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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Microwave-Hydrothermal Synthesis of Y{sub 3}Fe{sub 5}O{sub 12} Nanoparticles: Sintering Temperature Effect on Structural, Magnetic and Dielectric Properties

Herein, we report a facile microwave-assisted hydrothermal method for the preparation of yttrium iron garnet (YIG, Y{sub 3}Fe{sub 5}O{sub 12})nanocrystals and realized the synergy between its structural and magnetic properties. The as-prepared powder thermal stability was characterized in detail by using thermogravimetric-differential thermal analysis (TG-DTA). The synthesized powder was microwave sintered at six different temperatures ranging from 973 to 1373 K for 60 min and characterized using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). Magnetic properties were investigated by vibrating-sample magnetometer (VSM) and ferromagnetic resonance (FMR) studies. The frequency variation of dielectric and magnetic properties was measured in the frequency range of 100 kHz–1.8 GHz. The observed magnetic and dielectric parameters such as saturation magnetization, coercivity, permeability, linewidth, dielectric constant and magnetodielectric losses are strongly affected by sintering temperature. The saturation magnetization and coercivity of YIG were found in the range 14.4–28.0 emu/g and 35–87 Oe, respectively. Furthermore, the FMR linewidth decreases from 844 to 204 Oe. This analysis undoubtedly demonstrates that the synthesis method and sintering temperature have the prominent effect on the electrical and magnetic properties of YIG and would be very useful for the garnet-based microwave device applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Spectral, Electrical, Thermoelectrical and Dielectric Properties of (Zn,Zr) Co-doped CuFe{sub 2}O{sub 4}

The effects of Zr{sup + 4} and Zn{sup + 2} substitution on the electrical, dielectric and spectral properties of non-stoichiometric Cu{sub 1−x}Zn{sub x}Zr{sub y}Fe{sub 2−y}O{sub 4+} {sub δ} and stoichiometric Cu{sub 1−x}Zn{sub x+} {sub y}Zr{sub y}Fe{sub 2−2y}O{sub 4} ferrites prepared by double sintering ceramic technique have been investigated. IR absorption spectra confirm the formion of spinel structure. On the other hand, IR spectra can give an idea about the change of molecular structure of ferrites system due to the perturbation that occurred in Fe{sup 3+}–O{sup 2−} bond by introducing Zn and Zr elements. The phase identification of nonstoichiometric (ns) and stoichiometric (s) samples was confirmed by the presence of endothermic peak from DTA curves at around 936 {sup ∘}C in agreement with X-ray diffraction and IR results. The calculated low values of activation energies for conduction are in the range that suggests the conduction is due to thermally activated mobility and the presence of hopping conduction mechanism. Thermoelectric power exhibits positive sign for most s and ns samples. The concentration of charge carrier is constant in the ferromagnetic region. It is also noted that the dielectric constant decreases with increasing Zn and Zr contents. From the above discussion the samples containing Zn and Zr elements have lower ΔB{sub pp} values with low energy loss. From the ESR analysis it can be confirmed that the addition of Zn and Zr generally decrease the power loss which is very important in the application for the manufacturing of a material which is used as a core of transformer at the microwave frequencies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Experimental Investigation of Microstructure and Phase Transitions in Ag-Cu-Zn Brazing Alloys

Microstructure and phase transitions of selected brazing alloys from the Ag-Cu-Zn ternary system were investigated. Four ternary alloys with silver content in the compositional range from 25 to 60 wt.% were studied using x-ray diffraction (XRD) and scanning electron microscopy coupled with the energy-dispersive spectroscopy (SEM–EDS). Phase transitions of the investigated alloys were measured using differential scanning calorimetry (DSC). Experimentally obtained results were compared with the results of a thermodynamic calculation of the phase equilibria according to the CALPHAD method. The experiments confirmed the optimized thermodynamic parameters for the calculations from the thermodynamic assessment in literature. Phase compositions, liquidus and solidus temperatures were confirmed by the EDS and DTA methods. Additionally, the calculated solidification paths and predicted phase transformations were in agreement with the SEM images.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Formation and Decomposition Process of the Filled Skutterudite Sm{sub y}(Fe{sub x}Ni{sub 1−x}){sub 4}Sb{sub 12} (0.40 ≤ x ≤ 1) as Revealed by Differential Thermal Analysis

Filled skutterudites are among the most promising thermoelectric materials, and the obtainment of monophasic samples is crucial for the study of their transport properties. In this work, a differential thermal analysis study was performed on samples belonging to the Sm{sub y}(Fe{sub x}Ni{sub 1-x}){sub 4}Sb{sub 12} system with the aim to determine the most proper annealing temperature to possibly obtain skutterudite monophasic samples, and to study the effect of Sm addition on the thermodynamics of the Fe-Ni-Sb system. Samples were prepared through the traditional procedure consisting in melting–quenching–annealing the starting elements. DTA analyses were carried out on annealed samples, and results were interpreted using the Fe{sub 25}Sb{sub 75}-Ni{sub 25}Sb{sub 75} pseudobinary phase diagram taken from the literature as a starting point. They reveal that 870 K is the best annealing temperature, being the formation of a liquid phase just above this point; moreover, the Sm introduction results in widening the one-phase skutterudite stability region toward both higher temperatures and higher Fe concentrations compared with the Sm-free system.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Correlation between Antimicrobial Activity and Bioactivity of Na-Mica and Na-Mica/Fluorapatite Glass and Glass-Ceramics and Their Corrosion Protection of Titanium in Simulated Body Fluid

The improvement in bioactivity of titanium (Ti) surface was achieved via coating it with Na-mica and Na-mica/fluorapatite glass and glass-ceramic using the low-cost electrophoretic deposition technique. Two compositions from pure Na-mica (M) and 80 Na-mica/20 fluorapatite glasses (MF) were prepared in the system SiO{sub 2}-Al{sub 2}O{sub 3}-MgO-MgF{sub 2}-Na{sub 2}O-B{sub 2}O{sub 3} using melting–quenching technique. Characterization of the as-prepared glasses and their counterpart glass-ceramics was studied using differential thermal analysis (DTA), x-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Fourier Transform-IR (FTIR) spectroscopy techniques. The bioactivity behavior was proved by studying the XRD, FTIR and SEM after immersing both glass and glass-ceramic samples in simulated body fluid (SBF). Both M and MF glasses and glass-ceramics showed high microhardness measurements and good antibacterial behavior. In vitro biodegradation was studied by using electrochemical corrosion behavior of the prepared glass- and glass-ceramic-coated Ti in SBF. The prepared coated Ti showed good corrosion resistance in SBF at 37 °C using potentiodynamic polarization technique, and the impedance data fitting explained the structure of the coating and the adsorption of SBF ions on the Ti surface. The MFGC provides the best corrosion-resistant coating, especially after sintering it.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Chloro-Modified Magnetic Fe{sub 3}O{sub 4}@MCM-41 Core–Shell Nanoparticles for L-Asparaginase Immobilization with Improved Catalytic Activity, Reusability, and Storage Stability

This paper describes a new support that permits to efficient immobilization of L-asparaginase (L-ASNase). For this purpose, Fe{sub 3}O{sub 4} magnetic nanoparticles were synthesized and coated by MCM-41. 3-chloropropyltrimethoxysilane (CPTMS) was used as a surface modifying agent for covalent immobilization of L-ASNase on the magnetic nanoparticles. The chemical structure; thermal, morphological, and magnetic properties; chemical composition; and zeta potential value of Fe{sub 3}O{sub 4}@MCM-41-Cl were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential thermal analysis (DTA), differential scanning calorimetry (DSC), vibrating sample magnetometer (VSM), scanning electron microscope (SEM), energy dispersive X-ray (EDX), X-ray diffraction patterns (XRD), and zeta-potential measurement. The immobilization efficiency onto Fe{sub 3}O{sub 4}@MCM-41-Cl was detected as 63%. The reusability, storage, pH, and thermal stabilities of the immobilized L-ASNase were investigated and compared to that of soluble one. The immobilized enzyme maintained 42.2% of its original activity after 18 cycles of reuse. Furthermore, it was more stable towards pH and temperature compared with soluble enzyme. The Michaelis–Menten kinetic properties of immobilized L-ASNase showed a lower V{sub max} and a similar K{sub m} compared to soluble L-ASNase. Immobilized enzyme had around 47 and 32.5% residual activity upon storage a period of 28 days at 4 and 25 °C, respectively. In conclusion, the Fe{sub 3}O{sub 4}@MCM-41-Cl@L-ASNase core–shell nanoparticles could successfully be used in industrial and medical applications.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Solubility of U(VI) in chloride solutions. II. The stable oxides/hydroxides in alkaline KCl solutions: Thermodynamic description and relevance in cementitious systems

In this study, the solubility of U(VI) is investigated from undersaturation conditions in 0.1, 0.51, 1.03, 3.31 and 4.58 m KCl–KOH solutions at pHm = 7.5–14.6 (with pH m = –log [H + ] in molal units). All experiments were performed under Ar atmosphere at T = (22 ± 2)°C. XRD, quantitative chemical analysis, SEM–EDS and TG–DTA confirm that K 2 U 2 O 7 ·1.5H 2 O(cr) is the solid phase controlling the solubility in all evaluated systems at pH m ≥ 9.5. Below this pH m and with decreasing KCl concentration, the formation of sub-stoichiometric phases with K:U < 1 is indicated by XRD and solubility data. The concentration of uranium in equilibrium with K 2 U 2 O 7 ·1.5H 2 O(cr) shows a pH-independent behaviour up to pH m ≈ 11 regardless of ionic strength, whereas an increase of the solubility with a well–defined slope of +1 (log [U] vs. pH m ) is observed at pH m ≥11. These results are consistent with the predominance of UO 2 (OH) 3 – and UO 2 (OH) 4 2- species as previously reported in the literature. The combination of solubility data obtained in the present study with K 2 U 2 O 7 ·1.5H 2 O(cr) and the U(VI) hydrolysis scheme reported in Altmaier et al. (2017) yields a solubility product of log *K° s ,0{0.5K 2 U 2 O 7 ·1.5H 2 O(cr)} = (12.0 ± 0.2). SIT ion interaction coefficients for UO 2 (OH) 3 – and UO 2 (OH) 4 2- with K + are derived based on the newly generated experimental data in dilute to concentrated KCl systems and analogy with NaCl systems. This work extends the thermodynamic database available for U(VI) and allows more accurate source term calculations in the context of nuclear waste disposal under boundary conditions where significant K concentrations may be present and redox conditions lie in the stability field of U(VI). Finally, the K 2 U 2 O 7 ·1.5H 2 O(cr) solid phase can be considered to control the solubility of U(VI) in the degradation phase I of cement and cementitious materials.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Experimental and computational studies of melting of the spinel phase in the Fe–Al–O ternary system

The melting behavior of spinel in the Fe–Al–O system at high temperatures (1500–1800 °C) was studied by a combination of experimental and computational investigations. Differential thermal analysis (DTA) at ultra-high temperatures coupled with cooling traces on CO 2 laser-heated levitated samples provided melting temperatures and the heats of fusion of (Fe,Al) 3 O 4 spinel phases. The experimental results are in fair agreement with the predictions using a published CALPHAD description and areas for modeling improvement are identified. New insights into the melting of defect spinel are provided.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Deep eutectic solvent approach towards nickel/nickel nitride nanocomposites

Nickel nitride is an attractive material for a broad range of applications including catalysis. However preparations and especially those targeting nanoscale particles remain a major challenge. Herein, we report a wet-chemical approach to produce nickel/nickel nitride nanocomposites using deep eutectic solvents. A choline chloride/urea deep eutectic solvent was used as a reaction medium to form gels containing nickel acetate tetrahydrate. Heat treatment of the gel in inert atmosphere forms nanoparticles embedded within a nitrogen-doped carbon matrix. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were used to understand the decomposition profile of the precursors and to select pyrolysis temperatures located in regions of thermal stability. X-ray diffraction (XRD) confirmed the presence of metallic nickel, whereas X-ray photoelectron spectroscopy (XPS) suggested the existence of a nickel nitride surface layer. According to transmission electron microscopy (TEM) analysis these mixed phase, possibly core-shell type nanoparticles, have very defined facets. Furthermore, these materials represent a unique opportunity to tune catalytic properties of nickel-based catalysts through control of their composition, surface structure, and morphology; in addition to employing potential benefits of a nitrogen-doped carbon support.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Kinetics of lime/bentonite pozzolanic reactions at 20 and 50 °C: Batch tests and modeling

The effects of duration (1–100 days) and temperature (20 and 50 °C) were assessed from batch tests for Ca-bentonite mixed with 10 wt.% lime. The pozzolanic processes were monitored over time by {sup 29}Si NMR (Cement Concr. Res. 42, 2012), TGA-DTA, XRD and chemical analysis. Modeling considered kinetics and thermodynamics of mineralogical transformations and cation exchange. Kinetic laws were dependent on pH and temperature (Arrhenius energy). Lime hydration occurs within hours, modifying the bentonite exchangeable population and increasing the pH. These alkaline conditions initiate the pozzolanic reactions in a second stage. The rate-limiting step is the dissolution kinetics of the bentonite minerals, i.e. a relatively fast and total consumption of cristobalite in parallel to a long-term slower dissolution of montmorillonite. First C–S–H and then C–A–S–H are formed consequently. Temperature speeds up the pozzolanic reaction kinetics by a factor 5 from 20 to 50 °C, corresponding to an apparent activation energy of 40–50 kJ/mol.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Can calcium aluminates activate ternesite hydration?

Aluminum hydroxide (AH{sub 3}) has recently been shown to be able to activate hydration in ternesite, a phase found in some calcium sulfoaluminate (CSA) cements. This study explored the capacity of a number of calcium aluminates (C{sub 3}A, C{sub 12}A{sub 7}, CA and C{sub 4}A{sub 3} S-bar ) to activate ternesite hydraulic reactivity. After laboratory synthesis, the aluminates were blended with ternesite at a ratio of 1:2 and their hydration was monitored with isothermal conduction calorimetry for 7 days at 25 °C. The resulting pastes were analysed with XRD, FTIR and DTA. The presence of ternesite in the pastes altered the aluminate heat flow curves, shortening the induction period and bringing the reaction peak forward, an indication of hastened hydration. Ternesite also altered the reaction products, which included calcium monosulfoaluminate hydrate and strätlingite.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Hybrid bilayered vanadium oxide electrodes with large and tunable interlayer distances in lithium-ion batteries

The interlayer distances in layered electrode materials, influenced by the chemical composition of the confined interlayer regions, have a significant impact on their electrochemical performance. Chemical preintercalation of inorganic metal ions affects the interlayer spacing, yet expansion is limited by the hydrated ion radii. Herein, we demonstrate that using varying concentrations of decyltrimethylammonium (DTA + ) and cetyltrimethylammonium (CTA + ) cations in chemical preintercalation synthesis followed by hydrothermal treatment, the interlayer distance of hybrid bilayered vanadium oxides (BVOs) can be tuned between 11.1 Å and 35.6 Å. Our analyses reveal that these variations in interlayer spacing are due to different amounts of structural water and alkylammonium cations confined within the interlayer regions. Increased concentrations of alkylammonium cations not only expand the interlayer spacing but also induce local bending and disordering of the V-O bilayers. Electrochemical cycling of hybrid BVO electrodes in non-aqueous lithium-ion cells show that specific capacities decrease as interlayer regions expand, suggesting that the densely packed alkylammonium cations obstruct intercalation sites and hinder Li + ion transport. Furthermore, we found that greater layer separation facilitates the dissolution of active material into the electrolyte, resulting in rapid capacity decay during extended cycling. In conclusion, this study emphasizes that layered electrode materials require both spacious interlayer regions as well as high structural and chemical stabilities, providing guidelines for structural engineering of organic–inorganic hybrids.

25 ENERGY STORAGE↗
DOE OSTI2014

Effect of TiO 2 content on the crystallization and the color of (ZrO 2 ,TiO 2 )-doped Li 2 O-Al 2 O 3 -SiO 2 glasses

Glass–ceramics formed by controlled crystallization of Li 2 O–Al 2 O 3 –SiO 2 (LAS) parent glasses are well-known for their low thermal expansion and transparency. In order to promote bulk crystallization, it is necessary to add nucleating agents like TiO 2 and ZrO 2 to the glass composition leading to ZrTiO 4 nuclei during heating, followed by the crystallization of a β-quartz phase that transforms into β-spodumene at higher temperature. Generally, these glass–ceramics present a yellowish-brown coloration whose intensity increases with the crystallization rate and that is partly due to coloring elements like titanium. In this study, we investigated the origin of the evolution of the color of LAS glasses and glass–ceramics by varying the TiO 2 concentration. To do this, several TiO 2 -bearing LAS glasses (with TiO 2 ranging from 0 to 4 mol% and 1 mol% ZrO 2 ) were prepared and heat treated at a given temperature (925 °C) to study the impact of the TiO 2 concentration on their crystallization behavior and their color. The crystallization and microstructure of LAS glasses and glass–ceramics were studied by DTA, XRD and TEM whereas their structure was investigated by EPR, optical and X-ray absorption spectroscopies. From all the results obtained, the evolution of the optical absorption and coloration of LAS glasses and glass–ceramics was mainly explained by Ti 4+ –O 2- charge transfer (glasses) and by gap absorption and Rayleigh scattering of nanocrystals (glass–ceramics).

Chavoutier, M.↗
DOE OSTI2019

Structural characterization of ZnSO 4 -K 2 SO 4 -NaCl glasses

Glasses with compositions xNaCl-(50-x/2)K 2 SO 4 -(50-x/2)ZnSO 4 , x = 0 to 30 (in mol%), were characterized via vibrational spectroscopy and X-ray pair distribution function (xPDF) analysis. The xPDF's were modeled using Empirical Potential Structure Refinement (EPSR). From the modeled xPDF, the deconvoluted xPDFs were obtained along with cation-anion coordination numbers. The sulfate environment was elucidated through analysis of the vibrational spectroscopy paired with xPDFs. As determined via these techniques, the SO 4 2– oxyanions remain as distinct tetrahedra and dominate the overall structure of these ionic glasses, even with up to 30 mol% addition of NaCl. Addition of NaCl lowers the glass transition temperature (T g ) of these materials and increases the temperature between T g and the first crystallization temperature upon heating, as determined by differential thermal analysis (DTA). As a result, the composition-dependent xPDFs indicate that chloride ions are distributed equally and increasingly around Zn, K, and Na cations as x increases.

36 MATERIALS SCIENCE↗
DOE OSTI2014

2D→3D polycatenated and 3D→3D interpenetrated metal–organic frameworks constructed from thiophene-2,5-dicarboxylate and rigid bis(imidazole) ligands

Hydrothermal reactions of rigid 1,4-bis(imidazol-1-yl)benzene (dib) and 1,4-bis(imidazol-1-yl)-2,5-dimethylbenzene (dimb) with deprotonated thiophene-2,5-dicarboxylic acid (H{sub 2}tdc) in the presence of Zn(II) and Cd(II) salts in H{sub 2}O produced three new metal–organic frameworks, namely, [Zn(µ-tdc)(H{sub 2}O)(µ-dib)]{sub n} (1), [Cd(µ-tdc)(H{sub 2}O)(µ-dib)]{sub n} (2), and ([Cd{sub 2}(µ{sub 3}-tdc){sub 2}(µ-dimb){sub 2}]·(H{sub 2}O)){sub n}(3). These MOFs were characterized by FT-IR spectroscopy, elemental, thermal (TG, DTA, DTG and DSC), and single-crystal X-ray diffraction analyses. Isomorphous complexes 1 and 2 reveal polycatenated 2D+2D→3D framework based on an undulated (4,4)-sql layer. Complex 3 exhibits a new 4-fold interpenetrating 3D framework with the point symbol of 6{sup 6}. Molecular simulations were used to assess the potentials of the complexes for H{sub 2} storage application. Moreover, these coordination polymers exhibit blue fluorescent emission bands in the solid state at room temperature. - Graphical abstract: In this study, hydrothermal reactions of rigid 1,4-bis(imidazol-1-yl)benzene (dib) and 1,4-bis(imidazol-1-yl)-2,5-dimethylbenzene (dimb) with deprotonated thiophene-2,5-dicarboxylic acid (H{sub 2}tdc) in the presence of Zn(II) and Cd(II) salts in H{sub 2}O produced three new metal–organic frameworks. Isomorphous complexes 1 and 2 reveal polycatenated 2D+2D→3D framework based on an undulated (4,4)-sql layer. Complex 3 exhibits a new 4-fold interpenetrating 3D framework with the point symbol of 6{sup 6}. Molecular simulations were used to assess the potentials of the complexes for H{sub 2} storage application. These coordination polymers exhibit blue fluorescent emission bands in the solid state at room temperature. Display Omitted - Highlights: • Complexes 1 and 2 display polycatenated 2D+2D→3D framework. • Complex 3 exhibits a new 4-fold interpenetrating 3D framework. • Complex 1 adsorbs the highest amount of H{sub 2} at 100 bar and 298 K. • Complexes display blue fluorescent emission bands.

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

Synthesis, crystal structure and optical property of a novel metal chalcohalide: ZnHg{sub 3}Se{sub 2}Cl{sub 4}

A novel chalcohalide ZnHg{sub 3}Se{sub 2}Cl{sub 4} has been synthesized through a solid state method and structurally characterized by single-crystal X-ray diffraction. It crystallizes in the acentric space group Cmc2{sub 1} (No. 36) with cell parameters a=7.3262(8) Å, b=12.518(2) Å, c=11.3324(14) Å. The compound consists of 12-membered Hg{sub 6}Se{sub 6} rings edge-sharing with six neighbored rings to construct a 2D layered network and the ZnCl{sub 4} tetrahedra are sandwiched between layers. TG-DTA measurement shows that the compound is thermally stable up to 300 °C. The band gap of the crystal is about 2.23 eV, and the crystal exhibits a broad transparent range from 0.56 to 13.8 µm. - Highlights: • A novel chalcohalide ZnHg{sub 3}Se{sub 2}Cl{sub 4} was synthesized by a solid state method. • The structure contains 12-membered Hg{sub 6}Se{sub 6} rings and ZnCl{sub 4} tetrahedra. • The band gap of the as-prepared compound is about 2.23 eV.

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

Spectral, mechanical, thermal, optical and solid state parameters, of metal-organic bis(hydrogenmaleate)-CO(II) tetrahydrate crystal

Metal-organic bis(hydrogenmaleate)-Co(II) tetrahydrate single crystals have been grown by slow evaporation solution growth technique at room temperature. The crystal structure and the unit cell parameters were analyzed from the X-ray diffraction studies. Single-crystal X-ray diffraction analyses reveal that the grown crystal belongs to triclinic system with the space group P-1. Functional groups in bis(hydrogenmaleate)-Co(II) tetrahydrate were identified by Fourier transform infrared spectral analysis. The peak observed at 663 cm{sup −1} is assigned to the (Co–O) stretching vibrations. The optical transmission of the crystal was studied by UV–vis–NIR spectral analysis. The photoluminescence emission studies were carried out for the title compound in a wide wavelength range between 350 nm and 550 nm at 303 K. Mechanical strength was tested by Vickers microhardness test. The laser damage threshold value has been determined using Nd:YAG laser operating at 1064 nm. At various frequencies and temperatures the dielectric behavior of the material was investigated. Solid state parameters such as plasma energy, Penn gap, Fermi energy and electronic polarizability were evaluated. Photoconductivity measurements were carried out for the grown crystal in the presence of DC electric field at room temperature. Thermal stability and decomposition of the crystal were studied by TG–DTA. The weight loss of the title compound occurs in different steps. - Graphical abstract: Molecular structure of the bis(hydrogenmaleate)-Co(II) tetrahydrate drawn at 40% ellipsoid probability level. - Highlights: • Bis(hydrogenmaleate)-Co(II) tetrahydrate single crystal is grown by slow evaporation method. • Structural and optical properties were discussed. • The title complex crystal is thermally stable up to 91 °C. • Plasma energy, Fermi energy and electronic polarizability are evaluated. • It exhibits positive photoconductivity.

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

Cu-PDC-bpa solid coordination frameworks (PDC=2,5-pyrindinedicarboxylate; bpa=1,2-DI(4-pyridil)ethane)): 2D and 3D structural flexibility producing a 3-c herringbone array next to ideal

Combination of polycarboxylate anions and dipyridyl ligands is an effective strategy to produce solid coordination frameworks (SCF) which are crystalline materials based on connections between metal ions through organic ligands. In this context, this work is focused on two novel Cu{sup II}-based SCFs exhibiting PDC (2,5-pyridinedicarboxylate) and bpa (1,2-di(4-pyridyl)ethane), being the first structures reported in literature containing both ligands. Chemical formula are [Cu{sub 2}[(PDC){sub 2}(bpa)(H{sub 2}O){sub 2}]·3H{sub 2}O·DMF (1), and [Cu{sub 2}(PDC){sub 2}(bpa)(H{sub 2}O){sub 2}]·7H{sub 2}O (2), where DMF is dimethylformamide. Compounds 1 and 2 have been characterized by means of X-ray diffraction (XRD), infrared spectroscopy (IR), thermogravimetric (TG) analysis, differential thermal analysis (DTA) and dielectric measurements. The crystallographic analysis revealed that compounds 1 and 2 can be described as herringbone-type layers formed by helicoidal Cu-PDC-Cu chains connected through bpa ligands. Solvent molecules are crystallized between the layers, providing the inter-layer connections through hydrogen bonds. Differences between both compounds are attributable to the flexibility of bpa (in 2D) as well as to the 3D packing of the layers which is solvent dependent. This fact results in the fact that compound 2 is the most regular 3-c herringbone array reported so far. The structural dynamism of these networks is responsible for the crystalline to-amorphous to-crystalline (CAC) transformation from compound 1 to compound 2. Crystallochemical features for both compounds have also been studied and compared to similar 3-connected herringbone-arrays. - Graphical abstract: Cu-PDC-bpa 3-c herringbone arrays. - Highlights: • The most ideal herringbone array reported so far is a Cu-PDC-bpa SCF. • Conformational freedom of bpa results in 2D and 3D flexibility of the SCFs. • The flexibility of the SCFs is related to a phase transformation. • Dielectric measurements confirm the mobility of guest solvent molecules.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗