Lithium and transition-metal phosphates are promising cathode materials for lithium-ion batteries. Lithium manganese phosphate LiMnPO 4 has a higher specific energy density than LiFePO 4 used in practice: theoretical values of 700 and 580 W h/kg, respectively. However, its use is hampered by a number of disadvantages: reduced electronic and ionic conductivity, inferior stability of the structure in the charged form, and large changes in the volume during (de)lithiation. LiMnPO 4 and LiMn 0.95 Ni 0.05 PO 4 samples are synthesized by the solvothermal method and studied using X-ray powder diffraction, low-temperature nitrogen adsorption, scanning electron microscopy, and electrochemical methods. It is shown that a small degree of substitution of Mn for Ni (5 at %) leads to an increase in the capacity and Coulombic efficiency of LiMnPO 4 , a decrease in charge-transfer resistance, and an increase in Li + diffusion coefficients.

New La/Zn substituted strontium ferrites Sr(2 −x)La x [Fe(2 − x)Zn x ]O5, (0 ≤ x ≤ 0.3) with brownmillerite- type structure are obtained and studied via X-ray phase analysis and Mössbauer spectroscopy. Depending on the conditions of synthesis, substituting Zn2+ cations can either mainly occupy tetrahedral positions in a brownmillerite structure, or be uniformly distributed between the tetrahedral and octahedral positions. It is shown that they are reversibly oxidized by atmospheric oxygen at elevated temperatures.

Highly homogeneous mullite-type solid solutions Bi2Fe(4-x)CrxO9 (x = 0.5, 1, 1.2) were synthesized using a soft chemistry technique followed by a solid-state reaction in Ar. The crystal structure of Bi2Fe3CrO9 was investigated using X-ray and neutron powder diffraction, transmission electron microscopy and (57)Fe Mössbauer spectroscopy (S.G. Pbam, a = 7.95579(9) Å, b = 8.39145(9) Å, c = 5.98242(7) Å, RF(X-ray) = 0.022, RF(neutron) = 0.057). The ab planes in the structure are tessellated with distorted pentagonal loops built up by three tetrahedrally coordinated Fe sites and two octahedrally coordinated Fe/Cr sites, linked together in the ab plane by corner-sharing forming a pentagonal Cairo lattice. Magnetic susceptibility measurements and powder neutron diffraction show that the compounds order antiferromagnetically (AFM) with the Néel temperatures decreasing upon increasing the Cr content from TN ∼ 250 K for x = 0 to TN ∼ 155 K for x = 1.2. The magnetic structure of Bi2Fe3CrO9 at T = 30 K is characterized by a propagation vector k = (1/2,1/2,1/2). The tetrahedrally coordinated Fe cations form singlet pairs within dimers of corner-sharing tetrahedra, but spins on the neighboring dimers are nearly orthogonal. The octahedrally coordinated (Fe,Cr) cations form antiferromagnetic up-up-down-down chains along c, while the spin arrangement in the ab plane is nearly orthogonal between nearest neighbors and collinear between second neighbors. The resulting magnetic structure is remarkably different from the one in pure Bi2Fe4O9 and features several types of spin correlations even on crystallographically equivalent exchange that may be caused by the simultaneous presence of Fe and Cr on the octahedral site.

Novel Pr2-xSrxNi1-xCoxO4 +/-delta (x = 0.25; 0.5; 0.75) oxides with the tetragonal K2NiF4-type structure have been prepared. Room-temperature neutron powder diffraction (NPD) study of x = 0.25 and 0.75 phases together with iodometric titration results have shown the formation of hyperstoichiometric oxide for x = 0.25 (delta = 0.09(2)) and a stoichiometric one for x = 0.75. High-temperature X-ray powder diffraction (HT XRPD) showed substantial anisotropy of the thermal expansion coefficient (TEC) along the a-and c-axis of the crystal structure, which increases with increasing the Co content from TEC(c)/TEC(a) = 2.4 (x = 0.25) to 4.3 (x = 0.75). High-temperature NPD (HT NPD) study of the x = 0.75 sample reveals that a very high expansion of the axial (Ni/Co)-O bonds (75.7 ppm K-1 in comparison with 9.1 ppm K-1 for equatorial ones) is responsible for such behaviour, and is caused by a temperature-induced transition between low- and high-spin states of Co3+. This scenario has been confirmed by high-temperature magnetization measurements on a series of Pr2-xSrxNi1-xCoxO4 +/-delta samples. For compositions with high Ni content (x = 0.25 and 0.5) we synthesised K2NiF4-type oxides Pr2-x-ySrx+y(Ni1-xCox)O-4 +/-delta, y = 0.0-0.75 (x = 0.25); y = 0.0-0.5 (x = 0.5). The studies of the TEC, high-temperature electrical conductivity in air, chemical stability of the prepared compounds in oxygen and toward interaction with Ce2-xGdxO2-x/2 (GDC) at high temperatures reveal optimal behaviour of Pr1.35Sr0.65Ni0.75Co0.25O4+delta. This compound shows stability in oxygen at 900 degrees C and does not react with GDC at least up to 1200 degrees C. It features low TEC of 13 ppm K-1 and high-temperature electrical conductivity in air of 280 S cm(-1) at 900 degrees C, thus representing a promising composition for use as a cathode material in intermediate temperature solid oxide fuel cells (IT-SOFC).

Novel oxides PrSrCo1−yMnyO4±δ, 0.0≤y≤0.5 and Pr0.5Sr1.5Co1−yMnyO4±δ 0.3≤y≤0.5 with K2NiF4-type structure were synthesized. The crystal structure, oxygen content, thermal expansion and electrical conductivity of the obtained compounds were examined. A chemical titration showed that PrSrCo0.5Mn0.5O4±δ is slightly overstoichiometric (δ=0.03(2)), while Pr0.5Sr1.5Co0.5Mn0.5O4±δ is oxygen deficient (δ=−0.05(2)). Thermal expansion behavior was studied by both dilatometry and high-temperature X-ray powder diffraction in the temperature range of 298–1173K in air. Pr0.5Sr1.5Co0.5Mn0.5O3.95(2) exhibited linear thermal expansion along the a- and c-axes over the studied temperature range with thermal expansion coefficients (TECs) were 17.5ppmK−1 and 17.8ppmK−1, respectively. For PrSrCo0.5Mn0.5O4.03(2) two regions (298–600K and 600–1173K) observed, where the TEC along the a-axis decreased from 12.7ppmK−1 to 10.4ppmK−1 whereas the TEC along the c-axis increased from 14.5ppmK−1 to 26.7ppmK−1. Both compounds demonstrated lower in comparison with undoped PrSrCoO4 values of electrical conductivity of 7S/cm for PrSrCo0.5Mn0.5O4.03(2) and 23S/cm for Pr0.5Sr1.5Co0.5Mn0.5O3.95(2) at 1173K in air.

M.V. Lomonosov Moscow State University, M icr.chem.msu.ru A.V. Shubnikov Institute of Crystallography Joint Institute for Nuclear Research, Dubna National Institute of Chemical Physics and Experimental Physics VI, Centre for El University of Augsburg, 86159 Augsburg, Ge Department of Materials and Environmenta 91 Stockholm, Sweden The ISIS Facility, STFC Rutherford Ap Oxfordshire, UK IREC, Catalonia Institute for Energy Resea 08930 Sant Adria del Besos, Spain † Electronic supplementary information (E of the crystal structures using NPD data. Cite this: RSC Adv., 2016, 6, 33951

A novel anion-deficient perovskite-based compound, Pb(2.4)Ba(2.6)Fe(2)Sc(2)TiO(13), was synthesized via the citrate-based route. This compound is an n = 5 member of the AnBnO(3n-2) homologous series with unit-cell parameters related to the perovskite subcell a(p)≈ 4.0 Å as a(p)√2 ×a(p)× 5a(p)√2. The crystal structure of Pb(2.4)Ba(2.6)Fe(2)Sc(2)TiO(13) consists of quasi-2D perovskite blocks with a thickness of three octahedral layers separated by the 1/2[110](1[combining macron]01)(p) crystallographic shear (CS) planes, which are parallel to the {110} plane of the perovskite subcell. The CS planes transform the corner-sharing octahedra into chains of edge-sharing distorted tetragonal pyramids. Using a combination of neutron powder diffraction, (57)Fe Mössbauer spectroscopy and atomic resolution electron energy-loss spectroscopy we demonstrate that the B-cations in Pb(2.4)Ba(2.6)Fe(2)Sc(2)TiO(13) are ordered along the {110} perovskite layers with Fe(3+) in distorted tetragonal pyramids along the CS planes, Ti(4+) preferentially in the central octahedra of the perovskite blocks and Sc(3+) in the outer octahedra of the perovskite blocks. Magnetic susceptibility and Mössbauer spectroscopy indicate a broadened magnetic transition around T(N)∼ 45 K and the onset of local magnetic fields at low temperatures. The magnetic order is probably reminiscent of that in other AnBnO(3n-2) homologues, where G-type AFM order within the perovskite blocks has been observed.

Orthorhombic perovskites Y1-xCaxFe1-yCoyO3-delta (0.1 <= x <= 0.2, 0.1 <= y <= 0.2 and x = 0.1, y = 0.3) were synthesized in air by the citrate route at 1150-1300 degrees C. High-temperature X-ray powder diffraction (HT XRPD) data for Y0.9Ca0.1Fe0.8Co0.2O3-delta at 25-800 degrees C showed no phase transition with calculated thermal expansion coefficient (TEC) of 11.9 ppm K-1. High-temperature electrical conductivity measurements revealed almost composition independent conductivity values of 22-27 S/cm at 900 degrees C. No chemical interaction of Y0.8Ca0.2Fe0.9Co0.1O3-delta with (Zr,Y)O2-x, (YSZ) or (Ce,Gd)O2-x(GDC) was observed up to 1000 degrees C and 1100 C, respectively. Partial replacement of Y by Pr according to formula Y0.8-zPrzCa0.2Fe0.7Co0.3O3-delta, 0.1 <= z <= 0.35, leads to an increase of both electrical conductivity up to 50S/cm (z = 0.3) at 900 degrees C and dilatometry measured TEC up to 15.1 ppm K-1. Moderate values of electrical conductivity in combination with low TEC and stability towards chemical interaction with typical SOFC electrolytes make Co-doped Y1-xCaxFeO3-delta promissing cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFC). (C) 2015 Elsevier Ltd. All rights reserved.

A novel anion-deficient perovskite-based compound, Pb(2.4)Ba(2.6)Fe(2)Sc(2)TiO(13), was synthesized via the citrate-based route. This compound is an n = 5 member of the AnBnO(3n-2) homologous series with unit-cell parameters related to the perovskite subcell a(p)≈ 4.0 Å as a(p)√2 ×a(p)× 5a(p)√2. The crystal structure of Pb(2.4)Ba(2.6)Fe(2)Sc(2)TiO(13) consists of quasi-2D perovskite blocks with a thickness of three octahedral layers separated by the 1/2[110](1[combining macron]01)(p) crystallographic shear (CS) planes, which are parallel to the {110} plane of the perovskite subcell. The CS planes transform the corner-sharing octahedra into chains of edge-sharing distorted tetragonal pyramids. Using a combination of neutron powder diffraction, (57)Fe Mössbauer spectroscopy and atomic resolution electron energy-loss spectroscopy we demonstrate that the B-cations in Pb(2.4)Ba(2.6)Fe(2)Sc(2)TiO(13) are ordered along the {110} perovskite layers with Fe(3+) in distorted tetragonal pyramids along the CS planes, Ti(4+) preferentially in the central octahedra of the perovskite blocks and Sc(3+) in the outer octahedra of the perovskite blocks. Magnetic susceptibility and Mössbauer spectroscopy indicate a broadened magnetic transition around T(N)∼ 45 K and the onset of local magnetic fields at low temperatures. The magnetic order is probably reminiscent of that in other AnBnO(3n-2) homologues, where G-type AFM order within the perovskite blocks has been observed.

Novel anion-deficient perovskite-based ferrites Pb2Ba2BiFe5O13 and Pb(1.5)Ba(2.5)Bi2Fe6O16 were synthesized by solid-state reaction in air. Pb2Ba2BiFe5O13 and Pb(1.5)Ba(2.5)Bi2Fe6O16 belong to the perovskite-based A(n)B(n)O(3n-2) homologous series with n = 5 and 6, respectively, with a unit cell related to the perovskite subcell a(p) as a(p)√2 × a(p) × na(p)√2. Their structures are derived from the perovskite one by slicing it with 1/2[110]p(101)p crystallographic shear (CS) planes. The CS operation results in (101)p-shaped perovskite blocks with a thickness of (n - 2) FeO6 octahedra connected to each other through double chains of edge-sharing FeO5 distorted tetragonal pyramids which can adopt two distinct mirror-related configurations. Ordering of chains with a different configuration provides an extra level of structure complexity. Above T ≈ 750 K for Pb2Ba2BiFe5O13 and T ≈ 400 K for Pb(1.5)Ba(2.5)Bi2Fe6O16 the chains have a disordered arrangement. On cooling, a second-order structural phase transition to the ordered state occurs in both compounds. Symmetry changes upon phase transition are analyzed using a combination of superspace crystallography and group theory approach. Correlations between the chain ordering pattern and octahedral tilting in the perovskite blocks are discussed. Pb2Ba2BiFe5O13 and Pb(1.5)Ba(2.5)Bi2Fe6O16 undergo a transition into an antiferromagnetically (AFM) ordered state, which is characterized by a G-type AFM ordering of the Fe magnetic moments within the perovskite blocks. The AFM perovskite blocks are stacked along the CS planes producing alternating FM and AFM-aligned Fe-Fe pairs. In spite of the apparent frustration of the magnetic coupling between the perovskite blocks, all n = 4, 5, 6 A(n)Fe(n)O(3n-2) (A = Pb, Bi, Ba) feature robust antiferromagnetism with similar Néel temperatures of 623-632 K.

The complex oxide Ca7Mn2.14Ga5.86O17.93 was synthesized by the solid-state reaction in a sealed evacuated quartz tube at 1000 °C. Its crystal structure was determined by electron diffraction and X-ray powder diffraction. The structure can be represented as a tetrahedral framework, viz., the polyanion [(Mn0.285Ga0.715)15O29.86]19- stabilized by the incorporated cation [Ca14GaO6]19+. The polycation consists of the GaO6 octahedra surrounded by the Ca atoms, which are arranged to form a cube capped at all places. The tetrahedral framework is partially disordered due to the presence of tetrahedra with two possible orientations in the positions (0, 0, 0) and (x, x, x) with x ≈ 0.15 and 0.17. The relationship between the Ca7Mn2.14Ga5.86O17.93 structures and related ordered phases with the symmetry F23, as well as the influence of the oxygen content on the ordering in the tetrahedral framework, are discussed.

Single phase (Sb1-xPbx)(2)(Mn1-ySby)O-4 (0.0 less than or equal to x less than or equal to 0.608, 0.0 less than or equal to y less than or equal to 0.372) samples with the Sb-2-MnO4-type structure were prepared at 650 C by solid-state reaction in evacuated sealed silica tubes. A replacement of Sb by Pb results in the oxidation of Sb3+ to Sb5+, which in turn replaces Mn2+ cations in octahedrally coordinated positions within the infinite rutile-type chains. The crystal structures of Pb-0.44-Sb1.64Mn0.92O4, Pb0.75Sb1.48Mn0.77O4, Pb1.07Sb1.26Mn0.67O4, and Pb1.186Sb1.175Mn0.639O4 were refined from X-ray powder diffraction data. Increasing the Pb content leads to a decrease of the a parameter from a = 8.719(2) Angstrom to a = 8.6131(8) Angstrom and to an increase of the c parameter from c = 5.999(2) Angstrom to c = 6.2485(7) Angstrom (for Sb2MnO4 and Pb1.216Sb1.155Mn0.628O4, respectively). This occurs due to increasing average cation size at the Pb/Sb position and decreasing cation size at the Mn/Sb position that leads to strong deformation of the (Mn/Sb)O-6 octahedra. Starting from the Pb(0.75)Sb(1.48)Mno(0.77)O(4) composition a modulated structure with q = yc* was observed by electron diffraction. Hig-resolution electron microscopy observations revealed that Mn and Sb ions order forming layers of octahedrally coordinated positions filled either by Mn2+ or by Sb5+ cations and alternating along the c axis. The dilution of the magnetic Mn-2divided by cations by nonmagnetic Sb5+ entities leads to a suppression of the antiferromagnetic intrachain interaction and disappearance of long-range magnetic order at high doping level. At T = 20 K the A(xy) spin component was found to be dominant in the AFM structure of the Pb(0.44)Sp(1.64)Mn(0.92)O(4) sample by neutron diffraction.

The Ca2MnGa1-xAlxO5 solid solutions (0.2 <= x <= 1.0) with brownmillerite-type structure were synthesized by solid state reaction at 1250 degrees C for 40 h in Ar flow. The structures of the solid solutions were studied using X-ray powder diffraction, transmission electron microscopy and high resolution electron microscopy. Replacing Ga by A1 introduces a phase transformation from the brownmillerite structure with the Pnma space symmetry (x <= 0.5) to a structure with 12mb space symmetry (x > 0.5). The structures differ by the ordering pattern of the mirror-related tetrahedral chains (L and R): in the primitive structure the L and R chains form alternating layers whereas in the body-centered phase all chains are of the same type. The crystal structure of Ca2MnGa0.5Al0.5O5 was refined from X-ray powder diffraction data (space group Pnma, a = 5.25175(5) angstrom, b = 15.1426(2) angstrom, c = 5.46029(6) angstrom, R-I = 0.042, R-P = 0.017). A specific feature of this structure is disorder in the Ga layer with intermixing of the L and R chains in a approximate to 2:1 ratio. The disorder is related to the formation of numerous antiphase boundaries (APBs) with R = 1/2[111] as a displacement vector, which produces two adjacent tetrahedral layers with the same type of chains in the initial -L-R-L-R-L- layer sequence of the Pnma phase. The density of APBs increases with increasing x resulting in the formation of slabs of the 12mb phase up to a complete phase transformation. Dipole-dipole interactions between the tetrahedral chains are discussed as a possible driving force causing various patterns of tetrahedral chain ordering. (c) 2005 Elsevier SAS. All rights reserved.

Single-phase samples of the Sn2-2xSbxFexO4 Solid solution were prepared by solid-state reaction in air at 1300 degrees C for 0.26 <= x <= 0.66. The crystal structure of the Sn2-2xSbxFexO4 phases was studied by electron diffraction and X-ray powder diffraction. The compounds crystallize with the rutile type structure with a disordered arrangement of cations (P4(2)/mnm space group, a = 4.7127(6) A, c = 3.1595(4) A, R = 0.020, R-P = 0.019 for Sn1.48Sb0.26Fe0.26O4 and a = 4.6682(8) angstrom, c = 3.1147(6) angstrom, R, = 0.030, R-P = 0.022 for Sn0.68Sb0.66Fe0.66O4). The valence state of cations in the Sn1.48Sb0.26Fe0.26O4 and Sn0.68Sb0.66Fe0.66O4 samples was determined by means of Sn-119, Sb-121, and Fe-57 Mossbauer spectroscopy. The presence of Sn(II), Sb(III), or Fe(II) low valent state species was not detected in the samples. Resistivity vs temperature measurements revealed a semiconducting behavior from room temperature up to 900 degrees C with about four orders in magnitude decrease of the resistivity. Solubility tests in the cryolite-alumina melt showed that the steady-state concentration of dissolved tin for the samples with x = 0.26, 0.36 is significantly lower than that for SnO2. The electrocatalytic activity and solid degradation products of Sn2-2xSbxFexO4 are compared with those of another possible anode material (SnO2 with small amount of the CuO and Sb2O3 additives). These tests allow evaluation of the prospects of the Sn2-2xSbxFexO4 solid solutions as inert anode materials and to formulate an approach to further improvement of their degradation stability.

A new Ca6.3Mn3Ga44Al1.3O18 compound has been prepared by solid state reaction in a dynamic vacuum of 5 x 10(-6) mbar at 1200 degrees C. The crystal structure of Ca6.3Mn3Ga4.4Al1.3O18 was studied using X-ray powder diffraction (a = 15.07001(5) angstrom, SG F432, Z = 8, R-1 = 0.031, R-P = 0.068), electron diffraction and high resolution electron microscopy. The Ca(6.3)Mn(3)Ga(4.4)A(1.3)O(18) structure can be described as a tetrahedral [(Gao(0.59)Mn(0.24)Al(0.17))(15)O-30](18.24-) framework stabilized with embedded [(Ca0.9Mn0.1)(14)MnO6](18.24+) polycations, which consists of an isolated MnO6 octahedron surrounded by a capped cube of (Ca0.9Mn0.1) atoms. The Ca6.3Mn3Ga4.4Al1.3O18 structure is related to the structure of Ca7Zn3Al5O17.5, but appears to be significantly disordered due to the presence of two orientations of oxygen tetrahedra around the cationic 0,0,0 and x,x,x (x approximate to 0.17, 0.15) positions in a random way according to the F432 space symmetry. The analogy between the Ca6.3Mn3Ga4.4Al1.3O18 crystal structure and the structure of the "fullerenoid" Sr33Bi24+delta Al48O141+3 delta/2 oxide is discussed. Ca6.3Mn3Ga4.4Al1.3O18 adopts a Curie-Weiss behavior of chi(T) above T approximate to 50K with a Weiss temperature Theta = -60K and peer = 10.57 mu(B) per formula unit. At lower temperatures, the chi(T) deviates from the Curie-Weiss law indicating a strengthening of the ferromagnetic component of the exchange interaction. (c) 2005 Elsevier Inc. All rights reserved.

Systematic study on crystal chemistry of Sr2MnGaO5+δ layered perovskites upon variation of anion stoichiometry and the Mn oxidation state (VMn) was performed. Starting from fully oxygenated Sr2MnGaO5.5 compound, the samples with +3 ≤ VMn ≤ +4 were prepared either by a reduction of oxygen content at controlled partial oxygen pressure or by a partial replacement of oxygen by fluorine. Varying δ is accompanied by structural transformations from Imma (0.03 ≤ δ ≤ 0.13, a ≈ c ≈ , b ≈ 4ap) to Bmmm (0.41 ≤ δ ≤ 0.46, a ≈ c ≈ ,b ≈ 2ap) and to tetragonal P4/mmm (δ = 0.505, a ≈ ap, c ≈ 2ap). The tetragonal Sr2MnGaO5−xF1+x oxyfluorides (a ≈ ap, c ≈ 2ap) were prepared by treatment of Sr2MnGaO5.5 with XeF2. In the Sr2MnGaO4.78F1.22 structure the MnO6 octahedra are characterized by two short apical Mn-O distances and four long equatorial ones. This is interpreted as an “apically compressed” Jahn–Teller distortion, in contrast to the “apically elongated” one in Sr2MnGaO5+δ. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The fluorine-containing derivatives of Sr2MnGaO5.5 were prepared by treatment with XeF2 at temperatures ranging from 300°C to 600°C. The compounds crystallize in a tetragonal unit cell with at≈ap, ct≈2ap (ap—the parameter of the perovskite subcell). An increase in fluorine content is accompanied by a reduction of the Mn oxidation state due to a partial replacement of oxygen by fluorine. The crystal structure of Sr2MnGaO4.78F1.22 was determined by electron diffraction and X-ray powder diffraction (a=3.85559(2)Å, c=7.78289(6)Å, S.G. P4/mmm, RI=0.012, RP=0.019). The structure consists of alternating (MnO2), (SrO) and (GaO0.78F1.22) layers. The Ga atoms are situated in slightly elongated octahedra, the MnO6 octahedra are characterized by two short apical Mn–O distances of 1.876(8)Å and four long equatorial ones of 1.9278(1)Å. This is interpreted as an “apically compressed” type of Jahn–Teller distortion, in contrast to the “apically elongated” one in the Sr2MnGaO5+δ brownmillerites with different oxygen content. Possible structural reasons for the reversed Jahn–Teller effect are discussed.