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Polycrystalline ErFeCuGe4O12 has been prepared in a solid-state reaction. It adopts a tetragonal crystal structure; space group P4/nbm with a = 9.6416(1), c = 4.7532(1) at room temperature. The Er3+ cations are in square-antiprismatic coordination and the Fe3+ and Cu2+ cations are disordered over one six-coordinate site. The magnetic moments of the three cations adopt an antiferromagnetic arrangement on cooling below 20 K in H = 0 kOe. The magnetic structure consists of ferromagnetic (001) sheets with the spin direction in neighbouring sheets alternating between [001] and [00 1 ] At 5 K the ordered moment of Er3+ was determined by neutron diffraction to be 7.90(3) µB and the mean moment of Fe3+ and Cu2+ was 2.43(2) µB. The magnetic structure is unchanged in an applied field of 10 kOe but in fields ≥ 20 kOe the compound begins a metamagnetic transition to a ferromagnetic structure with all atomic moments aligned along [001].

Polycrystalline samples of CaLa2FeCoSbO9 and ALa2FeNiSbO9 (A ​= ​Ca, Sr, Ba) have been prepared in solid-state reactions and studied by a combination of transmission electron microscopy, magnetometry, X-ray diffraction, neutron diffraction and Mossbauer spectroscopy. Diffraction and TEM showed that each shows 1:1 ​B-site ordering in which Co2+/Ni2+ and Sb5+ tend to occupy two distinct crystallographic sites while Fe3+ is distributed over both sites. While X-ray and neutron diffraction agreed that all four compositions are monophasic with space group P21/n, TEM revealed different levels of compositional inhomogeneity at the subcrystal scale, which, in the case of BaLa2FeNiSbO9, leads to the occurrence of both a P21/n and an I2/m phase. Magnetometry and neutron diffraction show that these perovskites are ferrimagnets with a G-type magnetic structure. Their relatively low magnetisation can be attributed to their inhomogeneity. This work demonstrates the importance of studying the microstructure of complex compositions.

Polycrystalline samples of LnMnFeGe4O12 (Ln = Y, Eu, Lu) have been prepared using the ceramic method and characterised by a combination of magnetometry, Mossbauer spectroscopy, X-ray diffraction and neutron diffraction. They all adopt the space group P4/nbm with a ~ 9.670, c ~ 4.81 A and show long-range antiferromagnetic order with transition temperatures 15 ≤ TN/K ≤ 17. The magnetic structure is the same in each case and consists of an A-type ordering of (001) planes; the ordered spins lie in the (001) plane. Comparison with isostructural compounds leads to the conclusion that subtle structural changes play a greater role than the electronic configuration of the cation in determining the magnetic structure.

Spin-polarised neutron scattering experiments have facilitated the separation of the nuclear and magnetic diffuse scattering from the partially-ordered cation distribution in the perovskite La3Ni2SbO9. The nuclear component of the data collected at 110 and 175 K could be modelled using Monte-Carlo methods when it was assumed that the distribution of Ni2+ and Sb5+ cations over their shared six-coordinate site is that which minimises the repulsive interactions between Sb5+ cations ~5.5 A apart. Analysis of the diffuse magnetic scattering showed that nearest-neighbour and next-nearest neighbour spins show short-range antiferromagnetic and ferromagnetic coupling, respectively, at 110 K. The former persists to 175 K but the latter weakens with increasing temperature.

The use of non-equilibrium molecular dynamics facilitates the calculation of the cation diffusion constant of Li2O at temperatures too low to be accessible by other methods. Excellent agreement with experimental diffusion coefficients has been obtained over the temperature range 873 < T/K < 1603. Diffusion below 1200 K was shown to be dominated by a concerted nearest-neighbour hopping process, whereas in the high-temperature superionic region an additional mechanism involving a six-coordinate interstitial cation site in the anti-fluorite structure becomes increasingly dominant. Our model thus accounts for the transition from the superionic regime to the non-superionic regime.

La3Ni2-xCuxB'O-9 (x = 0.25; B' = Sb, Ta, Nb: x = 0.5; B' = Nb) have been synthesized and characterised by transmission electron microscopy, neutron diffraction and magnetometry. Each adopts a perovskite-like structure (space group P2(1)/n) with two crystallographically-distinct six-coordinate sites, one occupied by a disordered arrangement of Ni2+ and Cu2+ and the other by a disordered similar to 1:2 distribution of Ni2+ and B'(5+), although some Cu2+ is found on the latter site when x = 0.5. Each composition undergoes a magnetic transition in the range 90 = 30 K. A long-range ordered G-type ferrimagnetic structure is present in each composition, but small relaxor domains are also present. This contrasts with the pure relaxor and spin-glass behaviour of x = 0, B' = Ta, Nb, respectively.

Polycrystalline samples of Gd2CaGe4O12 and GdFeZnGe4O12 have been synthesised via a ceramic route. Both were characterised by X-ray diffraction, magnetometry and Mossbauer spectroscopy; GdFeZnGe4O12 was also studied by neutron diffraction. They adopt the SrNa2P4O12 structure: space group P4/nbm with a = 10.0766(1), c = 5.1043(1) A for Gd2CaGe4O12; a = 9.7298(1), c = 4.7515(1) A for GdFeZnGe4O12 at 293 K. Gd2CaGe4O12 is paramagnetic for 2 ≤ T/K ≤ 300 whereas GdFeZnGe4O12 is antiferromagnetic below 13.8(2) K. The six-coordinate Fe3+ and Zn2+ cations are disordered over the pseudo-cubic 4f sublattice and the Gd3+ cations occupy the eight-coordinate 2b sites. The Fe3+ and Gd3+ cations adopt an A-type, k = [0,0,½] antiferromagnetic arrangement with their ordered moments aligning in the xy plane. The Fe/Zn disorder results in relatively low ordered cation moments (Gd3+ = 6.02(13), Fe3+ = 3.84(15) µB) in the antiferromagnetic phase.

Polycrystalline samples of A2LaFe2SbO9 (A ​= ​Ca, Sr, Ba) perovskites appeared monophasic to X-ray or neutron powder diffraction but a single-crystal study utilising transmission electron microscopy revealed a greater level of complexity. Although local charge balance is maintained, compositional and structural variations are present among and within the submicron-sized crystals. Despite the inhomogeneity, A ​= ​Ca is monophasic with a partially-ordered distribution of Fe3+ and Sb5+ cations across two crystallographically-distinct octahedral sites, i.e. Ca2La(Fe1.25Sb0.25)2d (Fe0.75Sb0.75)2cO9. For A ​= ​Sr or Ba, the inhomogeneities result in differences in the tilting patterns of the octahedra and the ordering of the B cations. Particles of A ​= ​Sr contain a phase (Fe:Sb ~2:1) without B cation ordering and one (Fe:Sb ~1:1) with B cation ordering. Monophasic A ​= ​Ba lacks long-range cation order although ordered nanodomains are present within the disordered phase. The temperature dependence of the magnetic properties of each sample is discussed.

Polycrystalline samples of the monoclinic perovskites CaLa2Ni2-xCuxWO9 (x ​= ​0.25 and 0.5) have been prepared and characterised by neutron diffraction and magnetometry. The Ni2+, Cu2+ and W6+ cations are partially ordered over two crystallographically-distinct six-coordinate sites such that one is ~63% occupied by W6+ and both are occupied by Ni2+ and Cu2+ in a ratio of (2-x):x. The composition x ​= ​0.25 behaves as a spin glass below 35 ​K whereas x ​= ​0.5 is ferrimagnetic below 120 ​K with an ordered moment of 0.774(5) μB per magnetic cation. The atomic moments order in a G-type pattern and the imbalance in the number of magnetic cations on the two sites results in a net magnetisation.

AC susceptibility and muon spin relaxation data have been collected from a polycrystalline sample of LaSr2Cr2SbO9, a perovskite-like compound wherein the unequal distribution of Cr3+ and Sb5+ cations over two crystallographically-distinct six-coordinate B sites results in the onset of ferrimagnetism at ~150 K. The data are used to elucidate the dynamics of the ferrimagnetic domain walls, thought to lie in Sb-rich regions, and suggest an energy barrier of ~0.13 eV to their motion. The muon data confirm that the ferrimagnetic order is a true bulk phenomenon. The behaviour of this material is briefly compared to that of Ni2+- based relaxor ferromagnets.

A study of the solid solutions CeM2-xM’xGe4O12 (M = Mn, Co; M’ = Ni, Cu) by X-ray diffraction and magnetometry is described. For M = Co the introduction of Ni and Cu was possible for x ≤ 0.5; for M = Mn attempts to introduce Cu were unsuccessful but CeMn1.5Ni0.5GeO4 was obtained as a single phase. These compositions crystallise in the space group P4/nbm with a ~9.76, c ~4.85 Å. They all order antiferromagnetically with TN

Polycrystalline samples of compositions in the perovskite solid solution Sr2-xCaxCrSbO6 (x = 0, 0.25. 0.5, 0.75, 1.0, 1.25, 1.50, 1.75, 2.0) were synthesised and characterised by synchrotron x-ray diffraction and SQUID magnetometry. Neutron powder diffraction data were collected on the x = 0, 0.25, 0.5, 1.0, 1.5 and 2.0 compositions. It was found that Sr2CrSbO6 crystallised in the triclinic I 1 space group. The other compositions were all found to crystallise in the monoclinic space group P21/n although Sr1.5Ca0.5CrSbO6 was found to be phase separated into a calcium-deficient and calcium-rich phase, both having the space group P21/n. Sr2CrSbO6 was found to order antiferromagnetically at 12 K and the ordered Cr3+ moment was refined to be 2.39(1) µB. The antiferromagnetic order was rapidly quenched on doping with Ca and compositions with x ≥ 0.75 exhibited ferromagnetic order. TC increased with x to reach a maximum of 14 K at x = 2.0, with an ordered moment of 2.56(3) µB per Cr3+ cation. The tilt angles of the B-site octahedra about [110] and [001] increase from 5.4(1)° and 4.6(1)° to 13.7(1)° and 13.9(1)°, respectively, across the series; the switch from antiferromagnetism to ferromagnetism occurs when both tilts are at a value of ~ 8°.

A polycrystalline sample of SrLa2FeCoSbO9 has been prepared in a solid-state reaction and studied by a combination of electron microscopy, magnetometry, Mossbauer spectroscopy, X-ray diffraction, and neutron diffraction. The compound adopts a monoclinic (space group P2(1)/n; a = 5.6218(6), b = 5.6221(6), c = 7.9440(8) angstrom, beta = 90.050(7)degrees at 300 K) perovskite-like crystal structure with two crystallographically distinct six-coordinate sites. One of these sites is occupied by 2/3 Co-2(+),1/3 Fe3+ and the other by 2/3 Sb5+, 1/3 Fe3+. This pattern of cation ordering results in a transition to a ferrimagnetic phase at 215 K. The magnetic moments on nearest-neighbor, six-coordinate cations align in an antiparallel manner, and the presence of diamagnetic Sb5+ on only one of the two sites results in a nonzero remanent magnetization of similar to 1 mu(B) per formula unit at 5 K.

Polycrystalline samples of La3Ni2NbO9 and La3Ni2TaO9 have been characterised by X-ray and neutron diffraction, electron microscopy, magnetometry and muon spin relaxation (µSR); the latter technique was also applied to La3Ni2SbO9. On the length scale of a neutron diffraction experiment, the six-coordinate sites of the monoclinic perovskite structure are occupied in a 1:1 ordered manner by Ni and a random ⅓Ni/⅔B’ mixture. Electron microscopy demonstrated that this 1:1 ordering is maintained over microscopic distances, although diffuse scattering indicative of short-range ordering on the mixed site was observed. No magnetic Bragg scattering was observed in neutron diffraction patterns collected from La3Ni2B’O9(B’ = Nb or Ta) at 5 K although in each case µSR identified the presence of static spins below 30 K. Magnetometry showed that La3Ni2NbO9 behaves as a spin glass below 29 K but significant short-range interactions are present in La3Ni2TaO9 below 85 K. The contrasting properties of these compounds are discussed in terms of their microstructure.

Polycrystalline Y2CoGe4O12 has been prepared by standard ceramic methods. The crystal structure (space group P4/nbm; a=9.8465(2), c=4.92986(9) A) consists of metal-rich layers separated from each other by Ge4O12 groups comprised of four corner-sharing GeO4 tetrahedra. Two cation sites lie within the layers; an eight-coordinate site occupied by yttrium and a six-coordinate site occupied by a 1:1 disordered distribution of yttrium and cobalt. Neutron diffraction revealed two-fold disorder on the oxide sublattice; this has been elucidated using Co K-edge EXAFS spectroscopy. The availability of two sites allows each oxide ion to accommodate the coordination preferences of its single Co/Y neighbour; the GeO4 tetrahedra distort to absorb any consequent strain. The octahedron of anions around each Co2+ cation shows a pseudo-tetragonal distortion with a strain (Co–O)eq–(Co–O)ax/(Co–O)eq=−0.173. This results in an unusually large effective magnetic moment of 6.05 µB per Co2+ cation.

The crystal structure of the perovskite-related oxide Sr 3 NiSb 2 O 9 has been refined from X-ray and neutron powder diffraction data; space group P 2 1 / n , a =5.64381(2), b =5.62299(2), c =7.95687(3) A, β =90.014(2)°. The structure has two crystallographically-distinct six-coordinate cation sites with occupancies Sb 0.97(1), Ni 0.03 and Sb 0.36, Ni 0.64. The magnetic susceptibility has been measured over the temperature range 2≤ T / K ≤300. Fitting data recorded in the temperature range 150 T / K µ eff =3.49(1) µ B per Ni 2+ , θ =−138(1) K. Ferrimagnetic coupling in the vicinity of the antisite defects is suggested to be responsible for the enhanced susceptibility observed below ~90 K. The zero-field cooled susceptibility shows a maximum at 8.7 K that is not observed in the field-cooled susceptibility. Hysteresis is observed in M(H) at 2 K but not at 7.5 K.

La{sub 3}Ni{sub 2}SbO{sub 9} adopts a perovskite-related structure in which the six-coordinate cation sites are occupied alternately by Ni{sup 2+} and a disordered arrangement of Ni{sup 2+}/Sb{sup 5+}. A polycrystalline sample has been studied by neutron diffraction in applied magnetic fields of 0≤H/kOe≤50 at 5 K. In 0 kOe, weak magnetic Bragg scattering consistent with the adoption of a G-type ferrimagnetic structure is observed; the ordered component of the magnetic moment was found to be 0.89(7) µ{sub B} per Ni{sup 2+} cation. This increased to 1.60(3) µ{sub B} in a field of 50 kOe. Transmission electron microscopy revealed variations in the Ni:Sb ratio across crystallites of the sample. It is proposed that these composition variations disrupt the magnetic superexchange interactions within the compound, leading to domain formation and a reduced average moment. The application of a magnetic field aligns the magnetisation vectors across the crystal and the average moment measured by neutron diffraction increases accordingly. The role played by variations in the local chemical composition in determining the magnetic properties invites comparison with the behaviour of relaxor ferroelectrics. - Graphical abstract: Composition variations across a crystal of La3Ni2SbO9 result in anomalous magnetic behavior. - Highlights: • Ordered magnetic moment ofmore » Ni{sup 2+} increases in an applied magnetic field. • Composition variations detected by electron microscopy. • Increase in magnetic moment can be explained by presence of composition variations.« less

Polycrystalline samples of Ln2CoGe4O12 (Ln = Gd, Tb, Dy, Ho or Er) and LnBCoGe4O12 (B = Sc or Lu) have been prepared and characterised by a combination of magnetometry, 155Gd Mossbauer spectroscopy and, in the case of Tb2CoGe4O12 and TbScCoGe4O12, neutron diffraction. The holmium- and erbium-containing compositions remain paramagnetic down to 2 K, those containing dysprosium behave as spin glasses and the terbium and gadolinium-containing compounds show long-range magnetic order with transition temperatures below 4 K in all cases. The data can be rationalized qualitatively in terms of the interplay between magnetic anisotropy and crystal field effects.

Polycrystalline samples in the solid solution ZrMn

Polycrystalline samples in the solid solution ZrMn2-xCoxGe4O¬12 (x = 0.0, 0.5, 1.0, 1.5 and 2.0) have been prepared using the ceramic method and characterised by a combination of magnetometry, X-ray diffraction and neutron diffraction. They all adopt the space group P4/nbm with a ~ 9.60, c ~ 4.82 Å and show long-range magnetic order with transition temperatures, TC, in the range 2 ≤ TC/K ≤ 10. The underlying magnetic structure is the same in each case but the ordered spins lie along [001] when x = 0.0 and in the (001) plane for all other compositions. In all cases the magnetically-ordered phase is a weak ferromagnet although the magnitude of the spontaneous magnetisation and the strength of the coercive field are composition-dependent. The magnetic structure can be rationalized by considering the strengths of the interactions along the distinct M – O – Ge – O – M superexchange pathways in the crystal and the observed magnetic structure is entirely consistent with the predictions of ab initio calculations.

Polycrystalline samples, prepared by a solid-state route, of compositions in the solid solution CeMn

BaFe 0.9-x Y 0.1 Co x O 3-δ (0 ≤ x ≤ 0.15) is shown to adopt the cubic perovskite structure at temperatures up to 1400 K in air. The oxygen vacancy concentration increases with both cobalt content and temperature, with BaFe 0.75 Y 0.1 Co 0.15 O 2.35 being the most oxygen-deficient composition observed. At 700 K the conductivity is ∼2 S cm −1 across the whole composition range. Measurements of the Seebeck coefficient show that holes are the dominant carrier. The coefficient of thermal expansion is essentially constant above 800 K, but not at lower temperatures. Chemical reactivity tests, along with the coefficient of expansion, show that these perovskites would not be suitable electrodes for fuel cells with fluorite electrolytes but they might serve as permeable membranes in catalytic reactors.

Polycrystalline samples of Nd18Li8Fe 4M′O39 (M′=Al, Ga) and La18Li 8Fe4.5In0.5O39 have been prepared by the ceramic method and characterised by neutron diffraction and magnetometry. All three compounds adopt a cubic structure (space group Pm3̄n, a ~12 Å) based on intersecting 〈1 1 1⌠chains of cation sites with alternating octahedral and prismatic coordination geometry. These sites are occupied by Li, Fe and M′ or In; Nd or La cations occupy sites between the chains. The cation distribution over the octahedral and prismatic sites within the chains is disordered in all three compounds. The Nd-containing compositions show spin-glass behaviour below ~4.5 K whereas small, weakly-ferrimagnetic domains form in La18Li8Fe 4.5In0.5O39 below 7.60 K. The dependence of the magnetic properties on the nature of the lanthanide cation is discussed. © 2013 Published by Elsevier Inc.

The magnetic structures of Ca3LiRuO6 and Ca3NaRuO6 have been deduced from powder neutron diffraction data. In each case successive Ru5+ cations in the [001] chains of the Sr4PtO6-like structure are antiferromagnetically coupled, and nearest-neighbour Ru5+ cations in adjacent chains are also antiferromagnetically coupled.

The effects of magnetic dilution on the magnetism in the two-dimensional (2D) oxide systems Sr1 +xLa1 –x Fe1 –xSnxO4 and SrLaFe1 –xGaxO4 have been studied by Mossbauer spectroscopy and magnetometry. The end-member, SrLaFeO4, has a Neel temperature (TN) of 330 K, and shows some degree of magnetic relaxation for T/TN > 0.9. Diamagnetic substitution results in increased relaxation at concentrations where magnetic percolation is still effective. The magnetic susceptibility shows pronounced hysteresis effects. The possible role of the inter-planar interactions in determining the magnetic behaviour of these materials is discussed.

Time-of-flight powder neutron diffraction data have been used to refine the crystal structure of the ordered, distorted perovskite Sr2YRuO6. Yttrium and ruthenium are octahedrally coordinated in this material with average MO bond lengths of 2.202 and 1.955 A, respectively. Constant wavelength neutron diffraction data show that Sr2YRuO6 is a Type I antiferromagnet at 4.2 K with an ordered magnetic moment of 1.85 μB per Ru5+ ion. The Neel temperature of Sr2YRuO6 was determined to be 26 K. The data suggest that the 4d3 electrons in this material are localized rather than itinerant.

A polycrystalline sample of the perovskite La 2 NiRhO 6 has been prepared. Neutron diffraction shows the compound to be orthorhombic (space group Pbnm ; a =5.5350(4), b =5.5529(4), and c =7.8305(5) A at 5 K) with a disordered arrangement of Ni and Rh over the six-coordinate B sites. Consideration of the B –O bond lengths and the paramagnetic Curie constant suggests that the Ni and Rh cations are trivalent and low spin. Magnetization and neutron diffraction experiments show that a transition to a spin-glass phase occurs upon cooling below 12 K.

Neutron diffraction experiments have been performed to determine the structures of Ba 2 LaRuO 6 and Ca 2 LaRuO 6 . Both are ordered, distorted perovskites. Ba 2 LaRuO 6 is monoclinic, space group P 2 1 n with a 0 =6.0285(7) A , b 0 =6.0430(7) A , c 0 =8.5409(6) A , β =90.44(1) o . The A sites are occupied by barium and the B sites by an ordered arrangement of lanthanum and ruthenium. Ca 2 LaRuO 6 is triclinic, space group P1 with a 0 =5.6179(5), b 0 =5.8350(5), c 0 =8.0667(4), α =90.0 o , β =89.76(1) o , γ =90.0 o . The A sites are occupied by calcium and lanthanum in a disordered manner, and the B sites are occupied by an ordered arrangement of calcium and ruthenium. The results reported in this paper thus contradict those of previous workers. The low-temperature magnetic structures are discussed briefly.

The synthesis and characterization of a polycrystalline sample of the n = 2 Ruddlesden-Popper phase Nd 2BaLiRuO 7 are reported. X-ray and neutron diffraction show that the 6-coordinate sites are occupied by a 1:1 ordered arrangement of Li and Ru, that the 12-coordinate sites within the perovskite-like blocks are occupied by Ba, and that the cation sites on the block edges are occupied by Nd. Transmission electron microscopy shows that this compound is less susceptible to stacking faults then many other n = 2 phases, and 7Li MAS NMR spectroscopy shows that the environment of the single Li site in the structure is well-defined. The compound is an antiferromagnet below 32 K, with ordered magnetic moments of 2.2(2) μ B and 2.53(8) μ B on the Ru and Nd cations respectively at 2 K. © 2005 American Chemical Society.

The preparation and characterization of a number of mixed metal oxides of ruthenium and copper are described, the compounds being chosen to demonstrate the changes that occur on moving from the 3-D perovskite structure to the 2-D K 2 NiF 4 structure via the intermediate Ruddlesden-Popper structure. Full structure refinements by neutron powder diffraction are reported for SrLaCuRuO 6 , SrLaCuSbO 6 , Sr 3 NdCuRuO 8 , Sr 3 LaCuRuO 8 , Sr 3.5 La 0.5 CuRuO 8−δ , Sr 3 LaZnRuO 8 , Sr 2 LaCuRuO 7−δ , and Sr 2.15 La 0.85 CuRuO 7−δ . There is no evidence for the presence of Cu 3+ in any of these samples. The electrical conductivities of these phases, and also those of Sr 1.2 La 0.8 CuRuO 6−δ and Sr 2 LaZnRuO 7 , have been measured as a function of temperature. All these materials are semiconductors, but none shows long range magnetic order at 1.5 K.

The room-temperature crystal structure of the brownmillerite SrCaMnGaO5+δ (δ = 0.035) has been refined from neutron powder diffraction data; space group Ima2, a = 15.7817(6), b = 5.4925(2), c = 5.3196(2) Å. Mn and Ga occupy 99.0(2)% of the 6- and 4-coordinate sites, respectively. A combination of magnetometry, neutron diffraction and μSR spectroscopy has shown that the compound orders magnetically at 180 K, and that the low-temperature phase has a G-type antiferromagnetic structure, with an ordered magnetic moment of 3.30(2) μB per Mn at 2 K. Displaced hysteresis loops provide evidence that the atomic moment has an additional, glassy component. Magnetometry shows that significant short-range magnetic interactions persist above 180 K, and μSR that the spin fluctuations are thermally activated in this temperature region. The compound is an electrical insulator which at 159 K shows an unusually large magnetoresistance of 85% in 6T, increasing to 90% in 13 T. © 2002 Elsevier Science (USA).

Polycrystalline single-phase samples of BaIrO2.73 and BaIrO2.96 were successfully prepared. Superconducting quantum interference device data indicate the the magnetic susceptibility of both samples is low and only weakly temperature dependent in the range 180 K < T < 296 K, demonstrating the presence of delocalized electrons. The materials exhibit high electrical conductivity which is dependent on the oxygen stoichiometry. In addition, magnetic susceptibility data for both compositions show that a transition to a ferromagnetically ordered state occurs at 180 K. It is proposed that this ferromagnetism arises from a difference in the relative populations of the α and β spin bands and not from localized electrons. © 1993.

The structure proposed for Li(11)Nd(18)Fe(4)O(39-δ) (Chen et al. Inorg. Chem. 2012, 51, 8073) on the basis of diffraction and Mössbauer spectral data is compared to that determined previously for Nd(18)Li(8)Fe(5)O(39) (Dutton et al. Inorg. Chem.200847, 11212) using the same techniques. The Mössbauer spectrum reported by Chen et al. has been reinterpreted. The newly refined spectral parameters differ significantly from the published values but are similar to those reported for Nd(18)Li(8)Fe(5)O(39). The relative areas of the three components indicate that iron cations occupy the 2a, 8e, and 16i sites in space group Pm3n, in disagreement with the model determined from neutron diffraction by Chen et al. in which only the 2a and 8e sites are so occupied. The relationship between Li(11)Nd(18)Fe(4)O(39-δ) and Nd(18)Li(8)Fe(5)O(39) is discussed, and it is proposed that the sample prepared by Dutton et al. is a kinetic product whereas the sample prepared by Chen et al. is the thermodynamically preferred product.

A polycrystalline sample of Pr{sub 18}Li{sub 8}Fe{sub 4}RuO{sub 39} has been synthesized by a solid state method and characterized by neutron powder diffraction, magnetometry and Moessbauer spectroscopy; samples of Pr{sub 18}Li{sub 8}Fe{sub 5-x}Mn{sub x}O{sub 39} and Pr{sub 18}Li{sub 8}Fe{sub 5-x}Co{sub x}O{sub 39} (x=1, 2) have been studied by magnetometry. All these compounds adopt a cubic structure (space group Pm3-barn, a{sub 0}{approx}11.97 A) based on intersecting chains made up of alternating octahedral and trigonal-prismatic coordination sites. These chains occupy channels within a Pr-O framework. The trigonal-prismatic site in Pr{sub 18}Li{sub 8}Fe{sub 4}RuO{sub 39} is occupied by Li{sup +} and high-spin Fe{sup 3+}. The remaining transition-metal cations occupy the two crystallographically-distinct octahedral sites in a disordered manner. All five compositions adopt a spin-glass-like state at 7 K (Pr{sub 18}Li{sub 8}Fe{sub 4}RuO{sub 39}) or below. - Graphical abstract: Pr{sub 18}Li{sub 8}Fe{sub 5-x}M{sub x}O{sub 39} (M=Ru, Mn, Co) have been studied by neutron diffraction, Moessbauer spectroscopy and magnetometry, allowing the distribution of the different cation species over the octahedral and trigonal-prismatic coordination sites within the structure to be determined. All the compositions studied undergo a transition to a spin-glass-like phase on cooling below {approx}5 K.

The authors present results of a neutron scattering study of the fast oxide ion conductor delta Bi2O3; both pure and Y3+-doped materials are studied. The authors' results reveal extensive disorder with oxygen distributed over lattice and interstitial sites.

The crystal structures of Sr2CaMoO6 and Sr2CaTeO6 have been determined at room temperature by neutron powder diffraction. Both compounds crystallize in the perovskite structure with a rock-salt ordered array of Ca2+ and M6+ cations (M=Mo, Te) on the six-coordinate sites (space group P21/n (no. 14); for M=Mo, a = 5.76228 ( 7 ) , b = 5.84790 ( 7 ) , c = 8.18707 ( 9 ) A , β = 90.194 ( 1 ) ° , for M=Te, a = 5.79919 ( 9 ) , b = 5.83756 ( 8 ) , c = 8.2175 ( 1 ) A , β = 90.194 ( 1 ) ° ). Compositions in the solid solution Sr2CaMo1−xTexO6 have been synthesized and shown by X-ray diffraction to adopt the same ordered structure. The results are used in a discussion of the cation oxidation states in Ca2FeMoO6 and to establish the similarity between the structural chemistry of hexavalent Mo and Te.

For the first time, the chemistry in H(2) gas of a perovskite-like material, Pr(2)Sr(2)CrNiO(8), has been monitored at temperatures up to approximately 700 degrees C, in situ, by neutron powder diffraction.

Neutron and synchrotron X-ray powder diffraction techniques have been used to refine the crystal and magnetic structures of the n = 2 Ruddlesden-Popper (RP) system Sr2LaMn2O7. The sample is shown to be biphasic, although both phases are of the RP type and have similar structural parameters. The majority phase (81%) adopts a collinear antiferromagnetic structure below â?¼210 K whereas the minority phase is ferromagnetically ordered below â?¼125 K. The ordered magnetic moments lie in the xy plane in both phases. The behavior observed is discussed in terms of the interplay between structural and electronic factors. Comparison with data obtained previously by other workers leads to the conclusion that our results have some general significance in the study of n = 2 RP systems.

The crystal structures of Sr2HoMn2O7 and Sr2YMn2O7 have been determined at 290 and 1.7 K from neutron and X-ray powder diffraction data. Both are distorted Ruddlesden−Popper structures formed by the intergrowth of rock-salt-like layers and perovskite-like blocks of tilted MnO6 octahedra (space group P42/mnm; for Ho at 290 K a = 5.40388(5), c = 19.9050(2) A). The majority of the lanthanide cations are located in the rock-salt layers. Neither structure changes significantly on cooling to 1.7 K. There is evidence for neither charge ordering of Mn3+ and Mn4+ cations nor for long-range magnetic ordering. The magnetic susceptibility maximum observed previously is thus confirmed as signifying a transition to a spin-glass phase. The behavior of these compounds is contrasted with that of other Mn oxides which show long-range magnetic order and colossal magnetoresistance.

The magnetic susceptibilities of La2Mg1−xZnxIrO6 (0< x

A series of samples in the SrFeO3 –y(perovskite and brownmillerite) and SrCoO3 –y(hexagonal and brownmillerite) systems has been studied by extended X-ray absorption fine structure spectroscopy. In the cobalt system, evidence has been found for the existence of face-sharing CoO6 octahedra in the substoicheiometric low-temperature phase H–Sr2Co2O5 –x, and for both face- and edge-sharing CoO6 octahedra in H–Sr2Co2O5 +x. In the iron system, the perovskite phases show only corner-sharing polyhedra, and the short-range structure is seen to be more closely related to the brownmillerite structure.

We report on the results of X-ray absorption near edge structure (XANES) studies at the Mn:L2,3, Ru:K and O:K edges of novel manganites, Sr2Mn0.5Ru0.5O4 and Sr3MnRuO7. Measurements were carried out on polycrystalline powder samples at room temperature. From the analysis of the XANES spectra the average manganese valences of 3.4 in bilayer Sr3MnRuO7 and 3.1 in single layer Sr2Mn0.5Ru0.5O4 are obtained. The corresponding average valences for Ru ions are 4.6 and 4.9, respectively. This indicates that Ru doping gives rise to a decrease of Mn valence, whereas Ru valence increases, compared to Mn(IV) and Ru(IV) in undoped compounds. The effect of charge disproportionation is stronger in the single layered compound than in the bilayered one. © 2007 Elsevier B.V. All rights reserved.

Powder samples of the magnetically diluted cubic perovskite phases Sr2Fe1 − xGaxTaO6 have been prepared by high temperature ceramic methods. X-Ray powder diffraction data show that the cations occupying the 6-coordinate site are chemically disordered in the range 0.10 ≤ x ≤ 0.40 and that increasing the Ga3+ concentration above this value leads to partial cation ordering between Ga3+ and Ta5+. Magnetic susceptibility data collected from these compounds can be fitted to the Curie–Weiss law, resulting in estimates of the magnetic moment per Fe3+ cation of between 4.57(1) (x = 0.20) and 6.37(1) μB (x = 0.90). The cause of the unexpectedly low paramagnetic moment observed in most of these compositions is ascribed to the effect of superexchange interactions extending beyond the adjacent 6-coordinate sites in the simple cubic lattice.

The first example of ferromagnetism in a compound crystallizing with the filled beta-manganese structure is reported. Magnetometry and neutron diffraction show that Fe1.5Pd0.5Mo3N is ferromagnetic below 160 K, with a saturation magnetization of 2.44 μB/formula unit which is associated with the Fe/Pd sublattice. Self-consistent spin-polarized electronic structure calculations, performed within density functional theory, predict an average magnetic moment of 2.93 μB/formula unit at T = 0 K. The moment is shown to be a result of the fulfilment of a local Stoner criterion on the Fe sites.

A polycrystalline sample of Ba 4 Mn 3 O 10 has been prepared and characterized by X-ray diffraction (290 K), neutron diffraction (290, 80, 5 K) and magnetometry (5≤ T (K)≤1000). At 290 K the compound is paramagnetic and isostructural with Ba 4 Ti 2 PtO 10 . Mn 3 O 12 trimers, built up from MnO 6 octahedra, are linked through common vertices to form corrugated sheets perpendicular to the y -axis of the orthorhombic unit cell (Space group Cmca , a =5.6850(1), b =13.1284(1), c =12.7327(1) A); Ba atoms occupy the space between the layers. On cooling, the magnetic susceptibility shows a broad maximum at ∼130 K, and a sharp transition at 40 K. Neutron diffraction has shown that long-range antiferromagnetic order is present at 5 K but not at 80 K, although magnetometry at 5 K has revealed a remanent magnetization (0.002 μ B per Mn) which is below the detection limit of the neutron experiment.

New perovskite-related oxides of Ru V have been prepared and evaluated as catalysts for the partial oxidation of natural gas to synthesis gas. Their activity has been compared with that of Ru metal supported on alumina. Ba 3 NiRuTaO 9 adopts the 6H hexagonal perovskite structure (α = 5.754(3)A, c = 14.119(9)A). At 900°C it can facilitate 95% conversion of CH 4 with a 98% selectivity for synthesis gas formation and at 800°C it catalyses the total conversion of C 2 H 6 with a 94% selectivity for synthesis gas formation. When a mixed CH 4 /C 2 H 6 /O 2 stream flows over this oxide at 900°C, selective oxidation of ethane to synthesis gas is observed. The bulk structure of the perovskite catalyst remains unchanged, and no carbon deposition is observed during the course of these reactions. Although supported Ru metal gives a catalytic performance similar to that of Ba 3 NiRuTaO 9 , it also catalyses carbon formation when higher hydrocarbons, e.g. ethane, are present.

The crystal and magnetic structures of the n = 3 Ruddlesden−Popper phase with the ideal composition Ca4Mn3O10 have been studied using X-ray and neutron powder diffraction. The crystal structure at 293 K is relatively insensitive to the partial pressure of oxygen used in sample preparation. A sample prepared in air showed an orthorhombic distortion (space group Pbca, a = 5.26557(12), b = 5.26039(11), c = 26.8276(5) A) from the ideal n = 3 RP structure, as did a sample prepared under 800 atm of O2 pressure (a = 5.26005(4), b = 5.25569(4), c = 26.83543(20) A). Both samples showed a magnetic phase transition at 115 K from a paramagnetic phase with extensive short-range spin ordering to a weakly ferromagnetic (μferro = 2 × 10-3 μB per Mn) low-temperature phase. The antiferromagnetic components of the atomic magnetic moments (2.23(2) μB per Mn) order in a G-type manner within each perovskite block, and the interblock coupling reflects the orthorhombic symmetry of the structure.

Polycrystalline samples of La{sub 18}Li{sub 8}Rh{sub 4}MO{sub 39} (M=Ti, Mn, Ru) have been prepared by a solid-state method and studied by neutron powder diffraction. They are isostructural with La{sub 18}Li{sub 8}Rh{sub 5}O{sub 39} and adopt the cubic space group Pm3{sup -bar }n with a {approx}12.22 A. Their structure consists of a La-O framework containing intersecting channels that run along . These channels are occupied by chains made up of alternating, face-sharing trigonal-prismatic and octahedral coordination polyhedra; there are two crystallographically distinct types of octahedral site. The prisms are occupied by Li and the transition metals are disordered over the two octahedral sites. - Graphical abstract: The substitution of Ti, Mn or Ru into La{sub 18}Li{sub 8}Rh{sub 5}O{sub 39} results in the loss of the cation ordering seen in the parent compound.

A powder neutron-diffraction study and subsequent line-profile analysis of the nuclear and magnetic structure at 4.2 K of monoclinic anhydrous iron(III) sulfate indicate that it is a two-sublattice antiferromagnet. Each sublattice is made up of crystallographically distinct iron atoms in the space group P21/n (b-unique). The nuclear structure at 4.2 K is essentially the same as that found at room temperature by single-crystal X-ray analysis. An analysis of covalency in the material indicates that the degree of covalency is consistent with that found for other iron(III) ions octahedrally coordinated by oxygen. A Mössbauer effect study indicates that above 28.8 K this compound is paramagnetic with parameters typical of an octahedral high-spin iron(III) compound. Below 28.7 K the Mössbauer spectrum reveals the presence of spontaneous magnetic ordering with nonequivalent internal hyperfine fields on the two sublattices. The difference between these fields reaches a maximum at 23 K and decreases until, at 4.2 K, the field on each sublattice is essentially the same at ca. 550 kOe. The two sublattices have essentially the same isomer shifts while the quadrupole shifts are similar in magnitude but opposite in sign. Applied-field Mössbauer effect studies further support an antiferromagnetic coupling model. Magnetic susceptibility studies confirm that the material is paramagnetic with an effective magnetic moment of ca. 5.92 μB between 298 and 40 K. Below this temperature the magnetic susceptibility increases sharply to a maximum at 23 K and then decreases rapidly. This behavior results because of the nonequivalent magnitude of the spontaneous magnetization on each sublattice between 28 and 4.2 K. A magnetic superexchange coupling model is proposed to explain the magnetic nonequivalence of the two sublattices over this temperature range. © 1979 American Chemical Society.