P.D. Battle

The structural consequences of charge disproportionation in mixed-valence iron oxides. I. The crystal structure of Sr2LaFe3O8.94 at room temperature and 50 K

The crystal structure of the averaged-valence phase of the rhombohedrally distorted perovskite Sr{sub 2}LaFe{sub 3}O{sub 8.94} has been refined from neutron powder diffraction data collected at room temperature (spacegroup R{bar 3}c, a = 5.4712 {angstrom},{alpha} = 60.09{degree}). All iron sites are identical. The crystal and magnetic structures of the low-temperature antiferromagnetic phase showing a charge disproportionation have been similarly obtained at 50 K. The crystal structure has been refined in space group R{bar 3}c, a = 5.4580 {angstrom}, {alpha} = 60.19{degree}; the magnetic structure has been refined in P3m1 using a model derived from considerations of the exchange interactions between ideal localized electron configurations. The results are interpreted in terms of a charge density wave (CDW) and spin density wave (SDW) propagating along the (111) axis of the crystal and commensurate with the crystal lattice. The apparent absence of a periodic structural distortion (PSD) of the same period as the CDW is surprising, and it is suggested that local variations in the strain field brought about by the disordered arrangement of Sr and La may quench the PSD which would otherwise occur.

The crystal and magnetic structures of Sr2LuRuO6, Ba2YRuO6, and Ba2LuRuO6

Powder neutron diffraction data have been used to refine the crystal and magnetic structures of the ordered perovskites Sr2LuRuO6, Ba2YRuO6, and Ba2LuRuO6. Sr2LuRuO6 is monoclinic, with space groupP21n: a = 5.7400(1), b = 5.7375(1), c = 8.1118(2)A, β = 90.16(1)°. Ba2YRuO6 and Ba2LuRuO6 are cubic, with space groupFm3m: a = 8.3390(5) and 8.2720(4)A, respectively. All three compounds are Type I antiferromagnets at 4.2 K with an ordered magnetic moment of ∼2 μB per Ru5+. High-temperature magnetic susceptibility data suggest that the Ru5+d-electrons in all three compounds should be regarded as itinerant rather than localized.

Spin-glass behavior in Sr2FeRuO6 and BaLaNiRuO6: A comparison with antiferromagnetic BaLaZnRuO6

The crystal structures of the double perovskites BaLaZnRuO6, BaLaNiRuO6, and Sr2FeRuO6 have been refined in space group I2c using neutron powder diffraction data collected at room temperature. Data collected at 5 K led to refinements in I2c for Sr2FeRuO6 and BaLaZnRuO6, and in a triclinic space group for BaLaNiRuO6. BaLaZnRuO6 shows A-type antiferromagnetism at 5 K whereas Sr2FeRuO6 and BaLaNiRuO6 show no evidence of long-range magnetic ordering. Mossbauer and magnetic susceptibility data indicating low temperature transitions (<50 K) in these latter two materials have been interpreted in terms of spin-glass behavior, attributable to the long-range structural disorder of the B-site cations in the perovskite structure.

The structural and magnetic properties of SrMnO3: A reinvestigation

Abstract Neutron diffraction and Mo¨ssbauer spectroscopy have revealed that the phase 4H-SrMnO 3 is paramagnetic at 290 K, contrary to earlier reports. Mo¨ssbauer spectroscopy on 57 Fe-doped samples has revealed antiferromagnetic ordering with T N = 278 ± 5K . The susceptibility maximum at ∼350 K is thought to represent only short-range coupling between Mn 4+ ions in the Mn 2 O 9 pairs of face-sharing octahedra in the structure.

Structural and dynamical studies of δ-Bi2O3 oxide ion conductors: I. The structure of (Bi2O3)1−x(Y2O3)x as a function of x and temperature

We report the results of both Bragg and diffuse neutron scattering studies of the superionic solid solution, (Bi2O3)1-x(Y2O3)x. The Bragg data for polycrystalline samples show that the strutural features observed previously in (Bi2O3)0.73(Y2O3)0.27 are present across the entire range of the solid solution, 0.25 < x < 0.42. The number of 〈111〉-displaced anions in the defect fluorite structure decreases with increasing Y3+ content whereas the extent of short-range ordering on the anion sublattice increases. Both of these observations are consistent with the decrease in oxide ion conductivity which occurs as x increases. The basic crystal structure does not change between room temperature and 1023 K, although the unit cell volume increases by 3.78% for x = 0.27, and the number of 〈111〉-displaced anions increases, again consistent with the enhanced conductivity observed at high temperatures. It is suggested that Y3+ stabilizes the fluorite structure by ordering the vacancies on the oxygen sublattice in chains along the 〈111〉 and 〈110〉 directions.

The crystal and magnetic structures of Ca2NdRuO6, Ca2HoRuO6, and Sr2ErRuO6

Abstract The crystal structure of Sr2ErRuO6 has been refined from neutron powder diffraction data collected at room temperature; space group P2 1 n , a = 5.7626(2), b = 5.7681(2), c = 8.1489(2) A, β = 90.19(1)°. The structure is that of a distorted perovskite with a 1:1 ordered arrangement of Ru5+ and Er3+ over the 6-coordinate sites. Data collected at 4.2 K show the presence of long range antiferromagnetic order involving both Ru5+ and Er3+. The temperature dependence of the sublattice magnetizations is described. The crystal structure of Ca2NdRuO6 is also that of a distored perovskite ( P2 1 n , a = 5.5564(1), b = 5.8296(1), c = 8.0085(1) β = 90.19(1)°. The β = 90.07(1)°) with a random distribution of Ca2+ and Nd3+ on the A site and a 1:1 ordered arrangement of Ca2+ and Ru5+ on the 6-coordinate B sites. The Ru5+ sublattice is antiferromagnetic at 4.2 K but there is no evidence for magnetic ordering of the Nd3+ ions. Ca2HoRuO6 is also a distorted perovskite ( P2 1 n , a = 5.4991(1), b = 5.7725(1), c = 7.9381(2) , β = 90.18(1)° at 4.2 K) with a cation distribution best represented as Ca1.46Ho0.54[Ca0.54Ho0.46Ru]O6. There is no ordering among the Ca3+ or Ho3+ ions on either the A or the B sites, but the Ca Ho ions form a 1:1 ordered arrangement with Ru5+ on the B sites. At 4.2 K the Ru5+ ions adopt a Type I antiferromagnetic arrangement but there is no evidence of long range magnetic ordering among the Ho3+ ions.

Structural and dynamical studies of δ-Bi2O3 oxide-ion conductors: II. A structural comparison of (Bi2O3)1−x(M2O3)x for M = Y, Er, and Yb

The results of diffuse elastic neutron scattering studies of the superionic solid solutions (Bi/sub 2/O/sub 3/)/sub 1-x/(Er/sub 2/O/sub 3/)/sub x/ and (Bi/sub 2/O/sub 3/)/sub 1-x/(Yb/sub 2/O/sub 3/)/sub x/, and also the result of a Bragg diffraction study of (Bi/sub 2/O/sub 3/)/sub 0.75/(Er/sub 2/O/sub 3/)/sub 0.25/ are reported. All the data suggest that Er/sup 3 +/-doped delta-Bi/sub 2/O/sub 3/ is structurally very similar to the fluorite-related solid solution (Bi/sub 2/O/sub 3/)/sub 1-x/(Y/sub 2/O/sub 3/)/sub x/ studied previously, both in terms of the average structure as determined by Bragg scattering and in terms of local ordering on the anion sublattice as detected by diffuse scattering. The ordered regions are described as microdomains of a rhombohedral phase. The Yb/sup 3 +/-doped materials also show short-range anion ordering, but over shorter distances than in the other two cases. There is evidence of cation ordering between Bi/sup 3 +/ and Yb/sup 3 +/ near the low-dopant boundary of the fluorite phase. The possible use of quasi elastic neutron scattering to monitor oxide-ion transport in the system (Bi/sub 2/O/sub 3/)/sub 1-x/(Er/sub 2/O/sub 3/)/sub x/ is discussed. 13 references, 5 figures, 3 tables.

The crystal and magnetic structures of Ba3NiRu2O9, Ba3CoRu2O9, and Ba3ZnRu2O9

Abstract The crystal structures of the 6H perovskites Ba3NiRu2O9, and Ba3CoRu2O9 have been refined from neutron powder diffraction data collected at 5 or 2 K. Ba3NiRu2O9 and Ba3ZnRu2O9 have hexagonal symmetry, space group P6 3 mmc : a Ni = 5.7256(2). c Ni = 14.0596(2) A; aZn = 5.7549(2), cZn = 14.1328(2) A. Ba3CoRu2O9 undergoes a phase transition from hexagonal symmetry at room temperature to orthorhombic symmetry at 2 K, space group Cmcm: aCo = 5.7456(1), bCo = 9.9177(2), cCo = 14.0862(3) A. In all three compounds the cation sites within the face-sharing octahedra of the 6H structure are occupied by Ru5+; the corner-sharing octahedra are occupied by Zn2+, Ni2+, or Co2+. The neutron diffraction data show that Ba3NiRu2O9 is magnetically ordered at 5 K, with antiferromagnetic coupling between Ru5+ ions in the Ru2O9 dimers and ferromagnetic coupling along approximately linear Ni2+ORu5+ superexchange pathways. The magnetic moments align along z. Ba3CoRu2O9 is also magnetically ordered with antiferromagnetic coupling in the Ru2O9 dimers, but in this case antiferromagnetic superexchange between Co2+ ions leads to a more complex magnetic structure.

The crystal and magnetic structures of Sr2CoFeO5

Abstract The crystal and magnetic structures of the brownmillerite Sr 2 CoFeO 5 have been refined from neutron powder diffraction data collected at room temperature, space group Icmm , a = 5.6243(2), b = 15.6515(5), c = 5.5017(2) A. The transition metal ions are partially ordered over the 6- and 4-coordinate cation sites; in addition the 4-coordinate sites themselves have a positional disorder. The compound shows G-type antiferromagnetic order at room temperature with ordered magnetic moments of 3.2 and 2.9 μ B , aligned along z , at the 6- and 4-coordinate sites, respectively. The low magnitude of the ordered moments is discussed.

The crystal and magnetic structures of Sr2LaFe3O8

Abstract The crystal and magnetic structures of the anion-deficient perovskite Sr 2 LaFe 3 O 8 (space group Pmma , a = 5.5095(1), b = 11.8845(5), c = 5.6028(1) AA) have been refined from X-ray and neutron powder diffraction data collected at room temperature. The crystal structure consists of layers of octahedral (O) and tetrahedral (T) iron-oxygen polyhedra arranged in the stacking sequence … OOTOOT … perpendicular to theyˆaxis of the unit cell. The magnetic structure is that of a G-type antiferromagnet with ordered magnetic moments of 3.77(5) and 3.15(11) μ B at the octahedral and tetrahedral sites, respectively. The low moment at the tetrahedral site is consistent with the observed disorder and magnetic anisotropy.