Acta Cryst. (2007). E63, i196 [ doi:10.1107/S1600536807057583 ]
Large single crystals of the incongruently melting compound tribarium dichromium octaoxide, Ba3Cr2O8, were grown by the traveling solvent floating-zone technique for the first time and characterized by X-ray diffraction at room temperature. The structure is composed of CrO43- tetrahedra and Ba2+ ions. The chromium ions are found in the rare +5 valence state and form double-layered triangular lattices, which are stacked along the c axis with threefold periodicity. All atoms lie on special positions. One Ba, one O and the Cr atoms have site symmetry 3m, the other Ba atom has site symmetry 
m, and the other O atom has site symmetry m. Magnetic measurements suggest that this material is a spin dimer system with a spin-singlet ground state.
Large single crystals of the title compound were grown by the traveling solvent floating zone method in an Ar enviroment, using BaCO3 and Cr2O3 as starting materials. The growth rate was fast (both 27 mm/h and 18 mm/h were applied), which was necessary to maintain zone stability. The feed and seed rods were rotating in opposite directions at 20 rpm throughout the growth, and a 3 cm boule of the desired Ba3Cr2O8 phase was obtained on the seed rod. Due to the very fast growth, the as-obtained boule consisted of many well oriented crystalline grains.
Data collection: APEX2 (Bruker, 2006); cell refinement: APEX2 (Bruker, 2006); data reduction: APEX2 (Bruker, 2006); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997a); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997a); molecular graphics: GRETEP (Laugier & Bochu, 2003); software used to prepare material for publication: SHELXTL (Sheldrick, 1997b).
![[Figure 1]](./pk2063fig1thm.gif)
| Fig. 1. 50% displacement ellipsoid plot of the unit cell. Ba ions are shown in dark blue, Cr ions are shown in blue, and O ions are shown in red. |
| Ba3Cr2O8 | Z = 3 |
| Mr = 644.02 | F000 = 840 |
| Trigonal, R3m | Dx = 5.248 Mg m−3 |
| Hall symbol: -R 3 2" | Mo Kα radiation λ = 0.71073 Å |
| a = 5.7450 (2) Å | Cell parameters from 2788 reflections |
| b = 5.7450 (2) Å | θ = 2.9–42.1º |
| c = 21.3883 (10) Å | µ = 16.87 mm−1 |
| α = 90º | T = 296 (2) K |
| β = 90º | Rod, blue |
| γ = 120º | 0.30 × 0.05 × 0.02 mm |
| V = 611.35 (4) Å3 |
| Bruker APEXII CCD area-detector diffractometer | 928 independent reflections |
| Radiation source: fine-focus sealed tube | 779 reflections with I > 2σ(I) |
| Monochromator: graphite | Rint = 0.034 |
| T = 296(2) K | θmax = 52.2º |
| φ and ω scans | θmin = 2.9º |
| Absorption correction: numerical (face correction; APEX2; Bruker, 2006) | h = −8→12 |
| Tmin = 0.38, Tmax = 0.77 | k = −12→10 |
| 9434 measured reflections | l = −47→46 |
| Refinement on F2 | Secondary atom site location: difference Fourier map |
| Least-squares matrix: full | w = 1/[σ2(Fo2) + (0.0269P)2] where P = (Fo2 + 2Fc2)/3 |
| R[F2 > 2σ(F2)] = 0.021 | (Δ/σ)max = 0.001 |
| wR(F2) = 0.051 | Δρmax = 1.98 e Å−3 |
| S = 1.07 | Δρmin = −2.01 e Å−3 |
| 928 reflections | Extinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
| 19 parameters | Extinction coefficient: 0.0065 (3) |
| Primary atom site location: structure-invariant direct methods |
| Ba3Cr2O8 | γ = 120º |
| Mr = 644.02 | V = 611.35 (4) Å3 |
| Trigonal, R3m | Z = 3 |
| a = 5.7450 (2) Å | Mo Kα |
| b = 5.7450 (2) Å | µ = 16.87 mm−1 |
| c = 21.3883 (10) Å | T = 296 (2) K |
| α = 90º | 0.30 × 0.05 × 0.02 mm |
| β = 90º |
| Bruker APEXII CCD area-detector diffractometer | 928 independent reflections |
| Absorption correction: numerical (face correction; APEX2; Bruker, 2006) | 779 reflections with I > 2σ(I) |
| Tmin = 0.38, Tmax = 0.77 | Rint = 0.034 |
| 9434 measured reflections |
| R[F2 > 2σ(F2)] = 0.021 | 19 parameters |
| wR(F2) = 0.051 | Δρmax = 1.98 e Å−3 |
| S = 1.07 | Δρmin = −2.01 e Å−3 |
| 928 reflections |
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 > 2σ(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 | ||
| Ba1 | 0.0000 | 0.0000 | 0.0000 | 0.01420 (5) | |
| Ba2 | 0.0000 | 0.0000 | 0.205924 (6) | 0.00918 (5) | |
| Cr1 | 0.0000 | 0.0000 | 0.407042 (18) | 0.00721 (6) | |
| O1 | 0.82832 (9) | 0.17168 (9) | 0.89871 (5) | 0.01272 (17) | |
| O2 | 0.0000 | 0.0000 | 0.32872 (9) | 0.0273 (5) |
| U11 | U22 | U33 | U12 | U13 | U23 | |
| Ba1 | 0.01762 (7) | 0.01762 (7) | 0.00736 (7) | 0.00881 (3) | 0.000 | 0.000 |
| Ba2 | 0.00956 (5) | 0.00956 (5) | 0.00841 (6) | 0.00478 (3) | 0.000 | 0.000 |
| Cr1 | 0.00723 (8) | 0.00723 (8) | 0.00718 (11) | 0.00361 (4) | 0.000 | 0.000 |
| O1 | 0.0143 (3) | 0.0143 (3) | 0.0137 (4) | 0.0102 (3) | 0.00047 (14) | −0.00047 (14) |
| O2 | 0.0366 (8) | 0.0366 (8) | 0.0085 (7) | 0.0183 (4) | 0.000 | 0.000 |
| Ba1—O1i | 2.7589 (10) | Ba2—Cr1xix | 3.51010 (18) |
| Ba1—O1ii | 2.7589 (10) | Ba2—Cr1xx | 3.51011 (18) |
| Ba1—O1iii | 2.7589 (10) | Cr1—O2 | 1.675 (2) |
| Ba1—O1iv | 2.7589 (10) | Cr1—O1xxi | 1.7133 (9) |
| Ba1—O1v | 2.7589 (10) | Cr1—O1xxii | 1.7133 (9) |
| Ba1—O1vi | 2.7589 (10) | Cr1—O1xxiii | 1.7134 (9) |
| Ba1—O2vii | 3.31834 (13) | Cr1—Ba2xx | 3.51007 (19) |
| Ba1—O2viii | 3.31834 (13) | Cr1—Ba2xxiv | 3.51007 (18) |
| Ba1—O2ix | 3.31834 (13) | Cr1—Ba2xix | 3.51010 (18) |
| Ba1—O2x | 3.31834 (13) | Cr1—Ba1xxv | 3.6724 (2) |
| Ba1—O2xi | 3.31838 (13) | Cr1—Ba1xxvi | 3.6724 (2) |
| Ba1—O2xii | 3.31838 (13) | Cr1—Ba1xxvii | 3.6725 (2) |
| Ba2—O2 | 2.626 (2) | Cr1—Cr1xxiv | 4.5764 (6) |
| Ba2—O1i | 2.8155 (10) | Cr1—Cr1xx | 4.5764 (6) |
| Ba2—O1v | 2.8155 (10) | O2—Ba1xxvi | 3.31834 (13) |
| Ba2—O1iii | 2.8155 (10) | O2—Ba1xxv | 3.31834 (13) |
| Ba2—O1xiii | 2.9268 (2) | O2—Ba1xxvii | 3.31837 (13) |
| Ba2—O1xiv | 2.9268 (2) | O1—Cr1xxiii | 1.7133 (9) |
| Ba2—O1xv | 2.9268 (2) | O1—Ba1xxviii | 2.7589 (10) |
| Ba2—O1xvi | 2.9268 (2) | O1—Ba2i | 2.8155 (10) |
| Ba2—O1xvii | 2.9268 (2) | O1—Ba2xxix | 2.9268 (2) |
| Ba2—O1xviii | 2.9268 (2) | O1—Ba2xxx | 2.9268 (2) |
| O1i—Ba1—O1ii | 180.00 (3) | O1xvi—Ba2—O1xviii | 56.85 (4) |
| O1i—Ba1—O1iii | 64.86 (3) | O1xvii—Ba2—O1xviii | 116.445 (13) |
| O1ii—Ba1—O1iii | 115.14 (3) | O2—Ba2—Cr1xix | 70.902 (7) |
| O1i—Ba1—O1iv | 115.14 (3) | O1i—Ba2—Cr1xix | 71.74 (2) |
| O1ii—Ba1—O1iv | 64.86 (3) | O1v—Ba2—Cr1xix | 123.145 (7) |
| O1iii—Ba1—O1iv | 180.00 (3) | O1iii—Ba2—Cr1xix | 123.145 (7) |
| O1i—Ba1—O1v | 64.86 (3) | O1xiii—Ba2—Cr1xix | 87.343 (18) |
| O1ii—Ba1—O1v | 115.14 (3) | O1xiv—Ba2—Cr1xix | 87.343 (18) |
| O1iii—Ba1—O1v | 64.86 (3) | O1xv—Ba2—Cr1xix | 137.11 (2) |
| O1iv—Ba1—O1v | 115.14 (3) | O1xvi—Ba2—Cr1xix | 29.108 (18) |
| O1i—Ba1—O1vi | 115.14 (3) | O1xvii—Ba2—Cr1xix | 137.11 (2) |
| O1ii—Ba1—O1vi | 64.86 (3) | O1xviii—Ba2—Cr1xix | 29.109 (18) |
| O1iii—Ba1—O1vi | 115.14 (3) | O2—Ba2—Cr1xx | 70.900 (7) |
| O1iv—Ba1—O1vi | 64.86 (3) | O1i—Ba2—Cr1xx | 123.146 (7) |
| O1v—Ba1—O1vi | 180.00 (3) | O1v—Ba2—Cr1xx | 123.146 (7) |
| O1i—Ba1—O2vii | 70.56 (3) | O1iii—Ba2—Cr1xx | 71.74 (2) |
| O1ii—Ba1—O2vii | 109.44 (3) | O1xiii—Ba2—Cr1xx | 29.109 (18) |
| O1iii—Ba1—O2vii | 70.56 (3) | O1xiv—Ba2—Cr1xx | 137.11 (2) |
| O1iv—Ba1—O2vii | 109.44 (3) | O1xv—Ba2—Cr1xx | 29.109 (18) |
| O1v—Ba1—O2vii | 126.55 (4) | O1xvi—Ba2—Cr1xx | 87.343 (18) |
| O1vi—Ba1—O2vii | 53.45 (4) | O1xvii—Ba2—Cr1xx | 87.343 (18) |
| O1i—Ba1—O2viii | 70.56 (3) | O1xviii—Ba2—Cr1xx | 137.11 (2) |
| O1ii—Ba1—O2viii | 109.44 (3) | Cr1xix—Ba2—Cr1xx | 109.841 (7) |
| O1iii—Ba1—O2viii | 126.55 (4) | O2—Cr1—O1xxi | 110.14 (4) |
| O1iv—Ba1—O2viii | 53.45 (4) | O2—Cr1—O1xxii | 110.14 (4) |
| O1v—Ba1—O2viii | 70.56 (3) | O1xxi—Cr1—O1xxii | 108.80 (4) |
| O1vi—Ba1—O2viii | 109.44 (3) | O2—Cr1—O1xxiii | 110.14 (4) |
| O2vii—Ba1—O2viii | 119.913 (4) | O1xxi—Cr1—O1xxiii | 108.79 (4) |
| O1i—Ba1—O2ix | 109.44 (3) | O1xxii—Cr1—O1xxiii | 108.79 (4) |
| O1ii—Ba1—O2ix | 70.56 (3) | O2—Cr1—Ba2xx | 109.099 (7) |
| O1iii—Ba1—O2ix | 53.45 (4) | O1xxi—Cr1—Ba2xx | 56.202 (7) |
| O1iv—Ba1—O2ix | 126.55 (4) | O1xxii—Cr1—Ba2xx | 140.76 (4) |
| O1v—Ba1—O2ix | 109.44 (3) | O1xxiii—Cr1—Ba2xx | 56.204 (7) |
| O1vi—Ba1—O2ix | 70.56 (3) | O2—Cr1—Ba2xxiv | 109.099 (7) |
| O2vii—Ba1—O2ix | 60.087 (4) | O1xxi—Cr1—Ba2xxiv | 140.76 (4) |
| O2viii—Ba1—O2ix | 180.00 (7) | O1xxii—Cr1—Ba2xxiv | 56.202 (7) |
| O1i—Ba1—O2x | 109.44 (3) | O1xxiii—Cr1—Ba2xxiv | 56.204 (7) |
| O1ii—Ba1—O2x | 70.56 (3) | Ba2xx—Cr1—Ba2xxiv | 109.842 (7) |
| O1iii—Ba1—O2x | 109.44 (3) | O2—Cr1—Ba2xix | 109.098 (7) |
| O1iv—Ba1—O2x | 70.56 (3) | O1xxi—Cr1—Ba2xix | 56.205 (7) |
| O1v—Ba1—O2x | 53.45 (4) | O1xxii—Cr1—Ba2xix | 56.205 (7) |
| O1vi—Ba1—O2x | 126.55 (4) | O1xxiii—Cr1—Ba2xix | 140.76 (4) |
| O2vii—Ba1—O2x | 180.00 (7) | Ba2xx—Cr1—Ba2xix | 109.841 (7) |
| O2viii—Ba1—O2x | 60.087 (4) | Ba2xxiv—Cr1—Ba2xix | 109.841 (7) |
| O2ix—Ba1—O2x | 119.913 (4) | O2—Cr1—Ba1xxv | 64.579 (6) |
| O1i—Ba1—O2xi | 126.55 (4) | O1xxi—Cr1—Ba1xxv | 124.876 (11) |
| O1ii—Ba1—O2xi | 53.45 (4) | O1xxii—Cr1—Ba1xxv | 45.56 (4) |
| O1iii—Ba1—O2xi | 70.56 (3) | O1xxiii—Cr1—Ba1xxv | 124.874 (11) |
| O1iv—Ba1—O2xi | 109.44 (3) | Ba2xx—Cr1—Ba1xxv | 173.677 (12) |
| O1v—Ba1—O2xi | 70.56 (3) | Ba2xxiv—Cr1—Ba1xxv | 73.364 (2) |
| O1vi—Ba1—O2xi | 109.44 (3) | Ba2xix—Cr1—Ba1xxv | 73.365 (2) |
| O2vii—Ba1—O2xi | 119.912 (4) | O2—Cr1—Ba1xxvi | 64.579 (6) |
| O2viii—Ba1—O2xi | 119.912 (4) | O1xxi—Cr1—Ba1xxvi | 45.56 (4) |
| O2ix—Ba1—O2xi | 60.088 (4) | O1xxii—Cr1—Ba1xxvi | 124.876 (11) |
| O2x—Ba1—O2xi | 60.088 (4) | O1xxiii—Cr1—Ba1xxvi | 124.874 (11) |
| O1i—Ba1—O2xii | 53.45 (4) | Ba2xx—Cr1—Ba1xxvi | 73.364 (2) |
| O1ii—Ba1—O2xii | 126.55 (4) | Ba2xxiv—Cr1—Ba1xxvi | 173.677 (12) |
| O1iii—Ba1—O2xii | 109.44 (3) | Ba2xix—Cr1—Ba1xxvi | 73.365 (2) |
| O1iv—Ba1—O2xii | 70.56 (3) | Ba1xxv—Cr1—Ba1xxvi | 102.921 (7) |
| O1v—Ba1—O2xii | 109.44 (3) | O2—Cr1—Ba1xxvii | 64.579 (6) |
| O1vi—Ba1—O2xii | 70.56 (3) | O1xxi—Cr1—Ba1xxvii | 124.873 (11) |
| O2vii—Ba1—O2xii | 60.088 (4) | O1xxii—Cr1—Ba1xxvii | 124.873 (11) |
| O2viii—Ba1—O2xii | 60.088 (4) | O1xxiii—Cr1—Ba1xxvii | 45.56 (4) |
| O2ix—Ba1—O2xii | 119.912 (4) | Ba2xx—Cr1—Ba1xxvii | 73.365 (2) |
| O2x—Ba1—O2xii | 119.912 (4) | Ba2xxiv—Cr1—Ba1xxvii | 73.365 (2) |
| O2xi—Ba1—O2xii | 180.00 (7) | Ba2xix—Cr1—Ba1xxvii | 173.678 (12) |
| O2—Ba2—O1i | 142.65 (2) | Ba1xxv—Cr1—Ba1xxvii | 102.920 (7) |
| O2—Ba2—O1v | 142.64 (2) | Ba1xxvi—Cr1—Ba1xxvii | 102.920 (7) |
| O1i—Ba2—O1v | 63.40 (3) | O2—Cr1—Cr1xxiv | 46.451 (7) |
| O2—Ba2—O1iii | 142.64 (2) | O1xxi—Cr1—Cr1xxiv | 156.59 (4) |
| O1i—Ba2—O1iii | 63.40 (3) | O1xxii—Cr1—Cr1xxiv | 84.09 (3) |
| O1v—Ba2—O1iii | 63.40 (3) | O1xxiii—Cr1—Cr1xxiv | 84.09 (3) |
| O2—Ba2—O1xiii | 78.99 (2) | Ba2xx—Cr1—Cr1xxiv | 124.602 (5) |
| O1i—Ba2—O1xiii | 99.33 (2) | Ba2xxiv—Cr1—Cr1xxiv | 62.648 (3) |
| O1v—Ba2—O1xiii | 131.476 (10) | Ba2xix—Cr1—Cr1xxiv | 124.602 (5) |
| O1iii—Ba2—O1xiii | 68.34 (4) | Ba1xxv—Cr1—Cr1xxiv | 51.460 (3) |
| O2—Ba2—O1xiv | 78.99 (2) | Ba1xxvi—Cr1—Cr1xxiv | 111.030 (13) |
| O1i—Ba2—O1xiv | 99.33 (2) | Ba1xxvii—Cr1—Cr1xxiv | 51.460 (3) |
| O1v—Ba2—O1xiv | 68.34 (4) | O2—Cr1—Cr1xx | 46.451 (7) |
| O1iii—Ba2—O1xiv | 131.476 (10) | O1xxi—Cr1—Cr1xx | 84.09 (3) |
| O1xiii—Ba2—O1xiv | 157.90 (4) | O1xxii—Cr1—Cr1xx | 156.59 (4) |
| O2—Ba2—O1xv | 78.99 (2) | O1xxiii—Cr1—Cr1xx | 84.09 (3) |
| O1i—Ba2—O1xv | 131.476 (10) | Ba2xx—Cr1—Cr1xx | 62.648 (3) |
| O1v—Ba2—O1xv | 99.33 (2) | Ba2xxiv—Cr1—Cr1xx | 124.602 (5) |
| O1iii—Ba2—O1xv | 68.34 (4) | Ba2xix—Cr1—Cr1xx | 124.602 (5) |
| O1xiii—Ba2—O1xv | 56.85 (4) | Ba1xxv—Cr1—Cr1xx | 111.030 (13) |
| O1xiv—Ba2—O1xv | 116.445 (13) | Ba1xxvi—Cr1—Cr1xx | 51.460 (3) |
| O2—Ba2—O1xvi | 78.99 (2) | Ba1xxvii—Cr1—Cr1xx | 51.460 (4) |
| O1i—Ba2—O1xvi | 68.34 (4) | Cr1xxiv—Cr1—Cr1xx | 77.758 (11) |
| O1v—Ba2—O1xvi | 131.476 (10) | Cr1—O2—Ba2 | 180.0 |
| O1iii—Ba2—O1xvi | 99.33 (2) | Cr1—O2—Ba1xxvi | 88.29 (4) |
| O1xiii—Ba2—O1xvi | 60.73 (4) | Ba2—O2—Ba1xxvi | 91.71 (4) |
| O1xiv—Ba2—O1xvi | 116.445 (13) | Cr1—O2—Ba1xxv | 88.29 (4) |
| O1xv—Ba2—O1xvi | 116.445 (13) | Ba2—O2—Ba1xxv | 91.71 (4) |
| O2—Ba2—O1xvii | 78.99 (2) | Ba1xxvi—O2—Ba1xxv | 119.913 (4) |
| O1i—Ba2—O1xvii | 131.475 (10) | Cr1—O2—Ba1xxvii | 88.29 (4) |
| O1v—Ba2—O1xvii | 68.34 (4) | Ba2—O2—Ba1xxvii | 91.71 (4) |
| O1iii—Ba2—O1xvii | 99.33 (2) | Ba1xxvi—O2—Ba1xxvii | 119.912 (4) |
| O1xiii—Ba2—O1xvii | 116.445 (13) | Ba1xxv—O2—Ba1xxvii | 119.912 (4) |
| O1xiv—Ba2—O1xvii | 56.85 (4) | Cr1xxiii—O1—Ba1xxviii | 108.12 (5) |
| O1xv—Ba2—O1xvii | 60.73 (4) | Cr1xxiii—O1—Ba2i | 147.49 (5) |
| O1xvi—Ba2—O1xvii | 157.90 (4) | Ba1xxviii—O1—Ba2i | 104.39 (3) |
| O2—Ba2—O1xviii | 78.99 (2) | Cr1xxiii—O1—Ba2xxix | 94.688 (19) |
| O1i—Ba2—O1xviii | 68.34 (4) | Ba1xxviii—O1—Ba2xxix | 98.010 (19) |
| O1v—Ba2—O1xviii | 99.33 (2) | Ba2i—O1—Ba2xxix | 80.67 (2) |
| O1iii—Ba2—O1xviii | 131.476 (10) | Cr1xxiii—O1—Ba2xxx | 94.688 (19) |
| O1xiii—Ba2—O1xviii | 116.445 (13) | Ba1xxviii—O1—Ba2xxx | 98.009 (19) |
| O1xiv—Ba2—O1xviii | 60.73 (4) | Ba2i—O1—Ba2xxx | 80.67 (2) |
| O1xv—Ba2—O1xviii | 157.90 (4) | Ba2xxix—O1—Ba2xxx | 157.90 (4) |
| Symmetry codes: (i) −x+1, −y, −z+1; (ii) x−1, y, z−1; (iii) y, −x+y+1, −z+1; (iv) −y, x−y−1, z−1; (v) x−y−1, x−1, −z+1; (vi) −x+y+1, −x+1, z−1; (vii) −x+2/3, −y+1/3, −z+1/3; (viii) −x−1/3, −y−2/3, −z+1/3; (ix) x+1/3, y+2/3, z−1/3; (x) x−2/3, y−1/3, z−1/3; (xi) −x−1/3, −y+1/3, −z+1/3; (xii) x+1/3, y−1/3, z−1/3; (xiii) x−1/3, y+1/3, z−2/3; (xiv) x−4/3, y−2/3, z−2/3; (xv) −x+y+2/3, −x+4/3, z−2/3; (xvi) −y+2/3, x−y−2/3, z−2/3; (xvii) −y−1/3, x−y−2/3, z−2/3; (xviii) −x+y+2/3, −x+1/3, z−2/3; (xix) −x+1/3, −y−1/3, −z+2/3; (xx) −x+1/3, −y+2/3, −z+2/3; (xxi) x−y−1/3, x−2/3, −z+4/3; (xxii) y−1/3, −x+y+1/3, −z+4/3; (xxiii) −x+2/3, −y+1/3, −z+4/3; (xxiv) −x−2/3, −y−1/3, −z+2/3; (xxv) x−1/3, y−2/3, z+1/3; (xxvi) x+2/3, y+1/3, z+1/3; (xxvii) x−1/3, y+1/3, z+1/3; (xxviii) x+1, y, z+1; (xxix) x+1/3, y−1/3, z+2/3; (xxx) x+4/3, y+2/3, z+2/3. |
AAA is supported by an NSERC Postgraduate Award. Research at McMaster University is supported by NSERC and the Canadian Institute for Advanced Research Quantum Materials Program. The authors acknowledge Antoni Dabkowski for helpful discussions.
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The system Ba3Cr2O8 was recently synthesized in polycrystalline form to study its magnetic properties (Nakajima et al., 2006). Susceptibility and high-field magnetization measurements have provided evidence that this material is a new spin dimer system. The interesting magnetic properties observed motivated our growth of large single crystals up to 6 mm x 4 mm x 1 mm in size. Fig.1 shows the structure of Ba3Cr2O8, which consists of a series of CrO43− tetrahedra and Ba2+ ions.
Smaller single crystals of Ba3Cr2O8 (suitable for x-ray work) were previously grown using a flux method (Mattausch and Muller-Buschbaum, 1972), but the magnetic properties of these crystals were never investigated. The authors did solve the crystallographic structure, but the reported R values were quite high (> 0.08) and both the isotropic and anisotropic displacement parameters were not presented. It follows that the purpose of this work is to present a more accurate and complete solution of the crystallographic structure of this system. This work also proves that single crystals of materials containing the difficult-to-stabilize Cr5+ ion can be grown by the traveling solvent floating zone technique.