Neutron Powder Diffraction Refinement Research Articles

Mild nitridation of perovskite manganite: Synthesis, structure and magnetism

The nitrogen lightly doped perovskite manganite La0.5Ba0.5MnO(3-δ)-xNx was synthesized following a mild nitridation strategy by optimizing annealing temperature, annealing time and NH3/Ar flow rate ratio. Neutron powder diffraction (NPD) characterization evidences an N-doping triggered structural phase transition from pseudo-cubic Pm-3m to tetragonal P4/mmm and further confirms a preferable substitution at O1 and O2 sites closing to the Ba-rich layers. N 1s K-edge X-ray absorption near edge spectrum (XANES) with total fluorescence yield (TFY) mode, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectroscopy collectively convince the Mn–N bonded state. The O/N atomic ratio is determined to be 2.26/0.22 by XPS analysis closing to the value of 2.25/0.18 from NPD refinement. Magnetic property characterization reveals that both long-range Mn3+-O-Mn4+ ferromagnetic coupling and high Curie temperature (TC) are maintained upon N-doping. Besides, significant spin frozen with robust domain pinning is identified below TC which can be ascribed to the short-range Mn–N–Mn clusters and/or oxygen defects. This work expands the connotation of transition-metal based perovskite oxynitride and may inspire the development of photosensitive semiconductor device with magnetic response.

Effects of deuterium content on the thermal stability and deuterium site occupancy of TiZrHfMoNb deuterides

A series of high entropy alloy (HEA) hydrides/deuterides were synthesized and characterized to explore the relationship between thermal stability and the structure of TiZrHfMoNb deuterides. The X-ray diffraction, thermogravimetric analysis, and differential scanning calorimetry results reveal that the lattice constant and cell volume of TiZrHfMoNb hydrides increase with the increasing hydrogen content. The desorption temperature decreases with the increasing hydrogen content, indicating that the increased lattice constant arising from the introduction of deuterium atoms will destabilize the HEA deuterides. A density functional theory calculations demonstrate that the binding energies between hydrogen and metals in BCC TiZrHfMoNb hydrides decline with the increasing hydrogen content, meaning that the thermal stability decreases with the increasing hydrogen content. The HEA deuterides are found to be more stable than their hydrides, implying the remarkable isotopic effect of TiZrHfMoNb HEA. Neutron powder diffraction refinements confirm that deuterium atoms prefer to occupy both of the tetrahedral and octahedral interstitials in BCC structure, while a prior occupation of tetrahedral interstitial sites in FCC structure. The deuterium/hydrogen concentrations and the lattice constants are proposed to be the major factor regulating the thermal stability of HEA deuteride, making them suitable for different application field of hydrogen storage.

Time-of-Flight Elastic and Inelastic Neutron Scattering Studies on the Localized 4d Electron Layered Perovskite La5Mo4O16

The magnetic structure and spin-wave excitations in the quasi-square-lattice layered perovskite compound La$_5$Mo$_4$O$_{16}$ were studied by a combination of neutron diffraction and inelastic neutron scattering techniques using polycrystalline sample. Neutron powder diffraction refinement revealed that the magnetic structure is ferrimagnetic in the $ab$ plane with antiferromagnetic stacking along the $c$ axis where the magnetic propagation vector is $\mathbf{k}=\left(0,0,\frac{1}{2}\right)$. The ordered magnetic moments are estimated to be $0.54(2)\mu_\text{B}$ for Mo$^{5+}$ ($4d^1$) ions and $1.07(3)\mu_\text{B}$ for Mo$^{4+}$ ($4d^2$) ions at 4 K, which are about half of the expected values. The inelastic neutron scattering results display strong easy-axis magnetic anisotropy along the $c$ axis due to the spin-orbit interaction in Mo ions evidenced by the spin gap at the magnetic zone center. The model Hamiltonian consisting of in-plane anisotropic exchange interactions, the interlayer exchange interaction, and easy-axis single-ion anisotropy can explain our inelastic neutron scattering data well. Strong Ising-like anisotropy and weak interlayer coupling compared with the intralayer exchange interaction can explain both the high-temperature magnetoresistance and long-time magnetization decay recently observed in La$_5$Mo$_4$O$_{16}$.

Novel Chemically Stable Ba3Ca1.18Nb1.82–xYxO9−δ Proton Conductor: Improved Proton Conductivity through Tailored Cation Ordering

Simple perovskite-structured proton conductors encounter significant challenges to simultaneously achieving excellent chemical stability and proton conductivity that are desirable for many important applications in energy conversion and storage. This work demonstrates that Y-doped complex-perovskite-structured Ba3Ca1.18Nb1.82–xYxO9−δ materials possess both improved proton conductivity and exceptional chemical stability. Neutron powder diffraction refinement revealed a Fm3m perovskite-structure and increased oxygen vacancy concentration due to the Y doping. High-resolution TEM analysis confirmed the perturbation of the B site cation ordering in the structure for the Ba3Ca1.18Nb1.82–xYxO9−δ materials. Such combined effects led to improved proton conductivity with a value of 5.3 × 10–3 S cm–1 at 600 °C for Ba3Ca1.18Nb1.52Y0.3O9−δ (BCNY0.3), a value 2.4 times higher compared with that of the undoped Ba3Ca1.18Nb1.82O9−δ. The Ba3Ca1.18Nb1.82–xYxO9−δ materials showed remarkable chemical stability toward water a...

Considerable Improvement of Long-Persistent Luminescence in Germanium and Tin Substituted ZnGa2O4

The red long-lasting luminescence properties of the ZnGa2O4:Cr3+ spinel material are shown to be much improved when germanium or tin is substituted to the nominal composition. The resulting Zn1+xGa2–2x(Ge/Sn)xO4 (0 ≤ x ≤ 0.5) spinel solid solutions synthesized here by a classic solid state method have been structurally characterized by X-ray and neutron powder diffraction refinements coupled to 71Ga solid state NMR studies. In contrast to ZnGa2O4:Cr3+ for which long lasting luminescence properties have been reported to arise from tetrahedral positively charged defects resulting from the spinel inversion, our results show that a different mechanism occurs complementary for Zn1+xGa2–2x(Ge/Sn)xO4. Here, the great enhancement of the brightness and decay time of the long lasting luminescence properties is directly driven by the substitution mechanism which creates distorted octahedral sites surrounded by octahedral Ge and Sn positive substitutional defects which likely act as new efficient traps.

Synthesis, structural study and magnetic properties of TbFeMnO 5

We describe the preparation and characterization of a new ferrimagnetic oxide of composition TbFeMnO 5. It has been prepared by a soft-chemistry procedure, involving the thermal treatment at moderate temperatures (600 °C) of citrate precursors, subsequently annealed at 900 °C under high oxygen pressure (200 bar). The crystallographic and magnetic structures have been studied by neutron powder diffraction (NPD) experiments, in complement with magnetization and susceptibility measurements. TbFeMnO 5 is an orthorhombic, Pbam space group; the crystal structure contains infinite chains of Mn 4+O 6 edge-sharing octahedra running along the c axis and interconnected by Fe 3+O 5 pyramids and TbO 8 units. Some anti-site disorder is observed from the NPD refinements: about 9% of the 4 f octahedral sites are occupied by Fe 3+ cations and about 18% of the pyramidal 4 h positions contain Mn 4+. These structural features are confirmed by Mössbauer spectroscopy: two sites for Fe 3+ are identified; one of them corresponds to almost regular octahedra (at 4 f positions), characterized by nearly equal Mn/Fe–O distances of 1.906Å at RT (from NPD data), giving a quadrupole doublet in the Mössbauer spectra at RT; the second contributes to a more intensive doublet corresponding to a distorted square pyramid Fe 3+O 5 (at 4 h sites), for which NPD data demonstrates an axial distortion with three sets of Mn/Fe–O distances at 1.981(4), 1.851(5) and 1.944(3) Å. Both doublets are broadened by the Fe/Mn disorder over these sites. TbFeMnO 5 undergoes long-range magnetic ordering below T C ≈ 175 K , as shown from magnetization, NPD and Mössbauer spectroscopy data. The propagation vector k = 0 defines a ferrimagnetic structure that initially concerns the Mn 4+ and Fe 3+ cations, in a magnetic arrangement defined by the basis vectors ( 0 , 0 , F z ) and ( 0 , 0 , F z ′ ) respectively. The Tb 3+ sublattice is ordered at 2 K with a spin arrangement given by ( 0 , 0 , F z ″ ) . The refined magnetic moments at this temperature are 2.66 ( 12 ) μ B for the Mn 4+, − 0.8 ( 2 ) μ B for the Fe 3+ and − 2.0 ( 3 ) μ B for the Tb 3+ cations.

Crystal structure and oxide ion conductivity in cubic (disordered) and tetragonal (ordered) phases of Bi25Ln3Re2O49 (Ln = La, Pr)

Two bismuth oxide materials containing large lanthanide and rhenium cations, Bi25La3Re2O49 and Bi25Pr3Re2O49, have been synthesised in the stabilised face-centred cubic structure. They exhibit very high oxide ion conductivity but prolonged annealing at 600 °C causes a decrease in conductivity, which has been shown to relate to an order–disorder phase transformation. The details of this transition have been determined using neutron powder diffraction on annealed samples. Upon annealing, the samples undergo cation ordering to form a tetragonal phase (I4/m, a ≈ 8.7 Å, c ≈ 17.4 Å), which is structurally related to the unsubstituted phase, Bi28Re2O49. Neutron powder diffraction refinement reveals that the lanthanide cations enter only one of the three Bi sites in the ordered structure.

The crystal structure of a new bismuth tellurium oxychloride Bi 0.87Te 2O 4.9Cl 0.87 from neutron powder diffraction data

A new bismuth tellurium oxychloride was obtained by reaction of BiOCl and TeO 2 in air. According to energy dispersive X-ray spectroscopy and neutron powder diffraction refinement the composition of the substance was determined as Bi 0.87Te 2O 4.9Cl 0.87. The new compound crystallizes in the trigonal system space group R 3¯ (#148), Z=6, a=4.10793(4), c=31.1273(4) Å, χ 2=3.20, w R p=0.0369. Bi 0.87Te 2O 4.9Cl 0.87 has a new type of layered structure constructed by Bi–Te–O layers separated by chloride ions. The Te atoms in Bi 0.87Te 2O 4.9Cl 0.87 show an unusual umbrella-like environment. A comparison with known related structures has been made.

The Crystal Structure of the Intergrowth Compound Ba11TiNb8O33.

AbstractFor Abstract see ChemInform Abstract in Full Text.

The crystal structure of the intergrowth compound Ba 11TiNb 8O 33

The ternary oxide Ba 11TiNb 8O 33 was synthesized and, based on a combined X-ray and Neutron powder diffraction refinement, its crystal structure was examined. Ba 11TiNb 8O 33 is a B-site deficient “hexagonal” perovskite with a 33R stacking sequence of the BaO 3 layers leading to the cell parameters a=5.78634(2) Å, c=77.8011(4) Å with a space group R 3 ̄ m. It is an intergrowth compound whose crystal structure derives from that of the simple terms which constitute it, but possess its specific structural characteristics. No rotation of the oxygen octahedral network is observed in this compound.

Neutron powder diffraction refinement of the crystal structure of La4Ti3O12

Results from full profile analysis of powder neutron diffraction patterns (λ=1.05 A ̊ and λ=2.475 A ̊ ) taken at room temperature are presented. The refinements in space group R 3 ̄ yielded considerably better reliability factors than those obtained in group R 3 ̄ m as suggested in previous X-ray diffraction works.

New Structural and Electrical Data on Bi–Mo Mixed Oxides with a Structure Based on [Bi12O14]∞Columns

We recently described a new family of oxide anion conductors with a structure based on [Bi12O14]∞columns (J. Solid. State Chem.122, 394 (1996)). The parent compound of this series can be formulated as Bi26Mo10O69and formation of a solid solution, in the Bi2O3–MoO3binary system, in the range 2.57≤Bi/Mo≤2.77 was established. The stoichiometry of this series was questioned by R. Enjalbertet al.(J. Solid State Chem.131, 236 (1997)), but confirmed by D. J. Buttreyet al.(Mater. Res. Bull.32, 947 (1997)). The first part of this paper is devoted to a refutation criticisms by R. Enjalbertet al.In the second part, a comparison with other Bi2O3-based oxide anion conductors enables us to propose an iono-covalent description of this novel structure type, taking into account all the structural and electrical features, especially new neutron powder diffraction refinement and conductivity measurements under variable oxygen partial pressures.

Neutron powder diffraction refinement of boron carbides nature of intericosahedral chains

Our Rietveld structure refinements of neutron powder diffraction data of boron carbides with 10, 13, 16, and 20 at.% carbon indicate 15–25% vacancies at the central position of the intericosahedral chains. In addition, we find a comparable number of interstitials residing off the intericosahedral chains. However, X-ray diffraction studies on unirradiated boron carbide single crystals do not generally find these defects. This discrepancy may indicate that the observed defects are the remnants of defect cascades created by the energetic fission products of 10B during the neutron diffraction measurements. The tendency to form vacancies in the center of the intericosahedral chain is consistent with the weak and soft binding of chain-center atoms that we previously inferred from other measurements.

Structural studies of Li 5ReO 6, Li 4NpO 5 and Li 5NpO 6 by neutron and X-ray powder diffraction

This paper reports on the preparation of Li 5ReO 6, Li 4NpO 5 and Li 5NpO 6 by solid-state reactions, the results of X-ray and neutron powder diffraction measurements on all three compounds, and the determination of the structures of Li 5ReO 6 and Li 4NpO 5 from the neutron data. The neutron powder diffraction refinement for Li 5ReO 6 confirms a recent single-crystal X-ray diffraction study: monoclinic, space group C2/ m. This structure is retained by Li 5ReO 6 between 298 K and 10 K. The neutron powder diffraction refinement for Li 4NpO 5 confirms earlier X-ray powder diffraction results: tetragonal, space group I4/ m, a=6.698 A ̊ , c=4.415 A ̊ . The lithium and oxygen positional parameters of Li 4NpO 5 have been refined: coordination about Np is an extended octahedron, with each Np ion surrounded equatorially by four oxygen ions at 2.00 Å and axially by two oxygen ions at 2.21 Å. Li 5NpO 6 shows an X-ray powder pattern consistent with the original report, but the neutron diffraction data set could not be refined in terms of the originally proposed space group or any other plausible model structure.

The quadruple chains of SbO6 octahedra in Sb2Te2O9: an example of low extent of aggregation of pentavalent antimony polyhedra

Single crystals of Sb2Te2O9 have been grown by transport methods, and the crystal structure determined by X-ray single-crystal techniques. The results have been confirmed by a neutron powder diffraction refinement. The compound crystallizes in the monoclinic system, space group P21/c, Z= 8, with unit-cell parameters a= 21.79(1), b= 4.849(1), c= 14.574(9)Å and β= 109.21 (3)°. The structure consists of infinite quadruple chains of vertex-sharing SbVO6 octahedra, running along the b axis, bridged by (Te6O26)∞ strings parallel to the [0 0 1] direction and by isolated Te2O10 groups. The TeIV is five- and six-co-ordinated by oxygen, in very irregular environments making room for the free electron pairs. This structure is discussed in the framework of other pentavalent antimony complex oxides and contrasted with those of the known oxides in the M2O5–TeO2(M = V, Nb or Ta) systems.

Neutron diffraction study of the cationic distribution in Cu xCo 3− xO 4 (0< x⩽1.0) spinels prepared by thermal decomposition of layered hydroxide nitrate precursors

A neutron powder diffraction refinement of the structure parameters of six samples of copper cobalt oxide spinels Cu x Co 3− x O 4 (0 < x ⩽ 1.0), prepared by thermal decomposition of layered hydroxide nitrate precursors has been carried out. It was found that the Cu 2+ ions are statistically distributed over the tetrahedral ( A) and the octahedral ( B) lattice sites. This particular cationic distribution is responsible for the observed cubic lattice symmetry and the dependences of the unit cell parameters, the oxygen parameter and the tetrahedral and octahedral bond lengths on the copper content, x, in the formula unit. The results can be regarded as the first direct confirmation of the suggestion that the cationic distribution in the spinels is predetermined by the structure of the precursors and the mechanism of their thermal decomposition.

Further aspects of the structure and magnetism of the layered compound Fe(III)ClMoO 4: Mössbauer spectroscopy, susceptibility, and powder neutron diffraction studies

Aspects of the nuclear and magnetic structure of the three-dimensionally ordered state of the layered system Fe(III)ClMoO 4 are elucidated primarily on the basis of single crystal and powder Mössbauer spectroscopy and neutron powder diffraction refinements at various temperatures. The antiferromagnetically coupled spins and easy axis of magnetization for Fe(III)ClMoO 4 are indicated to lie in the tetragonal layers ( ab planes) perpendicular to the c axis, which is parallel to the FeCl bond vector of a local C 4 v FeO 4Cl chromophore. Additionally, the neutron diffraction data indicate a very significant c-axis contraction with decreasing temperature (2.7% between 295 and 5 K), with the rate of contraction being highest in the vicinity of the Néel temperature, T N (∼70 K). The structural changes that occur in the temperature range 300 to 5 K are discussed. Powder and single crystal magnetic susceptibility results to ∼1.6 K as well as high field Mössbauer spectra to ∼9 T are also presented. The latter indicate a s pin f lop transition with H sf ∼1 T. Alternate views of the low-dimensional magnetism of FeClMoO 4, evident as a broad maximum in its molar susceptibility at ∼105 K, are discussed.

Recognition and Treatment of Background Problems in Neutron Powder Diffraction Refinements

AbstractIrregular backgrounds in time-of-flight neutron powder diffraction data and nonlinear backgrounds in angle dependent neutron powder diffraction data. were corrected by fitting fifth degree polynomials to those portions of the data most affected. The anomalous background intensities were in both cases due to non Bragg scattering. The polynomial fitting was carried out over a sufficiently widerange of the profile to avoid interfering with the Bragg peaks. The corrected data gave internally consistent results for the crystallographically nonequivalent (Si,Al) -0 (1) and(Si, Al) -0 (2) bond lengths in zeolite rho and compare favorably with previous refinements of this Zeolite in space group Im3m. Internal and external in consistencies of bond lengths are just as diagnostic of refinement difficulties as negative isotropic temperature factors or non positive definite an isotropic temperature factors are.

Neutron diffraction study on the spinel Cu 0.72Co 2.28O 4

A neutron powder diffraction refinement of the positional and thermal structure parameters of Cu 0.72Co 2.28O 4 spinel has been carried out. It has been found that the spinel is inverse, with inversion parameter approximately equal to one half of the copper content value.