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At least 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Structural and magnetic characterisation of CoSb{sub 2}O{sub 4}, and the substitution of Pb{sup 2+} for Sb{sup 3+}

The nuclear and magnetic structures of the synthetic schafarzikite related material CoSb{sub 2}O{sub 4} have been determined from neutron powder diffraction data. The compound is tetragonal (P4{sub 2}/mbc) with refined lattice constants at 300 K of, a=8.49340(9) A, c=5.92387(8) A. The magnetic ordering is shown to be consistent with a C mode with moments aligned along [0 0 1]. Magnetic susceptibility measurements indicate a canted antiferromagnetic ground state, for which the ferromagnetic component shows unusually high coercivity. The thermal stability of CoSb{sub 2}O{sub 4} in air is reported. The substitution of Pb{sup 2+} for Sb{sup 3+} has been investigated and found to cause oxidation of both Co{sup 2+} to Co{sup 3+} and Sb{sup 3+} to Sb{sup 5+}. - Graphical Abstract: Structural changes on substitution of Pb{sup 2+} ions for Sb{sup 3+} ions in CoSb{sub 2}O{sub 4}. Highlights: Black-Right-Pointing-Pointer The structural details of CoSb{sub 2}O{sub 4} are reported for the first time. Black-Right-Pointing-Pointer The magnetic structure of CoSb{sub 2}O{sub 4} are reported for the first time. Black-Right-Pointing-Pointer The ordered magnetic structure has a canted antiferromagnetic arrangement. Black-Right-Pointing-Pointer The ferromagnetic component of the ordered arrangement has high coercivity. Black-Right-Pointing-Pointer Pb{sup 2+} can substitute for Sb{sup 3+} and oxidation of both Co{sup 2+} and Sb{sup 3+} occurs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

New metal-organic frameworks of [M(C{sub 6}H{sub 5}O{sub 7})(C{sub 6}H{sub 6}O{sub 7})(C{sub 6}H{sub 7}O{sub 7})(H{sub 2}O)] . H{sub 2}O (M=La, Ce) and [Ce{sub 2}(C{sub 2}O{sub 4})(C{sub 6}H{sub 6}O{sub 7}){sub 2}] . 4H{sub 2}O

Two novel materials, [M(C{sub 6}H{sub 5}O{sub 7})(C{sub 6}H{sub 6}O{sub 7})(C{sub 6}H{sub 7}O{sub 7})(H{sub 2}O)] . H{sub 2}O (M=La(1a), Ce(1b)) and [Ce{sub 2}(C{sub 2}O{sub 4})(C{sub 6}H{sub 6}O{sub 7}){sub 2}] . 4H{sub 2}O (2), with a metal-organic framework (MOF) were prepared with hydrothermal reactions and characterized with photoluminescence, magnetic susceptibility, thermogravimetric analysis and X-ray powder diffraction in situ. The crystal structures were determined by single-crystal X-ray diffraction. Compound 1 crystallized in triclinic space group P1-bar (No. 2); compound 2 crystallized in monoclinic space group P2{sub 1}/c (No. 14). The structure of 1 is built from a 1D MOF, composed of deprotonated citric ligands of three kinds. Compound 2 contains a 2D MOF structure consisting of citrate and oxalate ligands; the oxalate ligand arose from the decomposition in situ of citric acid in the presence of Cu{sup II} ions. Photoluminescence spectra of compounds 1b and 2 revealed transitions between the 5d{sup 1} excited state and two levels of the 4f{sup 1} ground state ({sup 2}F{sub 5/2} and {sup 2}F{sub 7/2}). Compounds 1b and 2 containing Ce{sup III} ion exhibit a paramagnetic property with weak antiferromagnetic interactions between the two adjacent magnetic centers. - Graphical Abstract: [M(C{sub 6}H{sub 5}O{sub 7})(C{sub 6}H{sub 6}O{sub 7})(C{sub 6}H{sub 7}O{sub 7})(H{sub 2}O)] . H{sub 2}O (M=La(1a), Ce(1b)) and [Ce{sub 2}(C{sub 2}O{sub 4})(C{sub 6}H{sub 6}O{sub 7}){sub 2}] . 4H{sub 2}O (2)-with 1D and 2D structures were synthesized and characterized. Highlights: Black-Right-Pointing-Pointer Two MOF - [M(C{sub 6}H{sub 5}O{sub 7})(C{sub 6}H{sub 6}O{sub 7})(C{sub 6}H{sub 7}O{sub 7})(H{sub 2}O)] . H{sub 2}O (M=La(1a), Ce(1b)) and [Ce{sub 2}(C{sub 2}O{sub 4})(C{sub 6}H{sub 6}O{sub 7}){sub 2}] . 4H{sub 2}O (2) - with 1D and 2D structures. Black-Right-Pointing-Pointer The adjacent chains of the 1D framework were correlated with each other through an oxalate ligand to form a 2D layer structure. Black-Right-Pointing-Pointer The source of the oxalate ligand was the decomposition in situ of citric acid oxidized in the presence of Cu{sup II} ions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Boron site preference in ternary Ta and Nb boron silicides

X-ray single crystal (XSC) and neutron powder diffraction data (NPD) were used to elucidate boron site preference for five ternary phases. Ta{sub 3}Si{sub 1-x}B{sub x} (x=0.112(4)) crystallizes with the Ti{sub 3}P-type (space group P4{sub 2}/n) with B-atoms sharing the 8g site with Si atoms. Ta{sub 5}Si{sub 3-x} (x=0.03(1); Cr{sub 5}B{sub 3}- type) crystallizes with space group I4/mcm, exhibiting a small amount of vacancies on the 4a site. Both, Ta{sub 5}(Si{sub 1-x}B{sub x}){sub 3}, x=0.568(3), and Nb{sub 5}(Si{sub 1-x}B{sub x}){sub 3}, x=0.59(2), are part of solid solutions of M{sub 5}Si{sub 3} with Cr{sub 5}B{sub 3}-type into the ternary M-Si-B systems (M=Nb or Ta) with B replacing Si on the 8h site. The D8{sub 8}-phase in the Nb-Si-B system crystallizes with the Ti{sub 5}Ga{sub 4}-type revealing the formula Nb{sub 5}Si{sub 3}B{sub 1-x} (x=0.292(3)) with B partially filling the voids in the 2b site of the Mn{sub 5}Si{sub 3} parent type. - Graphical abstract: The crystal structures of a series of compounds have been solved from X-ray single crystal diffractometry revealing details on the boron incorporation. Highlights: Black-Right-Pointing-Pointer Structure of a series of compounds have been solved by X-ray single crystal diffractometry. Black-Right-Pointing-Pointer Ta{sub 3}(Si{sub 1-x}B{sub x}) (x=0.112) crystallizes with the Ti{sub 3}P-type, B and Si atoms randomly share the 8g site. Black-Right-Pointing-Pointer Structure of Nb{sub 5}Si{sub 3}B{sub 1-x} (x=0.292; Ti{sub 5}Ga{sub 4}-type) was solved from NPD.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Dielectric properties and electrical conductivity of the hybrid organic-inorganic polyvanadates (H{sub 3}N(CH{sub 2}){sub 4}NH{sub 3})[V{sub 6}O{sub 14}]

Plate-like crystals of the polyvanadate (H{sub 3}N(CH{sub 2}){sub 4}NH{sub 3})[V{sub 6}O{sub 14}] have been synthesized via an hydrothermal treatment. X-ray powder diffraction, scanning electron microscope, Fourier transform infrared spectroscopy, electron spin resonance and complex impedance spectroscopy were used to analyze the hybrid material. The frequency dependence of AC conductivity at different temperatures indicates that the CBH model is the probable mechanism for the AC conduction behavior. The conductivity was measured by complex impedance spectroscopy which is equal to 31.10{sup -3} {Omega}{sup -1} m{sup -1} at 443 K. The Arrhenius diagram is not linear, it presents a rupture situated at 357 K and the activation energies' average values are 0.22 eV and 0.14 eV, deduced from the Arrhenius relation. - Graphical abstract: At high temperature {epsilon} Double-Prime increases more rapidly which is due to the increasing conduction loss which rises with the increment in the DC conductivity. Highlights: Black-Right-Pointing-Pointer Rectangular plate-like crystals (H{sub 3}N(CH{sub 2}){sub 4}NH{sub 3})[V{sub 6}O{sub 14}] were synthesized. Black-Right-Pointing-Pointer frequency and temperature dependence of AC conductivity indicate CBH model. Black-Right-Pointing-Pointer The temperature dependence of DC conductivity exhibits two conduction mechanisms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Crystal structures and magnetic properties of strontium and copper doped lanthanum ferrites

The crystal and magnetic structures of La{sub 0.8}Sr{sub 0.2}Fe{sub 1-x}Cu{sub x}O{sub 3-w} compounds, which exhibit coercive fields larger than any others reported for iron-based perovskites, have been analyzed at room temperature with the neutron powder diffraction technique and the Rietveld method of profile fitting. For x in the range 0.05-0.10 the material is monophasic with orthorhombic symmetry (space group Pnma), and crystallizes in the perovskite-like cell of LaFeO{sub 3}, Fe/Cu cations occupy octahedral sites, La/Sr cations are twelve-fold coordinated. For x=0.20 the material is biphasic, with a main orthorhombic phase (space group Pnma) and a secondary rhombohedral phase with space group R-3c (hexagonal setting). The structural transition from the orthorhombic to the rhombohedral phase reduces the structural distortion of the (Fe/Cu)O{sub 6} octahedron. The average bond distance (Fe/Cu)-O and the pseudo-cubic unit cell volume decrease with increasing Cu content in accordance with the presence of higher valence states of the transition metals. The magnetic structure was modeled for the monophasic samples (x=0.05 and 0.10) assuming an antiferromagnetic interaction between Fe/Cu neighboring cations (G-type): the magnetic moments order antiferromagnetically along the b-axis, with the spin direction along a-axis. The magnetic moments of the Fe/Cu atoms are {mu}{sub x}=2.66(3){mu}{sub B} and 2.43(3){mu}{sub B} for the compositions x=0.05 and 0.10, respectively. By measuring the first magnetization curve and the hysteresis loops, coexisting antiferromagnetic and weak ferromagnetic interactions were observed for all samples. - Graphical abstract: Hysteresis loops measured at room temperature of the sample with x=0.05. Highlights: Black-Right-Pointing-Pointer Iron based perovskites with the largest coercive fields. Black-Right-Pointing-Pointer Sr and Cu lanthanum ferrites as magnetic materials. Black-Right-Pointing-Pointer Doped lanthanum ferrites show antiferromagnetic and weak ferromagnetic interactions. Black-Right-Pointing-Pointer Sr and Cu lanthanum ferrites show distorted perovkite structure.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Influence of structural distortions upon photoluminescence properties of Eu{sup 3+} and Tb{sup 3+} activated Na{sub 3}Ln(BO{sub 3}){sub 2} (Ln=Y, Gd) borates

The comparative study of the structure and photoluminescence (PL) properties of the Eu{sup 3+} and Tb{sup 3+} activated Na{sub 3}Ln(BO{sub 3}){sub 2}, with Ln=Y, Gd, showed the important role of the host lattice structure upon PL. Higher emission intensities of Eu{sup 3+} and Tb{sup 3+} are observed for Na{sub 3}Gd(BO{sub 3}){sub 2} than for Na{sub 3}Y(BO{sub 3}){sub 2}, through direct Eu{sup 3+} excitation at 395 nm for Eu{sup 3+} doped borates, and through Gd{sup 3+} excitation around 280 nm for Tb{sup 3+} doped borates. This higher performance for Na{sub 3}Gd(BO{sub 3}){sub 2} is due to the less regular environment of Eu{sup 3+} (Tb{sup 3+}) in the Gd sites than in the Y sites and to energy transfer from Gd{sup 3+} to Eu{sup 3+}(Tb{sup 3+}). The smaller critical concentration in Na{sub 3}Ln{sub 1-x}Tb{sub x}(BO{sub 3}){sub 2} observed for Ln=Gd, x=0.5, compared to x=0.6 for Ln=Y, is explained by shorter Ln-Ln distances (4.11 A for Gd-Gd vs. 4.59 A for Y-Y). Both Na{sub 3}Y{sub 0.4}Tb{sub 0.6}(BO{sub 3}){sub 2} and Na{sub 3}Gd{sub 0.5}Tb{sub 0.5}(BO{sub 3}){sub 2} show intense green emission under UV excitation. - Graphical abstract: The PL properties of Eu{sup 3+} and Tb{sup 3+} are studied in Na{sub 3}Ln(BO{sub 3}){sub 2} (Ln=Y, Gd) borates. Eu{sup 3+} and Tb{sup 3+}exhibits higher emission intensity in Na{sub 3}Gd(BO{sub 3}){sub 2} compared to Na{sub 3}Y(BO{sub 3}){sub 2} due to the less regular environment of the Gd{sup 3+} ion. Energy transfer from Gd{sup 3+} to Tb{sup 3+} is observed. Highlights: Black-Right-Pointing-Pointer Crystal structure of Na{sub 3}Gd(BO{sub 3}){sub 2} by X-ray powder diffraction. Black-Right-Pointing-Pointer Photoluminescence properties of Eu{sup 3+} and Tb{sup 3+} doped Na{sub 3}Ln(BO{sub 3}){sub 2} (Ln=Y, Gd). Black-Right-Pointing-Pointer Higher Eu{sup 3+} and Tb{sup 3+} emission for Na{sub 3}Gd(BO{sub 3}){sub 2} due to an irregular environment of Gd{sup 3+}. Black-Right-Pointing-Pointer Higher Eu{sup 3+} and Tb{sup 3+} emission for Na{sub 3}Gd(BO{sub 3}){sub 2} due to energy transfer from Gd{sup 3+}. Black-Right-Pointing-Pointer Lower Tb{sup 3+} critical concentration for Na{sub 3}Gd(BO{sub 3}){sub 2} due to short Gd{sup 3+}-Gd{sup 3+} distances.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Structural and electrical properties of the sol-gel prepared Sr{sub 1-x}Er{sub x}SnO{sub 3-{delta}} compounds

Erbium-substituted strontium stannates, with Er content 0{<=}x{<=}0.09, have been prepared by sol-gel method. The solubility limit of Er was found to be about 3%. The influence of temperature and the duration of the calcination, on the confirmation of single phase of Er doped SrSnO{sub 3} were investigated by using X-ray powder diffraction. The distribution of Er{sup 3+} in the crystal structure has been studied. Rietveld refinement of the data revealed that the crystal structure of the representative compound (Sr{sub 0.97}Er{sub 0.03}SnO{sub 3-{delta}}) is orthorhombic perovskite (space group Pbnm). The cell dimensions are: a=5.7152(1) A, b=5.7092(1) A and c=8.0710(2) A. The IR spectroscopy measurements of the samples with x{<=}0.03 were done in a wavelength range 400-2000 cm{sup -1} and confirmed the observed tilting in the SnO{sub 6} octahedra. The transport properties in the system Sr{sub 1-x}Er{sub x}SnO{sub 3-{delta}}, x{<=}0.03, were investigated at high temperature. The Sr{sub 0.97}Er{sub 0.03}SnO{sub 3-{delta}} compound exhibits semiconductive behaviour and the electrical transport mechanism agrees with the non-adiabatic small polaron hopping model between nominal states Sn{sup 4+}/Sn{sup 2+} in the temperature ranges 350-525 and 525-693 K separately. - Graphical abstract: The Sr{sub 0.97}Er{sub 0.03}SnO{sub 3-{delta}} compound exhibits semiconductive behaviour and the electrical transport mechanism agrees with the non-adiabatic small polaron hopping model between nominal states Sn{sup 4+}/Sn{sup 2+}. Highlights: Black-Right-Pointing-Pointer Er showed a maximum solubility of 3 mol% in SrSnO{sub 3} perovskite at 1173 K. Black-Right-Pointing-Pointer SnO{sub 6} octahedra in Sr{sub 1-x}Er{sub x}SnO{sub 3-{delta}} are tilted. Black-Right-Pointing-Pointer The expansion of the cell parameters ascribed to the apparition of Sn{sup 2+} ions. Black-Right-Pointing-Pointer Transport mechanism in Sr{sub 0.97}Er{sub 0.03}SnO{sub 3-{delta}} agrees with the non-adiabatic small polaron hopping model.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Crystal structure and non-stoichiometry of cerium brannerite: Ce{sub 0.975}Ti{sub 2}O{sub 5.95}

The crystal structure of cerium brannerite, Ce{sub 0.975}Ti{sub 2}O{sub 5.95}, was determined from Rietveld analysis of high resolution neutron powder diffraction data (space group C2/m, a=9.8320(1) A, b=3.75287(6) A, c=6.8852(1) A, {beta}=119.230(1) Degree-Sign ). The presence of both cerium and oxygen vacancies was confirmed from Rietveld analysis and defect energy calculations, combined with careful investigation of the phase diagram. Formation of oxygen vacancies at the O1 site, charge compensated by Ce vacancies, relieves considerable Coulombic repulsion and hence structural strain associated with short O1-O1 contacts forming the shared edge of neighbouring TiO{sub 6} polyhedra. Consideration of the bond valence sum of Ce{sup 4+} in Ce{sub 0.975}Ti{sub 2}O{sub 5.95} afforded a revised value of the r{sub 0}=2.098{+-}0.039 A for the reference bond length, based on analysis of 21 crystal structures mined from the ICSD. - Graphical abstract: Neutron diffraction and atomistic defect energy calculations reveal the mechanism of nonstochiometry in cerium brannerite, Ce{sub 0.975}Ti{sub 2}O{sub 5.95}. Highlights: Black-Right-Pointing-Pointer The defect brannerite Ce{sub 0.975}Ti{sub 2}O{sub 5.95} was prepared by solid state synthesis. Black-Right-Pointing-Pointer Neutron diffraction confirmed the presence of Ce vacancies charge compensated by O vacancies. Black-Right-Pointing-Pointer Defect energy calculations show oxygen vacancies relieve structural strain associated with short O-O contact distances.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Crystal structure of Sr{sub 6}Y{sub 2}Al{sub 4}O{sub 15}: XRD refinements and first-principle calculations

The ternary oxide phase Sr{sub 6}Y{sub 2}Al{sub 4}O{sub 15} (SYA) was synthesized and the crystal structure was determined by using the X-ray powder diffraction data. Structure of the phase can be considered as an oxygen-deficient perovskite Sr(Y{sub 1/3}Al{sub 2/3})O{sub 2.5} and has a monoclinic C2 (S.G. No. 5) unit cell with the unit cell parameters: a=17.597(1) A, b=5.7408(1) A, c=7.6860(1) A, {beta}=90.7659(3) Degree-Sign , V{sub cell}=776.37(1) A{sup 3}, Z=2. By bond parameter analysis and first-principle calculations, we confirmed the reasonability of our crystal structure model. According to the calculated band structure, SYA has an indirect band gap {approx}4.3 eV and a direct band gap {approx}4.4 eV, which is wide to be transparent to UV and visible lights. We also synthesized other rare-earth isomorphs Sr{sub 6}Ln{sub 2}Al{sub 4}O{sub 15} (Ln=Tb, Dy, Ho, Er, Tm, Yb and Lu) and obtained their cell parameters. - Graphical abstract: Sr{sub 6}Y{sub 2}Al{sub 4}O{sub 15} has a monoclinic unit cell with space group C2 (5) with unit cell parameters: a=17.597(1) A, b=5.7408(1) A, c=7.6860(1) A, {beta}=90.7659(3) Degree-Sign . Highlights: Black-Right-Pointing-Pointer Sr{sub 6}Y{sub 2}Al{sub 4}O{sub 15} (SYA) has an oxygen-deficient perovskite structure Sr(Y{sub 1/3}Al{sub 2/3})O{sub 2.5}. Black-Right-Pointing-Pointer SYA shows C2 symmetry: a=17.597(1) A, b=5.7408(1) A, c=7.6860(1) A, {beta}=90.7659(3) Degree-Sign . Black-Right-Pointing-Pointer SYA has an indirect band gap {approx}4.3 eV and a direct band gap {approx}4.4 eV.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Liquidus projection of the Ag-Ba-Ge system and melting points of clathrate type-I compounds

The liquidus and solidus projection has been constructed for the Ag-Ba-Ge system up to 33.3 at% Ba, using electron micro probe analysis (EPMA), X-ray powder diffraction (XRD) and differential thermal analysis (DSC/DTA). Eight different primary crystallization regions were found: (Ge), Ba{sub 8}Ag{sub x}Ge{sub 46-x-y}{open_square}{sub y} ({kappa}{sub I}) ({open_square} is a vacancy), Ba{sub 6}Ag{sub x}Ge{sub 25-x} ({kappa}{sub Ix}), BaGe{sub 2}, Ba(Ag{sub 1-x}Ge{sub x}){sub 2} ({tau}{sub 1}), BaAg{sub 2-x}Ge{sub 2+x} ({tau}{sub 2}) BaAg{sub 5} and (Ag). The ternary invariant reactions have been determined for the region investigated and are the basis for a Schulz-Scheil diagram. The second part of this work provides a comprehensive compilation of melting points of ternary A{sub 8}T{sub x}M{sub 46-x} and quaternary (A=Sr, Ba, Eu; T=Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga; M=Si, Ge, Sn) clathrate type-I compounds and decomposition temperatures of inverse clathrate type-I Ge{sub 38}{l_brace}P,As,Sb{r_brace}{sub 8}{l_brace}Cl,Br,I{r_brace}{sub 8}, Si{sub 46-x}P{sub x}Te{sub y} and tin based compounds. - Graphical Abstract: Partial liquidus projection of the Ag-Ba-Ge system. Highlights: Black-Right-Pointing-Pointer The liquidus and solidus projection has been constructed for the Ag-Ba-Ge system up to 33.33 at% Ba. Black-Right-Pointing-Pointer Eight different primary crystallization fields have been found. Black-Right-Pointing-Pointer All the ternary compounds form congruently from the melt. Black-Right-Pointing-Pointer The ternary invariant reactions have been determined and are the basis for a Schulz-Scheil diagram.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Structural distortions in Sr{sub 3-x}A{sub x}MO{sub 4}F (A=Ca, Ba; M=Al, Ga, In) anti-Perovskites and corresponding changes in photoluminescence

The ordered oxyfluoride family Sr{sub 3}-{sub x}A{sub x}MO{sub 4}F (A=Ca, Ba and M=Al, Ga) has formed the basis of several new inorganic phosphors, and shows great potential for use in phosphor-conversion LED lamp devices. This study examines the correlation between subtle structural changes and photoluminescent behaviour in some of these materials. In order to ascertain whether cation charge compensation has any influence on structure and subsequent photoluminescent behaviour, a comparison was carried out between phases with the nominal compositions Sr{sub 2.975}Ce{sub 0.025}AlO{sub 4}F and Sr{sub 2.95}Ce{sub 0.025}Na{sub 0.025}AlO{sub 4}F using structural characterisation based upon high-resolution neutron powder diffraction (NPD) data. Additionally, NPD data has been used to elucidate the role of different M cations in these materials, using Sr{sub 2.25}Ba{sub 0.6}Eu{sub 0.1}M{sub 0.95}In{sub 0.05}O{sub 4-{alpha}}F{sub 1-{delta}} (M=Al, Ga) to determine the effect M cation size has on structure and photoluminescent properties. - Graphical abstract: The structure of Sr3-xAxMO4F (A=Ca, Ba and M=Al, Ga) and excitation and emission spectra for Sr{sub 2.25}Ba{sub 0.6}Eu{sub 0.1}Ga{sub 0.95}In{sub 0.05}O{sub 4-{alpha}}F{sub 1-{delta}}. Highlights: Black-Right-Pointing-Pointer Correlation between structural changes and photoluminescence in Sr{sub 3-x}A{sub x}MO{sub 4}F (A=Ca, Ba, M=Al, Ga). Black-Right-Pointing-Pointer Comparison of Sr{sub 2.975}Ce{sub 0.025}AlO{sub 4}F and Sr{sub 2.95}Ce{sub 0.025}Na{sub 0.025}AlO{sub 4}F using high-resolution NPD. Black-Right-Pointing-Pointer Study of the effect of cation charge-compensation on structure and photoluminescent behaviour. Black-Right-Pointing-Pointer Examination of high-resolution NPD data for Sr{sub 2.25}Ba{sub 0.6}Eu{sub 0.1}M{sub 0.95}In{sub 0.05}O{sub 4-{alpha}}F{sub 1-{delta}} (M=Al, Ga). Black-Right-Pointing-Pointer Determination of the effect M cation size has on structure and photoluminescent properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Structural consideration on the emission properties of Eu{sup 2+}-doped Li{sub 2}BaMgP{sub 2}O{sub 8} and Na{sub 2}BaMgP{sub 2}O{sub 8} orthophosphates

Li{sub 2}BaMgP{sub 2}O{sub 8} and Na{sub 2}BaMgP{sub 2}O{sub 8} were synthesized by a standard solid state reaction. Structural analyses have revealed that Li{sub 2}BaMgP{sub 2}O{sub 8} is a member of the olgite family, as is the case with Na{sub 2}BaMgP{sub 2}O{sub 8}. The layer-framework build up by corner-sharing MgO{sub 6} octahedra and PO{sub 4} tetrahedra twists around C{sub 3} axes to match the size of B-site cation (Li{sup +} or Na{sup +}). This twisting affects the coordination number for the B-site cation and unit cell size. Eu-doped Li{sub 2}BaMgP{sub 2}O{sub 8} and Na{sub 2}BaMgP{sub 2}O{sub 8} exhibited intense violet-blue emission under ultraviolet excitation. They were characterized by two emission centers; Eu{sup 2+} ions replacing A-site cations (Ba{sup 2+}) and B-site cations (Li{sup +} or Na{sup +}). The B-site Eu{sup 2+} emission was very sensitive to the twisting behavior caused by original B-site cation. - Graphical abstract: Emission properties of Eu{sup 2+}-doped M{sup I}{sub 2}BaMgP{sub 2}O{sub 8} (M{sup I}: Li, Na) are discussed from the viewpoint of the host crystal structure solved by X-ray powder diffraction technique and Raman spectroscopy. Highlights: Black-Right-Pointing-Pointer Olgite-type Li{sub 2}BaMgP{sub 2}O{sub 8} has been prepared by a solid state reaction. Black-Right-Pointing-Pointer Crystal structure of M{sup I}{sub 2}BaMgP{sub 2}O{sub 8} changes, depending on M{sup I} ion size. Black-Right-Pointing-Pointer Eu{sup 2+}-doped M{sup I}{sub 2}BaMgP{sub 2}O{sub 8} exhibits violet-blue emission under ultraviolet irradiation. Black-Right-Pointing-Pointer Emission from M{sup I}{sub 2}BaMgP{sub 2}O{sub 8} is characterized by two Eu{sup 2+} emission centers. Black-Right-Pointing-Pointer One emission component of the two is sensitive to the structural change induced by M{sup I}.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Phase relations and crystal structures in the system Ce-Ni-Zn at 800 Degree-Sign C

Phase relations have been established for the system Ce-Ni-Zn in the isothermal section at 800 Degree-Sign C using electron microprobe analysis and X-ray powder diffraction. Phase equilibria at 800 Degree-Sign C are characterized by a large region for the liquid phase covering most of the Ce-rich part of the diagram, whereas a Zn-rich liquid is confined to a small region near the Zn-corner of the Gibbs triangle. Whereas solubility of Ce in the binary Ni-Zn phases is negligible, mutual solubilities of Ni and Zn at a constant Ce content are large at 800 Degree-Sign C for most Ce-Zn and Ce-Ni compounds. The solid solution Ce(Ni{sub 1-x}Zn{sub x}){sub 5} with the CaCu{sub 5}-type is continuous throughout the entire section and for the full temperature region from 400 to 800 Degree-Sign C. Substitution of Zn by Ni is found to stabilize the structure of CeZn{sub 11} to higher temperatures. At 800 Degree-Sign C Ce(Ni{sub x}Zn{sub 1-x}){sub 11} (0.03{<=}x{<=}0.22) appears as a ternary solution phase. Similarly, a rather extended solution forms for Ce{sub 2}(Ni{sub x}Zn{sub 1-x}){sub 17} (0{<=}x{<=}0.53). Detailed data on atom site occupation and atom parameters were derived from X-ray structure analyses for single crystals of Ce{sub 2+y}(Ni{sub x}Zn{sub 1-x}){sub 17}, y=0.02, x=0.49 (a=0.87541(3), c=1.25410(4) nm; Th{sub 2}Zn{sub 17} type with space group R3{sup Macron }m,R{sub F{sup 2}}=0.018) and Ce(Ni{sub 0.18}Zn{sub 0.82}){sub 11} (a=1.04302(2), c=0.67624(3)nm, BaCd{sub 11} type with space group I4{sub 1}/amd, R{sub F{sup 2}}=0.049). - Graphical abstract: Ce-Ni-Zn isothermal section at 800 Degree-Sign C. Highlights: Black-Right-Pointing-Pointer Phase relations were determined for the system Ce-Ni-Zn in the section at 800 Degree-Sign C. Black-Right-Pointing-Pointer A continuous solid solution Ce(Ni{sub 1-x}Zn{sub x}){sub 5}, 0{<=}x{<=}1, forms between 400 and 800 Degree-Sign C. Black-Right-Pointing-Pointer Zn/Ni substitution stabilizes the ternary phase Ce(Zn{sub 1-x}Ni{sub x}){sub 11}, 0.03{<=}x{<=}0.22, 800 Degree-Sign C. Black-Right-Pointing-Pointer An extended solution forms for Ce{sub 2}(Ni{sub x}Zn{sub 1-x}){sub 17} (0{<=}x{<=}0.53). Black-Right-Pointing-Pointer Crystal data are given: Ce{sub 2+y}(Ni{sub x}Zn{sub 1-x}){sub 17} (Th{sub 2}Zn{sub 17}), Ce(Ni{sub 0.18}Zn{sub 0.82}){sub 11} (BaCd{sub 11}).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Bi-antimony capped Keggin polyoxometalate modified with Cu-ligand fragment

Three polyoxometalates consisting of bi-antimony capped Keggin-type clusters: [Cu(mbpy){sub 2}]{sub 2}[PMo{sub 12}O{sub 40}Sb{sub 2}]{center_dot}4H{sub 2}O (1), [Cu(mbpy){sub 2}][PMo{sub 12}O{sub 40}Sb{sub 2}] (2) and {l_brace}Cu(mbpy)[Cu(mbpy){sub 2}]{sub 2}{r_brace}[VMo{sub 8}V{sub 4}O{sub 40}Sb{sub 2}]{center_dot}2H{sub 2}O (3) (mbpy=4,4 Prime -dimethyl-2,2 Prime - dipyridyl in 1 and 2; 5,5 Prime -dimethyl-2,2 Prime -dipyridyl in 3) have been synthesized and characterized by IR, X-ray powder diffraction, TG analysis and electrochemical property. Single-crystal analysis revealed that all of three compounds are built upon bi-antimony capped Keggin-type polyoxoanions and Cu-mbpy cations. In 1-3, two Sb{sup III} centers located at the two opposite of anionic surface adopt fundamentally tetragonal pyramidal coordination geometry. Both compounds 1 and 2 consist of P-centered Keggin structure, while compound 3 presents a V-centered Keggin anion. The Keggin-type anions present different structural features: isolated cluster in 1 and Cu-ligand-supported cluster in 2 and 3. - Graphical abstract: Three hybrid compounds consisting of bi-antimony capped Keggin-type clusters modified with Cu-ligand cations have been synthesized and characterized. Highlights: Black-Right-Pointing-Pointer Three hybrid compounds consisting of bi-antimony capped Keggin-type clusters have been synthesized. Black-Right-Pointing-Pointer Two Sb{sup III} centers located at the two opposite of anionic surface adopt tetragonal pyramidal coordination geometry. Black-Right-Pointing-Pointer The anions present different structural features: isolated and Cu-ligand-supported cluster.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Synthesis and crystal structures of new oxyapatites BiCa{sub 4-x}La{sub x}(VO{sub 4}){sub 3-x}(GeO{sub 4}){sub x}O, x=1-3

New germanate-vanadates with the general formula BiCa{sub 4-x}La{sub x}(VO{sub 4}){sub 3-x}(GeO{sub 4}){sub x}O, x=1-3, have been synthesized by the nitrate-citrate method and characterized. Structural refinement based on X-ray powder diffraction data showed that these compounds are isostructural with BiCa{sub 4}(VO{sub 4}){sub 3}O (space group P6{sub 3}/m (N 176), Z=2, a=9.8327-9.8755(3), and c=7.1203-7.2133(2) ). They may be viewed as continuous series of solid solutions where Ca{sup 2+} and V{sup 5+} cations in the crystal lattice of vanadate BiCa{sub 4}(VO{sub 4}){sub 3}O are replaced by La{sup 3+} and Ge{sup 4+} cations. In the process of substitution, the La{sup 3+} cations occupy mainly the 4f lattice sites of the germanate-vanadate oxyapatites, but the filling of the 4f and 6h lattice sites in the germanate BiCaLa{sub 3}(GeO{sub 4}){sub 3} is equivalent. IR and Raman spectra were studied. The Raman spectra clearly show a two-mode behavior: the lines of GeO{sub 4} and VO{sub 4} are separated from each other, and the (V/Ge)O{sub 4} tetrahedra exhibit a quasi-independent behavior. - Graphical abstract: Schematic drawing of the BiCa{sub 3}La(VO{sub 4}){sub 2}(GeO{sub 4})O structure in projection on the ac plane. Green-V and Ge, red-Ca(1) and La(1), yellow-Ca(2), La(2) and Bi, dark-blue-O(1)-O(4), blue-O(5). Highlights: Black-Right-Pointing-Pointer The citrate synthesis of germanate-vanadate oxyapatites. Black-Right-Pointing-Pointer The synthesized compounds crystallize in the hexagonal symmetry. Black-Right-Pointing-Pointer A single series of solid solutions BiCa{sub 4-x}La{sub x}(VO{sub 4}){sub 3-x}(GeO{sub 4}){sub x}O, (x=0-3). Black-Right-Pointing-Pointer IR an Raman spectra of mixed crystals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Preparation, crystal structure and thermal expansion of a novel layered borate, Ba{sub 2}Bi{sub 3}B{sub 25}O{sub 44}

Single crystals of a new compound, Ba{sub 2}Bi{sub 3}B{sub 25}O{sub 44}, were grown by cooling a melt of non-stoichiometric composition. The crystal structure was solved by direct methods and refined to R=0.030 (wR=0.090). The compound is trigonal, R3{sup Macron }m, a=7.851(2), c=46.20(1) A, V=2466.6(6) A{sup 3}, Z=3. The structure is based upon a borate layered anion of the type not previously observed in inorganic compounds. The layer consists of three sublayers; it is {approx}13 A thick and oriented parallel to (001). Two of the sublayers are built from triborate groups, [B{sub 3}O{sub 8}]{sup 7-}, whereas the central sublayer consists of triborate groups, [B{sub 3}O{sub 6}]{sup 3-}. The interlayer space is occupied by the Bi{sup 3+} ions in octahedral coordination. The Ba{sup 2+} cations are located in the cavities within borate layer. The single-phase polycrystalline sample of Ba{sub 2}Bi{sub 3}B{sub 25}O{sub 44} prepared by solid-state reactions from a stoichiometric mixture has been investigated by high-temperature X-ray powder diffraction in air. Anisotropic character of the thermal expansion is not typical for layered structures: {alpha}{sub a}=12, {alpha}{sub c}=6, {alpha}{sub V}=30 Multiplication-Sign 10{sup -6} Degree-Sign S{sup -1} at 25 Degree-Sign S; anisotropy increases on heating: {alpha}{sub a}=12, {alpha}{sub c}=0, {alpha}{sub V}=24 Multiplication-Sign 10{sup -6} Degree-Sign S{sup -1} at 700 Degree-Sign S. - Graphical abstract: Correlation between the pole figure of the thermal expansion coefficients and the structure of Ba{sub 2}Bi{sub 3}B{sub 25}O{sub 44} projected onto ac plane. The pole figures are presented for room temperature and 700 Degree-Sign C. Highlights: Black-Right-Pointing-Pointer A novel borate Ba{sub 2}Bi{sub 3}B{sub 25}O{sub 44} has been synthesized by cooling a non-stoichiometric melt. Black-Right-Pointing-Pointer The crystal structure is based upon a novel borate layered anion ({approx}13 A thick). Black-Right-Pointing-Pointer Anisotropy of thermal expansion increases on heating. Black-Right-Pointing-Pointer Anisotropy dictated by the orientation of triborate groups.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Structural investigation and luminescence of nanocrystalline lanthanide doped NaNbO{sub 3} and Na{sub 0.5}K{sub 0.5}NbO{sub 3}

Nd{sup 3+} and Eu{sup 3+} doped NaNbO{sub 3} and Na{sub 0.5}K{sub 0.5}NbO{sub 3} nanostructured multiferroics (nanoparticles or nanorods) were prepared by a sol-gel route. X-Ray powder diffraction results evidence that the sodium and mixed sodium-potassium niobates show orthorhombic (Pmc2{sub 1} space group), and monoclinic structure (Pm space group), respectively, confirmed by the Raman spectra. The local structure around the trivalent lanthanides was investigated with Extended X-ray Absorption Fine Structure spectroscopy at the Ln-K edge and luminescence spectroscopy. The Ln{sup 3+} ions enter the structure by substituting the alkali metals, with a 12-fold oxygen coordination, and inducing a large amount of static disorder. The visible emission bands of the Eu{sup 3+} ions indicate that multiple sites exist for the lanthanide ions, in agreement with the EXAFS results showing the largest amount of static disorder in these samples. A possible indication of clustering of oxygen vacancies around the Ln{sub Na} Double-Prime defect is obtained by VBS calculations. - Graphical Abstract: Ln{sup 3+} doped NaNbO{sub 3} and Na{sub 0.5}K{sub 0.5}NbO{sub 3} nanoparticles or nanorods can be prepared by a simple sol-gel procedure. The synergy of X-ray diffraction, EXAFS and luminescence spectroscopy gives important information on the Ln{sup 3+} local environment. Highlights: Black-Right-Pointing-Pointer Nd{sup 3+} and Eu{sup 3+} doped NaNbO{sub 3} and Na{sub 0.5}K{sub 0.5}NbO{sub 3} nanoparticles or nanorods are prepared by sol-gel. Black-Right-Pointing-Pointer EXAFS indicates that the Ln{sup 3+} ions substitutes the Na{sup +} and K{sup +} ions, inducing a large amount of static disorder. Black-Right-Pointing-Pointer The visible emission bands of the Eu{sup 3+} ions confirm that multiple sites exist for the lanthanide ions.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Rietveld refinement and ionic conductivity of Ca{sub 8.4}Bi{sub 1.6}(PO{sub 4}){sub 6}O{sub 1.8}

The structure of Ca{sub 8.4}Bi{sub 1.6}(PO{sub 4}){sub 6}O{sub 1.8}, isostructural with Fluoroapatite, was determined by X-ray powder diffraction methods. The results of Rietveld refinement revealed that the formula of this compound is [Ca{sub 4}]{sup 4f}[Ca{sub 4.4}Bi{sub 1.6}]{sup 6h}(PO{sub 4}){sub 6}[O{sub 1.8}]{sup 2a}, space group P63/m (a=9.468 (3) A, c=6.957 (3) A). A total substitution of Bi{sup 3+} ions in the (6h) sites was related particularly to the high polarizability of the Bi{sup 3+} ion compared to Ca{sup 2+}. The observed frequencies in the Raman and infrared spectra were explained and discussed on the basis of unit-cell group analyses and in comparison with Fluoroapatite and other oxyapatites. The ionic conductivity over a wide range of temperature was investigated according to the complex impedance method. The highest overall conductivity values were found at {sigma}{sub 700 Degree-Sign C} =5.03 Multiplication-Sign 10{sup -7} S cm{sup -1} and E{sub a}=0.50 eV. - Graphical abstract: The final Rietveld refinement plot of the Ca{sub 8.4}Bi{sub 1.6} (PO{sub 4}){sub 6}O{sub 1.8}. Highlights: Black-Right-Pointing-Pointer The Rietveld refinement revealed that the formula of this compound is Ca{sub 8.4}Bi{sub 1.6}(PO{sub 4}){sub 6}O{sub 1.8}. Black-Right-Pointing-Pointer Vibrational spectroscopy supports the high symmetry P63/m space group for this apatite. Black-Right-Pointing-Pointer This apatite contained channels where oxygen ions were located in 2a sites. Black-Right-Pointing-Pointer The possibility of anionic conduction along these channels was considered.

36 MATERIALS SCIENCE↗