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LaInO3, a promising ion conductor for a holistic solid oxide fuel cell, was synthesized by a solid-state reaction method. The structure was refined by the Rietveld method using X-ray powder diffraction data. The structure of LaInO3 is distorted by the in-phase and antiphase tilting of oxy­gen octahedra in the a+b-b- system of the InO6 polyhedra. In the Pmna space group, the In atom lies on an inversion centre and the La atom and one of the O atoms lie on a mirror plane.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270103024806/sq1033sup1.cif
Contains datablocks global, I

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0108270103024806/sq1033Isup2.rtv
Contains datablock I

Comment top

Oxides with a perovskite structure have a variety of electrical, optical and electrochemical applications, e.g. ferroelectric memories, luminescence and solid oxide fuel cells. LaInO3 is an example of one of these oxides. The chemical formula LaInO3 simply indicates that the oxide is a member of the perovskite family, but its crystallographic structure has not yet been assessed in detail. The room-temperature structure of LaXO3 (X = B, Al, Ga, In and Tl) exhibits different space groups (viz. Pmcn, R3 m, Pnma, Pnma and P63, respectively; Galasso, 1990; Lerch, 2001) depending on the increasing ionic radius of X. Padurow et al. (JCPDS diffraction card data number 09–0034) reported only the cell parameters (a=11.402 Å, b=8.198 Å and c=11.796 Å in the orthorhombic system) of LaInO3, without determining the space group. Keith & Roy (1954) reported that LaInO3 had a YCrO3-type structure, while presenting only the X-ray powder pattern without the space group. Roth (1957) reported that LaInO3 is orthorhombic (with cell parameters a= 5.723 Å, b= 8.207 Å and c= 5.914 Å) but could not determine the structure of LaInO3. Therefore, we report here a detailed analysis of the crystal structure of LaInO3, obtained by the X-ray Rietveld method.

Fig. 1 shows the observed X-ray diffraction pattern, the calculated pattern and the difference profile for LaInO3. The structure, illustrated in Fig. 2, is composed of distorted InO6 octahedra, with La atoms lying in between. In this structure, three kinds of In—O bonds exist, the average bond lengths of which are 2.11, 2.164 and 2.22 Å, respectively. Each In atom is located at the center of an oxygen octahedron. The InO6 octahedron at the center of the unit cell has b=1/2. La atoms are at b=1/4 and 3/4. Selected interatomic distances and bond angles are listed in Table 1. Although LaInO3 has an orthorhombic cell, it may be transformed to a cubic one for comparison with a simple perovskite cell. Most of the diffraction peaks shown in Fig. 1 could be indexed on the basis of the cubic cell (ao = 4.12 Å), except for some extra peaks, which are indicated by asterisks (see inset). Two such peaks, labelled as 1/2(111)c and 1/2(311)c, have been attributed to the antiphase tilting of oxygen octahedra (Glazer, 1972; Glazer, 1975), the 1/2(310)c peak can be explained by the inphase tilting of oxygen octahedra, and the last extra peak, 1/2(210)c, indicates the antiparallel shift of the A site cations in LaInO3. On the basis of these results, we are able to conclude that the orthorhombic LaInO3 is distorted by the inphase and antiphase tilting of oxygen octahedra with the a+bb tilt system proposed by Glazer (Glazer, 1972; Glazer, 1975). The ionic radius difference, which can be represented by the tolerance factor, plays an important role in determining the crystal structure in these LaXO3 compounds. The tolerance factor (t) is given by

t = (rLa + rO) / 1.414 (rX + rO), (1)

where rLa, rO and rX are the radii of the La, O, X ions, respectively.

The ionic radii used were those of Shannon (1976) [r(La3+)=0.136 nm, r(O2−)=0.140 nm, r(Ga3+)=0.062 nm, r(In3+)=0.080 nm and r(Tl3+)=0.089 nm]. The tolerance factors of LaGaO3, LaInO3 and LaTlO3 are 0.966, 0.887 and 0.852, respectively. From the changes of the tolerance factors, it could be expected that these compounds might have the same structure. Recently, Lerch et al.(2001) reported that the crystal structure of pure LaGaO3 at ambient temperature was a distorted perovskite similar to LaInO3, with the space group Pnma. By contrast, it is reported that LaTlO3 has the space group P63 (Inorganic Crystal Structure Database No. 200088, https://icsd.ill.fr/icsd/). From the present results, it appears that LaInO3 is in satisfactory agreement with the relationship between crystal symmetry and tilting, which is influenced by the tolerance factor.

Experimental top

Samples of LaInO3 were synthesized by a conventional solid-state reaction method (He et al., 2000) from individual oxide and carbonate powders, La2O3 (99.9%, Aldrich) and In2O3 (99.9%, Trinitech International Inc., Twinsburg, OH). The materials were weighed in the appropriate molar ratio and mixed with ZrO2 balls in ethanol for 24 h. The powders were dried, calcined at 1573 K for 4 h in air, pressed into discs and then sintered at 1723 K for 4 h in air. The crystal structures of sintered specimens were investigated by conventional X-ray powder diffractometry (Model Geigerflex, D/max-B, Rigaku Corporation, Tokyo, Japan; Cu Kα radiation, produced at 40 kV and 35 mA). To obtain the precise data for Rietveld refinement, the scan width and time were 0.02° and 10 sec at the range of 10–140° 2θ and the crystal structure was refined by the FULLPROF program (Carvajal, 2000).

Refinement top

We checked using PLATON program to publish the CIF data and several alerts were found. However most of alerts in CIF/PLATON report are not applicable to our experiment because our work is powder diffraction data.

Computing details top

Data collection: D/max-B Software (Rigaku Corporation, 1990); cell refinement: FULLPROF98 (Carvajal, 2000)); program(s) used to refine structure: FULLPROF98; molecular graphics: ATOMS (Dowty, 1997); software used to prepare material for publication: PLATON (Spek, 1990).

Figures top
[Figure 1] Fig. 1. Observed, calculated and difference profiles for LaInO3. The inset shows the peaks that could not be indexed in the cubic perovskite cell (ao = 4.12 Å), marked with asterisks.
[Figure 2] Fig. 2. The crystal structure of LaInO3, viewed along the b axis.
Lanthanum Indium Oxide top
Crystal data top
LaInO3Z = 4
Mr = 301.73F(000) = 520
Orthorhombic, PnmaDx = 7.173 Mg m3
Hall symbol: -p 2ac 2nCu Kα radiation, λ = 1.5418 Å
a = 5.9404 (1) ÅT = 295 K
b = 8.2158 (1) ÅParticle morphology: irregular
c = 5.7229 (1) Åyellow
V = 279.31 (1) Å3flat sheet, 20 × 25 mm
Data collection top
Rigaku D/max-B
diffractometer
Data collection mode: reflection
Radiation source: sealed X-ray tubeScan method: step
Graphite monochromator2θmin = 10°, 2θmax = 140°, 2θstep = 0.02°
Specimen mounting: packed powder pellet
Refinement top
Refinement on Inetχ2 = 0.656
Least-squares matrix: full with fixed elements per cycle6501 data points
Rp = 0.044Profile function: pseudo-Voigt
Rwp = 0.06030 parameters
Rexp = 0.074(Δ/σ)max = 0.01
R(F) = 0.030Background function: 6 polynomials coefficients
R(F2) = 0.0367
Crystal data top
LaInO3V = 279.31 (1) Å3
Mr = 301.73Z = 4
Orthorhombic, PnmaCu Kα radiation, λ = 1.5418 Å
a = 5.9404 (1) ÅT = 295 K
b = 8.2158 (1) Åflat sheet, 20 × 25 mm
c = 5.7229 (1) Å
Data collection top
Rigaku D/max-B
diffractometer
Scan method: step
Specimen mounting: packed powder pellet2θmin = 10°, 2θmax = 140°, 2θstep = 0.02°
Data collection mode: reflection
Refinement top
Rp = 0.044R(F2) = 0.0367
Rwp = 0.060χ2 = 0.656
Rexp = 0.0746501 data points
R(F) = 0.03030 parameters
Special details top

Experimental. The full pattern refinement of X-ray powder diffraction data was performed as follows. First, we assigned the space group as Pnma (No. 62). The unit-cell parameters that had previously been obtained from the pattern with an Si internal standard were used as the starting model of the Rietveld refinement. The validity of this model was confirmed through the profile-matching method. To refine the structure, initially only the scale factor, six background coefficients, the unit-cell parameters and the W parameter among three variables of FWHM were varied. In subsequent refinements, the positional, displacement and site- occupancy parameters were refined. Each occupancy factor was constrained according to the stoichiometric ratio. The U and V parameters of the FWHM were then varied. Refinement was terminated when Rp, Rwp and goodness-of-fit (S) parameters of 4.35%, 6.02% and 0.81, respectively, were obtained. In the final refinement, isotropic temperature factors were successfully refined for all atoms, although the goodness-of-fit was not ideal for the refinement. S is a useful numerical criterion for assessing the relevancy of a refinement process. An S value of 1.3 or less is usually considered to be quite satisfactory. However, a value of S that is too small may simply mean that the counting statistical errors outweigh the model errors, either because of poor counting statistics or because of high background (Young, 1993). To confirm the exact model relevancy, we performed a differential Fourier synthesis with SHELXL97 (Sheldrick, 1997). The maximum and minimum electron densities on the difference Fourier map are 0.97 and −0.96/Å3, respectively. We regarded this refined structural model as correct.

Young, R. A. (1993). The Rietveld Method. New York: IUCR, Oxford University Press Inc.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
O10.029 (5)0.250.615 (5)1.12 (8)
O20.209 (3)0.0623 (17)0.192 (4)0.21 (6)
In000.50.15 (2)
La0.0551 (4)0.250.0169 (9)0.24 (2)
Geometric parameters (Å, º) top
In—O2i2.11 (2)La—O22.417 (16)
In—O12.164 (9)La—O1iv2.59 (3)
In—O1ii2.164 (9)La—O2iv2.67 (2)
In—O22.22 (2)La—O2v2.975 (17)
In—O2ii2.22 (2)La—O2vi2.975 (17)
La—O1iii2.35 (3)
O2i—In—O190.4 (8)O1iii—La—O2iv136.2 (6)
O2i—In—O1ii89.6 (8)O2—La—O2iv116.8 (4)
O2i—In—O290.6 (3)O1iv—La—O2iv71.4 (7)
O1—In—O288.8 (8)O1iii—La—O2v70.9 (5)
O1ii—In—O291.2 (8)O2—La—O2v79.4 (7)
O2i—In—O2ii89.4 (3)O1iv—La—O2v65.7 (4)
O1—In—O2ii91.2 (8)O2iv—La—O2v126.0 (3)
O1ii—In—O2ii88.8 (8)O1iii—La—O2vi70.9 (5)
O1iii—La—O2105.5 (7)O1iv—La—O2vi65.7 (4)
O1iii—La—O1iv85.2 (6)O2iv—La—O2vi65.8 (2)
O2—La—O1iv137.9 (5)O2v—La—O2vi119.2 (7)
Symmetry codes: (i) x+1/2, y, z+1/2; (ii) x, y, z+1; (iii) x, y, z1; (iv) x1/2, y+1/2, z+1/2; (v) x, y, z; (vi) x, y+1/2, z.

Experimental details

Crystal data
Chemical formulaLaInO3
Mr301.73
Crystal system, space groupOrthorhombic, Pnma
Temperature (K)295
a, b, c (Å)5.9404 (1), 8.2158 (1), 5.7229 (1)
V3)279.31 (1)
Z4
Radiation typeCu Kα, λ = 1.5418 Å
Specimen shape, size (mm)Flat sheet, 20 × 25
Data collection
DiffractometerRigaku D/max-B
diffractometer
Specimen mountingPacked powder pellet
Data collection modeReflection
Scan methodStep
2θ values (°)2θmin = 10 2θmax = 140 2θstep = 0.02
Refinement
R factors and goodness of fitRp = 0.044, Rwp = 0.060, Rexp = 0.074, R(F) = 0.030, R(F2) = 0.0367, χ2 = 0.656
No. of data points6501
No. of parameters30
No. of restraints?

Computer programs: D/max-B Software (Rigaku Corporation, 1990), FULLPROF98 (Carvajal, 2000)), FULLPROF98, ATOMS (Dowty, 1997), PLATON (Spek, 1990).

Selected geometric parameters (Å, º) top
In—O2i2.11 (2)La—O1iii2.35 (3)
In—O12.164 (9)La—O1iv2.59 (3)
In—O1ii2.164 (9)La—O2iv2.67 (2)
In—O22.22 (2)La—O2v2.975 (17)
In—O2ii2.22 (2)La—O2vi2.975 (17)
O2i—In—O190.4 (8)O1iii—La—O1iv85.2 (6)
O2i—In—O1ii89.6 (8)O2—La—O1iv137.9 (5)
O2i—In—O290.6 (3)O1iii—La—O2iv136.2 (6)
O1—In—O288.8 (8)O2—La—O2iv116.8 (4)
O1ii—In—O291.2 (8)O2iv—La—O2v126.0 (3)
O2i—In—O2ii89.4 (3)O1iii—La—O2vi70.9 (5)
O1—In—O2ii91.2 (8)O1iv—La—O2vi65.7 (4)
O1ii—In—O2ii88.8 (8)O2iv—La—O2vi65.8 (2)
O1iii—La—O2105.5 (7)O2v—La—O2vi119.2 (7)
Symmetry codes: (i) x+1/2, y, z+1/2; (ii) x, y, z+1; (iii) x, y, z1; (iv) x1/2, y+1/2, z+1/2; (v) x, y, z; (vi) x, y+1/2, z.
 

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