AC conductivity,structural, and dielectric properties of zinc supported on titanium dioxide: Facile synthesis and DFT calculation

We present a simple and systematic synthesis method of Zn doped TiO₂ (Zn/TiO₂) that is usually prepared with sophisticated preparation procedures. Zn/TiO₂ have been synthesized following a facile and efficient incipient wet impregnation method. The resulting Zn/TiO₂ has been characterized by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy, which revealed the successful formation of the anatase phase and traces of the rutile phase. The existence of the rutile phase in smaller proportion was a clear sign of the Zn doping induced anatase-to-rutile phase transition. Sensible enhancement in the dielectric constant due to Zn addition has also been observed from experiment and approximate first-principle calculation. Thus, our results have significant impact on TiO₂ based semiconductor technology.     

Ferromagnetic and dielectric properties of lead free KNbO3-CoFe2O4 composites

Multiferroic (1-x)KNbO₃-(x)CoFe₂O₄ (x = 0.0, 0.25, 0.5, 0.75 and 1.0 mol) composites were prepared by solid state reaction method. X-ray diffraction results showed that the prepared (1-x)KNbO₃-(x)CoFe₂O₄ composites belong to orthorhombic system for x = 0.0 (perovskite KNbO₃), cubic system for x = 1.0 (spinel CoFe₂O₄) and mixed phase of KNbO₃ and CoFe₂O₄ for x = 0.25, 0.5 and 0.75. Nb-O and Fe-O stretching vibrational modes were observed in the Fourier transform and Raman spectral analyses, respectively. The HR-SEM analysis showed that the morphology of KNbO₃ and CoFe₂O₄ composites was significantly modified by CoFe₂O₄ content. Energy dispersive X-ray spectroscopy results confirmed the presence of K, Nb, Fe, Co and O in (1-x)KNbO₃-(x)CoFe₂O₄ composites. The ionic state of Nb, Co, Fe and O was examined by X-ray photoelectron spectroscopy analysis. The high value of coercivity (H_c = ∼981Oe) for x = 0.5 and the enhanced dielectric constant for x = 0.5 and 0.75 were observed.     

Effect of phase purity on dielectric properties of CaCu3+xTi4O12 ceramics

Different amounts of CuO are used to synthesize CaCu_3+xTi₄O₁₂ (CC_xTO, −1 ≤ x ≤ 1) powders in this work. In order to investigate the effects of Cu constituent on the componential, morphological, and dielectric properties, 975 °C is selected as the sintering temperature to prepare the ceramic pellets with different x values from −0.2 to 0.2. They basically keep the same component and morphology despite the different Cu constituents in the ceramics. Cu component has complex effects on their dielectric properties, whose changes are not linear with the Cu increase. However, the CC_0.2TO ceramic sample has the most frequency-independent dielectric constant and the lowest dielectric loss.     

Determination of the dielectric tensor function of triclinic CuSO4·5H2O

We present the first successful dispersion analysis of a triclinic crystal in the infrared spectral region. The corresponding scheme involves the parallel evaluation of 12 polarized reflection spectra recorded from three mutual perpendicular faces of a cube-shaped crystal. The dispersion analysis was carried out on a CuSO₄·5H₂O single crystal. The determined oscillator parameters and the corresponding dielectric function tensor were used to model the spectra of polycrystalline CuSO₄·5H₂O. The good correspondence between modeled and experimental spectra of the polycrystalline species proves the correctness of the approach.     

Synthesis,characterization, dielectric and rectification properties of PANI/Nd2O3:Al2O3 nanocomposites

Polyaniline–Nd₂O₃:Al₂O₃ nanocomposites were prepared by in situ oxidative polymerization method using different weight percentages of oxide powders. The prepared nanocomposites were characterized by Fourier transform infrared spectroscopy and X‐ray diffraction for molecular and crystal structures. Scanning electron microscopy and transmission electron microscopy images show the tubular structure of polyaniline nanocomposite with embedded metal oxides. The electrical conductivity of the nanocomposites increases with increase in temperature as well as with concentration of Nd₂O₃:Al₂O₃ particles in polyaniline. This is because of the hopping of charge polarons and extended chain length of the nanocomposites as evidenced by the negative thermal coefficient (NTC) characteristic. A high NTC value of 2.67 was found in nanocomposites with 15 wt% of oxide particles. These nanocomposites show low dielectric constant and dielectric loss; the electrical conductivity is higher than 0.3 S/cm as confirmed by Cole–Cole plot that indicates a decrease in both grain resistance and bulk resistance of the nanocomposites. The current–voltage and capacitance–voltage measurements were also carried out. The carrier mobility μ values of pure polyaniline and nanocomposites were found to be 4.27 × 10^?3 and 1.45 × 10^–2 H.M^?1, respectively. A significant enhancement in carrier mobility was observed in comparison with the literature. Copyright © 2016 John Wiley & Sons, Ltd.     

Impedance and electric modulus approaches to investigate four origins of giant dielectric constant in CaCu3Ti4O12 ceramics

The frequency dependence of electric modulus of polycrystalline CaCu₃Ti₄O₁₂ (CCTO) ceramics has been investigated. The experimental data have also been analyzed in the complex plane of impedance and electric modulus, and a suitable equivalent circuit has been proposed to explain the dielectric response. Four dielectric responses are first distinguished in the impedance and modulus spectroscopies. The results are well interpreted in terms of a triple insulating barrier capacitor model. Using this model, these four dielectric relaxations are attributed to the domain, domain-boundary, grain-boundary, and surface layer effects with three Maxwell–Wagner relaxations. Moreover, the values of the resistance and capacitance of bulk CCTO phase, domain-boundary, grain-boundary and surface layer contributions have been calculated directly from the peak characteristics of spectroscopic plots.     

Synthesis,spectroscopic, and crystallographic characterizations of an antiferromagnetically coupled,oxobridged trinuclear manganese(IV) cluster [Mn3O4(H2O)2(phen)4](NO3)4 · 3H2O [phen = 1,10-phenanthroline]

Design and synthesis of a triangular manganese compound, [Mn₃O₄(H₂O)₂(phen)₄](NO₃)_4?·?3H₂O (1) with mono-µ-oxo and di-µ-oxo, is described. The complex has been characterized by elemental analysis, spectroscopy, single crystal and powder diffraction measurements, thermogravimetric analysis, etc. Bond Valence Sum calculations and X-ray photoelectron spectroscopy reveal that each manganese at each vertex of the triangle is +IV oxidation state. Variable temperature magnetic measurements show strong antiferromagnetic coupling between metal ions with the following set of parameters: g?=?1.99, J ₁?=??50.0?cm^?1, and J ₂?=??90.2?cm^?1 (where J ₁ describes the interaction across the two mono-µ-oxo bridges and J ₂ is the exchange coupling across the di-µ-oxo bridge). The compound breaks down in three steps when heated from room temperature to 900°C. The final ash of the compound is confirmed by infrared spectrum with standard MnO₂.     

Crystal structure,physical properties and bond valence analysis of NaLuP2O7

Single crystals of a diphosphate NaLuP₂O₇ have been synthesized by the flux method and characterized by single-crystal X-Ray diffraction. NaLuP₂O₇ crystallizes in the monoclinic system with P2₁/n space group with cell parameters: a = 8.9985(8) Å, b = 5.3473(5) Å, c = 12.756(1) Å, β = 103.174° (1), V = 597.67 (9) Å³, Z = 4. Its structure consists of a three-dimensional framework of P₂O₇ units that are corner-shared by LuO₆ octahedra, forming tunnels running parallel to [010] which are occupied by Na atoms. NaLuP₂O₇ powder was characterized by XRD, SEM, FTIR and Raman spectroscopy. The activation energy of (1.49 eV) obtained by electrical measurements suggests the charge carriers to be the sodium cations. The activation energies obtained from impedance and loss spectra were analyzed in order to explain the mechanism of conduction. The correlation between ionic conductivity of NaLuP₂O₇ and its crystallographic structure was investigated and the most probable transport pathway model was determined.     

Apparent giant dielectric constants, dielectric relaxation, and ac-conductivity of hexagonal perovskites La1.2Sr2.7BO7.33 (B=Ru, Ir)

We present a thorough dielectric investigation of the hexagonal perovskites La_1.2Sr_2.7IrO_7.33 and La_1.2Sr_2.7RuO_7.33 in a broad frequency and temperature range, supplemented by additional infrared measurements. The occurrence of giant dielectric constants up to 10⁵ is revealed to be due to electrode polarization. Aside of dc and ac conductivity contributions, we detect two intrinsic relaxation processes that can be ascribed to ionic hopping between different off-center positions. In both materials we find evidence for charge transport via hopping of localized charge carriers. In the infrared region, three phonon bands are detected, followed by several electronic excitations. In addition, these materials provide further examples for the occurrence of a superlinear power law in the broadband ac conductivity, which recently was proposed to be a universal feature of all disordered matter.     

Crystal Structure and Properties of Some Filled and Unfilled Skutterudites: GdFe4P12, SmFe4P12, NdFe4As12, Eu0.54Co4Sb12, Fe0.5Ni0.5P3, CoP3, and NiP3

The new cubic compound Fe_0.5Ni_0.5P₃ (a = 775.29(5) pm) as well as the known compounds CoP₃ and NiP₃ were synthesized from the elemental components using tin as a flux. Their skutterudite (CoAs₃) type structures were refined from single‐crystal X‐ray data. The new compound GdFe₄P₁₂ was prepared by reaction of an alloy Gd_1/3Fe_2/3 with phosphorus in a tin flux. Its cubic “filled” skutterudite (LaFe₄P₁₂ type) structure was refined from single‐crystal X‐ray data: a = 779.49(4) pm, R = 0.019 for 304 structure factors and 11 variable parameters. SmFe₄P₁₂ shows Van Vleck paramagnetism while GdFe₄P₁₂ is a soft ferromagnet with a Curie temperature of T_C = 22(5) K. Both are metallic conductors. The new isotypic polyarsenide NdFe₄As₁₂ (a = 830.9(1) pm) was obtained by reacting NdAs₂ with iron and arsenic in the presence of a NaCl/KCl flux. The new isotypic polyantimonide Eu_0.54(1)Co₄Sb₁₂ (a = 909.41(8) pm) was prepared by reaction of EuSb₂ with cobalt and antimony. Its structure was refined from single‐crystal X‐ray data to a residual of 0.024 (137 F values, 12 variables). A comparison of the Fe–P and P–P bond lengths in the compounds AFe₄P₁₂, where the A atoms (A = Ce, Eu, Gd, Th) have differing valencies, suggests that the Fermi level cuts through Fe–P bonding and P–P antibonding bands.     

Synthesis,structure and ionic conductivity of the molybdenum arsenate: Ag12.4Na1.6Mo18As4O71

The syntheses, structure and ionic conductivity of Ag_12.4Na_1.6Mo₁₈As₄O₇₁ are reported. Crystals and polycrystalline powders are synthesized by solid state reaction. It crystallized in the monoclinic space group C2/c with a = 20.032 Å, b = 16.872 Å, c = 19.373 Å and β = 112.14°. The structure can be described by the assemblage of Mo₈As₂O₃₄ ribbons interconnected through Mo₂O₇ groups. Monovalent cations are located around these ribbons. The ionic conductivities have been measured, on pellets of polycrystalline powders, between 423 and 663 K in the frequency range 1–13000 Hz, using diagrams of complex impedance. Impedance analysis suggests the presence of a dependent electrical relaxation temperature process in the material. Activation energy was obtained from Arrhenius plots (log σT versus 1000/T) and found to be 0.6 eV. The activation energies obtained from impedance and loss spectra are close. It suggests that the ionic transport in the elaborated material is due to a hopping mechanism. The dependence in frequency of the ac conductivity is found to obey Jonsher's relation.     

Mixed-metal tellurites: synthesis, structure, and characterization of Na1.4Nb3Te4.9O18 and NaNb3Te4O16

Two new mixed-metal tellurites, Na1.4Nb3Te4.9O18 and NaNb3Te4O16, have been synthesized by standard solid-state techniques using Na2CO3, Nb2O5, and TeO2 as reagents. The structures of Na1.4Nb3Te4.9O18 and NaNb3Te4O16 were determined by single-crystal X-ray diffraction. Both of the materials exhibit three-dimensional structures composed of NbO6 octahedra, TeO4, and TeO3 polyhedra. The Nb5+ and Te4+ cations are in asymmetric coordination environments attributable to second-order Jahn-Teller (SOJT) effects. The Nb5+ cations undergo an intraoctahedral distortion toward a corner (local C4 direction), whereas the Te4+ cations are in distorted environments owing to their nonbonded electron pair. Infrared and Raman spectroscopy, UV-vis diffuse reflectance spectroscopy, thermogravimetric analysis, and dielectric measurements were also performed on the reported materials. Crystal data: Na1.4Nb3Te4.9O18, monoclinic, space group C2/m (No. 12), with a = 32.377(5) A, b = 7.4541(11) A, c = 6.5649(9) A, beta = 95.636(5) degrees, V = 1576.7(4) A3, and Z = 4; NaNb3Te4O16, monoclinic, space group P2(1)/m (No. 11), with a = 6.6126(13) A, b = 7.4738(15) A, c = 14.034(3) A, beta = 102.98(3) degrees, V = 675.9(3) A3, and Z = 2.     

The effect of the linear charge density of carrageenan on the ion binding investigated by differential scanning calorimetry, dc conductivity, and kHz dielectric relaxation

The effect of the linear charge density of natural polyelectrolyte, carrageenan, on the ion binding to carrageenan molecules in relation to the gelation was investigated by using the dielectric relaxation spectroscopy, dc conductivity, optical rotation, and differential scanning calorimetry (DSC). Although carrageenan is an anionic polysaccharide, carrageenan molecules in the helix state at low temperatures can bind not only cation, such as potassium and cesium, but also anion, such as iodide. The dc conductivity steeply decreases just below the coil–helix transition temperature, which indicates the binding of ion to the carrageenan molecules in the helix state due to the increase of the linear charge density compared with that in the coil state. The addition of NaI promotes the helix formation, and prevents from aggregation of helices, which was suggested by the results of the dynamic shear modulus and the DSC, and resulted in an increase of the relaxation amplitude of the lowest frequency relaxation (kHz) attributed to the fluctuation of the tightly bound counter ions along the high charge density region (helix). It is concluded that binding of iodide induces (1) the increase in the amount of tightly bound counterions to carrageenan molecules and (2) the formation of non-aggregated helix.     

类钙钛矿新铌酸盐Ba5LaTi2Nb3O18的合成、结构与介电特性

为满足现代通信技术小型化、集成化与高可靠性的迫切要求,探索具有高介电常数、低介电损耗与低温度系数的微波介电材料引起了材料科学、化学、物理和电子科学等领域科学工作者的广泛关注,并已开发出复合钙钛矿结构的Ba(Mg1/3Ta2/3)O3、Ba(Zn1/3Ta2/3)O3和钨青铜结构的Ba6-3xLn8+2x·Ti18O54及Ba2Ti9O20等实用化的高性能材料[1～7].这类材料均由氧八面体共顶连接,而且氧八面体内(B位)、外(A位)阳离子比例等于或略大于1,由此,我们推测在B位与A位阳离子比例略小于1的类钙钛矿结构中也极有可能存在具有优良介电性能的新材料,因此对通式为AnBn-1O3n(n=5,6,7,8)的系列新化合物进行了系统的合成、结构与介电性能研究[8,9].本文报道在BaO-La2O3-TiO2-Nb2O5体系中合成的具有5层类钙钛矿结构的新铌酸盐Ba5LaTi2Nb3O18,发现该材料具有较好的介电性能.     

Effect of the addition of B2O3 and BaO-B2O3-SiO2 glasses on the microstructure and dielectric properties of giant dielectric constant material CaCu3Ti4O12

The effect of the addition of glassy phases on the microstructure and dielectric properties of CaCu₃Ti₄O₁₂ (CCTO) ceramics was investigated. Both single-component (B₂O₃) and multi-component (30 wt% BaO-60 wt% B₂O₃-10 wt% SiO₂ (BBS)) glass systems were chosen to study their effect on the density, microstructure and dielectric properties of CCTO. Addition of an optimum amount of B₂O₃ glass facilitated grain growth and an increase in dielectric constant. However, further increase in the B₂O₃ content resulted in its segregation at the grain boundaries associated with a reduction in the grain size. In contrast, BBS glass addition resulted in well-faceted grains and increase in the dielectric constant and decrease in the dielectric loss. An internal barrier layer capacitance (IBLC) model was invoked to correlate the dielectric constant with the grain size in these samples.     

类钙钛矿新铌酸盐Ba3La2Ti2Nb2O15的合成、结构与介电特性

为满足现代通信技术的小型化、集成化与高可靠性的迫切要求,探索具有高介电常数、低介电损耗与低温度系数的微波介电材料引起了材料科学、化学、物理和电子学等领域科学工作者的广泛关注,并已开发出复合钙钛矿结构[Ba(Zn1/3Ta2/3)O3]和钨青铜结构[Ba6-3xLn8+2xTi18O54]等实用化的高性.     

Crystal structure, magnetic, and dielectric properties of Aurivillius-type Bi3Fe0.5Nb1.5O9

Bi₃Fe_0.5Nb_1.5O₉ was synthesized using conventional solid state techniques and its crystal structure was refined by the Rietveld method using neutron powder diffraction data. The oxide adopts an Aurivillius-type structure with non-centrosymmetric space group symmetry A2₁am (a=5.47016(9) Å, b=5.43492(9) Å, c=25.4232(4) Å), analogous to other Aurivillius compounds that exhibit ferroelectricity. The Fe and Nb cations are disordered on the same crystallographic site. The [(Fe,Nb)O₆] octahedra exhibit tilting and distortion to accommodate the bonding requirements of the Bi cations located in the perovskite double layers. Magnetic measurements indicate non-Curie-Weiss-type paramagnetic behavior from 300 to 6 K. Measurements of dielectric properties and electrical resistivity exhibited changes near 250-260 °C and are suggestive of a ferroelectric transition.     

Effect of different reaction parameters on the conductivity and dielectric properties of polyaniline synthesized electrochemically and modeling of conductivity against reaction parameters through regression analysis

The polyaniline (PAni) is prepared electrochemically from an aqueous solution of aniline and HCl in a single compartment electrochemical cell. Different PAni samples obtained by varying monomer concentration, acid concentration, applied potential, reaction time, and reaction temperature are subjected to conductivity and dielectric tests. The degree of crystallinity, d‐spacing, interchain separation, and crystallite size are determined form X‐ray analysis, the oxidation state is determined from infrared spectroscopy (FTIR) analysis, and the doping level is estimated from TGA analysis for all the PAni samples synthesized under different conditions. All these structural properties are correlated with electrical properties. The whole result reveals that all the aforementioned reaction parameters affect the structural properties, which in turn affect the electrical properties of PAni. The mathematical model correlations between conductivity and reaction parameters are established from the regression analysis for individual variables as well as for all the variables together. These relationships give the conductivity as an output when we input the value of reaction variables. The output obtained from the model relations found in well agreement with the experimental results under identical conditions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2046–2059, 2007