Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270105017518/bc1071sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270105017518/bc1071Isup2.hkl |
Single crystals of nominal composition La0.8Ba0.2MnO3 were grown by the non-crucible floating zone technique (Mukovskii et al., 2001). Electron microprobe analysis revealed a La:Ba:Mn ratio of 0.815 (10):0.185 (6):0.996 (8). The nominal and real Ba contents differ as a result of a strong evaporation of barium during melting.
A piece of about 0.13 × 0.06 × 0.05 mm was cut from the crystalline material and used for single-crystal X-ray diffraction. We found a crystal structure with space group R-3c at room temperature (T = 296 K), in accordance with previous studies (Arkhipov et al., 2000). At 160 K, the diffraction peaks appeared to be split in ω scans. The centering of 25 reflections showed an eightfold pseudo-cubic supercell 2ac × 2ac × 2ac (the subscript c refers to the primitive cubic perovskite unitcell) with a = 7.830 (3) Å b = 7.802 (3) Å, c = 7.832 (2) Å, α = 90.12 (2)° β = 90.56 (3)° and γ = 90.13 (3)°. The distortions from cubic lattice symmetry indicate that the true lattice is 21/2ac × 21/2ac × 2ac with either orthorhombic Pbnm or Imcm, or monoclinic I2/c symmetries (see Fig. 1 of Tamazyan et al., 2002). The splitting of reflections can be explained by twinning. Because the transition is first-order, every symmetry operator of the m3m point group that is not part of the crystal class (mmm or 2/m) may become a twinning operator (Tamazyan et al., 2002) and any orientation of the low-temperature structure within the hypothetical cubic perovskite lattice may occur. This is confirmed by the orientations of the five twin domains (out of a total of 12) with significant volume fractions (Table 2). Among them, two pairs of domains are related by a fourfold axis. The characteristic n-fold splitting of the pseudocubic (hh0)c and (hhh)c reflections is identified by means of measured ω–θ sections and compared with the number of maxima expected for different symmetries (Tamazyan et al., 2002). Fig. 2 shows that the (333)c reflection is split into three peaks in accordance with monoclinic symmetry and at variance with orthorhombic symmetry. Twin matrices applied to the Miller indices (hkl are multiplied from the left) are the following: M1 = (1 0 0|0 1 0|0 0 1), M2 = (1/2 − 1/2 1/2|-1/2 1/2 1/2|-1 − 1 0), M3 = (1/2 1/2 1/2|-1/2 − 1/2 1/2|1 − 1 0), M4 = (−1/2 − 1/2 1/2|-1/2 − 1/2 − 1/2|1 − 1 0), M5 = (0 − 1 0|1 0 0|0 0 1). Structure refinements against all reflections led to R(obs) = 2.70, 3.23 and 3.46% for I2/c, Pbnm and Imcm, respectively. Additional tests were made by computing partial R values with the contributions of superlattice reflections only, which led to R(obs)/R(all) = 8.50/17.7, 11.93/74.1 and 18.27/31.1 for I2/c, Pbnm and Imcm, respectively. Measured intensity data show 45 observed reflections violating the I-centering. However, they are weak and they mainly belong to {110} in the eightfold pseudocubic superlattice. Such reflections can be explained as produced by λ/2 radiation since {220} reflections are very strong. The particularly high partial R(all) value for Pbnm demonstrates that the observed reflections violating the I-centering are not a result of structural effects. Because many studies of orthorhombic and monoclinic manganites report lattice parameters with a > b, we performed additional refinements in this setting and we checked the possibility of β < 90°. However, the splitting of the reflections prevented the unambiguous assignment of correct values to a and b (a > b or a < b). The best fit to the diffraction data was obtained in the monoclinic setting with a > b. This choice is confirmed by the observed maxima positions in the ω–θ section in Fig. 2, since the middle position of the strongest peak is only possible by assuming a > b (by assuming a < b, the strongest peak would have occurred on the right side at higher theta). In the difference Fourier map the largest residuals are located 0.4 (s.u.?) and 0.6 (s.u.?) Å, respectively, from the La/Ba atom.
Data collection: DATCOL in CAD-4 Software (Enraf–Nonius, 1989); cell refinement: SETANG LS in CAD-4 Software; data reduction: HELENA (Spek, 1997) and HABITUS (Herrendorf & Bärnighausen, 1997); program(s) used to solve structure: program (reference?); program(s) used to refine structure: Jana2000 (Petricek et al., 2000); molecular graphics: DIAMOND (Brandenburg, 2005); software used to prepare material for publication: Jana2000 (Petricek et al., 2000).
Ba0.185La0.815MnO3 | F(000) = 423.2 |
Mr = 241.6 | Dx = 6.706 Mg m−3 |
Monoclinic, I2/c | Mo Kα radiation, λ = 0.71069 Å |
Hall symbol: -I 2yc | Cell parameters from 25 reflections |
a = 5.564 (2) Å | θ = 18.4–29.8° |
b = 5.510 (2) Å | µ = 22.37 mm−1 |
c = 7.802 (3) Å | T = 160 K |
β = 90.18 (3)° | Rectangular prism, translucent dark brown |
V = 239.19 (14) Å3 | 0.13 × 0.06 × 0.05 mm |
Z = 4 |
Nonius MACH3 diffractometer | 1184 reflections with I > 3σ(I) |
Radiation source: Rotating Anode | Rint = 0.000 |
Graphite monochromator | θmax = 39.9°, θmin = 4.5° |
ω scans | h = −9→9 |
Absorption correction: ψ scan (HABITUS; Herrendorf & Bärnighausen, 1997) | k = −10→10 |
Tmin = 0.193, Tmax = 0.327 | l = −9→14 |
1567 measured reflections | 3 standard reflections every 60 min |
1567 independent reflections | intensity decay: none |
Refinement on F | Weighting scheme based on measured s.u.'s w = 1/(σ2(F) + 0.0001F2) |
R[F2 > 2σ(F2)] = 0.027 | (Δ/σ)max = 0.0001 |
wR(F2) = 0.033 | Δρmax = 3.02 e Å−3 |
S = 1.68 | Δρmin = −2.99 e Å−3 |
1567 reflections | Extinction correction: B-C type 1 Gaussian isotropic (Becker & Coppens, 1974) |
31 parameters | Extinction coefficient: 0.0028 (1) |
Ba0.185La0.815MnO3 | V = 239.19 (14) Å3 |
Mr = 241.6 | Z = 4 |
Monoclinic, I2/c | Mo Kα radiation |
a = 5.564 (2) Å | µ = 22.37 mm−1 |
b = 5.510 (2) Å | T = 160 K |
c = 7.802 (3) Å | 0.13 × 0.06 × 0.05 mm |
β = 90.18 (3)° |
Nonius MACH3 diffractometer | 1184 reflections with I > 3σ(I) |
Absorption correction: ψ scan (HABITUS; Herrendorf & Bärnighausen, 1997) | Rint = 0.000 |
Tmin = 0.193, Tmax = 0.327 | 3 standard reflections every 60 min |
1567 measured reflections | intensity decay: none |
1567 independent reflections |
R[F2 > 2σ(F2)] = 0.027 | 31 parameters |
wR(F2) = 0.033 | Δρmax = 3.02 e Å−3 |
S = 1.68 | Δρmin = −2.99 e Å−3 |
1567 reflections |
x | y | z | Uiso*/Ueq | Occ. (<1) | |
Mn | 0 | 0 | 0 | 0.00250 (15) | |
La | 0 | 0.49717 (5) | 0.75 | 0.00399 (7) | 0.815 |
Ba | 0 | 0.4972 | 0.75 | 0.00399 (7) | 0.185 |
O1 | 0 | 0.0569 (7) | 0.25 | 0.0107 (10) | |
O2 | 0.2513 (7) | 0.2495 (4) | −0.0298 (4) | 0.0117 (8) |
U11 | U22 | U33 | U12 | U13 | U23 | |
Mn | 0.0018 (3) | 0.0038 (2) | 0.0020 (3) | 0.0002 (2) | 0.0013 (2) | −0.00013 (19) |
La | 0.00413 (12) | 0.00502 (12) | 0.00281 (13) | 0 | 0.00096 (9) | 0 |
Ba | 0.00413 (12) | 0.00502 (12) | 0.00281 (13) | 0 | 0.00096 (9) | 0 |
O1 | 0.012 (2) | 0.0134 (15) | 0.0064 (16) | 0 | −0.0003 (13) | 0 |
O2 | 0.0131 (15) | 0.0111 (12) | 0.0110 (12) | −0.0043 (9) | 0.0009 (11) | 0.0004 (9) |
Mn—O1 | 1.9755 (7) | La—O2xi | 2.932 (3) |
Mn—O1i | 1.9755 (7) | La—O2xii | 2.947 (3) |
Mn—O2 | 1.975 (3) | La—O2xiii | 2.594 (3) |
Mn—O2i | 1.975 (3) | O1—O2 | 2.805 (4) |
Mn—O2ii | 1.968 (3) | O1—O2xiv | 2.784 (4) |
Mn—O2iii | 1.968 (3) | O1—O2i | 2.782 (4) |
La—O1iv | 2.8014 (5) | O1—O2ix | 2.793 (4) |
La—O1v | 2.8014 (5) | O1—O2x | 2.805 (4) |
La—O1vi | 3.053 (4) | O1—O2ii | 2.784 (4) |
La—O1vii | 2.457 (4) | O1—O2xv | 2.782 (4) |
La—O2viii | 2.599 (3) | O1—O2iii | 2.793 (4) |
La—O2iv | 2.932 (3) | O2—O2ii | 2.794 (3) |
La—O2vii | 2.947 (3) | O2—O2xvi | 2.794 (3) |
La—O2ix | 2.594 (3) | O2—O2iii | 2.782 (6) |
La—O2x | 2.599 (3) | O2—O2xvii | 2.782 (6) |
O1—Mn—O1i | 180 | O2ix—La—O2viii | 82.86 (10) |
O2—Mn—O2i | 180 | O2ix—La—O2iv | 90.40 (9) |
O2ii—Mn—O2iii | 180 | O2ix—La—O2vii | 173.68 (9) |
O1—Mn—O2 | 90.46 (12) | O2ix—La—O2x | 64.79 (11) |
O1—Mn—O2i | 89.54 (12) | O2ix—La—O2xi | 119.35 (11) |
O1—Mn—O2ii | 89.81 (12) | O2ix—La—O2xii | 60.15 (8) |
O1—Mn—O2iii | 90.19 (12) | O2ix—La—O2xiii | 116.80 (9) |
O1i—Mn—O2 | 89.54 (12) | O2x—La—O2viii | 116.65 (8) |
O1i—Mn—O2i | 90.46 (12) | O2x—La—O2iv | 60.33 (8) |
O1i—Mn—O2ii | 90.19 (12) | O2x—La—O2vii | 118.87 (11) |
O1i—Mn—O2iii | 89.81 (12) | O2x—La—O2ix | 64.79 (11) |
O2—Mn—O2ii | 90.25 (14) | O2x—La—O2xi | 173.23 (9) |
O2—Mn—O2iii | 89.75 (14) | O2x—La—O2xii | 90.83 (9) |
O2i—Mn—O2ii | 89.75 (14) | O2x—La—O2xiii | 82.86 (10) |
O2i—Mn—O2iii | 90.25 (14) | O2xi—La—O2viii | 60.33 (8) |
O1iv—La—O1v | 166.51 (12) | O2xi—La—O2iv | 123.37 (7) |
O1iv—La—O1vi | 96.75 (8) | O2xi—La—O2vii | 56.48 (10) |
O1iv—La—O1vii | 83.25 (8) | O2xi—La—O2ix | 119.35 (11) |
O1iv—La—O2viii | 126.44 (9) | O2xi—La—O2x | 173.23 (9) |
O1iv—La—O2iv | 58.52 (8) | O2xi—La—O2xii | 95.91 (9) |
O1iv—La—O2vii | 58.06 (8) | O2xi—La—O2xiii | 90.40 (9) |
O1iv—La—O2ix | 126.40 (9) | O2xii—La—O2viii | 118.87 (11) |
O1iv—La—O2x | 61.93 (10) | O2xii—La—O2iv | 56.48 (10) |
O1iv—La—O2xi | 114.25 (9) | O2xii—La—O2vii | 123.47 (7) |
O1iv—La—O2xii | 114.69 (9) | O2xii—La—O2ix | 60.15 (8) |
O1iv—La—O2xiii | 61.95 (10) | O2xii—La—O2x | 90.83 (9) |
O1v—La—O1iv | 166.51 (12) | O2xii—La—O2xi | 95.91 (9) |
O1v—La—O1vi | 96.75 (8) | O2xii—La—O2xiii | 173.68 (9) |
O1v—La—O1vii | 83.25 (8) | O2xiii—La—O2viii | 64.79 (11) |
O1v—La—O2viii | 61.93 (10) | O2xiii—La—O2iv | 119.35 (11) |
O1v—La—O2iv | 114.25 (9) | O2xiii—La—O2vii | 60.15 (8) |
O1v—La—O2vii | 114.69 (9) | O2xiii—La—O2ix | 116.80 (9) |
O1v—La—O2ix | 61.95 (10) | O2xiii—La—O2x | 82.86 (10) |
O1v—La—O2x | 126.44 (9) | O2xiii—La—O2xi | 90.40 (9) |
O1v—La—O2xi | 58.52 (8) | O2xiii—La—O2xii | 173.68 (9) |
O1v—La—O2xii | 58.06 (8) | Mn—O1—Mnx | 161.7 (2) |
O1v—La—O2xiii | 126.40 (9) | Mn—O1—Laxviii | 89.11 (3) |
O1vi—La—O1iv | 96.75 (8) | Mn—O1—Laxix | 88.76 (3) |
O1vi—La—O1v | 96.75 (8) | Mn—O1—Lavi | 80.87 (12) |
O1vi—La—O1vii | 180 | Mn—O1—Lavii | 99.13 (12) |
O1vi—La—O2viii | 58.33 (6) | Mnx—O1—Mn | 161.7 (2) |
O1vi—La—O2iv | 118.31 (5) | Mnx—O1—Laxviii | 88.76 (3) |
O1vi—La—O2vii | 118.26 (5) | Mnx—O1—Laxix | 89.11 (3) |
O1vi—La—O2ix | 58.40 (6) | Mnx—O1—Lavi | 80.87 (12) |
O1vi—La—O2x | 58.33 (6) | Mnx—O1—Lavii | 99.13 (12) |
O1vi—La—O2xi | 118.31 (5) | Laxviii—O1—Laxix | 166.51 (17) |
O1vi—La—O2xii | 118.26 (5) | Laxviii—O1—Lavi | 83.25 (8) |
O1vi—La—O2xiii | 58.40 (6) | Laxviii—O1—Lavii | 96.75 (8) |
O1vii—La—O1iv | 83.25 (8) | Laxix—O1—Laxviii | 166.51 (17) |
O1vii—La—O1v | 83.25 (8) | Laxix—O1—Lavi | 83.25 (8) |
O1vii—La—O1vi | 180 | Laxix—O1—Lavii | 96.75 (8) |
O1vii—La—O2viii | 121.67 (6) | Lavi—O1—Laxviii | 83.25 (8) |
O1vii—La—O2iv | 61.69 (5) | Lavi—O1—Laxix | 83.25 (8) |
O1vii—La—O2vii | 61.74 (5) | Lavi—O1—Lavii | 180 |
O1vii—La—O2ix | 121.60 (6) | Lavii—O1—Laxviii | 96.75 (8) |
O1vii—La—O2x | 121.67 (6) | Lavii—O1—Laxix | 96.75 (8) |
O1vii—La—O2xi | 61.69 (5) | Lavii—O1—Lavi | 180 |
O1vii—La—O2xii | 61.74 (5) | Mn—O2—Mnxvi | 166.44 (17) |
O1vii—La—O2xiii | 121.60 (6) | Mn—O2—Laxx | 93.66 (14) |
O2viii—La—O2iv | 173.23 (9) | Mn—O2—Laxix | 85.11 (9) |
O2viii—La—O2vii | 90.83 (9) | Mn—O2—Lavii | 84.54 (12) |
O2viii—La—O2ix | 82.86 (10) | Mn—O2—Laix | 95.31 (10) |
O2viii—La—O2x | 116.65 (8) | Mnxvi—O2—Mn | 166.44 (17) |
O2viii—La—O2xi | 60.33 (8) | Mnxvi—O2—Laxx | 94.97 (10) |
O2viii—La—O2xii | 118.87 (11) | Mnxvi—O2—Laxix | 85.09 (12) |
O2viii—La—O2xiii | 64.79 (11) | Mnxvi—O2—Lavii | 85.15 (9) |
O2iv—La—O2viii | 173.23 (9) | Mnxvi—O2—Laix | 93.98 (14) |
O2iv—La—O2vii | 95.91 (9) | Laxx—O2—Laxix | 173.23 (13) |
O2iv—La—O2ix | 90.40 (9) | Laxx—O2—Lavii | 89.17 (10) |
O2iv—La—O2x | 60.33 (8) | Laxx—O2—Laix | 97.14 (10) |
O2iv—La—O2xi | 123.37 (7) | Laxix—O2—Laxx | 173.23 (13) |
O2iv—La—O2xii | 56.48 (10) | Laxix—O2—Lavii | 84.09 (8) |
O2iv—La—O2xiii | 119.35 (11) | Laxix—O2—Laix | 89.60 (10) |
O2vii—La—O2viii | 90.83 (9) | Lavii—O2—Laxx | 89.17 (10) |
O2vii—La—O2iv | 95.91 (9) | Lavii—O2—Laxix | 84.09 (8) |
O2vii—La—O2ix | 173.68 (9) | Lavii—O2—Laix | 173.68 (13) |
O2vii—La—O2x | 118.87 (11) | Laix—O2—Laxx | 97.14 (10) |
O2vii—La—O2xi | 56.48 (10) | Laix—O2—Laxix | 89.60 (10) |
O2vii—La—O2xii | 123.47 (7) | Laix—O2—Lavii | 173.68 (13) |
O2vii—La—O2xiii | 60.15 (8) |
Symmetry codes: (i) −x, −y, −z; (ii) −x+1/2, y−1/2, −z; (iii) x−1/2, −y+1/2, z; (iv) x−1/2, y+1/2, z+1/2; (v) x+1/2, y+1/2, z+1/2; (vi) −x, −y, −z+1; (vii) −x, −y+1, −z+1; (viii) x, y, z+1; (ix) −x+1/2, −y+1/2, −z+1/2; (x) −x, y, −z+1/2; (xi) −x+1/2, y+1/2, −z+1; (xii) x, −y+1, z+1/2; (xiii) x−1/2, −y+1/2, z+1; (xiv) x−1/2, y−1/2, z+1/2; (xv) x, −y, z+1/2; (xvi) −x+1/2, y+1/2, −z; (xvii) x+1/2, −y+1/2, z; (xviii) x−1/2, y−1/2, z−1/2; (xix) x+1/2, y−1/2, z−1/2; (xx) x, y, z−1. |
Experimental details
Crystal data | |
Chemical formula | Ba0.185La0.815MnO3 |
Mr | 241.6 |
Crystal system, space group | Monoclinic, I2/c |
Temperature (K) | 160 |
a, b, c (Å) | 5.564 (2), 5.510 (2), 7.802 (3) |
β (°) | 90.18 (3) |
V (Å3) | 239.19 (14) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 22.37 |
Crystal size (mm) | 0.13 × 0.06 × 0.05 |
Data collection | |
Diffractometer | Nonius MACH3 diffractometer |
Absorption correction | ψ scan (HABITUS; Herrendorf & Bärnighausen, 1997) |
Tmin, Tmax | 0.193, 0.327 |
No. of measured, independent and observed [I > 3σ(I)] reflections | 1567, 1567, 1184 |
Rint | 0.000 |
(sin θ/λ)max (Å−1) | 0.903 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.027, 0.033, 1.68 |
No. of reflections | 1567 |
No. of parameters | 31 |
No. of restraints | ? |
Δρmax, Δρmin (e Å−3) | 3.02, −2.99 |
Computer programs: DATCOL in CAD-4 Software (Enraf–Nonius, 1989), SETANG LS in CAD-4 Software, HELENA (Spek, 1997) and HABITUS (Herrendorf & Bärnighausen, 1997), program (reference?), Jana2000 (Petricek et al., 2000), DIAMOND (Brandenburg, 2005).
Mn—O1 | 1.9755 (7) | La—O1iv | 2.457 (4) |
Mn—O2 | 1.975 (3) | La—O2v | 2.599 (3) |
Mn—O2i | 1.968 (3) | La—O2ii | 2.932 (3) |
La—O1ii | 2.8014 (5) | La—O2iv | 2.947 (3) |
La—O1iii | 3.053 (4) | La—O2vi | 2.594 (3) |
O1—Mn—O2vii | 89.54 (12) | Mn—O1—Mnix | 161.7 (2) |
O1—Mn—O2i | 89.81 (12) | Mn—O2—Mnx | 166.44 (17) |
O2—Mn—O2viii | 89.75 (14) |
Symmetry codes: (i) −x+1/2, y−1/2, −z; (ii) x−1/2, y+1/2, z+1/2; (iii) −x, −y, −z+1; (iv) −x, −y+1, −z+1; (v) x, y, z+1; (vi) −x+1/2, −y+1/2, −z+1/2; (vii) −x, −y, −z; (viii) x−1/2, −y+1/2, z; (ix) −x, y, −z+1/2; (x) −x+1/2, y+1/2, −z. |
Twin Domain | V1 | V2 | V3 | V4 | V5 | |
Volume Fraction | 0.61 (2) | 0.29 (1) | 0.05 (1) | 0.04 (1) | 0.02 (1) |
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La0.815Ba0.185MnO3 is one of the manganese oxides in which colossal magnetoresistance (CMR) was found (Jonker & van Santen, 1950; van Santen & Jonker, 1950). These compounds exhibit various superstructures on the basis of tilting of octahedra (Glazer, 1972). Accordingly, rhombohedral, orthorhombic and monoclinic symmetries have been found in A1 − x A'xMnO3 systems (A = La, Nd, Pr and Sm, and A' = Ca, Ba and Sr) with x ≈ 0.2 (Goodenough, 2004).
Dabrowski et al. (1998) have reported the results of X-ray powder diffraction on vacancy-free La1 − xBaxMnO3 ceramic compounds with 0.1 < x < 0.24. A t room temperature, these authors found orthorhombic Pbnm symmetry for x = 0.1 and rhombohedral R-3c symmetry for x = 0.14–0.24. For x = 0.12, the sample contained both phases. Arkhipov et al. (2000) reported the temperature dependence of the lattice parameters of La0.8Ba0.2MnO3, also employing X-ray powder diffraction. According to their work, orthorhombic Pbnm symmetry is found at temperatures of less than 185 K, whereas a phase with R-3c symmetry is stable for temperatures higher than 196 K, with a first-order structural phase transition at Tc = 190.5 K.
Our investigations confirm the rhombohedral phase at high temperatures as well as the occurrence of a first-order phase transition at Tc = 187.1 (3) K, determined on cooling. However, we have found a structure with monoclinic I2/c symmetry for the low-temperature phase.
Both the rhombohedral and the monoclinic phases of La0.815Ba0.185MnO3 are distorted perovskite-type structures composed of corner-linked MnO6 octahedra with La/Ba cations lying in the 12-fold coordinated cavities (Fig.1). The tilting of the octahedra occurs in the same direction for both but with different magnitude, as described by the Mn—O—Mn angle, which is only one [164.7 (1)°] in the rhombohedral phase, whereas it splits into two in the monoclinic phase (Table 1). The tilting pattern is expressed as a−a−a− and a−b−b− for rhombohedral R-3c and monoclinic I2/c, respectively, which is significantly different from a+a−a− expected for the orthorhombic Pbnm (Glazer, 1972). Distortions of the octahedra in the two structures are also different, as described by the Mn—O distances and by the O—Mn—O angles, which are 1.9742 (2) Å and 89.1 (1)°, respectively, in the rhombohedral phase whereas they both split into three different values in the monoclinic one.
A monoclinic I2/c structure was first reported for the compound La0.788Sr0.212Mn0.958O3 (Tamazyan et al., 2002). Compared with the La/Sr analogue, which exhibits almost equal Mn—O—Mn angles, La0.815Ba0.185MnO3 has two different Mn—O—Mn angles (Table 1). The Mn—O bonds have almost equal lengths indicating a very small coherent Jahn-Teller distortion, as was also found for the La/Sr compound. The degree of shear distortion of the MnO6 octahedra is smaller in the La/Ba compound, as shown by the smaller deviations of O—Mn—O bond angles from 90°. The effect of the larger cation radius is evidenced by larger lattice parameters as well as by different A—O (A = La, Ba or La, Sr) distances than in La0.788Sr0.212Mn0.958O3.
We report here the second finding of a monoclinic structure for the class of perovskite-type compounds A1 − xA'xMnO3 with x ≈ 0.2. In light of this result, the (x, T) phase diagrams of these systems would need to be revised (Zhou & Goodenough, 2001).