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At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

On AgRhO{sub 2}, and the new quaternary delafossites AgLi{sub 1/3}M{sub 2/3}O{sub 2}, syntheses and analyses of real structures

Two new quaternary delafossite type oxides with the general formula Ag(Li{sub 1/3}M{sub 2/3})O{sub 2}, M=Rh, Ir, have been synthesized, and their structures characterized. Based on X-ray and electron diffraction analyses the structural similarity with AgRhO{sub 2} delafossite, has been evidenced. The real structures of the quaternary delafossites have been revealed, which has allowed to fully explain the diffuse scattering as observed in X-ray powder diffraction. AgRhO{sub 2} is thermally stable up to 1173 K, the behavior of the two quaternary compounds AgLi{sub 1/3}Rh{sub 2/3}O{sub 2} and AgLi{sub 1/3}Ir{sub 2/3}O{sub 2} is comparable, and they decompose above 950 and 800 K, respectively. AgRhO{sub 2} shows temperature independent paramagnetism, while for the other two an effective magnetic moment of 1.77{mu}{sub B} for Ir, and 1.70{mu}{sub B} for Rh were determined, applying the Curie-Weiss law. All compounds are semiconducting with activation energies of 4.97 kJ mol{sup -1} (AgLi{sub 1/3}Rh{sub 2/3}O{sub 2}), 11.42 kJ mol{sup -1} (AgLi{sub 1/3}Ir{sub 2/3}O{sub 2}) and 17.58 kJ mol{sup -1} (AgRhO{sub 2}). -- graphical abstract: Two new quaternary delafossite type oxides with the general formula Ag(Li{sub 1/3}M{sub 2/3})O{sub 2}, M=Rh, Ir, have been synthesized, and their structures characterized. The real structures of the quaternary delafossites have been revealed, which has allowed to fully explain the diffuse scattering as observed in X-ray powder diffraction. Display Omitted Highlights: {yields}Analysis of the real structures of the Ag(Li{sub 1/3}Rh{sub 2/3})O{sub 2} and Ag(Li{sub 1/3}Ir{sub 2/3})O{sub 2}. {yields} Diffuse scattering has been rationalized by severe disorder in the stacking sequences. {yields} The oxygen atom layer stacking sequence needs to change.

36 MATERIALS SCIENCE↗
DOE OSTI2012

A novel approach for enhanced visible light activity in doped nanosize titanium dioxide through the excitons trapping

Titanium dioxide doped with iron oxide (0-10 mol%) has been synthesized by an aqueous sol-gel method. The extent of phase transformation is higher in presence of up to 1 mol% of Fe{sup 3+} ions in doped titania. A further increase in Fe{sup 3+} content was found to decrease the phase transformation. A composition which contains {approx}90% rutile and the remaining anatase phase shows the highest photocatalytic activity. Even though surface area values are dramatically decreased by the modification of TiO{sub 2} by Fe{sup 3+} doping, crystallinity plays a major role in photocatalytic activity enhancement. UV-vis reflectance spectra indicate a red-shift in band gap energy and thus an enhanced photoactivity in visible light, suitable for application in photodegradation of toxic industrial effluents as well as other organic contaminants, is achieved. Low concentrations of Fe{sup 3+} ions act as excitons trapping centers, while higher concentrations act as recombination centers. The synergy between the rutile-anatase ratios and optimum amount of Fe{sup 3+} ions improve the interfacial charge transfer and trapping which enhanced the photochemical degradation of MB dye. The Fe{sup 3+} doped TiO{sub 2} composition has the highest photoactivity, having an apparent rate constant of 11.1 Multiplication-Sign 10{sup -3} min{sup -1}, which is much higher than that of commercial P25 Degussa titania (6.03 Multiplication-Sign 10{sup -3} min{sup -1}). - Graphical abstract: Model explaining the transfer and trapping of e{sup -}/h{sup +} pairs in mixed phase titania by Fe{sup 3+} ions suggests the reason for the increased lifetime of e{sup -}/h{sup +} pairs and enhanced photocatalytic activity. Highlights: Black-Right-Pointing-Pointer An aqueous sol-gel method for the preparation of doped TiO{sub 2} is being reported. Black-Right-Pointing-Pointer High photocatalytic activity and simplicity are the novelty of this work. Black-Right-Pointing-Pointer Enhanced activity is explained by the mechanism of trapping of charges.

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

Substitutions into the trigonal bipyramidal site of InGaCuO{sub 4}

Solid solutions of InMCu{sub 1-x}Mg{sub x}O{sub 4} (M=Ga{sup 3+}, Al{sup 3+}) have been synthesized to understand the influence of the trigonal bipyramidal (TBP) crystallographic M{sup 3+}/Cu{sup 2+} site of the YbFe{sub 2}O{sub 4}-type structure through powder X-ray and neutron diffraction, dielectric and magnetism measurements. The addition of Mg{sup 2+} in the InGaCuO{sub 4} lattice results in a decrease of the dielectric constant, but the dielectric loss is not affected until the concentration of Mg{sup 2+} is above x=0.50. The shift in the diffraction peaks, and subsequently the change in the lattice parameters, cannot be exclusively explained by the change in ionic radii. These results show the first observation of the reduction in axial bond lengths for TBP Cu{sup 2+} in a YbFe{sub 2}O{sub 4}-type crystal lattice. - Graphical abstract: Solid solutions of InMCu{sub 1-x}Mg{sub x}O{sub 4} (M=Ga{sup 3+}, Al{sup 3+}) have been synthesized and analyzed with powder X-ray and neutron diffraction, dielectric and magnetism measurements. A shift in the lattice parameters that cannot be explained by the change in ionic radii is addressed through a study of the trigonal bipyramidal site. Highlights: Black-Right-Pointing-Pointer Solid solutions of InMCu{sub 1-x}Mg{sub x}O{sub 4} (M=Ga{sup 3+}, Al{sup 3+}) have been synthesized. Black-Right-Pointing-Pointer The observed dielectric properties decreased with the dilution of Cu{sup 2+}. Black-Right-Pointing-Pointer Antiferromagnetic interactions, without ordering, were observed in InGaCu{sub 1-x}Mg{sub x}O{sub 4}. Black-Right-Pointing-Pointer A reduction in the axial TBP bond lengths produced a large change in the c/a ratio. Black-Right-Pointing-Pointer Orbital overlap across the TBP layers greatly affected the observed properties.

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

Structural variation and optical properties of ZnO-LiGaO{sub 2} pseudo-binary system

The structural variation in the x(LiGaO{sub 2}){sub 1/2}(1-x)ZnO alloy system was studied by powder XRD, TEM-SAD and Raman spectroscopy. It was elucidated that the phase varied upon increasing the alloying level was the wurtzite-type for 0{<=}x<0.2, the Zn{sub 2}LiGaO{sub 4}-type for 0.2{<=}x{<=}0.5 and the {beta}-LiGaO{sub 2}-type for 0.8{<=}x{<=}1, and the 0.5<x<0.8 region was the immiscible region of ZnO with LiGaO{sub 2}. The solubility limit of LiGaO{sub 2} in ZnO was explained by the c{sub 0}/a{sub 0} ratio based on the fact that there is no binary wurtzite phase for a c{sub 0}/a{sub 0} less than 1.6. The optical phonons of wurtzite and its derived phase were simply explained by the lattice shrinkage and reduced mass upon reduction the alloying of ZnO with LiGaO{sub 2}. The bowing parameter of the optical band gap of y(Zn{sub 2}LiGaO{sub 4}){sub 1/4}(1-y)ZnO was determined to be 0.67 eV. The value was very low, and it was related to the small lattice and chemical mismatches between the Zn{sub 2}LiGaO{sub 4} and ZnO. - Graphical abstract: The structure of ZnO varied upon alloying with LiGaO{sub 2}. Highlights: Black-Right-Pointing-Pointer We studied structural variation in the x(LiGaO{sub 2}){sub 1/2}(1-x)ZnO alloy system. Black-Right-Pointing-Pointer The wurtzite- and its related Zn{sub 2}LiGaO{sub 4}-type phase appeared for 0{<=}x{<=}0.5. Black-Right-Pointing-Pointer The solubility limit of LiGaO{sub 2} in ZnO was related to the wurtzite c{sub 0}/a{sub 0} ratio. Black-Right-Pointing-Pointer The energy band gap of ZnO was widened up to 4.04 keV by the alloying with LiGaO{sub 2}. Black-Right-Pointing-Pointer The bowing parameter of y(Zn{sub 2}LiGaO{sub 4}){sub 1/4}(1-y)ZnO was determined to be 0.67 eV.

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

Tetragonal YBaFe{sub 4}O{sub 7.0}: A stoichiometric polymorph of the '114' ferrite family

The exploration of the phase diagram of the ferrite YBaFe{sub 4}O{sub 7+{delta}} versus the oxygen content {delta} and temperature shows the complex crystal chemistry of this system. Besides the cubic form (F4 Macron 3m), which is observed up to 600 Degree-Sign C and for 0<{delta}{<=}0.65, a stoichiometric tetragonal form ({delta}=0) is isolated below 300 Degree-Sign C that is stable only in the absence of oxidizing atmosphere. The resolution of the structure of this new YBaFe{sub 4}O{sub 7.0} form, from combined neutron and synchrotron data, in the space group I4 Macron , shows significant displacements of the atoms with respect to the cubic form, especially concerning the oxygen atoms surrounding the barium cations. The decrease of several Ba-O distances around the underbonded barium cations is explained by the existence of hybridized Ba{sup (2-{delta})+}-O{sup 2-}-Fe{sup (2+{delta})+} bonds, in agreement with Moessbauer spectroscopy. The role of coulombic repulsions in the [Fe{sub 4}O] and [Fe{sub 4}] tetrahedra of the [Fe{sub 4}]{sub {infinity}} sublattice on the structural transition is also discussed. - Graphical abstract: A new form of YBaFe{sub 4}O{sub 7} '114' ferrite which is only stable in oxygen free atmosphere, even at room temperature has been prepared. This new ferrite has its structure closely related to the cubic form YBaFe{sub 4}O{sub 7+{delta}} but differently from the latter which is stable for 0<{delta}<0.65, it requires a rigorous oxygen 'O{sub 7}' stoichiometry, i.e., {delta}=0. We describe herein the phase diagram of the oxides YBaFe{sub 4}O{sub 7+{delta}} and we determine the structure of this new YBaFe{sub 4}O{sub 7.0} form, from combined neutron and synchrotron data. Highlights: Black-Right-Pointing-Pointer Oxygen stoichiometry control in '114' YBaFe{sub 4}O{sub 7+d} ferrites. Black-Right-Pointing-Pointer A new structural transition leading to a new form of YBaFe{sub 4}O{sub 7+d} '114' ferrite for d=0. Black-Right-Pointing-Pointer Structural resolution from combined neutron and synchrotron data. Black-Right-Pointing-Pointer Phase diagram of the oxides YBaFe{sub 4}O{sub 7+d}.

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

Characterization of zirconium carbides using electron microscopy, optical anisotropy, Auger depth profiles, X-ray diffraction, and electron density calculated by charge flipping method

Samples with five different zirconium carbide compositions (C/Zr molar ratio=0.84, 0.89, 0.95, 1.05, and 1.17) have been fabricated and studied using a variety of experimental techniques. Each sample was zone refined to ensure that the end product was polycrystalline with a grain size of 10-100 {mu}m. It was found that the lattice parameter was largest for the x=0.89 composition and smallest for the x=1.17 total C/Zr composition, but was not linear; this nonlinearity is possibly explained using electron densities calculated using charge flipping technique. Among the five samples, the unit cell of the ZrC{sub 0.89} sample showed the highest electron density, corresponding to the highest carbon incorporation and the largest lattice parameter. The ZrC{sub 0.84} sample showed the lowest carbon incorporation, resulting in a larger number of carbon vacancies and resultant strain. Samples with larger carbon ratios (x=0.95, 1.05, and 1.17) showed a slight decrease in lattice parameter, due to a decrease in electron density. Optical anisotropy measurements suggest that these three samples contained significant amounts of a graphitic carbon phase, not bonded to the Zr atoms. - Graphical abstract: Characterization of zirconium carbides using electron microscopy, optical anisotropy, Auger depth profiles, X-ray diffraction, and electron density calculated by the charge flipping method. Highlights: Black-Right-Pointing-Pointer The lattice parameter variation: ZrC{sub 0.89}>ZrC{sub 0.84}>ZrC{sub 0.95}>ZrC{sub 1.05}>ZrC{sub 1.17}. Black-Right-Pointing-Pointer Surface oxygen with no correlation to the lattice parameter variation. Black-Right-Pointing-Pointer ZrC{sub 0.89} had highest electron densities correspond to highest carbon incorporation. Black-Right-Pointing-Pointer Second highest lattice parameter in ZrC{sub 0.84} due to strain. Black-Right-Pointing-Pointer Unit cell electron density order: ZrC{sub 0.95}>ZrC{sub 1.05}>ZrC{sub 1.17}.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Local structures of Sr{sub 2}FeMnO{sub 5+y} (y=0, 0.5) and Sr{sub 2}Fe{sub 1.5}Cr{sub 0.5}O{sub 5} from reverse Monte Carlo modeling of pair distribution function data and implications for magnetic order

The local structures of the oxygen deficient perovskites Sr{sub 2}FeMnO{sub 5}, Sr{sub 2}FeMnO{sub 5.5}, and Sr{sub 2}Fe{sub 1.5}Cr{sub 0.5}O{sub 5} have been analyzed using neutron pair distribution function data. The results show that locally all three structures are more complex than implied by their average cubic structures and that the distributions of oxygen vacancies are not completely random on a local level. For both Sr{sub 2}FeMnO{sub 5+y} compounds it is found that there is no short range ordering of the Fe and Mn cations. For Sr{sub 2}Fe{sub 1.5}Cr{sub 0.5}O{sub 5} there is evidence to suggest that the Fe/Cr distribution is not completely random and is locally ordered such that there are fewer Fe--Fe nearest neighbor pairs than in a random distribution. Reverse Monte Carlo modeling of the pair distribution function data has provided the Fe--O, Mn--O, and Cr--O bond length distributions and information on the coordination numbers of the Fe, Mn, and Cr cations. In Sr{sub 2}FeMnO{sub 5} it is found that the Fe{sup 3+} cations are most often in 4-fold coordination but there is also a large amount of Fe{sup 3+} in 5-fold coordination and a small amount in 6-fold coordination. The Mn{sup 3+} is split between 5-fold and 6-fold coordination. The Mn--O bond length distributions indicate that the Mn{sup 3+}O{sub 6} octahedra and Mn{sup 3+}O{sub 5} square pyramids are locally Jahn-Teller distorted. In Sr{sub 2}FeMnO{sub 5.5} the Fe{sup 3+} is almost entirely 5 coordinate while the Mn{sup 4+} is almost entirely 6 coordinate. The Cr{sup 3+} in Sr{sub 2}Fe{sub 1.5}Cr{sub 0.5}O{sub 5} is almost entirely 6-fold coordinated, giving the Fe{sup 3+} an average coordination number of 4.67. In Sr{sub 2}FeMnO{sub 5} and Sr{sub 2}Fe{sub 1.5}Cr{sub 0.5}O{sub 5} the Fe{sup 3+} and Sr{sup 2+} cations undergo local displacements which are driven by the oxygen vacancies, while the Mn{sup 3+} and Cr{sup 3+} cations remain near their positions in the average structures. In Sr{sub 2}FeMnO{sub 5.5} these cations are not significantly displaced. The local coordination geometries are used to explain previously observed but yet poorly understood magnetic properties of these materials. - Graphical abstract: The actual bond angle distributions in the cubic perovskite Sr{sub 2}FeMnO{sub 5} obtained from reverse Monte Carlo modeling of the local structure using neutron pair distribution function data. Highlights: Black-Right-Pointing-Pointer No long range ordering of oxygen vacancies, but short range order is present. Black-Right-Pointing-Pointer No short range Fe/Mn order but short range Fe/Cr order is present. Black-Right-Pointing-Pointer Fe tends to have lower coordination numbers while Mn and Cr have higher ones. Black-Right-Pointing-Pointer Local bond distances and bond angles have been determined. Black-Right-Pointing-Pointer Local structures can help explain long range magnetic ordering behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Effect of cation ordering on the electronic and lattice dynamic properties of Ag₂CdGeS₄ polytypes: First-principle calculation

The electronic and lattice dynamic properties of I₂–II–IV–VI₄ quaternary diamond-like semiconductors have a tight connection with their application in the area of solar cell absorption, thermoelectric conversion and so on. Structural configuration of these compounds is focused in present study, although previous researches always pay close attention to compositional modulation. In this paper, Ag₂CdGeS₄ polytypes (two types of Pna2₁, one type of Pmn2₁) have chosen as the representation to establish the relationship between cation ordering and physiochemical properties based on first-principle theory. The results show that cation arrangement practically affects their electronic and lattice dynamic properties such as bonding strength, band structure as well as their infrared spectrum. Due to different cation arrangement, two types (named model S and model P) of the same space group Pna2₁ demonstrate different properties. For both model P and Pmn2₁ of different space group, their related properties are alike because of similar cation arrangement. With the resulting cationic Born effective charges, the origin of the difference in electronic properties for three types of Ag₂CdGeS₄ can be reasonably explained from the viewpoint of vibrational polarization. - Graphical abstract: First-principle calculations were used to investigate the effect of cation ordering on the electronic and lattice dynamic properties of Ag₂CdGeS₄ polytypes. Highlights: • Structural configuration was focused other than compositional modulation. • Establish the relationship between cation ordering and physicochemical properties. • Explain the reason of different band gap with Born effective charges. • Calculated infrared spectrum can be used to distinguish different polytypes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Magnetocrystalline interactions and oxidation state determination of Mn{sub (2−x)}V{sub (1+x)}O{sub 4} (x=0, 1/3 and 1) magnetorresistive spinel family

Oxidation states of transition metal cations in spinels-type oxides are sometimes extremely difficult to determine by conventional spectroscopic methods. One of the most complex cases occurs when there are different cations, each one with several possible oxidation states, as in the case of the magnetoresistant Mn{sub (2−x)}V{sub (1+x)}O{sub 4} (x=0, 1/3 and 1) spinel-type family. In this contribution we describe the determination of the oxidation state of manganese and vanadium in Mn{sub (2−x)}V{sub (1+x)}O{sub 4} (x=0, 1/3,1) spinel-type compounds by analyzing XANES and high-resolution Kβ X-ray fluorescence spectra. The ionic models found are Mn{sup 2+}{sub 2}V{sup 4+}O{sub 4}, Mn{sup 2+}{sub 5/3}V{sup 3.5+}{sub 4/3}O{sub 4} and Mn{sup 2+}V{sup 3+}{sub 2}O{sub 4}. Combination of the present results with previous data provided a reliable cation distribution model. For these spinels, single magnetic electron paramagnetic resonance (EPR) lines are observed at 480 K showing the interaction among the different magnetic ions. The analysis of the EPR parameters show that g-values and relative intensities are highly influenced by the concentration and the high-spin state of Mn{sup 2+}. EPR broadening linewidth is explained in terms of the bottleneck effect, which is due to the presence of the fast relaxing V{sup 3+} ion instead of the weak Mn{sup 2+} (S state) coupled to the lattice. The EPR results, at high temperature, are well explained assuming the oxidation states of the magnetic ions obtained by the other spectroscopic techniques. - Graphical abstract: View of the crystallographic structure of a spinel. It shows as an example one of the models of ion distribution determined for the spinels Mn{sub (2−x)}V{sub (1+x)}O{sub 4} (x=0, 1/3,1). Display Omitted - Highlights: • Determination of oxidation state of the metallic ions in Mn{sub (2−x)}V{sub (1+x)}O{sub 4} (x=0,1/3,1) by XAS and XES techniques. • The ionic models found are Mn{sup 2+}{sub 2}V{sup 4+}O{sub 4}, Mn{sup 2+}{sub 5/3}V{sup 3.5+}{sub 4/3}O{sub 4} and Mn{sup 2+}V{sup 3+}O{sub 4}. • EPR spectra correspond almost exclusively to a resonance of Mn{sup 2+}.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Fabrication of p-type porous silicon nanowire with oxidized silicon substrate through one-step MACE

In this paper, the simple pre-oxidization process is firstly used to treat the starting silicon wafer, and then MPSiNWs are successfully fabricated from the moderately doped wafer by one-step MACE technology in HF/AgNO{sub 3} system. The PL spectrum of MPSiNWs obtained from the oxidized silicon wafers show a large blue-shift, which can be attributed to the deep Q. C. effect induced by numerous mesoporous structures. The effects of HF and AgNO{sub 3} concentration on formation of SiNWs were carefully investigated. The results indicate that the higher HF concentration is favorable to the growth of SiNWs, and the density of SiNWs is significantly reduced when Ag{sup +} ions concentrations are too high. The deposition behaviors of Ag{sup +} ions on oxidized and unoxidized silicon surface were studied. According to the experimental results, a model was proposed to explain the formation mechanism of porous SiNWs by etching the oxidized starting silicon. - Graphical abstract: Schematic cross-sectional views of PSiNWs array formation by etching oxidized silicon wafer in HF/AgNO{sub 3} solution. (A) At the starting point; (B) during the etching process; and (C) after Ag dendrites remove. - Highlights: • Prior to etching, a simple pre-oxidation is firstly used to treat silicon substrate. • The medially doped p-type MPSiNWs are prepared by one-step MACE. • Deposition behaviors of Ag{sup +} ions on oxidized and unoxidized silicon are studied. • A model is finally proposed to explain the formation mechanism of PSiNWs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Synthesis and characterisation of In-doped MnWO{sub 4}-type solid-solutions: Mn{sub 1−3x}In{sub 2x}□{sub x}WO{sub 4} (x=0–0.11)

Substitution of In{sup 3+} for Mn{sup 2+} in MnWO{sub 4}, which is one of the most studied multiferroics, was conducted systematically by solid-state reactions at 1050 °C to obtain a series of Mn{sub (1−3x)}In{sub 2x}□{sub x}WO{sub 4} solid solutions (x=0–0.11; the box indicates vacancy). The successful In-doping could be proven by electron microprobe, and statically disordered structures of this solid solution series were elucidated by Rietveld analyses with X-Ray powder diffraction (XPD) data. Its average structure maintains the space group P2/c at least up to the replacement of 33 at% Mn. The tendency of their unit cells proportionally enlarging with In-doping is an unexpected observation because In{sup 3+} is smaller than Mn{sup 2+}. This could not be explained alone by average atomic bonding distances and angles evaluated from XPD data analyses. Complimentarily, micro-Raman spectra of Mn{sub (1−3x)}In{sub 2x}□{sub x}WO{sub 4} materials feature a hardening of Raman modes due to stronger atomic bonds in W{sub 2}O{sub 4} and WO{sub 2} units with increasing In-doping. This is considered as an inevitable consequence of broken bonding in directly neighbouring Mn–O bonds as the presence of In{sup 3+} in MnWO{sub 4} accompanies the creation of defects at Mn sites. The current study using XRD and micro-Raman suggests the enlarging local space around the bridging oxygen as the reason for the unexpected cell expansion when smaller In{sup 3+} along with defects replace Mn{sup 2+} in MnWO{sub 4}. - Graphical abstract: Despite of substitution of smaller In{sup 3+} for larger Mn{sup 2+}, the In-rich solid solution Mn{sub 0.71(2)}In{sub 0.19(1)}□{sub 0.10}WO{sub 4} undergoes a volume expansion of 0.4% with respect to MnWO{sub 4}. This could be explained by a local space expansion of 0.13% around bridging oxygen at O2 sites, as illustrated by dashed lines for clarity. - Highlights: • Investigation of Mn{sub (1−3x)}In{sub 2x}□{sub x}WO{sub 4} solid solutions (x=0–0.11). • An unexpected lattice expansion by In-doping. • Strong change in local environment around bridging oxygens. • Enhancement of atomic bonds in W{sub 2}O{sub 4} and WO{sub 2} units with increasing In-doping.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Luminescent lanthanide coordination polymers synthesized via in-situ hydrolysis of dimethyl-3,4-furandicarboxylate

Dimethyl-3,4-furandicarboxylate undergoes hydrolysis under hydrothermal conditions with lanthanide (Ln) ions to form two-dimensional coordination polymers, [Ln(C{sub 6}H{sub 2}O{sub 5})(C{sub 6}H{sub 3}O{sub 5})(H{sub 2}O)]{sub n} (Ln=Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu). The resulting materials exhibit luminescent properties with quantum yields and lifetimes for the Eu(III) and Tb(III) compounds of 1.1±0.3% and 0.387±0.0001 ms, and 3.3±0.8% and 0.769±0.006 ms, respectively. Energy values for the singlet and triplet states were determined for dimethyl-3,4-furandicarboxylate and 3,4-furandicarboxylic acid. Excited state dynamics and structural features are examined to explicate the reported quantum yields. A series of other FDC structures is briefly presented. - Graphical abstract: A new two-dimensional coordination polymer derived from the in-situ hydrolysis of a furan dimethyl ester with lanthanide(III) ions was obtained in order to study its photophysical behavior when constructed from trivalent Eu and Tb. Quantum yields, lifetime measurements, and singlet/triplet state energies values were obtained. The nature of the material's excited state dynamics is examined and correlated to its structure in order to explain the overall luminescent efficiency of the system. - Highlights: • A new lanthanide–furandicarboxylate coordination polymer is presented. • Eu and Tb compounds display luminescent properties, albeit with low quantum yields. • Photophysical behavior explained through the compound's triplet state and structure. • Nonradiative deactivation of luminescence through high-energy oscillators was noted. • Molecular modeling of the organic moiety was conducted.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Structure of oxides prepared by decomposition of layered double Mg–Al and Ni–Al hydroxides

Abstracts: Thermal decomposition of Mg–Al and Ni–Al layered double hydroxides LDH at temperatures lower than 800 °C leads to the formation of oxides with different structures. Mg–Al oxide has a very defective structure and consists of octahedral layers as in periclase MgO and mixed octahedral–tetrahedral layers as in spinel MgAl{sub 2}O{sub 4}. Mixed Ni–Al oxide has a sandwich-like structure, consisting of a core with Al-doped NiO-like structure and some surface layers with spinel NiAl{sub 2}O{sub 4} structure epitaxial connected with the core. Suggested models were verified by simulation of X-ray diffraction patterns using DIFFaX code, as well as HRTEM, IR-, UV-spectroscopies, and XPS. - Graphical abstract: In the Mg–Al layered double hydroxide Al{sup 3+} ions migrate into interlayers during decomposition. The Mg–Al oxide represents sequence of octahedral and octahedral–tetrahedral spinel layers with vacancies. The Ni–Al oxide has a sandwich-like structure with NiO-like core and surface spinel layers as a result of migration of Al{sup 3+} ions on the surface. The models explain the presence and absence of “memory effect” for the Mg–Al and Ni–Al oxides, respectively. - Highlights: • We study products of Mg(Ni)–Al LDH decomposition by calcination at 500(400)–800 °C. • In Mg–Al/Ni–Al LDH Al ions migrate into interlayers/on the surface during decomposition. • Mg–Al oxide represents sequence of periclase- and spinel-like layers with vacancies. • Ni–Al oxide has a sandwich-like structure with NiO-like core and surface spinel layers. • The models explain the presence/absence of “memory effect” for Mg–Al/Ni–Al oxides.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

First evidence of P2{sub 1}/n to P2{sub 1}/c structural transformation in pyroxene-type LiAlGe{sub 2}O{sub 6} under high-pressure conditions

The high-pressure behavior of the pyroxene-type compound LiAlGe{sub 2}O{sub 6}, the unique representative of a P2{sub 1}/n-pyroxene, was investigated by in-situ X-ray diffraction and Raman spectroscopy on single-crystal samples hydrostatically pressurized in a diamond-anvil cell. The structure was found to undergo a first-order phase transition on compression, with a critical transition at 5.23±0.02 GPa. Together with a strong volume discontinuity of −ΔV/V{sub 0}=−4.1% the transition shows a remarkable hysteresis loop over at least 0.70 GPa pressure interval. The bulk modulus of the low- and high-pressure polymorphs corresponds to K{sub 0}=114(1) and 123(2) GPa, respectively, as described by a 2{sup nd} order Birch–Murnaghan equation of state. Based on the systematic extinctions the transition was identified as a P2{sub 1}/n-to-P2{sub 1}/c transformation. The mechanism of structural transformation was identified to be controlled by the stereochemistry of the Li atoms at the M2 site, which changes its coordination number from 5 to 6. The formation of new Li–O bonds involves the co-operative folding of Ge{sub 2}O{sub 6}-chains, which explains the anisotropy of axial elasticities and the spontaneous strain across the transformation. Simultaneously the distortion correction of AlO{sub 6} units associated with the transition further explains the preference of the P2{sub 1}/c structure under pressure. - Graphical abstract: Detail of the crystal structures of LP-LAG at 3.48 GPa (left) and HP-LAG at 4.51 GPa (right). Li on M2 are green; AlO{sub 6} octahedra (Al at M1) are orange; tetrahedra sites in LP-LAG: T1 (yellow) and T2 (blue); tetrahedra sites in HP-LAG: A-chains (yellow), B-chains (blue). - Highlights: • A new high-pressure phase transition P2{sub 1}/n–P2{sub 1}/c was found for LaAlGe{sub 2}O{sub 6}. • The transition was also followed by micro-Raman spectroscopy. • The high-pressure polymorph shows a higher bulk modulus. • The structural evolution of the two symmetries was determined.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Non-aqueous metathesis as a general approach to prepare nanodispersed materials: Case study of scheelites

A general approach to the preparation of inorganic nanoparticles is proposed, using metathesis of precursor salts in non-aqueous liquids. Nanoparticles of scheelites AMO{sub 4} (A=Ba, Sr, Ca; M=Mo, W), were obtained with a quantitative yield. Precipitations in formamide, N-methylformamide, propylene carbonate, DMSO and polyols often provide narrow particle size distributions. Advantageous morphology was explained by strong ionic association in non-aqueous solvents, leading to slow nucleation and negligible Ostwald ripening. Mean particle size below 10 nm and high specific surface areas were obtained for several Ca(Sr)Mo(W)O{sub 4} materials, making them promising for applications as adsorbents or catalysts. Zeta-potential of scheelites in aqueous suspensions showed negative values in a wide range of pH. Systematic study of optical properties demonstrated variation of optical gap in the sequences W>Mo and Ba>Sr>Ca. The observed trends were reproduced by DFT calculations. No quantum confinement effect was observed for small particles, though the surface states induce low-energy features in the optical spectra. - Graphical abstract: Scheelites AMO{sub 4} (A=Ca, Sr, Ba; M=Mo, W) were prepared in various non-aqueous liquids with high specific surface areas and narrow size distributions. The optical gap of scheelites changes in the series Ca<Sr<Ba and Mo<W. - Highlights: • Scheelites AMO{sub 4} (A=Ca, Sr, Ba; M=Mo, W) were prepared in various non-aqueous liquids. • Narrow size distributions explained by ionic association in non-aqueous media. • Nanoparticles of less than 10 nm size and highest ever specific surface areas were obtained. • Optical gap of scheelites changes in the series Ca<Sr<Ba and Mo <W.

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DOE OSTI2015

Inhibition of precipitation of carbonate apatite by trisodium citrate analysed in base of the formation of chemical complexes in growth solution

Effect of trisodium citrate on the precipitation of carbonate apatite is studied. The experimental series are performed in the solution of artificial urine. The investigations are related to infectious urinary stones formation as carbonate apatite is one of the main components of this kind of stones. To mimic a real infection in urinary tract the aqueous ammonia solution was added to the solution of artificial urine. The spectrophotometric results demonstrate that trisodium citrate increases induction time with respect to carbonate apatite formation and decreases the efficiency of carbonate apatite precipitation. The inhibitory effect of trisodium citrate on the precipitation of carbonate apatite is explained in base of chemical speciation analysis. Such an analysis demonstrates that the inhibitory effect is mainly related with the fact that trisodium citrate binds Ca{sup 2+} ions and causes the formation of CaCit{sup −} and Ca{sub 10}(PO{sub 4}){sub 6}CO{sub 3} complexes. Trisodium citrate binds Ca{sup 2+} ions in the range of pH from 6 to 9.5 for which carbonate apatite is favored to be formed. - Highlights: • Trisodium citrate (TC) increases induction time of carbonate apatite (CA) formation. • TC decreases the efficiency of CA precipitation. • The inhibitory effect of TC is explained in base of chemical speciation analysis. • The inhibitory effect is mainly related with the fact that TC binds Ca{sup 2+} ions. • TC binds Ca{sup 2+} ions in the range of pH from 6 to 9.5 for which CA is formed.

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DOE OSTI2016

Mechanical properties and negative thermal expansion of a dense rare earth formate framework

The fundamental mechanical properties of a dense metal–organic framework material, [NH{sub 2}CHNH{sub 2}][Er(HCOO){sub 4}] (1), have been studied using nanoindentation technique. The results demonstrate that the elastic moduli, hardnesses, and yield stresses on the (021)/(02−1) facets are 29.8/30.2, 1.80/1.83 and 0.93/1.01 GPa, respectively. Moreover, variable-temperature powder and single-crystal X-ray diffraction experiments reveal that framework 1 shows significant negative thermal expansion along its b axis, which can be explained by using a hinge–strut structural motif. - Graphical abstract: The structure of framework, [NH{sub 2}CHNH{sub 2}][Er(HCOO){sub 4}], and its indicatrix of thermal expansion. - Highlights: • The elastic modulus, hardness, and yield stress properties of a rare earth metal–organic framework material were studied via nanoindentation technique. • Variable-temperature powder X-ray diffraction experiments reveal that this framework shows significant negative thermal expansion along its b axis. • Based on variable-temperature single-crystal X-ray diffraction experiments, the mechanism of negative thermal expansion can be explained by a hinge–strut structural motif.

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DOE OSTI2016

A novel reduction synthesis of the graphene/Mn{sub 3}O{sub 4} nanocomposite for supercapacitors

Graphene/Mn{sub 3}O{sub 4} nanocomposite is successfully synthesized from graphene oxide (GO)/MnO{sub 2} precursor using dilute hydrazine hydrate assisted hydrothermal reaction (DAH method). X-ray photoelectron spectroscopy (XPS) and Raman characterizations confirm the decrease of oxygen-containing functional groups of GO. The results indicate that GO have been reduced to graphene to a large degree to increase the electronic conductive channels. The morphology and the phase transformation of MnO{sub 2} can be ascribed to the “dissolution-recrystallization” mechanism. Such nanocomposite, as electrode material for supercapacitor, exhibits a high specific capacitance of 326.9 F g{sup −1}, almost 4 times that of GO/MnO{sub 2} precursor (81.3 F g{sup −1}). The good cycle stability of 94.6% capacitance retention after 1000 cycles, can be explained by the firm interfacial cohesion between graphene and Mn{sub 3}O{sub 4} nanoparticle. This soft chemical DAH process could be readily extended to the preparation of other classes of hybrids. - Graphical abstract: The phase transition can be explained by the “dissolution-recrystallization” model. The GO/MnO{sub 2} precursor is reduced into graphene/Mn{sub 3}O{sub 4} by the DAH process, and the electrochemical property is dramatically enhanced. - Highlights: • Graphene/Mn{sub 3}O{sub 4} nanocomposite is firstly synthesized successfully from GO/MnO{sub 2} precursor. • The phase transformation from MnO{sub 2} to Mn{sub 3}O{sub 4} has occurred. • The specific capacitance of the graphene/Mn{sub 3}O{sub 4} (326.9 F/g) is 4 times that of GO/MnO{sub 2} precursor.

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