetry codes: (i) x, y, z; (ii) -x, -y, z+1/2; (iii) (x+1/2)-1, -y+1/2, -z; (iv) -x+1/2, (y+1/2)-1, 1-(-z+1/2); (v) -x, -y, -z; (vi) x, y, 1-(-z+1/2); (vii) -x+1/2, y+1/2, z; (viii) (x+1/2)-1, -y+1/2, z+1/2; (ix) -x, -y+1, (z+1/2)-1]. |
| Na0.01Ca0.96Fe0.02Ti0.98Ce0.01O3 | F000 = 262.9 |
| Mr = 136.40 | Dx = 4.045 Mg m−3 |
| Orthorhombic, Pbnm | Mo Kα radiation λ = 0.71073 Å |
| Hall symbol: -P 2c 2ab | Cell parameters from 40 reflections |
| a = 5.3818 (4) Å | θ = 4.6–56.8º |
| b = 5.4431 (4) Å | µ = 5.94 mm−1 |
| c = 7.6450 (5) Å | T = 298 (2) K |
| V = 223.95 (3) Å3 | Octahedral, grey |
| Z = 4 | 0.2 × 0.15 × 0.15 mm |
| Siemens P4 diffractometer | Rint = 0.033 |
| Radiation source: fine-focus sealed tube | θmax = 56.8º |
| Monochromator: graphite | θmin = 4.6º |
| T = 298 K | h = −1→12 |
| θ/2θ scans | k = −1→12 |
| Absorption correction: part of the refinement model (ΔF) (SHELXL97; Sheldrick, 2008) | l = −1→18 |
| Tmin = 0.356, Tmax = 0.409 | 3 standard reflections |
| 2383 measured reflections | every 197 reflections |
| 1594 independent reflections | intensity decay: 0.8% |
| 1527 reflections with I > 2s(I) |
| Refinement on F2 | Secondary atom site location: difference Fourier map |
| Least-squares matrix: full | w = 1/[σ2(Fo2) + (0.0192P)2 + 1.1174P] where P = (Fo2 + 2Fc2)/3 |
| R[F2 > 2σ(F2)] = 0.041 | (Δ/σ)max < 0.001 |
| wR(F2) = 0.103 | Δρmax = 2.01 e Å−3 |
| S = 1.25 | Δρmin = −2.88 e Å−3 |
| 1594 reflections | Extinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
| 31 parameters | Extinction coefficient: 0.045 (5) |
| Primary atom site location: structure-invariant direct methods |
| Na0.01Ca0.96Fe0.02Ti0.98Ce0.01O3 | V = 223.95 (3) Å3 |
| Mr = 136.40 | Z = 4 |
| Orthorhombic, Pbnm | Mo Kα |
| a = 5.3818 (4) Å | µ = 5.94 mm−1 |
| b = 5.4431 (4) Å | T = 298 (2) K |
| c = 7.6450 (5) Å | 0.2 × 0.15 × 0.15 mm |
| Siemens P4 diffractometer | 1527 reflections with I > 2s(I) |
| Absorption correction: part of the refinement model (ΔF) (SHELXL97; Sheldrick, 2008) | Rint = 0.033 |
| Tmin = 0.356, Tmax = 0.409 | 3 standard reflections |
| 2383 measured reflections | every 197 reflections |
| 1594 independent reflections | intensity decay: 0.8% |
| R[F2 > 2σ(F2)] = 0.041 | 31 parameters |
| wR(F2) = 0.103 | Δρmax = 2.01 e Å−3 |
| S = 1.25 | Δρmin = −2.88 e Å−3 |
| 1594 reflections |
Experimental. Room temperature single-crystal X-ray diffraction standard experiment |
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. |
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger. |
| x | y | z | Uiso*/Ueq | Occ. (<1) | |
| Ca | 0.50660 (7) | 0.53492 (7) | 0.2500 | 0.00739 (7) | 0.951 (7) |
| Ce | 0.50660 (7) | 0.53492 (7) | 0.2500 | 0.0074 (11) | 0.01 |
| Na | 0.50660 (7) | 0.53492 (7) | 0.2500 | 0.0074 (11) | 0.01 |
| Ti | 0.0000 | 0.5000 | 0.5000 | 0.00487 (6) | 0.977 (7) |
| Fe | 0.0000 | 0.5000 | 0.5000 | 0.0049 (11) | 0.02 |
| O1 | 0.0713 (3) | 0.4842 (3) | 0.2500 | 0.00743 (19) | |
| O2 | 0.21101 (17) | 0.21143 (18) | 0.53714 (14) | 0.00728 (15) |
| U11 | U22 | U33 | U12 | U13 | U23 | |
| Ca | 0.00587 (16) | 0.00800 (13) | 0.00831 (13) | 0.00138 (8) | 0.000 | 0.000 |
| Ce | 0.006 (3) | 0.00800 (16) | 0.00831 (13) | 0.00138 (13) | 0.000 | 0.000 |
| Na | 0.006 (3) | 0.00800 (16) | 0.00831 (13) | 0.00138 (13) | 0.000 | 0.000 |
| Ti | 0.00482 (11) | 0.00595 (10) | 0.00384 (9) | 0.00000 (6) | −0.00004 (6) | −0.00027 (6) |
| Fe | 0.005 (3) | 0.00595 (11) | 0.00384 (10) | 0.00000 (6) | −0.00004 (6) | −0.00027 (9) |
| O1 | 0.0072 (4) | 0.0104 (4) | 0.0047 (4) | −0.0005 (3) | 0.000 | 0.000 |
| O2 | 0.0060 (3) | 0.0072 (3) | 0.0087 (3) | 0.0020 (2) | 0.0005 (2) | 0.0010 (2) |
| Ca—O1 | 2.3586 (16) | Fe—O2iii | 1.9555 (9) |
| Ca—O2i | 2.3783 (11) | Fe—O2x | 1.9555 (9) |
| Ca—O2ii | 2.3783 (11) | Fe—O2ix | 1.9589 (9) |
| Ca—O1iii | 2.4814 (16) | Fe—O2 | 1.9589 (9) |
| Ca—O2iv | 2.6199 (11) | Fe—Cexi | 3.1721 (4) |
| Ca—O2v | 2.6199 (11) | Fe—Caxi | 3.1721 (4) |
| Ca—O2vi | 2.6671 (11) | Fe—Cevii | 3.1721 (4) |
| Ca—O2iii | 2.6671 (11) | Fe—Cavii | 3.1721 (4) |
| Ca—O1vii | 3.0266 (16) | Fe—Caxii | 3.2772 (3) |
| Ca—O1viii | 3.0518 (16) | Fe—Cexii | 3.2772 (3) |
| Ti—O1 | 1.9513 (3) | O1—Fexiii | 1.9513 (3) |
| Ti—O1ix | 1.9513 (3) | O1—Tixiii | 1.9513 (3) |
| Ti—O2iii | 1.9555 (9) | O1—Cavii | 2.4814 (16) |
| Ti—O2x | 1.9555 (9) | O1—Cevii | 2.4814 (16) |
| Ti—O2ix | 1.9589 (9) | O1—Caiii | 3.0266 (16) |
| Ti—O2 | 1.9589 (9) | O1—Caxii | 3.0518 (16) |
| Ti—Cexi | 3.1721 (4) | O2—Feii | 1.9555 (9) |
| Ti—Caxi | 3.1721 (4) | O2—Tiii | 1.9555 (9) |
| Ti—Cevii | 3.1721 (4) | O2—Cax | 2.3783 (11) |
| Ti—Cavii | 3.1721 (4) | O2—Cex | 2.3783 (11) |
| Ti—Caxii | 3.2772 (3) | O2—Caiv | 2.6199 (11) |
| Ti—Cexii | 3.2772 (3) | O2—Ceiv | 2.6199 (11) |
| Fe—O1 | 1.9513 (3) | O2—Cevii | 2.6671 (11) |
| Fe—O1ix | 1.9513 (3) | O2—Cavii | 2.6671 (11) |
| O1—Ca—O2i | 113.17 (4) | O2ix—Fe—O2 | 180.0 |
| O1—Ca—O2ii | 113.17 (4) | O1—Fe—Cexi | 128.54 (5) |
| O2i—Ca—O2ii | 86.35 (5) | O1ix—Fe—Cexi | 51.46 (5) |
| O1—Ca—O1iii | 86.98 (4) | O2iii—Fe—Cexi | 55.53 (3) |
| O2i—Ca—O1iii | 129.34 (3) | O2x—Fe—Cexi | 124.47 (3) |
| O2ii—Ca—O1iii | 129.34 (3) | O2ix—Fe—Cexi | 56.90 (3) |
| O1—Ca—O2iv | 129.62 (3) | O2—Fe—Cexi | 123.10 (3) |
| O2i—Ca—O2iv | 116.99 (3) | O1—Fe—Caxi | 128.54 (5) |
| O2ii—Ca—O2iv | 66.66 (2) | O1ix—Fe—Caxi | 51.46 (5) |
| O1iii—Ca—O2iv | 65.08 (3) | O2iii—Fe—Caxi | 55.53 (3) |
| O1—Ca—O2v | 129.62 (3) | O2x—Fe—Caxi | 124.47 (3) |
| O2i—Ca—O2v | 66.66 (2) | O2ix—Fe—Caxi | 56.90 (3) |
| O2ii—Ca—O2v | 116.99 (3) | O2—Fe—Caxi | 123.10 (3) |
| O1iii—Ca—O2v | 65.08 (3) | O1—Fe—Cevii | 51.46 (5) |
| O2iv—Ca—O2v | 76.80 (5) | O1ix—Fe—Cevii | 128.54 (5) |
| O1—Ca—O2vi | 66.80 (3) | O2iii—Fe—Cevii | 124.47 (3) |
| O2i—Ca—O2vi | 80.97 (4) | O2x—Fe—Cevii | 55.53 (3) |
| O2ii—Ca—O2vi | 165.78 (3) | O2ix—Fe—Cevii | 123.10 (3) |
| O1iii—Ca—O2vi | 64.58 (3) | O2—Fe—Cevii | 56.90 (3) |
| O2iv—Ca—O2vi | 125.177 (19) | Cexi—Fe—Cevii | 180.0 |
| O2v—Ca—O2vi | 63.491 (11) | Caxi—Fe—Cevii | 180.0 |
| O1—Ca—O2iii | 66.80 (3) | O1—Fe—Cavii | 51.46 (5) |
| O2i—Ca—O2iii | 165.78 (3) | O1ix—Fe—Cavii | 128.54 (5) |
| O2ii—Ca—O2iii | 80.97 (4) | O2iii—Fe—Cavii | 124.47 (3) |
| O1iii—Ca—O2iii | 64.58 (3) | O2x—Fe—Cavii | 55.53 (3) |
| O2iv—Ca—O2iii | 63.491 (11) | O2ix—Fe—Cavii | 123.10 (3) |
| O2v—Ca—O2iii | 125.177 (19) | O2—Fe—Cavii | 56.90 (3) |
| O2vi—Ca—O2iii | 110.78 (5) | Cexi—Fe—Cavii | 180.0 |
| O1—Ca—O1vii | 75.32 (5) | Caxi—Fe—Cavii | 180.0 |
| O2i—Ca—O1vii | 60.38 (3) | O1—Fe—Caxii | 65.84 (4) |
| O2ii—Ca—O1vii | 60.38 (3) | O1ix—Fe—Caxii | 114.16 (4) |
| O1iii—Ca—O1vii | 162.30 (6) | O2iii—Fe—Caxii | 134.03 (3) |
| O2iv—Ca—O1vii | 127.03 (3) | O2x—Fe—Caxii | 45.97 (3) |
| O2v—Ca—O1vii | 127.03 (3) | O2ix—Fe—Caxii | 53.08 (3) |
| O2vi—Ca—O1vii | 107.21 (3) | O2—Fe—Caxii | 126.92 (3) |
| O2iii—Ca—O1vii | 107.21 (3) | Cexi—Fe—Caxii | 108.311 (8) |
| O1—Ca—O1viii | 168.10 (7) | Caxi—Fe—Caxii | 108.311 (8) |
| O2i—Ca—O1viii | 59.23 (3) | Cevii—Fe—Caxii | 71.689 (8) |
| O2ii—Ca—O1viii | 59.23 (3) | Cavii—Fe—Caxii | 71.689 (8) |
| O1iii—Ca—O1viii | 104.92 (5) | O1—Fe—Cexii | 65.84 (4) |
| O2iv—Ca—O1viii | 57.99 (3) | O1ix—Fe—Cexii | 114.16 (4) |
| O2v—Ca—O1viii | 57.99 (3) | O2iii—Fe—Cexii | 134.03 (3) |
| O2vi—Ca—O1viii | 118.03 (2) | O2x—Fe—Cexii | 45.97 (3) |
| O2iii—Ca—O1viii | 118.03 (2) | O2ix—Fe—Cexii | 53.08 (3) |
| O1vii—Ca—O1viii | 92.78 (5) | O2—Fe—Cexii | 126.92 (3) |
| O1—Ti—O1ix | 180.0 | Cexi—Fe—Cexii | 108.311 (8) |
| O1—Ti—O2iii | 90.66 (5) | Caxi—Fe—Cexii | 108.311 (8) |
| O1ix—Ti—O2iii | 89.34 (5) | Cevii—Fe—Cexii | 71.689 (8) |
| O1—Ti—O2x | 89.34 (5) | Cavii—Fe—Cexii | 71.689 (8) |
| O1ix—Ti—O2x | 90.66 (5) | Fexiii—O1—Fe | 156.74 (9) |
| O2iii—Ti—O2x | 180.0 | Tixiii—O1—Fe | 156.74 (9) |
| O1—Ti—O2ix | 90.42 (6) | Fexiii—O1—Ti | 156.74 (9) |
| O1ix—Ti—O2ix | 89.58 (6) | Tixiii—O1—Ti | 156.74 (9) |
| O2iii—Ti—O2ix | 90.586 (13) | Fexiii—O1—Ca | 100.97 (4) |
| O2x—Ti—O2ix | 89.414 (13) | Tixiii—O1—Ca | 100.97 (4) |
| O1—Ti—O2 | 89.58 (6) | Fe—O1—Ca | 100.97 (4) |
| O1ix—Ti—O2 | 90.42 (6) | Ti—O1—Ca | 100.97 (4) |
| O2iii—Ti—O2 | 89.414 (13) | Fexiii—O1—Cavii | 90.58 (5) |
| O2x—Ti—O2 | 90.586 (13) | Tixiii—O1—Cavii | 90.58 (5) |
| O2ix—Ti—O2 | 180.0 | Fe—O1—Cavii | 90.58 (5) |
| O1—Ti—Cexi | 128.54 (5) | Ti—O1—Cavii | 90.58 (5) |
| O1ix—Ti—Cexi | 51.46 (5) | Ca—O1—Cavii | 106.45 (6) |
| O2iii—Ti—Cexi | 55.53 (3) | Fexiii—O1—Cevii | 90.58 (5) |
| O2x—Ti—Cexi | 124.47 (3) | Tixiii—O1—Cevii | 90.58 (5) |
| O2ix—Ti—Cexi | 56.90 (3) | Fe—O1—Cevii | 90.58 (5) |
| O2—Ti—Cexi | 123.10 (3) | Ti—O1—Cevii | 90.58 (5) |
| O1—Ti—Caxi | 128.54 (5) | Ca—O1—Cevii | 106.45 (6) |
| O1ix—Ti—Caxi | 51.46 (5) | Fexiii—O1—Caiii | 85.94 (5) |
| O2iii—Ti—Caxi | 55.53 (3) | Tixiii—O1—Caiii | 85.94 (5) |
| O2x—Ti—Caxi | 124.47 (3) | Fe—O1—Caiii | 85.94 (5) |
| O2ix—Ti—Caxi | 56.90 (3) | Ti—O1—Caiii | 85.94 (5) |
| O2—Ti—Caxi | 123.10 (3) | Ca—O1—Caiii | 91.25 (5) |
| O1—Ti—Cevii | 51.46 (5) | Cavii—O1—Caiii | 162.30 (6) |
| O1ix—Ti—Cevii | 128.54 (5) | Cevii—O1—Caiii | 162.30 (6) |
| O2iii—Ti—Cevii | 124.47 (3) | Fexiii—O1—Caxii | 78.47 (4) |
| O2x—Ti—Cevii | 55.53 (3) | Tixiii—O1—Caxii | 78.47 (4) |
| O2ix—Ti—Cevii | 123.10 (3) | Fe—O1—Caxii | 78.47 (4) |
| O2—Ti—Cevii | 56.90 (3) | Ti—O1—Caxii | 78.47 (4) |
| Cexi—Ti—Cevii | 180.0 | Ca—O1—Caxii | 168.10 (7) |
| Caxi—Ti—Cevii | 180.0 | Cavii—O1—Caxii | 85.45 (4) |
| O1—Ti—Cavii | 51.46 (5) | Cevii—O1—Caxii | 85.45 (4) |
| O1ix—Ti—Cavii | 128.54 (5) | Caiii—O1—Caxii | 76.85 (4) |
| O2iii—Ti—Cavii | 124.47 (3) | Feii—O2—Ti | 155.77 (6) |
| O2x—Ti—Cavii | 55.53 (3) | Tiii—O2—Ti | 155.77 (6) |
| O2ix—Ti—Cavii | 123.10 (3) | Feii—O2—Fe | 155.77 (6) |
| O2—Ti—Cavii | 56.90 (3) | Tiii—O2—Fe | 155.77 (6) |
| Cexi—Ti—Cavii | 180.0 | Feii—O2—Cax | 97.78 (4) |
| Caxi—Ti—Cavii | 180.0 | Tiii—O2—Cax | 97.78 (4) |
| O1—Ti—Caxii | 65.84 (4) | Ti—O2—Cax | 106.45 (4) |
| O1ix—Ti—Caxii | 114.16 (4) | Fe—O2—Cax | 106.45 (4) |
| O2iii—Ti—Caxii | 134.03 (3) | Feii—O2—Cex | 97.78 (4) |
| O2x—Ti—Caxii | 45.97 (3) | Tiii—O2—Cex | 97.78 (4) |
| O2ix—Ti—Caxii | 53.08 (3) | Ti—O2—Cex | 106.45 (4) |
| O2—Ti—Caxii | 126.92 (3) | Fe—O2—Cex | 106.45 (4) |
| Cexi—Ti—Caxii | 108.311 (8) | Feii—O2—Caiv | 86.50 (4) |
| Caxi—Ti—Caxii | 108.311 (8) | Tiii—O2—Caiv | 86.50 (4) |
| Cevii—Ti—Caxii | 71.689 (8) | Ti—O2—Caiv | 90.22 (4) |
| Cavii—Ti—Caxii | 71.689 (8) | Fe—O2—Caiv | 90.22 (4) |
| O1—Ti—Cexii | 65.84 (4) | Cax—O2—Caiv | 98.07 (4) |
| O1ix—Ti—Cexii | 114.16 (4) | Cex—O2—Caiv | 98.07 (4) |
| O2iii—Ti—Cexii | 134.03 (3) | Feii—O2—Ceiv | 86.50 (4) |
| O2x—Ti—Cexii | 45.97 (3) | Tiii—O2—Ceiv | 86.50 (4) |
| O2ix—Ti—Cexii | 53.08 (3) | Ti—O2—Ceiv | 90.22 (4) |
| O2—Ti—Cexii | 126.92 (3) | Fe—O2—Ceiv | 90.22 (4) |
| Cexi—Ti—Cexii | 108.311 (8) | Cax—O2—Ceiv | 98.07 (4) |
| Caxi—Ti—Cexii | 108.311 (8) | Cex—O2—Ceiv | 98.07 (4) |
| Cevii—Ti—Cexii | 71.689 (8) | Feii—O2—Cevii | 91.02 (4) |
| Cavii—Ti—Cexii | 71.689 (8) | Tiii—O2—Cevii | 91.02 (4) |
| O1—Fe—O1ix | 180.0 | Ti—O2—Cevii | 85.12 (4) |
| O1—Fe—O2iii | 90.66 (5) | Fe—O2—Cevii | 85.12 (4) |
| O1ix—Fe—O2iii | 89.34 (5) | Cax—O2—Cevii | 99.03 (4) |
| O1—Fe—O2x | 89.34 (5) | Cex—O2—Cevii | 99.03 (4) |
| O1ix—Fe—O2x | 90.66 (5) | Caiv—O2—Cevii | 162.90 (4) |
| O2iii—Fe—O2x | 180.0 | Ceiv—O2—Cevii | 162.90 (4) |
| O1—Fe—O2ix | 90.42 (6) | Feii—O2—Cavii | 91.02 (4) |
| O1ix—Fe—O2ix | 89.58 (6) | Tiii—O2—Cavii | 91.02 (4) |
| O2iii—Fe—O2ix | 90.586 (13) | Ti—O2—Cavii | 85.12 (4) |
| O2x—Fe—O2ix | 89.414 (13) | Fe—O2—Cavii | 85.12 (4) |
| O1—Fe—O2 | 89.58 (6) | Cax—O2—Cavii | 99.03 (4) |
| O1ix—Fe—O2 | 90.42 (6) | Cex—O2—Cavii | 99.03 (4) |
| O2iii—Fe—O2 | 89.414 (13) | Caiv—O2—Cavii | 162.90 (4) |
| O2x—Fe—O2 | 90.586 (13) | Ceiv—O2—Cavii | 162.90 (4) |
| Symmetry codes: (i) x+1/2, −y+1/2, z−1/2; (ii) x+1/2, −y+1/2, −z+1; (iii) −x+1/2, y+1/2, z; (iv) −x+1, −y+1, −z+1; (v) −x+1, −y+1, z−1/2; (vi) −x+1/2, y+1/2, −z+1/2; (vii) −x+1/2, y−1/2, z; (viii) x+1, y, z; (ix) −x, −y+1, −z+1; (x) x−1/2, −y+1/2, −z+1; (xi) x−1/2, −y+3/2, −z+1; (xii) x−1, y, z; (xiii) −x, −y+1, z−1/2. |
| A-O1 | 2.359 (2) | O1iv-A-O1iv | 162.30 (6) |
| A-O1iv | 2.481 (2) | O2iv-A-O2viii | 80.97 (4) |
| A-O1iv | 3.027 (2) | O1-A-O2vii | 118.03 (2) |
| A-O1 | 3.052 (2) | O2ii-A-O1iv | 65.08 (3) |
| A-O2viii | 2.378 (1) | ||
| A-O2ii | 2.620 (1) | ||
| A-O2iv | 2.667 (1) | ||
| A-O2vi | 3.233 (1) | ||
| B-O1ii | 1.9513 (3) | O1-B-O1ii | 180.0 |
| B-O2vii | 1.956 (1) | O2-B-O2vii | 89.41 (1) |
| B-O2v | 1.959 (1) | O1-B-O2 | 89.58 (6) |
| Notes: [Symmetry code: i) x, y, z; ii) -x, -y, z + 1/2; iii) (x + 1/2) -1, -y + 1/2, -z; iv) -x + 1/2, (y + 1/2) - 1, 1- (-z + 1/2); v) -x, -y, -z; vi) x, y, 1 - (-z + 1/2); vii) -x + 1/2, y + 1/2, z; viii) (x + 1/2) - 1, -y + 1/2, z + 1/2; ix) -x, -y + 1, (z + 1/2) -1]. |
The authors are grateful to Dr José Affonso Brod, University of Brasília, Brazil, for providing the perovskite samples, and to Mr William T. Soares for the microprobe analysis. This work was supported by the Minas Gerais Foundation for Research Development, FAPEMIG (Grant CEX 1123/90). EGG is grateful to the Brazilian Science Research Council, CNPq, for providing a graduate fellowship.
Banfield, J. F. & Veblen, D. R. (1992). Am. Mineral. 77, 545-557.
Beran, A., Libowittzky, E. & Armbruster, T. (1996). Can. Mineral. 34, 803-809.
Chakhmouradian, A. R. & Mitchell, R. H. (1998). Can. Mineral. 36, 953-969.
CrystalMaker (2007). CrystalMaker for Windows. CrystalMaker Software Ltd, Yarnton, England.
Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837–838.
Haggerty, S. E. & Mariano, A. N. (1983). Contrib. Mineral. Petrol. 84, 365-381.
Kay, H. F. & Bailey, P. C. (1957). Acta Cryst. 10, 219–226.
Lloyd, F. E. & Bailey, D. K. (1991). 5th International Kimberlite Conference (Extended Abstracts), edited by O. H. Leonardos, H. O. A. Meyer & J. C. Gaspar, pp. 263–269. Araxá, Brazil, CPRM, Special Publication 3/91.
Mariano, A. N. & Mitchell, R. H. (1991). Proceedings of the 5th International Conference, Araxa, Brazil, pp. 251–253. Extended Abstracts.
Seer, H. J. & Moraes, L. C. (1988). Rev. Bras. Geo. 18, 134-140.
Sgarbi, P. B. A. & Gaspar, J. C. (1995). 6th International Kimberlite Conference (Extended Abstracts), Novosibirsk, Rússia, pp. 498–499.
Sgarbi, P. B. A. & Valença, J. G. (1994). International Symposium on the Physics and Chemistry of the Upper Mantle (Extended Abstracts), pp. 27–29. São Paulo, Brazil: CPRM/FAPESP.
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122.
Siemens (1991). XSCANS User's Manual. Siemens Analytical X-ray Instruments Inc., Madison, Wisconsin, USA.
Soubies, F., Melfi, A. J. & Autefage, F. (1991). Rev. Bras. Geo. 21, 3-16.
The term perovskite refers to both natural and synthetic compounds ABX3 based on the mineral CaTiO3. CaTiO3 itself is the most commonly occurring perovskite in the Earth's crust (Chakhmouradian & Mitchell, 1998) and an important material to immobilize high-level radioactive waste. The first structure determination was reported for a synthetic material (Kay & Bailey, 1957), but structural studies of natural CaTiO3 are quite rare and have been mostly limited to twinned crystals (Beran et al., 1996). In central and southeastern Brazil, perovskite can be found as essential and accessory minerals of the Alto Paranaíba Igneous Province (Seer & Moraes, 1988; Sgarbi & Valença, 1994; Sgarbi & Gaspar, 1995), where they form part of five important carbonatite complexes, as in Tapira (Lloyd & Bailey, 1991). In these complexes, the conversion of perovskite in anatase (Soubies et al., 1991) resulted in some of the biggest known titanium concentrations, but even so these deposits are not still economically explored for technological reasons. There are many geological studies (Haggerty & Mariano, 1983; Mariano & Mitchell, 1991; and others) describing crystals of perovskite in the Brazilian carbonatite complexes as belonging to the system lueshite (NaNbO3)-loparite [(NaCe)TiO3]-perovskite (CaTiO3) but with the end member perovskite sensu stricto as the principal component.
In this work, a naturally occurring perovskite from the Tapira Alkaline Complex, localized at Minas Gerais State in Brazil (19°52' south and 46°50' west), has been investigated. The economic importance of this complex is due to the phosphates, titanium, and lanthanide and actinide elements drifts, which were formed by intemperism from primary magmatic rocks. From electron microprobe analyses (major elements: Ca - 38.9 (8) wt% CaO; Ti - 56.6 (9) wt% TiO2; minor elements: Na - 0.224 (8) wt% Na2O; Fe - 1.2 (1) wt% Fe2O3; Ce - 1.4 (3) wt% Ce2O3), it can be concluded that the sample is essentially the mineral CaTiO3, with the calculated formula: Ca2+0.96 (2) Ce3+0.011 (2) Na+0.010 (4) Fe3+0.022 (2) Ti4+0.98 (1) O2-3. The infrared spectra reveal characteristic bands for Ti-O and Ca-O, but importantly, the absence of bands related to OH- and water suggests that the Tapira perovskite is indeed an anhydrous mineral. The bands at 348, 423, 528, 695 and 703 cm-1 observed are also present in spectra of TiO2 polymorphs, especially anatase and TiO2(B) as reported by Banfield & Veblen (1992). This could be due to the octahedral TiO6 or even to the Ca2+ leaching from the perovskite, which has those two polymorphs as byproducts. Figure 1 shows the perovskite structure.