inorganic papers
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Bas B. van Akenet al. ErMnO3 DOI: 101107/S160053680100811X Acta Cryst.(2001). E57, i38±i40Acta Crystallographica Section E
Structure Reports Online
ISSN 1600-5368
Hexagonal ErMnO3
Bas B. Van Aken,* Auke Meetsma and Thomas T. M. Palstra
Solid State Chemistry Laboratory, Materials Science Centre, University of Groningen, Nijenborgh 4, NL-9747 AG Groningen, The Netherlands
Correspondence e-mail: [email protected]
Key indicators Single-crystal X-ray study T= 293 K
Mean(Mn±O) = 0.005 AÊ Rfactor = 0.034 wRfactor = 0.079
Data-to-parameter ratio = 23.0
For details of how these key indicators were automatically derived from the article, see http://journals.iucr.org/e.
#2001 International Union of Crystallography Printed in Great Britain ± all rights reserved
The crystal structure of hexagonal ErMnO3, erbium
manga-nese trioxide, has been determined at room temperature. It is isomorphous with YMnO3. Although we observed inversion
twinning, similar to YMnO3, the twin fractions do not have a
1:1 ratio, and the crystals are expected to show net ferroelectricity.
Comment
The compounds LnMnO3, where Ln is a lanthanide, have
attracted much interest in two different ®elds of materials science. The large ionic radius lanthanides, La and Ce±Dy, crystallize in a distorted orthorhombic perovskite structure (Yakel, 1955). These compounds have recently gained enor-mous interest, because of a colossal magneto-resistance effect,
i.e.a metal±insulator transition that changes the conductivity by many orders of magnitude at the Curie temperature (Ramirez, 1997). The Mn is octahedrally coordinated by O. The octahedra form a corner-shared three-dimensional network. The small ionic radius lanthanides, Ho±Lu, crystal-lize in a hexagonal structure (Yakelet al., 1963). Here, the Mn ions are coordinated by a trigonal bipyramid of O, forming a pseudo-layered structure by corner sharing of the trigonal basal plane O ions. These compounds are of interest because of the combination of ferroelectric and magnetic ordering (Smolenskii & Bokov, 1964).
Despite various reports on single-crystal growth of ErMnO3
(Yakelet al., 1963; Bertautet al., 1963), we could not ®nd in the literature the crystallographic structure determination. We report here the details of the re®nement of the crystal struc-ture (Fig. 1).
The metal±oxygen bond lengths are given in Table 1. Both erbium positions and the manganese position have unusual oxygen environments. Manganese is surrounded by ®ve O ions in a trigonal bipyramid. There is a striking difference in bond length between in-plane and out-of-plane bonds, respectively
'2.05 and'1.87 AÊ. The origin of this difference is the orbital occupation given by the crystal-®eld splitting of Mn3+. The 3d
states split in a trigonal bipyramidal ®eld according to the magnetic quantum number (Van Aken, Boset al., 2001), with thez2orbital highest in energy and two doublets. Thus the 3d4
ground state is non-degenerate and therefore not Jahn±Teller active. The emptyz2orbital is in agreement with the shorter
Mn±O distances along thecaxis than in theabplane. The non-equivalent Mn±O atomic distances, both within the basal plane and to the apices, have smaller differences than in isomorphous YbMnO3(Isobeet al., 1991).
The erbium has a distorted eightfold co-ordination, in the form of a bicapped trigonal antiprism. Due to this distortion
the capping O ions are displaced with respect to the erbium in such a way that the Er±O bond length changes from twice 2.9 AÊ to 2.4 AÊ and 3.3 AÊ. As a result the erbium ions are non-centrosymmetrically surrounded by the O ions. Both erbium positions have a similar distorted environment, which are 180
rotated with respect to each other. The combined environment yields a ferrielectric con®guration with four Er2 parallel dipole moments antiparallel to the two Er1 dipole moments. Consequently, ErMnO3 is ferroelectric and an ordering
temperature of '833 K has been reported (Smolenskii & Chupis, 1982). The macroscopic electric polarization is cancelled by an inversion twin, as found in YMnO3 (Van
Aken, Meetsma & Palstra, 2001). The origin of the ferroe-lectricity is not known at present, although the hexagonal manganites are less densely packed than the perovskite manganites.
We conclude that ErMnO3 is ferrielectric. Both erbium
positions have a dipole moment parallel to the c axis and antiparallel to each other. The electric polarization is cancelled by inversion twinning.
Experimental
Single crystals of ErMnO3 were obtained using a ¯ux method by weighing appropriate amounts of Er2O3and MnO2with Bi2O3in a 1:12 ratio (Yakelet al., 1963). The powders were mixed thoroughly and heated for 48 h at 1523 K in a Pt crucible. The separation of the crystals from the ¯ux was carried out by increasing the temperature to 1723 K and evaporating the Bi2O3¯ux (Bertautet al., 1963).
Crystal data
ErMnO3
Mr= 270.20 Hexagonal,P63cm
a= 6.1121 (5) AÊ
c= 11.4200 (14) AÊ
V= 369.47 (6) AÊ3
Z= 6
Dx= 7.286 Mg mÿ3
MoKradiation Cell parameters from 3929
re¯ections
= 3.5±38.4 = 38.68 mmÿ1
T= 293 K
Triangular platelet, black 0.110.100.08 mm
Data collection
Bruker SMART APEX diffrac-tometer
Area-detector scans
Absorption correction: Gaussian (XPREP, Bruker, 2000)
Tmin= 0.018,Tmax= 0.083
7178 measured re¯ections
759 independent re¯ections 569 re¯ections withF> 4(F)
Rint= 0.068
max= 38.5
h=ÿ6!10
k=ÿ10!8
l=ÿ18!19
Re®nement
Re®nement onF2
R[F2> 2(F2)] = 0.034
wR(F2) = 0.079
S= 1.03 759 re¯ections 33 parameters
w= 1/[2(F
o2) + (0.0457P)2] whereP= (Fo2+ 2Fc2)/3
(/)max< 0.001
max= 3.8 (9) e AÊÿ3
min=ÿ6.4 (9) e AÊÿ3
Extinction correction:SHELXL97 (Sheldrick, 1997)
Extinction coef®cient: 0.0223 (11)
Table 1
Selected geometric parameters (AÊ,).
Er2ÐO4 2.437 (15) Er2ÐO2 2.244 (7) Er2ÐO1i 2.306 (5)
Er2ÐO4ii 3.273 (15)
Er1ÐO3 2.32 (3) Er1ÐO1 2.312 (6)
Er1ÐO2iii 2.281 (8)
Er1ÐO3iii 3.39 (3)
Mn1ÐO3 2.092 (4) Mn1ÐO4 2.030 (2) Mn1ÐO1 1.854 (8) Mn1ÐO2 1.886 (8)
O3ÐMn1ÐO4 119.49 (7)
O4ÐMn1ÐO4iv 120.76 (13) O1ÐMn1ÐO2Mn1ÐO3ÐMn1v 178.5 (3)118.5 (4)
Symmetry codes: (i) 1xÿy;1x;1
2z; (ii)ÿxy;y;12z; (iii)xÿy;x;zÿ12; (iv)
yÿ1;x;z; (v)ÿy;xÿy;z.
The space group is determined to beP63cm, taking into consid-eration the unit-cell parameters, statistical analyses of intensity distributions and, where appropriate, systematic extinctions (hhl:l6 2n; 00l:l62n). Other space groups that satisfy the same extinction conditions were discarded during the re®nement. Attempts to ®t the data with a crystal structure in space group P63/mcm were unsuc-cessful withwR= 0.479 and R= 0.195. Furthermore, the principal mean-square atomic displacements of Er1 have a ratio of 14:1 for the perpendicular and parallel directions in this `wrong' space group.
SHELXL97 suggests a splitting of this atom in a position above and
Acta Cryst.(2001). E57, i38±i40 Bas B. van Akenet al. ErMnO3
i39
inorganic papers
Figure 1
Schematic view of the crystallographic structure of ErMnO3. The upper
view is along the basal plane. Er is represented by blue spheres, and the MnO5 clusters are represented by red trigonal bipyramids. This panel
inorganic papers
i40
Bas B. van Akenet al. ErMnO3 Acta Cryst.(2001). E57, i38±i40below the mirror plane. The structure was solved by using initial coordinates, which are taken from a previous reported hexagonal manganite, YMnO3 (Van Aken, Meetsma & Palstra, 2001). The positional and anisotropic displacement parameters were re®ned. The principal mean-square atomic displacements for the cations in the right space group do not show any signi®cant anisotropy. The ®nal difference Fourier map showed a peak of 3.9 (9) e AÊÿ3near the Er1 position and a hole of 6.4 (9) e AÊÿ3also near the Er1 position. No other signi®cant peaks having chemical meaning above the general background (0.9 e AÊÿ3) were observed in the ®nal difference Fourier map. The Flack parameter (Flack, 1983) of an initial re®nement indicated that the crystal was twinned. The model without a twin yielded a Flack parameterx= 0.3484 andx= 0.6147 for the inverse structure. TheRvalues arewR= 0.0811 andR= 0.0355,wR= 0.0857 andR= 0.0363, respectively. Therefore, an inversion twin was added to the structure model, similar to the one reported for YMnO3(Van Aken, Meetsma & Palstra, 2001). The ®nal re®nement gave a twin fraction of 36 (5)%. We expect a 50±50% distribution because this yields no net electrical polarization (Rao & Gopalakrishnan, 1997). The deviation from the 50±50% can be caused during the cutting process of the crystals.
Data collection:SMART(Bruker, 2000); cell re®nement:SAINT
(Bruker, 2000); data reduction:XPREP(Bruker, 2000); program(s) used to re®ne structure: SHELXL97 (Sheldrick, 1997); molecular
graphics:ORTEP(Farrugia, 2000); software used to prepare material for publication:PLATON(Spek, 2001).
References
Bertaut, E. F., Forrat, E. F. & Fang, P. (1963).C.R.Acad. Sci.256, 1958±1961. Bruker, (2000).SMART(Version 5.168),SAINT(Version 6.02A),SADABS,
XPREP(Version 5.1/NT) andSHELXTL/NT. Bruker AXS Inc., Madison, Wisconsin, USA.
Farrugia, L. J. (2000).J. Appl. Cryst.30, 565. Flack, H. D. (1983).Acta Cryst.A39, 876±881.
Isobe, M., Kimizuka, N., Nakamura, M. & Mohri, T. (1991).Acta Cryst.C47, 423±424.
Ramirez, A. P. (1997).J. Phys. Condens.Mater.9, 8171±8199.
Rao, C. N. R. & Gopalakrishnan, J. (1997). New Directions in Solid State Chemistry, 2nd ed., p. 385. Cambridge University Press.
Sheldrick, G. M. (1997).SHELXL97. University of GoÈttingen, Germany. Smolenskii, G. A. & Bokov, V. A. (1964).J. Appl. Phys.35, 915±918. Smolenskii, G. A. & Chupis, I. E. (1982).Sov. Phys. Usp.25, 475±493. Spek, A. L. (2001).PLATON.Utrecht University, The Netherlands. Van Aken, B. B., Meetsma, A. & Palstra, T. T. M. (2001).Acta Cryst.C57, 230±
232.
Van Aken, B. B., Bos, J. W. G., de Groot, R. A. & Palstra, T. T. M. (2001).Phys. Rev. B,63, 125±127.
Yakel, H. L. (1955).Acta Cryst.8, 394±398.
supporting information
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Acta Cryst. (2001). E57, i38–i40
supporting information
Acta Cryst. (2001). E57, i38–i40 [https://doi.org/10.1107/S160053680100811X]
Hexagonal ErMnO
3Bas B. Van Aken, Auke Meetsma and Thomas T. M. Palstra
Erbium Manganese Oxide
Crystal data
ErMnO3
Mr = 270.20
Hexagonal, P63cm
Hall symbol: P 6c -2
a = 6.1121 (5) Å
c = 11.4200 (14) Å
V = 369.47 (6) Å3
Z = 6
F(000) = 702
Dx = 7.286 Mg m−3
Mo Kα radiation, λ = 0.71073 Å Cell parameters from 3929 reflections
θ = 3.5–38.4°
µ = 38.68 mm−1
T = 293 K
Triangular platelet, black 0.11 × 0.10 × 0.08 mm
Data collection
Bruker SMART Apex diffractometer
Radiation source: fine focus sealed Siemens Mo tube
Parallel mounted graphite monochromator Detector resolution: 4096x4096 62x62(binned
512) pixels mm-1
area detector scans
Absorption correction: gaussian (XPREP, Bruker, 2000)
Tmin = 0.019, Tmax = 0.083
7178 measured reflections 759 independent reflections 569 reflections with F > 4σ(F)
Rint = 0.068
θmax = 38.5°, θmin = 3.6°
h = −6→10
k = −10→8
l = −18→19
Refinement
Refinement on F2
Least-squares matrix: full
R[F2 > 2σ(F2)] = 0.034
wR(F2) = 0.079
S = 1.03 759 reflections 33 parameters 1 restraint
Primary atom site location: structure-invariant direct methods
Secondary atom site location: none
w = 1/[σ2(F
o2) + (0.0457P)2]
where P = (Fo2 + 2Fc2)/3
(Δ/σ)max < 0.001
Δρmax = 3.8 (9) e Å−3
Δρmin = −6.4 (9) e Å−3
Extinction correction: SHELXL97 (Sheldrick, 1997), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Extinction coefficient: 0.0223 (11)
Special details
supporting information
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Acta Cryst. (2001). E57, i38–i40
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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2)
x y z Uiso*/Ueq
Er1 0.00000 0.00000 −0.22783 (9) 0.0084 (2) Er2 0.33333 0.66667 0.22951 (2) 0.0089 (1) Mn1 0.00000 0.3396 (3) −0.00248 (17) 0.0090 (3) O1 0.00000 0.3593 (12) −0.1645 (7) 0.012 (2) O2 0.00000 0.3113 (14) 0.1620 (7) 0.012 (2) O3 0.00000 0.00000 −0.025 (3) 0.010 (3) O4 0.33333 0.66667 0.0161 (13) 0.011 (2)
Atomic displacement parameters (Å2)
U11 U22 U33 U12 U13 U23
Er1 0.0093 (3) 0.0093 (3) 0.0067 (3) 0.0047 (2) 0.0000 0.0000 Er2 0.0090 (2) 0.0090 (2) 0.0088 (2) 0.0045 (1) 0.0000 0.0000 Mn1 0.0122 (8) 0.0105 (5) 0.0048 (3) 0.0061 (4) 0.0000 0.0015 (4) O1 0.030 (5) 0.008 (2) 0.004 (3) 0.015 (3) 0.0000 −0.001 (2) O2 0.018 (5) 0.012 (3) 0.008 (3) 0.009 (2) 0.0000 0.001 (2) O3 0.010 (4) 0.010 (4) 0.009 (7) 0.005 (2) 0.0000 0.0000 O4 0.013 (4) 0.013 (4) 0.008 (4) 0.0066 (19) 0.0000 0.0000
Geometric parameters (Å, º)
Er2—O4 2.437 (15) Er1—O1viii 2.312 (7)
Er2—O2 2.244 (7) Er1—O2ix 2.281 (7)
Er2—O1i 2.306 (5) Er1—O1x 2.312 (7)
Er2—O2ii 2.244 (9) Er1—O2xi 2.281 (8)
Er2—O1iii 2.306 (5) Er1—O3vii 3.39 (3)
Er2—O2iv 2.244 (5) Mn1—O3 2.092 (4)
Er2—O4v 3.273 (15) Mn1—O4 2.030 (2)
Er2—O1vi 2.306 (7) Mn1—O1 1.854 (8)
Er1—O3 2.32 (3) Mn1—O2 1.886 (8)
Er1—O1 2.312 (6) Mn1—O4xii 2.0296 (18)
Er1—O2vii 2.281 (8)
O4—Er2—O2 69.9 (2) O1viii—Er1—O2xi 164.8 (3)
O4—Er2—O1i 121.66 (17) O1x—Er1—O2ix 77.08 (19)
O4—Er2—O2ii 69.9 (2) O2ix—Er1—O2xi 92.5 (3)
O4—Er2—O1iii 121.66 (18) O1x—Er1—O2xi 77.1 (3)
O4—Er2—O2iv 69.9 (2) O3—Mn1—O4 119.49 (7)
O4—Er2—O1vi 121.66 (19) O3—Mn1—O1 86.7 (9)
supporting information
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Acta Cryst. (2001). E57, i38–i40
O2—Er2—O2ii 108.8 (2) O3—Mn1—O4xii 119.49 (9)
O1iii—Er2—O2 76.7 (2) O4—Mn1—O1 94.2 (5)
O2—Er2—O2iv 108.8 (2) O4—Mn1—O2 86.6 (5)
O1vi—Er2—O2 77.9 (3) O4—Mn1—O4xii 120.76 (13)
O1i—Er2—O2ii 77.9 (3) O1—Mn1—O2 178.5 (3)
O1i—Er2—O1iii 95.0 (3) O4xii—Mn1—O1 94.2 (4)
O1i—Er2—O2iv 76.7 (2) O4xii—Mn1—O2 86.6 (4)
O1i—Er2—O1vi 95.0 (2) Er1—O3—Mn1 97.1 (9)
O1iii—Er2—O2ii 168.4 (3) Er1—O3—Mn1viii 97.1 (9)
O2ii—Er2—O2iv 108.8 (3) Er1—O3—Mn1x 97.1 (9)
O1vi—Er2—O2ii 76.7 (3) Mn1—O3—Mn1viii 118.5 (4)
O1iii—Er2—O2iv 77.9 (3) Mn1—O3—Mn1x 118.5 (4)
O1iii—Er2—O1vi 95.0 (3) Mn1viii—O3—Mn1x 118.5 (4)
O1vi—Er2—O2iv 168.4 (3) Er2—O4—Mn1 96.0 (4)
O3—Er1—O1 71.8 (2) Er2—O4—Mn1iv 96.0 (4)
O3—Er1—O2vii 123.5 (2) Mn1—O4—Mn1ii 118.92 (16)
O3—Er1—O1viii 71.8 (2) Mn1—O4—Mn1iv 118.92 (16)
O3—Er1—O2ix 123.47 (19) Mn1ii—O4—Mn1iv 118.92 (16)
O3—Er1—O1x 71.8 (2) Er1—O1—Mn1 104.5 (3)
O3—Er1—O2xi 123.5 (2) Er2vii—O1—Er1 101.0 (3)
O1—Er1—O2vii 77.08 (18) Er2xiii—O1—Er1 101.0 (2)
O1—Er1—O1viii 110.7 (2) Er2vii—O1—Mn1 123.2 (2)
O1—Er1—O2ix 164.8 (3) Er2xiii—O1—Mn1 123.2 (3)
O1—Er1—O1x 110.69 (16) Er2vii—O1—Er2xiii 99.8 (3)
O1—Er1—O2xi 77.1 (3) Er2—O2—Mn1 107.2 (3)
O1viii—Er1—O2vii 77.1 (2) Er2—O2—Er1xiv 103.8 (3)
O2vii—Er1—O2ix 92.5 (2) Er2—O2—Er2xii 103.6 (3)
O1x—Er1—O2vii 164.8 (3) Er1xiv—O2—Mn1 128.7 (4)
O2vii—Er1—O2xi 92.5 (3) Er2xii—O2—Mn1 107.2 (2)
O1viii—Er1—O2ix 77.1 (3) Er2xii—O2—Er1xiv 103.8 (3)
O1viii—Er1—O1x 110.7 (2)
O2—Er2—O4—Mn1 4.11 (14) O3—Mn1—O4—Er2 −94.7 (11) O4—Er2—O2—Mn1 −4.61 (16) O1—Mn1—O4—Er2 176.74 (15) O1—Er1—O3—Mn1 0.00 (14) O2—Mn1—O4—Er2 −4.61 (16) O3—Er1—O1—Mn1 0.00 (14) O3—Mn1—O1—Er1 0.02 (15) O4—Mn1—O3—Er1 −92.9 (7) O4—Mn1—O1—Er1 119.35 (16) O1—Mn1—O3—Er1 −0.02 (13) O3—Mn1—O2—Er2 124.64 (18) O2—Mn1—O3—Er1 −180.00 (18) O4—Mn1—O2—Er2 5.21 (18)
