Electrical characterization of LiCo3/5Fe2/5VO4 ceramics

LiCo_3/5Fe_2/5VO₄ has been synthesized by solution-based chemical method. X-ray diffraction study at room temperature reveals an orthorhombic phase of the compound. Electrical properties are studied using complex impedance spectroscopy (CIS) technique in a range of frequency and temperature. The complex impedance plots identify the grain interior, grain boundary and electrode–material interface contributions to electrical response in the material. Temperature dependence of a.c. and d.c. conductivity indicates that electrical conduction in the material is a thermally activated process. The value of activation energy computed from the Arrhenius plot of σ_dc with 10³/T is ～(0.356 ± 0.012) eV (25–275 °C). Frequency dependence of a.c. conductivity at different temperatures is found to obey Jonscher's universal law.     

Solubility of CO2 in the solvent system (water + monoethanolamine + triethanolamine)

This report presents a new set of values for the solubility of carbon dioxide in the solvent system {water (1) + monoethanolamine (2) + triethanolamine (3)} at T = (313.2, 333.2, 353.2, and 373.2) K and CO₂ partial pressures ranging (1.0 to 120) kPa. The results are specific to solvent systems with the following compositions: (i) ω₂ = 0.24, ω₃ = 0.06, (ii) ω₂ = 0.18, ω₃ = 0.12, (iii) ω₂ = 0.12, ω₃ = 0.18, (iv) ω₂ = 0.06, ω₃ = 0.24, and (v) ω₂ = 0, ω₃ = 0.30, where ω refers to the mass fraction of the component. The results fit the Deshmukh and Mather model well.     

Synthesis and characterization of LiCo3/5Mn2/5VO4 ceramics

Dielectric and a.c. conductivity properties of LiCo_3/5Mn_2/5VO₄ ceramic are investigated. This compound is prepared by solution-based chemical method and the formation is checked by X-ray diffraction (XRD) study. XRD analysis at room temperature shows an orthorhombic phase. Frequency dependence of dielectric constant (?_r) at different temperatures shows a dispersive behavior at low frequencies. Temperature dependence of ?_r at different frequencies indicates the transition temperature (T_c) = 235 °C, 245 °C, 257 °C and 265 °C with (?_r)_max. ～3689, 1373, 750 and 386 for 10, 50, 100 and 200 kHz respectively. A.c. conductivity analysis indicates that electrical conduction in the material is a thermally activated process.     

Influence of the RE2O3 (RE = Y,Gd) and CaO nanoadditives on the electromagnetic properties of nanocrystalline Co0.2Ni0.3Zn0.5Fe2O4

The present work reports the influence of the nanoadditives Y₂O₃, Gd₂O₃, and CaO on the magnetic, electrical and dielectric properties of sintered nanoferrites Co_0.2Ni_0.3Zn_0.5Fe₂O₄. All powders were synthesized via the polyol method. XRD analysis showed that except the nanoferrite which was obtained by in an one-post procedure, subsequent calcinations of the as-produced additives were necessary to obtain nanocrystals of the desired phases. The mean particle size inferred from TEM images of the nanoadditives sintered at 1000 °C ranges from 87 nm for Y₂O₃ to 126 nm for CaO. IR spectroscopy provided useful information on the nature of the core and the surface chemistry of the as-produced additives and their associated annealed powders. Upon sintering, it was found that the incorporation of 5 wt.% additives remarkably increased the densification of the doped materials. The most important increase in densification was observed with CaO due to its larger particles. dc M-H hysteresis loops taken at 300 K revealed a superparamagnetic behavior of the produced ferrite/nanoadditives. Additionally, as expected, the ferrite/nanoadditives showed reasonable saturation magnetization and high Curie temperature. The electrical and dielectric properties, namely the resistivity, the loss factor, and the relation frequency were found to be clearly affected by doping. The resistivity decreased with increasing temperature indicating a semiconducting behavior. Further, at room temperature, the highest resistivity was observed with Y₂O₃. The major role was attributed to the high fraction of insulating Y₂O₃ owing to its smallest particles combined with the low Fe²⁺ concentration in the ferrite nanoparticles taking advantages of the moderate sintering temperature. In addition, the dc conductivity was found to follow the Arrhenius law with a slope change observed at the Curie temperature. Further, all the additives clearly affected the ac conductivities of the pure ferrite. The variation of the dielectric permittivity with frequency and temperature was explained on the basis of M-W type of interfacial polarization. Additionally, at high frequencies, the lower dielectric loss was found with Y₂O₃ doping. It was found to be of about 10 times lower than the undoped material and much larger than reported for similar undoped bulk ferrites.     

Study of the ionic conductivity of Ca6La4(PO4)2(SiO4)4F2 and Ca4La6(SiO4)6F2

In order to enhance our knowledge about the Ca_10−xLa_x(PO₄)_6−x(SiO₄)_xF₂ (0 ≤ x ≤ 6) series, whose chemical stability decreases as the substitution degree increases, Ca₆La₄(PO₄)₂(SiO₄)₄F₂ and Ca₄La₆(SiO₄)₆F₂ compounds were prepared through a solid-state reaction. Their ionic conductivity was measured by impedance spectroscopy. The results indicate that the conductivity increases with substitution, and fits the Arrhenius equation over the investigated temperature range. At high temperatures, a change in the activation energy has been observed, which has been related to the nature of the Ca/La–F bond, i.e. to the polarizability of lanthanum.     

Synthesis,structure and NMR characterization of a new monomeric aluminophosphate [dl-Co(en)3]2[Al(HPO4)2(H1.5PO4)2(H2PO4)2](H3PO4)4 containing four different types of monophosphates

A new zero-dimensional (0D) aluminophosphate monomer [dl-Co(en)₃]₂[Al(HPO₄)₂(H_1.5PO₄)₂(H₂PO₄)₂](H₃PO₄)₄ (designated AlPO-CJ38) with Al/P ratio of 1/6 has been solvothermally prepared by using racemic cobalt complex dl-Co(en)₃Cl₃ as the template. The Al atom is octahedrally linked to six P atoms via bridging oxygen atoms, forming a unique [Al(HPO₄)₂(H_1.5PO₄)₂(H₂PO₄)₂]^6? monomer. Notably, there exists intramolecular symmetrical O?H?O bonds, which results in pseudo-4-rings stabilized by the strong H-bonding interactions. The structure is also featured by the existence of four different types of monophosphates that have been confirmed by ³¹P NMR and ¹H NMR spectra. The crystal data are as follows: AlPO-CJ38, [dl-Co(en)₃]₂[Al(HPO₄)₂(H_1.5PO₄)₂(H₂PO₄)₂](H₃PO₄)₄, M = 1476.33, monoclinic, C2/c (No. 15), a = 36.028(7) Å, b = 8.9877(18) Å, c = 16.006(3) Å, β = 100.68(3)°, U = 5093.2(18) Å³_, Z = 4, R₁ = 0.0509 (I > 2σ(I)) and wR₂ = 0.1074 (all data). CCDC number 689491.     

Spin-crossover in dimeric hydrogen-bonded iron(II) 2-(pyrazolyl)-pyridine and 2-(imidazolyl)-pyridine complexes

Five new hydrogen-bonded solvated iron(II) complexes of pyrazolyl- and imidazolyl-based N,N-chelating ligands have been synthesised. Water to ligand-NH hydrogen-bonded bridges occur in the pseudo-dimeric complexes {cis-[Fe(pypzH)₂(NCX)₂]₂(μ-OH₂)(H₂O)₂} · H₂O · MeOH (where X = S or Se), and in the chain complex {cis-[Fe(pypzH)₂(NCS)₂](μ-OH₂)}_n. A “half” spin-crossover (T_c = 125 K) was observed in the dimeric X = Se complex by means of magnetic measurements and no thermal hysteresis occurred between 4 and 300 K. The crystal structure at 123 K showed Fe–N distances consistent with the magnetism. Each Fe in the dimeric unit was structurally equivalent in the HS–LS state. Removal of the solvate molecules led to HS–HS behaviour over the temperature range 4–300 K. The pseudo-dimer with X = S also showed HS–HS behaviour as did the monomeric analogue cis-[Fe(pypzH)₂(NCS)₂]H₂O and a structurally different methanol-bridged dimer {cis-[Fe(pyimH)₂(NCS)₂]₂(μ-MeOH)₂} · 2MeOH (pypzH = 2-(1H-pyrazol-3-yl)-pyridine; pyimH = 2-(1H-imidazol-2-yl)-pyridine).     

Crystal structures of Th(OH)PO4, U(OH)PO4 and Th2O(PO4)2. Condensation mechanism of MIV(OH)PO4 (M = Th,U) into M2O(PO4)2

Three new crystal structures, isotypic with β-Zr₂O(PO₄)₂, have been resolved by the Rietveld method. All crystallize with an orthorhombic cell (S.G.: Cmca) with a = 7.1393(2) Å, b = 9.2641(2) Å, c = 12.5262(4) Å, V = 828.46(4) Å³ and Z = 8 for Th(OH)PO₄; a = 7.0100(2) Å, b = 9.1200(2) Å, c = 12.3665(3) Å, V = 790.60(4) Å³ and Z = 8 for U(OH)PO₄; a = 7.1691(3) Å, b = 9.2388(4) Å, c = 12.8204(7) Å, V = 849.15(7) Å³ and Z = 4 for Th₂O(PO₄)₂. By heating, the M(OH)PO₄ (M = Th, U) compounds condense topotactically into M₂O(PO₄)₂, with a change of the environment of the tetravalent cation that lowers from 8 to 7 oxygen atoms. The lower stability of Th₂O(PO₄)₂ compared to that of U₂O(PO₄)₂ seems to result from this unusual environment for tetravalent thorium.     

Ce(H2O)(PO4)3/2(H3O)1/2(H2O)1/2, a second entry in the structural chemistry of cerium(IV) phosphates

A cerium(IV) phosphate has been prepared using precipitation methods and its structure has been solved by single crystal X-ray diffraction (R₁ = 0.0292 for 3092 reflections with I>2σ(I) and wR₂ = 0.0540). Ce(H₂O)(PO₄)_3/2(H₃O)_1/2(H₂O)_1/2 crystallises in the monoclinic space group C2/c (a = 15.7058(17) Å, b = 9.6261(9) Å, c = 10.1632(4) Å, ß = 121.623(7)°, and V = 1308.4 (2) Å³). Its structure is based on a negatively charged 3D framework, made of cerium atoms connected by PO₄ tetrahedra. There are two types of PO₄ units; one shares only corners with the cerium coordination polyhedra while the other one shares edges and corners. This structure also includes hydronium cations, to balance the framework charge, and water molecules. One special feature of this 3D framework is the formation of interconnected tunnels which extend along the c axis and contain the hydronium cations and the water molecules. This open framework and the presence of cationic species in the tunnels are in perfect agreement with the previously reported ion exchange properties.     

Hopping conduction in double layered La2−2xCa1+2xMn2O7 manganite

Double layered La_2−2xCa_1+2xMn₂O₇ manganite has been synthesized using solid state reaction method for different dopant concentration x = 0.0–0.5. Their temperature dependence of resistivity (ρ − T) has been studied in the semiconducting region. The experimental observations were compared with the theoretically simulated temperature dependence of resistivity curves based on nearest neighbour hopping, Efros–Shklovskii variable range hopping, and Mott's 2D and 3D variable range hopping models. From the analysis of these results, Mott's 3D variable range hopping mechanism seemed to be most suitable mechanism describing the semiconducting behaviour of these double layered manganites. Temperature dependent activation energy also supported the Mott's 3D variable range hopping model. The Mott's activation energy was found to vary with the dopant concentration x and it showed a minimum value for x = 0.3.     

Synthesis and electrical properties of (LiCo3/5Fe1/5Mn1/5)VO4 ceramics

(LiCo_3/5Fe_1/5Mn_1/5)VO₄ ceramic was synthesized via solution-based chemical method. X-ray diffraction analysis was carried out on the synthesized powder sample at room temperature, which confirms the orthorhombic structure with the lattice parameters of a = 10.3646 (20) Å, b = 3.7926 (20) Å, c = 9.2131 (20) Å. Field emission scanning electron microscopic analysis was carried out on the sintered pellet sample that indicates grains of unequal sizes (～0.1 to 2 μm) presents average grains size with polydisperse distribution on the surface of the ceramic. Complex impedance spectroscopy (CIS) technique is used for the study of electrical properties. CIS analysis identifies: (i) grain interior, grain boundary and electrode–material interface contributions to electrical response (ii) the presence of temperature dependent electrical relaxation phenomena in the ceramics. Detailed conductivity study indicates that electrical conduction in the material is a thermally activated process. The variation of A.C. conductivity with frequency at different temperatures obeys Jonscher's universal law.     

Apparent molar heat capacities and apparent molar volumes ofY2(SO4)3(aq),La2(SO4)3(aq),Pr2(SO4)3(aq),Nd2(SO4)3(aq),Eu2(SO4)3(aq),Dy2(SO4)3(aq),Ho2(SO4)3(aq), andLu2(SO4)3(aq)atT = 298.15 K andp = 0.1 MPa

The apparent molar heat capacities C_{p, φ} ^∘ and apparent molar volumes V_φ ^∘ of Y₂(SO₄)₃(aq), La₂(SO₄)₃(aq), Pr₂(SO₄)₃(aq), Nd₂(SO₄)₃(aq), Eu₂(SO₄)₃(aq), Dy₂(SO₄)₃(aq), Ho₂(SO₄)₃(aq), and Lu₂(SO₄)₃(aq) were measured at T =  298.15 K and p =  0.1 MPa with a Sodev (Picker) flow microcalorimeter and a Sodev vibrating-tube densimeter, respectively. These measurements extend from lower molalities of m =  (0.005 to 0.018) mol ·kg ^− 1to m =  (0.025 to 0.434) mol ·kg ^− 1, where the upper molality limits are slightly below those of the saturated solutions. There are no previously published apparent molar heat capacities for these systems, and only limited apparent molar volume information. Considerable amounts of the R SO₄ ⁺ (aq) and R(SO₄)₂ ⁻ (aq) complexes are present, where R denotes a rare-earth, which complicates the interpretation of these thermodynamic quantities. Values of the ionic molar heat capacities and ionic molar volumes of these complexes at infinite dilution are derived from the experimental information, but the calculations are necessarily quite approximate because of the need to estimate ionic activity coefficients and other thermodynamic quantities. Nevertheless, the derived standard ionic molar properties for the various R SO₄ ⁺ (aq) and R(SO₄)₂ ⁻ (aq) complexes are probably realistic approximations to the actual values. Comparisons indicate that V_φ ^∘ {RSO₄ ⁺ , aq, 298.15K}  =  − (6  ±  4)cm³· mol ^− 1and V_φ ^∘ {R(SO₄)₂ ⁻ , aq, 298.15K}  =  (35  ±  3)cm³· mol ^− 1, with no significant variation with rare-earth. In contrast, values of C_{p, φ} ^∘ { RSO₄ ⁺ , aq, 298.15K } generally increase with the atomic number of the rare-earth, whereas C_{p, φ} ^∘ { R(SO₄)₂ ⁻ , aq, 298.15K } shows a less regular trend, although its values are always positive and tend to be larger for the heavier than for the light rare earths.     

Spectroscopic studies and crystal structure of tetrabutylammonium trichlorodimethylstannate(IV): Bu4NSnMe2Cl3

The structure of Bu₄NSnMe₂Cl₃ is found to be monomer, containing a 5-coordinated bipyramidal trigonal tin(IV) center. Crystals belong to the monoclinic space group C2/c, with unit-cell dimensions a = 26.633(4) Å; b = 9.880(2) Å; c = 21.510(2) Å; β = 114.82(2)°; Z = 8; D = 1.287 Mg/m³; R is refined to 0.0537 and R_w = 0.0642 for 3330 reflections (F > 2σ(F)).     

Electrical properties of LiBBaTe glass doped with Nd2O3

The dc and ac electrical conductivity of barium tellurite borate glass doped with Nd₂O₃ in the composition 50 B₂O₃- (20-X) BaO- 20TeO₂ 10 LiF or Li₂O where x = 0.5, 1, 1.5 and 2 Nd₂O₃ were measured in the temperature range 303–648 K and in the frequency range 0.1–100 kHz. The dc and ac conductivities values increase, whereas the activation energy of conductivities decreases with increasing Nd₂O₃ content in the glasses containing LiF and by the replacement of LiF by Li₂O the conductivity was found to decrease with addition of Nd₂O₃. The electrical conduction has been observed to be due to small polaron hopping at high temperatures. The frequency dependence of the ac conductivity follows the power law σ_AC (ω) = A ω^s. The frequency exponent (s) values (in the range 0.94 and 0.33) decreases with increasing temperature. The dielectric constant and dielectric loss increased with increasing temperature and decreased with increase in frequency for all glasses studied. In LiF glasses, it is observed that, the values of ?^\ and tan δ are observed to increase with the addition of Nd₂O₃ whereas they decrease in the glasses containing Li₂O. The electrical modulus formalism has been used for studying electrical relaxation behavior in studied glasses. It is for first time that the Nd₂O₃ doped barium tellurite borate glasses have been investigated for dc and ac conductivities and dielectric properties over a wide range of frequency and temperature.     

Structural characterization,molecular dynamics,dielectric and spectroscopic properties of tetrakis(pyrazolium) bis(μ2-bromo-tetrabromobismuthate(III)) dihydrate, [C3N2H5]4[Bi2Br10]·2H2O

The structure of [C₃N₂H₅]₄[Bi₂Br₁₀]·2H₂O, (PBB) was determined by single crystal X-ray diffraction at 100 K. It crystallizes in the monoclinic space group C2/m, with a = 12.992(4) Å, b = 16.326(5) Å, c = 8.255(3) Å, β = 108.56°(3), V = 1659.9(9) Å³ and Z = 2. The structure consists of discrete binuclear [Bi₂Br₁₀]⁴⁻ anions, ordered pyrazolium cations and water molecules. The crystal packing is governed by strong N–H⋯O and weak O–H⋯Br hydrogen bonds. A sequence of structural phase transitions in PBB was established on the basis of differential scanning calorimetry and dilatometric studies. Two reversible first-order phase transitions were found: (I → II) at 381/371 K (on heating/cooling) and (II → III) at 348/338 K. Dielectric response near both phase transitions is characteristic of crystals with the “plastic-like” phases. Over the phase III a low frequency dielectric relaxator is disclosed. The possible molecular motions in the PBB compound are characterized by the ¹H NMR studies. The infrared spectra of polycrystalline compound in the temperature range 300–380 K are reported for the region 4000–400 cm⁻¹. The observed spectral changes through the structural phase transition III → II are attributed to an onset of motion both of the pyrazolium cations and water molecules.     

Heat capacities and electrical conductivities of 1-ethyl-3-methylimidazolium-based ionic liquids

We present the heat capacities and electrical conductivities of five [Emim] 1-ethyl-3-methylimidazolium-based ionic liquids: [Emim][BF₄] (tetrafluoroborate), [Emim][CF₃SO₃] (trifluoromethanesulfonate), [Emim][C₂N₃] (dicyanamide), [Emim][C₂H₅SO₄] (ethylsulfate), and [Emim][MDEGSO₄] (2-(2-methoxyethoxy) ethylsulfate). The heat capacities were measured using a differential scanning calorimeter (DSC) over the temperature ranging from (303.2 to 358.2) K. The electrical conductivities were measured over the temperature ranging from (293.2 to 353.2) K using a commercial conductivity meter. The estimated uncertainties of heat capacity C_p and electrical conductivity σ measurements were ±0.015 kJ · kg^?1 · K^?1 and ±0.001 mS · cm^?1, respectively. The measured C_p and σ are presented as a function of temperature. The temperature dependency of the C_P value was correlated using an empirical equation. A modified version of VTF-type (Vogel–Tamman–Fulcher) equation was used to describe the temperature dependency of σ values. The correlations give satisfactory results. Also, the results of this study are in good agreement with the available literature data. The heat capacities and electrical conductivities presented in this work are in good agreement with the available literature data. The results of this study can be applied to numerous chemical processes, since C_p and σ data are essential information for rational design.     

Comparison of the spin exchange interactions in PbCu2(PO4)2 and SrCu2(PO4)2 on the basis of spin dimer analysis

The spin exchange interactions of PbCu₂(PO₄)₂ were examined by performing the spin dimer analysis based on the extended Hückel tight-binding method, and were compared with those of SrCu₂(PO₄)₂. The two strongest Cu–O⋯O–Cu super–superexchange interactions, J₁ (with Cu⋯Cu = 5.868 Å) and J₂ (with Cu⋯Cu = 5.184 Å), are strong and lead to a linear-four-spin-cluster model for both PbCu₂(PO₄)₂ and SrCu₂(PO₄)₂. Adjacent linear-four-spin-clusters interact substantially in SrCu₂(PO₄)₂, but weakly in PbCu₂(PO₄)₂. The difference in the magnetization behaviors of the two compounds was examined by calculating the magnetic excitation energies of the linear-four-spin-cluster model.     

New metastable hybrid phase,Zn2(OH)2(C8H4O4), exhibiting unique oxo-penta-coordinated Zn(II) atoms

The metastable phase (phase 1) Zn(OH)₂(tp)₂ (tp = C₈H₄O₄^2?) was found to be an intermediate forming during the hydrothermal synthesis of Zn₃(OH)₄tp (phase 2). Its structure has been determined ab initio from synchrotron powder diffraction data and refined with the Rietveld method: space group P2₁/c, a = 3.48856(2) Å, b = 5.84645(2) Å, c = 22.1331(1) Å, β = 103.46(1)°, D_x = 2.488 g/cm³, R_p = 0.10, R_B = 0.095 (402 independent reflections). The structures of the two analogues were compared. Whereas a mixed coordination of the zinc atoms was found in phase 2, phase 1 exhibits only penta-coordinated Zn(II). Moreover, different optical properties were observed, Zn₂(OH)₂(tp) showing photoluminescence at 378 nm under λ_ex = 316 nm.     

Synthesis,crystal structure,and magnetic properties of K4Mn3(HPO4)4(H2PO4)2

A new layered compound, K₄Mn₃(HPO₄)₄(H₂PO₄)₂ (1), has been synthesized under hydrothermal conditions. It crystallizes in the monoclinic space group P2₁/n with a = 8.874(2) Å, b = 6.554(1) Å, c = 18.075(4) Å, and β = 93.39(3)°. The structure consists of zigzag [Mn₃O₁₄]_n chains of edge-sharing MnO₆ octahedrons and MnO₇ pentagonal bi-pyramids, which form layers of formula [Mn₃(HPO₄)₄(H₂PO₄)₂]^4? in the ab plane via H₂PO₄ and HPO₄ units with vertex-sharing. Potassium ions lie between these layers. Magnetic measurements indicate Curie–Weiss behavior above 6 K for 1. A Heisenberg model, with alternating exchange interactions J₁J₁J₂… within the chain and exchange interactions J₃J₃… between the chains, is proposed to describe the magnetic behavior.     

Structural and spectroscopic properties of Ru(II) complexes of 4-(aryl)thiosemicarbazones of thiophen-2-carbaldehyde

Six Ru(II) complexes of formula [Ru(L)₂(PPh₃)₂] have been prepared where LH = 4-(aryl)thiosemicarbazones of thiophen-2-carbaldehyde. X-ray crystal structures of five of the complexes are reported. In all the complexes ruthenium is six coordinate with a distorted octahedral cis-P₂, cis-N₂, trans-S₂ donor environment, and each of the two thiosemicarbazone ligands are coordinated in a bidentate fashion forming a four membered chelate ring. The complexes undergo a one-electron oxidation at ～0.5 V vs. Ag/AgCl. The EPR spectrum of the electrochemically oxidized solution at 100 K shows a rhombic signal, with transitions at g₁ = 2.27, g₂ = 2.00 and g₃ = 1.80. DFT calculations on one of the complexes suggest that there is 35% ruthenium and 17% sulfur orbital contribution to the HOMO. These results suggest that the assignment of metal atom oxidation states in these compounds is not unambiguous.