Bond Valence Analysis Research Articles

Li0.97FeII0.79FeIII0.15(PO4), a new oxidized triphylite-type phosphate

This paper reports a new partially oxidized triphylite-type phosphate (lithium iron phosphate), which has been synthesized hydrothermally at 973 K and 0.1 GPa. The structure is similar to that of natural triphylite, LiFe(PO(4)), and is characterized by two chains of edge-sharing octahedra parallel to the b axis. The weakly distorted M1 octahedra contain Li atoms, whereas the more strongly distorted M2 octahedra contain Fe(II) and Fe(III) atoms. Refined site occupancies and bond-valence analysis show the presence of Fe(III) and vacancies on the M2 site, mainly explained by the substitution mechanism 3 Fe(II) = 2 Fe(III) + vacancies.

A New Partially Deprotonated Mixed-Valence Manganese(II,III) Hydroxide–Arsenate with Electronic Conductivity: Magnetic Properties of High- and Room-Temperature Sarkinite

A new three-dimensional hydroxide-arsenate compound called compound 2 has been synthesized by heating (in air) of the sarkinite phase, Mn(2)(OH)AsO(4) (compound 1), with temperature and time control. The crystal structure of this high-temperature compound has been solved by Patterson-function direct methods. A relevant feature of this new material is that it is actually the first member of the adamite-type family with mixed-valence manganese(II,III) and electronic conductivity. Crystal data: a = 6.7367(5) Å, b = 7.5220(6) Å, c = 9.8117(6) Å, α = 92.410(4)°, β = 109.840(4)°, γ = 115.946(4)°, P1̅. The unit cell content derived from Rietveld refinement is Mn(8)(O(4)H(x))(AsO(4))(4). Its framework, projected along [111], is characterized by rings of eight Mn atoms with the OH(-)/O(2-) inside the rings. These rings form an almost perfect hexagonal arrangement with the AsO(4) groups placed in between. Bond-valence analysis indicates both partial deprotonation (x ≅ 3) and the presence of Mn in two different oxidation states (II and III), which is consistent with the electronic conductivity above 300 °C from electrochemical measurements. The electron paramagnetic resonance spectra of compound 1 and of its high-temperature form compound 2 show the presence of antiferromagnetic interactions with stronger magnetic coupling for the high-temperature phase. Magnetization measurements of room-temperature compound 1 show a complex magnetic behavior, with a three-dimensional antiferromagnetic ordering and magnetic anomalies at low temperatures, whereas for compound 2, an ordered state is not reached. Magnetostructural correlations indicate that superexchange interactions via oxygen are present in both compounds. The values of the magnetic exchange pathways [Mn-O-Mn] are characteristic of antiferromagnetic couplings. Notwithstanding, the existence of competition between different magnetic interactions through superexchange pathways can cause the complex magnetic behavior of compound 1. The loss of three-dimensional magnetic ordering by heating of compound 1 could well be based on the presence of Mn(3+) ions (d(4)) in compound 2.

Thermal behavior of afghanite, an ABABACAC member of the cancrinite group

Thermal behavior of afghanite, (Na15K5Ca11)Σ31[Si24Al24O96](SO4)6Cl6, P31c, a = 12.7961(7) Å, c = 21.4094(13) Å, an eight-layer member of the cancrinite group, has been investigated by combined electron microprobe analysis, X-ray single-crystal diffraction, and high-temperature X-ray powder diffraction. Non-ambient X-ray powder diffraction data were collected in the 323-1223 K thermal range on a specimen from Case Collina, Latium, Italy. Structural refinement and site assignment based on the bond-valence analysis, performed on room-temperature single-crystal X-ray diffraction data, provided more accurate site allocation of cations than the available model in the literature. The results show that the cancrinite cages alternating with the liottite cages are more compressed along the c-axis than the remaining ones. As a result the chlorine atom, located at the center of the cages, is driven off-axis to release the steric strain due to the cage compression. Thermal expansion shows a discontinuity at 448 K for both a and c unit-cell parameters, a feature previously reported for other cancrinite-like minerals. Up to 448 K, the c-parameter expands significantly and more than the aparameter. A further discontinuity has been detected at 1073 K for the c-parameter. Mean linear and volume thermal expansion coefficients (×10-6 K-1) in the 323 < T < 448 K thermal range are ᾱa = 12.9(4), ᾱc = 17.9(9), and ᾱV = 43.7(18). Above this discontinuity temperature, the thermal expansion is reverted becoming greater for the a-parameter. Mean linear and volume thermal expansion coefficients in the 448 < T < 1073 K thermal range are ᾱc = 8.22(3), ᾱc = 3.52(4), and ᾱV = 19.68(8). In the 1073 < T < 1223 K thermal range the values are ᾱa = 6.35(9), ᾱc = 5.02(14), and ᾱV = 17.74(9). Afghanite shows a significant microstrain at RT that increases up to ca. 700 K and subsequently decreases as a function of T. Cooling to RT allows a significantly release of ε0 microstrain, which is coupled with a significant expansion of the c-parameter as compared to the starting RT data. The expansion of the c-parameter has been mainly attributed to the full expansion of the cancrinite cages alternating with the liottite cages. Upon reheating at 1173 K, the microstrain increases back to approximately the same value calculated for the first heating process. Repeated heating-RT-cooling cycles led to the partial afghanite structure disruption and the partial conversion, via an intermediate disordered phase, to haüyne. As repeated heating/cooling cycles did not modify the ε0 values both at RT and at HT, it can therefore be concluded that the strain release occurs prevalently during the first heating/cooling cycle.

Synthesis, characterization, and crystal structures of uranyl compounds containing mixed chromium oxidation states

The mixed-valence chromium uranyl compounds Li5[(UO2)4(Cr(V)O5)(Cr(VI)O4)4](H2O)17 (1), (Mg(H2O)6)5[(UO2)8(Cr(V)O5)2(Cr(VI)O4)8] (2) and (NH4)5[(UO2)4(Cr(V)O5)(Cr(VI)O4)2]H2O11 (3) have been synthesized and characterized. Each contains an identical sheet of cation-centered polyhedra. Central to the connectivity of the sheet are four uranyl pentagonal bipyramids that share some of their equatorial vertices, giving a four-membered ring. The Cr(V) cation located near the center of this ring is coordinated by O atoms in a square pyramidal arrangement. The Cr(VI) is tetrahedrally coordinated by O atoms, and these tetrahedra link the four-membered rings of bipyramids. The mixed-valence nature of the sheet was verified by XANES, an EPR spectrum, and bond-valence analysis. Low-valence cations and H2O groups reside between the sheets of uranyl and chromate polyhedra, where they provide linkages between adjacent sheets.

Pb3TeCo3V2O14: A Potential Multiferroic Co Bearing Member of the Dugganite Series

Polycrystalline Pb3TeCo3V2O14, a structural analogue of the multiferroic Ba3NbFe3Si2O14, was synthesized and characterized using X-ray diffraction, magnetic susceptibility, specific heat, dielectric constant, and neutron diffraction. Magnetic susceptibility, specific heat capacity measurements, and bond valence analysis confirmed that the V5+ ion is nonmagnetic, while Co2+ is in its high spin state (S = 3/2). Two magnetic transitions were seen at TN1 = 8.6 K and TN2 = 6.0 K where the spins first adopt a magnetic structure with propagation vector k = (0.752,0,1/2) and reorder into a commensurate structure with propagation vector k = (5/6,5/6,1/2). Changes in the dielectric constant at both magnetic phase transitions suggest that magnetoelectric coupling exists in Pb3TeCo3V2O14.

A crystal chemical approach to superconductivity. II. An analysis of local bond-valence distribution in inorganic compounds

Abstract A crystal chemical approach to superconductivity based upon a bond-valence sum analysis of inorganic compounds is extended by an analysis of local bond-valence distribution. The notions of stoichiometric and structural valence together with Pauling’s rule of equal distribution of valences among the ligands of a given atom allow to provide a characterization for the strength of bonds which is used to define structurally distinguished bond paths. Combinations of these paths represent infinite units of strongly overlapping orbitals. Such units are assumed to be the conducting units in superconductors. A large number of crystal-structure data determined at ambient temperature and pressure has been analyzed including data of chalcogenides and pnictides as well as cuprates. It is shown that infinite units of strongly overlapping orbitals always exist in compounds which become superconducting on cooling with or without applied pressure and/or by doping. As a consequence, a systematic search for potential unconventional superconductors in inorganic crystallographic databases seems to be promising.

Crystal-chemical investigation of Fe3(PO4)2· 8 H2O vivianite minerals

Crystal-chemistry of Fe3(PO4)2 · 8 H2O vivianite minerals was investigated by means of a multi-methodological approach based on electron microprobe analysis in wavelenght dispersive mode, single-crystal X-ray diffraction and infrared spectroscopy. To this aim, three specimens coming from Commentry (France) (1), Settefrati (Frosinone, Italy) (2) and Ibex Mine (Colorado, USA) (3), have been subject to EMPA analysis, indicating chemical composition (Fe2.94Mg0.06Mn0.01)Σ3.02(P1.99O8) · 8 H2O (1), (Fe2.96Mg0.01Mn0.04)Σ3.01((P1.96Si0.03Al0.02)Σ2.01O8) · 8 H2O (2) and (Fe2.65Zn0.27Mn0.06Na0.03Mg0.02)Σ3.03(P1.99O8) · 8 H2O (3); successively they have been subject to structural refinement by means of single-crystal X-ray diffraction within monoclinic space group C2/m, with the following unit cell constants: a = 10.100(3), b = 13.494(3), c = 4.709(3) Å; β = 104.24(4)° and V = 622.1(7) Å3 (1); a = 10.116(3); b = 13.473(3), c = 4.7064(7) Å; β = 104.33(4)° and V = 621.5(2) Å3 (2); a = 10.083(2), b = 13.468(2), c = 4.718(1) Å, β = 104.47(2)° and V = 620.3(2) Å3 (3). Iron cations occupy two special positions, making up single and dimerical octahedral groups, joined by (PO4) tetrahedra groups, in order to form infinite layers down b, making up, via consistent O—H … O hydrogen bonds, the three-dimensional framework. The present vivianite samples were subject to geochemical and crystal chemical comparisons, the latter also by means of bond valence analysis with literature available phases. Last, IR spectra were performed for the three phases, in order to provide information on bending and stretching modes of the minerals, as well as to investigate H bonds by means of Libowitzki formula application.

Preparation and mobile ion transport studies of Ta and Nb doped Li6Zr2O7 Li-fast ion conductors

Pure and doped Li6−x(Zr2−xMx)O7, M = Nb and Ta; x = 0, 0.15 compounds have been prepared by the urea combustion method followed by annealing at 950 °C for 8 h. The samples are characterized by X-ray diffraction and impedance spectroscopy. Ionic conductivities, σionic, were determined in the temperature range of 60–360 °C by impedance spectroscopy. We observe that the Ta doped Li6Zr2O7 has a measurable σionic at ∼160 °C, and at 300 °C exhibits a conductivity value of 1 × 10−3 S/cm. The temperature dependence of the conductivity in the range 100–360 °C obeys an Arrhenius relation, yielding an activation energy of Ea = 0.95 eV (for M = Ta and x = 0.15). The bond valence approach has been used to visualise Li+ ion migration pathways and the conductivity mechanism in these compounds. The lowest energy pathway is found to extend along the [0 1 2] direction. The Bond valence analysis also indicates a significantly anisotropic Li-ion conductivity in compounds with Li6Zr2O7 type structure, predicting activation energies of 1.1 and 0.9 eV for the low energy pathway in undoped and doped Li6Zr2O7.

Ce2[MoO5][MoO4] and Ce5[MoO4]8: Two New Cerium Oxomolybdates, Each Exhibiting a Special Structural Feature

Ce2[MoO5][MoO4] crystallizes monoclinically in space group P21/c (a = 2241.98(9), b = 712.95(3), c = 2044.19(8) pm, β = 116.936(2), Z = 16). Besides eight crystallographically different Ce3+ cations with coordination numbers ranging from seven plus one to ten, its structure contains two isolated oxomolybdate(VI) species, namely [MoO4]2− tetrahedra and [MoO5]4− trigonal bipyramids and square pyramids. The oxygen polyhedra around the Ce3+ cations build up a three-dimensional ∞ 3 {[Ce2O9]12−} network by vertex-, edge-, and face-connections with the Mo6+ cations residing in tetrahedral, square-pyramidal, and trigonal-bipyramidal voids therein. Ce5[MoO4]8 also crystallizes monoclinically in space group P21/c (a = 1133.14(5), b = 1704.96(7), c = 1406.21(6) pm, β = 90.749(2)° Z = 4). In its structure eight isolated [MoO4]2− tetrahedra are present, which display an overall negative charge of −16. To maintain electroneutrality, mixed-valency of the five crystallographically independent cerium cations must be considered. A thorough bond-valence analysis reveals cerium at the Ce1 site as tetravalent, while the other four cerium cations prove to be trivalent. The polyhedra around all cerium cations form chains with a V-shaped profile along [100] via vertex-, edge-, and face-connections to result in a sawblade pattern. These chains are interlocked into sheets parallel to the (001) plane and linked by the Mo6+ cations to form a three-dimensional network.

Lattice Strains in the Ligand Framework in the Octahedral Metal Cluster Compounds as the Origin of Their Instability

The bond description for cluster compounds is commonly based on the molecular orbital diagrams, where the whole material is characterized by the specific electron population at various energetic levels. In contrast, this work is focused on the distribution of valence electrons between different liganding atoms, calculated first for a wide variety of octahedral metal cluster compounds (mainly Mo6 and Re6 chalcohalides) by the bond valence model. This distribution was found to be extremely nonuniform for most of the materials; it depends mostly on the ligand distances from the cluster center: The closer the ligand to the center, the higher is its charge (defined as its bond valence sum). To explain these results, a new model for the electrostatic interactions in the cluster compounds was proposed: The octahedral metal cluster with high polarizing power creates a strong electrostatic field, in which the adjacent separate anions behave as a part of a continuous dielectric medium, adjusting their charge to the distance from the cluster center. The valence violations related to this adjustment are the source of the material instability. Moreover, the bond valence analysis allows for the unveiling of the stabilization mechanisms existing in this type of cluster compounds. It was shown that the formation of mixed chalcohalides with an unusual anion arrangement, and chalcogen linkers with a reduced oxidation state, decreases the valence violation on the ligands. This work also illustrates additional ways of material stabilization, such as ion insertion inside the clusters or into the interstitials between the clusters, an increase in the number of inner ligands from 8 to 12, as well as increasing the connectivity of the structural units, Me6X8L6 and Me6X12L6 (Me is the transition metal; X and L are internal and outer ligands, respectively).

Synthesis and Li+ ion Migration Studies of Li6PS5X (X = Cl, Br, I)

ABSTRACTLithium ion conducting argyrodite-type Li6PS5X (X = Cl, Br, I) compounds were prepared using mechanical milling followed by annealing. XRD characterization reveals the formation and growth of Li6PS5X crystals in samples under varying annealing conditions. Temperature dependent XRD data showed the monotonic increase of lattice constant within the range of study. For Li6PS5Cl and Li6PS5Br an ionic conductivity of the order of 10-3 S/cm is reached at room temperature, which is close to the Li mobility in conventional liquid electrolytes and well suitable for all-solid-state safe electrochemical energy storage devices. Bond valence analysis of Li ion migration paths for the argyrodites showed the formation of low energy pathway cages around halide ion for Li6PS5Cl, around the sulfide ion for Li6PS5I. For higher activation energies these cages are interconnected to form a 3-D pathway network. In the case of Li6PS5Br cages around Cl and Br require about the same activation energy.

Ten Layered Hexagonal Perovskite Sr5Ru5−xO15 (x = 0.90), a Weak Ferromagnet with a Giant Coercive Field Hc ∼ 12 T

A single crystal of Sr5Ru5−xO15 (x = 0.90(2)) with mixed valence of Ru(IV) and Ru(V) was synthesized under a high pressure of 4 GPa with an oxidizer. Sr5Ru5−xO15 crystallizes in a hexagonal perovskite-type structure with a space group P63/mmc (No.194), a = 5.5600(11) Å, and c = 22.830(5) Å. An alternative stacking of four corner-sharing (c) SrO3 layers and one face-sharing (h) SrO3 layer linking RuO6 octahedra and its doubling along c-axis gives a 10 layer period hexagonal cell (10H) which is denoted by (cccch)2. The partial deficiency of Ru found in face-sharing octahedra, as reported for 8H-Sr4Ru4−xO12 (x = 0.95) with (ccch)2 stacking, yields an average Ru valence estimate of 4.87. The bond valence analysis indicates that the valence of Ru in fully corner-sharing octahedra is nearly 5, while that of Ru in face-sharing octahedra is considerably lower than 5. This compound is a weakly ferromagnetic metal with Curie temperature Tc = 160 K and a saturated moment of 0.07 and 0.05 μB/Ru in H ⊥ c and H // c, respectively. In the ferromagnetic state, we found remarkable enhancement of the coercivity below 50 K. At 1.7 K, a giant coercive field of ∼12 T was observed. We argue that Ru(IV,V) in face-sharing layers are responsible for the ferromagnetism and that possible glassy character due to frustration and disorder may at least in part contribute to the giant coercivity.

Chevrel Phases, MxMo6T8 (M = Metals, T = S, Se, Te) as a Structural Chameleon: Changes in the Rhombohedral Framework and Triclinic Distortion

It is commonly accepted that the nature of triclinic distortion, responsible for the superconductivity loss in Chevrel phases, is different for the two main structural types: electronic instability of the Mo6-cluster in the compounds with large cations (type I) and “freezing” of the formerly mobile small cations in fixed positions (type II). Recently, for Chevrel phases with small cations, we proposed an alternative mechanism of the phase transition as one of the ways to attain the steric matching between the cations and the framework. It was shown that the triclinic structure is more flexible than the rhombohedral because it allows for additional deformations and a relative tilt of the main structural elements. Bond valence analysis performed for the first time for a variety of Chevrel phases in this work shows that the intrinsic instability of the binary compounds, Mo6T8, does not arise from the Mo6-cluster anisotropy, but rather from the extremely non-uniform distribution of the anion charge in their c...

Ion transport pathways in molecular dynamics simulated alkali silicate glassy electrolytes

The xM 2O–(1 − x)SiO 2 (M = Li, Na, and K, and 0.1 ≤ x ≤ 0.5) glass systems have been studied by constant volume molecular dynamics (MD) simulations. The bond valence (BV) method is applied to the equilibrated configurations to analyse the structural variation in these glass systems with increasing network modifier content, its consequence for M + ion mobility, as well as the distribution of bridging and non-bridging oxygen atoms and the variation of the Q i values. The contribution of non-bridging oxygen atoms to the BV sums exhibits a transition around x = 1/3 for Li 2O and Na 2O doped glasses. The observed Q i variation is consistent with a bond order model. Despite slight deviations of the interatomic distances in the MD-simulated glasses, their BV analysis reveals characteristic features of the ion transport pathway. For complex disordered systems with low ion mobilities the bond valence analysis of the pathway characteristics for the mobile ion is thus a viable method to extract ion transport properties even if the mobilities are too low to be directly analysed from the mean square displacements over the simulated period.

Ion transport pathways in molecular dynamics simulated lithium silicate glasses

The xLi 2O–(1 − x)SiO 2 ( x = 0.1, 0.15, 0.2, 0.25, 0.3, 0.33, 0.4, 0.45, and 0.5) glass systems have been studied by constant volume molecular dynamics (MD) simulations, using empirical pairwise Morse-type potentials. Bond valence (BV) method is applied to the equilibrated configurations to analyse the structural variation in these glass systems with increasing network modifier content, its consequence for Li + ion mobility, as well as the distribution of bridging and non-bridging oxygen atoms and the variation of the Q i values. The contribution of non-bridging oxygen atoms to the Lithium BV sums exhibits a transition around x = 1/3. The observed Q i variation can be explained by a bond order model. Despite slight deviations of the interatomic distances in the MD-simulated glasses, their BV analysis reveals features of the ion transport pathway (such as volume fraction and local dimensionality of the percolating pathway). Results are compared to pathway models for related glassy solid electrolytes based on reverse Monte Carlo modelling of diffraction data. For complex disordered systems with low ion mobilities the bond valence analysis of the pathway characteristics for the mobile ion is thus a viable method to extract ion transport properties even if the mobilities are too low to be directly analysed from the mean square displacements over the simulated period.

Structure and Ion Transport Pathways in 0.45Li2O-(0.55-x)P2O5-xB2O3 Glasses

AbstractLithium borophosphate glasses 0.45Li2O-(0.55-x)P2O5-xB2O3 (where 0 ≤ x ≤ 0.40) were investigated focusing on the influence of cation mobility changes due to mixed glass former effect. It was found that glass transition temperature (Tg) increases and molar volume decreases with B2O3 addition. X-ray photoelectron spectroscopy (XPS) spectra showed that besides P-O-P, B-O-B and P=O, P-O-, B-O- bond peaks, an intermediate O1s peak due to P-O-B bonds emerges in glasses with B2O3 contents x ≥ 0.15. Molecular dynamics (MD) simulations for the same systems have been performed with an optimized potential, fitted to match bond lengths, coordination numbers and ionic conductivity (σdc). Structural effects on ion transport as the origin of the mixed glass former effect can be quantified by applying the bond valence analysis (BV) approach to the equilibrated MD trajectories.

X-ray Rietveld structure refinement and bond-valence analysis of Cs2TeI6

The crystal structure of the ternary iodide Cs2TeI6 has been refined by Rietveld analysis of X-ray powder diffraction data. The refinement procedure was stopped when the intensity residual RB = 3.7 % had been reached. Cs2TeI6 crystallizes in the cubic K2PtCl6 structure type, space group Fm-3m (No. 225), with the lattice parameter a = 11.6939(8) A, Z = 4, Dc = 4.797(1) g/cm . The reliability of the structural model obtained for Cs2TeI6 in the Rietveld refinement was confirmed by a bond-valence analysis of the structure. For the first time, the bond-valence parameters (r0 = 2.782 A and b = 0.37 A) have been determined for the Te /I ion pair, from a set of 14 well-determined coordination shells [TeIn]. These parameters show a reasonably high performance and can be recommended for routine bond-valence analyses of structures containing Te–I chemical bonds.

Structural Investigation of Activated Lattice Oxygen in Ce1−xSnxO2 and Ce1−x−ySnxPdyO2−δ by EXAFS and DFT calculation

Substitution of Sn4+ ion in CeO2 creates activated oxygen in Ce0.8Sn0.2O2 leading to higher oxygen storage capacity compared to Ce0.8Zr0.2O2. With Pd ion substitution in Ce0.8Sn0.2O2, activation of oxygen is further enhanced as observed from the H2/TPR study. Both EXAFS analysis and DFT calculation reveal that in the solid solution Ce exhibits 4 + 4 coordination, Sn exhibits 4 + 2 + 2 coordination and Pd has 4 + 3 coordination. While the oxygen in the first four coordination with short M−O bonds are strongly held in the lattice, the oxygens in the second and higher coordinations with long M−O bonds are weakly bound, and they are the activated oxygen in the lattice. Bond valence analysis shows that oxygen with valencies as low as 1.65 are created by the Sn and Pd ion substitution. Another interesting observation is that H2/TPR experiment of Ce1−xSnxO2 shows a broad peak starting from 200 to 500 °C, while the same reduction is achieved in a single step at ∼110 °C in presence Pd2+ ion. Substitution of Pd2+ ion thus facilitates synergistic reduction of the catalyst at lower temperature. We have shown that simultaneous reduction of the Ce4+ and Sn4+ ions by Pd0 is the synergistic interaction leading to high oxygen storage capacity at low temperature.

Origin of activation of Lattice Oxygen and Synergistic Interaction in Bimetal-Ionic Ce0.89Fe0.1Pd0.01O2−δ Catalyst

Flourite-type nanocrystalline Ce0.9Fe0.1O2-delta and Ce0.89Fe0.1Pd0.01O2-delta solid solutions have been synthesized by solution combustion method,'.which show higher oxygen storage/release property (OSC) compared to CeO2 and Ce0.8Zr0.2O2. Temperature programmed reduction an XPS study reveal that the presence of Pd ion in Ce0.9Fe0.1O2-delta facilitates complete reduction of Fe3+ to Fe2+ state and partial reduction of Ce4+ to Ce3+ state at.temperatures as low as 105 degrees C compared to 400 degrees C for monometal-ionic Ce0.9Fe0.1O2-delta. Fe3+ ion is reduced to Fe2+ and not to Feo due to favorable redox potential for Ce4+ + Fe2+ -> Ce3+ + Fe3+ reaction. Using first-principles density functional theory calculation we determine M-O (M = Pd, Fe, Ce) bond lengths, and find that bond lengths vary from shorter (2.16 angstrom) to longer (2.9 angstrom) bond distances compared to mean Ce-O bond distance of 2.34 angstrom. for CeO2. Using these results in bond valence analysis, we show that oxygen with bond valences as low as -1.55 are created, leading to activation of lattice oxygen in the bimetal ionic catalyst. Temperatures of CO oxidation and NO reduction by CO/H-2 are lower with the bimetalionic Ce0.89Fe0.1Pd0.01O2-delta catalyst compared to monometal-ionic Ce0.9Fe0.1O2-delta and Ce0.99Pd0.01O2-delta catalysts. From XPS studies of Pd impregnated on CeO2 and Fe2O3 oxides, we show that the synergism leading to low temperature activation of lattice oxygen in bimetal-ionic catalyst Ce0.89Fe0.1Pd0.01O2-delta is due to low-temperature reduction of Pd2+ to Pd-0, followed by Pd-0 + 2Fe(3+) -> Pd2+ + 2Fe(2+), Pd-0 + 2Ce(4+) -> Pd2+ + 2Ce(3+) redox reaction.

Bond-valence analysis in lanthanide complexes with planar tridentate ligand

Bond-valence analysis in lanthanide complexes with planar tridentate ligand