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1.
The Na superionic conductor (NASICON) NaNbAlP3O12 compound was prepared by the conventional solid-state reaction method. The formation of single-phase material was confirmed by X-ray diffraction studies, and it was found to be a hexagonal phase at room temperature. The electrical conductivity was measured in the frequency range from 200 Hz to 5 MHz and temperatures between 573 and 773 K using impedance spectroscopy technique. The obtained results were analyzed by fitting the experimental data to the equivalent circuit model. The analysis of Nyquist plots has revealed the contribution of three electrically active regions corresponding to the bulk mechanism, distribution of grain boundaries, and electrode processes. Besides, the frequency dependence of the conductivity is interpreted in terms of Jonscher’s law. Temperature dependence of the power law exponent s strongly suggests that the non-overlapping small polaron tunneling (NSPT) model is the dominant transport process. The variation of the imaginary part of the complex modulus as a function of angular frequency at several temperatures shows a double relaxation peak suggesting the presence of grains and grain boundaries in the sample. An analysis of the dielectric constants ε″ and loss tangent tan (δ) with frequency shows a distribution of relaxation times.  相似文献   

2.
The lithium dihydrogen phosphate LiH2PO4 has been investigated by X-ray powder diffraction, scanning electron microscopy (SEM), and electrical impedance spectroscopy. The Rietveld refinements based on the XRD patterns show that the compound is crystallized in the orthorhombic system with Pna21 space group, and the refined unit cell parameters are a = 6.2428 Å, b = 7.6445 Å, and c = 6.873 Å. The electrical properties were studied using complex impedance spectroscopy as a function of frequency (104–107 Hz) at various temperatures (300–400 K). The Nyquist plots are well fitted to an equivalent circuit consisting of a series of combination of grains and inhomogeneous electrode surface effect. The frequency dependence of the conductivity is interpreted in terms of Jonscher’s law. Moreover, the near value of the activation energies obtained from the equivalent circuit and analysis of M″ confirms that the transport is through ion hopping mechanism dominated by the motion of the proton in the structure of the investigated material.  相似文献   

3.
A. Oueslati 《Ionics》2017,23(4):857-867
A lithium yttrium diphosphate LiYP2O7 was prepared by a solid-state reaction method. Rietveld refinement of the X-ray diffraction pattern suggests the formation of the single phase desired compound with monoclinic structure at room temperature. The infrared and Raman spectrum of this compound was interpreted on the basis of P2O7 4? vibrations. The AC conductivity was measured in the frequency range from 100 to 106 Hz and temperatures between 473 and 673 K using impedance spectroscopy technique. The obtained results were analyzed by fitting the experimental data to the equivalent circuit model. The Cole–Cole diagram determined complex impedance for different temperatures. The angular frequency dependence of the AC conductivity is found to obey Jonscher’s relation. The temperature dependence of σ AC could be described in terms of Arrhenius relation with two activation energies, 0.87 eV in region I and 1.36 eV in region II. The study of temperature variation of the exponent(s) reveals two conduction models: the AC conduction dependence upon temperature is governed by the correlated barrier hopping (CBH) model in region I (T < 540 K) and non-overlapping small polaron tunneling (NSPT) model in region II (T > 540 K). The near value of activation energies obtained from the equivalent circuit and DC conductivity confirms that the transport is through ion hopping mechanism dominated by the motion of the Li+ ion in the structure of the investigated material.  相似文献   

4.
The sample of Mg0. 5+y (Zr1-y Fey) 2 (PO4) 3 (0.0 ≤y ≤0.5) was synthesized using the sol-gel method. The structures of the samples were investigated using X-ray diffraction and Fourier transform infrared spectroscopy measurement. XRD studies showed that samples had a monoclinic structure which was iso-structured with the parent compound, Mg0.5Zr (PO4) 3. The complex impedance spectroscopy was carried out in the frequency range 1–6 MHz and temperature range 303 to 773 K to study the electrical properties of the electrolytes. The substitutions of Fe3+ with Zr4+ in the Mg0.5Zr (PO4) 3 structure was introduced as an extrainterstitial Mg2+ ion in the modified structured. The compound of Mg0.5+y (Zr1-y Fey)2(PO4)3 with y?=?0.4 gives a maximum conductivity value of 1.25?×?10?5 S cm?1 at room temperature and 7.18?×?10?5 S cm?1 at 773 K. Charge carrier concentration, mobile ion concentration, and ion hopping rate are calculated by fitting the conductance spectra to power law variation, σ ac (ω)?=?σ o ? +?Aω α . The charge carrier concentration and mobile ion concentration increases with increase of Fe3+ inclusion. This implies the increase in conductivity of the compounds was due to extra interstitial Mg2+ ions.  相似文献   

5.
A new perovskite-like compound Er0.73Cu3V4O12 (space group Im \(\bar 3\), Z = 2, a = 7.266 Å) has been synthesized barothermally (P = 8.0 GPa, t = 1000°C). Its electrical and magnetic properties have been studied. It is found that the temperature dependence of the electrical conductivity (in the range 78–300 K) has of semiconductor type. The behavior of the impedance and admittance has been analyzed at 290 K and frequencies of 200 Hz to 200 kHz under atmospheric pressure and at high (15–42 GPa) pressures.  相似文献   

6.
In order to establish the mechanism and to determine the parameters of lithium transport in electrodes based on lithium-vanadium phosphate (Li3V2(PO4)3), the kinetic model was designed and experimentally tested for joint analysis of electrochemical impedance (EIS), cyclic voltammetry (CV), pulse chronoamperometry (PITT), and chronopotentiometry (GITT) data. It comprises the stages of sequential lithium-ion transfer in the surface layer and the bulk of electrode material’s particles, including accumulation of lithium in the bulk. Transfer processes at both sites are of diffusion nature and differ significantly, both by temporal (characteristic time, τ) and kinetic (diffusion coefficient, D) constants. PITT data analysis provided the following D values for the predominantly lithiated and delithiated forms of the intercalation material: 10?9 and 3 × 10?10 cm2 s?1, respectively, for transfer in the bulk and 10?12 cm2 s?1 for transfer in the thin surface layer of material’s particles. D values extracted from GITT data are in consistency with those obtained from PITT: 3.5–5.8 × 10?10 and 0.9–5 × 10?10 cm2 s?1 (for the current and currentless mode, respectively). The D values obtained from EIS data were 5.5 × 10?10 cm2 s?1 for lithiated (at a potential of 3.5 V) and 2.3 × 10?9 cm2 s?1 for delithiated (at a potential 4.1 V) forms. CV evaluation gave close results: 3 × 10?11 cm2 s?1 for anodic and 3.4 × 10?11 cm2 s?1 for cathodic processes, respectively. The use of complex experimental measurement procedure for combined application of the EIS, PITT, and GITT methods allowed to obtain thermodynamic E,c dependence of Li3V2(PO4)3 electrode, which is not affected by polarization and heterogeneity of lithium concentration in the intercalate.  相似文献   

7.
The present paper reports the synthesis, crystal structure, 13C and 111Cd cross-polarization magic-angle spinning nuclear magnetic resonance(CP-MAS-NMR) analysis and ac conductivity for a new organic–inorganic hybrid salt, [C7H12N2][CdCl4]. The compound crystallizes in the triclinic system, space group P\( \overline 1 \), with unit cell dimensions: a?=?7.1050(3) Å, b?=?8.9579(3) Å, c?=?9.4482(3) Å, α?=?81.415(1)°, β?=?89.710(2)°, γ?=?85.765(1)°, V?=?592.97(4) Å3, and Z?=?2. The asymmetric unit is composed of one-2,4-diammonium toluene cation and one [CdCl4]2? anion. The Cd atom is in a slightly distorted octahedra coordination environment. Its structure can be described by infinite chains of CdCl6 octahedron linked to organic cations by a strong charge-assisted N–H???Cl interactions in order to build organic–inorganic layers staked along \( \left[ {0\overline 1 1} \right] \) direction. The solid state 13C CP-MAS-NMR spectra has shown seven isotropic resonances, confirming the existence of seven non-equivalent carbon atoms, which is consistent with crystal structure determined by X-ray diffraction. As for 111Cd MAS-NMR, it has shown one cadmium site with isotropic chemical shift observed at 167.2 ppm. The complex impedance of the compound has been investigated in the temperature range of 403–460 K and in the frequency range of 200 Hz–5 MHz. The impedance plots have shown semicircle arcs at different temperatures and an electrical equivalent circuit has been proposed to explain the impedance results. The circuits consist of the parallel combination of bulk resistance R p and constant phase elements.  相似文献   

8.
The temperature-dependent field cooling (FC) and zero-field cooling (ZFC) magnetizations, i.e., M FC and M ZFC, measured under different magnetic fields from 500 Oe to 20 kOe have been investigated on two exchange–spring CoFe2O4/CoFe2 composites with different relative content of CoFe2. Two samples exhibit different magnetization reversal behaviors. With decreasing temperature, a progressive freezing of the moments in two composites occurs at a field-dependent irreversible temperature T irr. For the sample with less CoFe2, the curves of ?d(M FC ? M ZFC)/dT versus temperature T exhibit a broad peak at an intermediate temperature T 2 below T irr , and the moments are suggested not to fully freeze till the lowest measuring temperature 10 K. However, for the ?d(M FC ? M ZFC)/dT curves of the sample with more CoFe2, besides a broad peat at an intermediate temperature T 2, a rapid rise around the low temperature T 1~15 K is observed, below which the moments are suggested to fully freeze. Increase of magnetic field from 2 kOe leads to the shift of T 2 and T irr towards a lower temperature, and the shift of T 2 is attributable to the moment reversal of CoFe2O4.
Graphical abstract CoFe2O4/CoFe2 composites with different relative content of CoFe2 were prepared by reducing CoFe2O4 in H2 for 4 h (S4H) and 8 h (S8H). The temperature-dependent FC and ZFC magnetizations, i.e., M FC and M ZFC, under different magnetic fields from 500 Oe to 20 kOe have been investigated. Two samples exhibit different magnetization reversal behaviors. With decreasing temperature, a progressive freezing of the moments in two composites occurs at field-dependent irreversible temperature T irr. For the S4H sample, the curves of ?d(M FC ? M ZFC)/dT versus temperature T exhibit a broad and field-dependent relaxing peak at T 2 below T irr (figure a), and the moments were suggested not to fully freeze till the lowest measuring temperature 10 K. However, for the S8H sample, it exhibits the reentrant spin-glass state around 50 K, as evidenced by a peak in the M FC curve (inset in figure b) and as a result of the cooperative effects of the random anisotropy of CoFe2O4, exchange–spring occurring at the interface of CoFe2O4 and CoFe2 together with the inter-particle dipolar interaction (figure c); in ?d(M FC ? M ZFC)/dT curves, besides a broad relaxing peat at T 2, a rapid rise around the low-temperature T 1~15 K is observed, below which the moments are suggested to fully freeze. Increase of magnetic field from 2 kOe leads to the shift of T 2 and T irr towards a lower temperature, and the shift of T 2 is attributable to the moment reversal of CoFe2O4.
  相似文献   

9.
Lead-free Na0.5Bi0.5TiO3 (NBT) and (1 ? x)Na0.5Bi0.5TiO3 + xBaTiO3 with x = 0.1 and 0.2 (where x = 0.1 and 0.2 are named as NBT1 and NBT2, respectively), (1 ? y)Na0.5Bi0.5TiO3 + yBa0.925Nd0.05TiO3 with y = 0.1 and 0.2 (where y = 0.1 and 0.2 are named as NBT3 and NBT4, respectively)-based relaxor ferroelectric ceramics were prepared using the sol-gel method. The crystal structure was investigated by X-ray diffraction (XRD) at room temperature (RT). The XRD patterns confirmed the presence of the rhombohedral phase in all the samples. The electrical properties of the present NBT-based samples were investigated by complex impedance and the modulus spectroscopy technique in the temperature range of RT–600 °C. The AC conductivity was found to increase with the substitution of Ba2+ ions to the NBT sample whereas it significantly decreased with the addition of Nd3+ ions. The more anion vacancies in Ba-added samples and the lower anion vacancies in Nd-added samples were found to be responsible for higher and lower conductivities, respectively.  相似文献   

10.
CoO and Li2O mixed with borotellurite glasses in the compositions, (B2O3)0.2-(TeO2)0.3-(CoO) x -(Li2O)0.5?x, where x = 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, and 0.50 were synthesized by fast cooling the melt to room temperature. Absence of crystalline phases in the samples was confirmed by X-ray diffraction studies. Changes in dielectric properties with frequency and temperature over wide ranges have been measured. Dielectric constant and loss increased with increase in CoO content. AC conductivity has been analyzed using Mott’s small polaron model and activation energy was determined. Activation energy decreased and conductivity increased with increase in CoO content up to 0.3 mole fractions, and they behaved oppositely for higher concentration of CoO. This observed change of trend in activation energy and conductivity at 0.3 mole fraction of CoO ascribed to switch over of conduction mechanism occurring from predominantly ionic to electronic regime. For the first time, a transition of conduction mechanism is observed in borotellurite glasses. Temperature and composition independent relaxation mechanism in these glasses has been confirmed by plotting the scaled conductivity master curves. Hunt’s model has been invoked to understand the frequency dispersion of conductivity.
Graphical abstract Plots of ln(ε′′) versus ln(F) for BTCL2 glass at different temperatures
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11.
NaNi1.5P2O7 compound was obtained by the classic ceramic method at high temperature and was characterized by XRD. It was found to crystallize in the triclinic symmetry with the P-1 space group. The electrical conductivity and modulus characteristics of the system have been investigated in the temperature and the frequency range 586–723 K and 200 Hz–1 MHz, respectively, by means of impedance spectroscopy. The ac conductivity for grain contribution was interpreted using the universal Jonscher’s power law. The exponent s decreased with increasing temperature revealing that the conduction inside the studied material is insured by the correlated barrier hopping (CBH) model. The conduction mechanism was explained with the help of Elliot’s theory, and the Elliot’s parameters were determined. Thermodynamic parameters such as the free energy for dipole relaxation ΔG, the enthalpy ΔH, and the change in entropy ΔS have been calculated.  相似文献   

12.
Temperature dependences of specific heat Cp(T) and coefficient of thermal expansion ;(T) for Na0.95Li0.05NbO3 sodium-lithium niobate ceramic samples are investigated in the temperature range of 100–800 K. The Cp(T) and α(T) anomalies at T3 = 310 ± 3 K, T2 = 630 ± 8 K, and T1 = 710 ± 10 K are observed, which correspond to the sequence of phase transitions N ? Q ? S(R) ? T2(S). The effect of heat treatment of the samples on the sequence of structural distortions was established. It is demonstrated that annealing of the samples at 603 K leads to splitting of the anomaly corresponding to the phase transition QR/S in two anomalies. After sample heating to 800 K, the only anomaly is observed in both the Cp(T) and ;(T) dependence. Possible mechanisms of the observed phenomena are discussed.  相似文献   

13.
The temperature behavior of I-U curves and the field and temperature dependences of the electrical resistivity and dielectric permittivity of crystals of the LiCu2O2 phase have been studied. It was established that the crystals belong to p-type semiconductors and that their static resistivity in the range 80–260 K follows the Mott law ρ=Aexp(T0/T)1/4 describing variable-range hopping over localized states. At comparatively low electric fields, the crystals exhibit threshold switching and characteristic S-shaped I-U curves containing a region of negative differential resistivity. In the critical voltage region, jumps in the conductivity and dielectric permittivity are observed. Possible mechanisms of the disorder and electrical instability in these crystals are discussed.  相似文献   

14.
The conditions of synthesizing a new Ag6SnS4Br2 compound were studied. The crystallographic parameters of the unit cell were determined as follows: space group Pnma, a=6.67050(10) Å, b=7.82095(9) Å, c=23.1404(3) Å, and Z=4. The total electrical conductivity and its ionic component were measured by a dc probe method in the temperature range 210–380 K. Kinks in the conductivity curve and the differential thermogram of heating the alloy were revealed at 235 K. It was concluded that the mass and charge transfers in the compacted Ag6SnS4Br2 alloy powder have an intragrain character.  相似文献   

15.
The transition of the hexagonal ice phase Ih to the clathrate phase sII has been found in the H2O-H2 system at a pressure of about 1 kbar under conditions of an excess of gaseous hydrogen. The pressures of the IhsII and sII → Ih transitions have been determined over a temperature range from ?36 to ?18°C, and the pressure dependence of the synthesis temperature of the clathrate phase from a liquid at pressures from 1.0 to 1.8 kbar has been constructed. The solubility of hydrogen in the Ih and sII phases and in liquid water has been measured. The concentration of hydrogen in the clathrate phase sII is about 1.2 wt % (10 mol %) near the boundary of the sII → Ih transition, and it increases to 2 wt % (16 mol %) at a pressure of 1.8 kbar.  相似文献   

16.
Indium oxide-multi-walled carbon nanotubes (In2O3-MWCNTs) were prepared by sol-gel method for DSSCs. The synthesis of indium oxide (In2O3) was carried out by dissolving indium chloride (InCl3) in a solvent of 2-methoxyethanol. Different annealing temperatures of 400, 450, 500, 550, and 600 °C were proposed in this study. The changes in the structural properties were analyzed by means of X-ray diffraction (XRD) and atomic force microscopy (AFM) analysis. The XRD spectrum estimated the average crystallite sizes of 3 nm for each sample. AFM results indicated very rough surface area of the films where it increased linearly from 1.8 to 11 nm as the annealing temperature increases. The In2O3-MWCNTs-based DSSC exhibited good photovoltaic performance with power conversion efficiency (η), photocurrent density (J sc ), open circuit voltage (V oc ), and fill factor (FF) of 1.13 %, 5.5 mA/cm2, 0.53 V, and 0.42, respectively. Even though the film annealed at 450 °C exhibited low τ eff, it achieved the greatest D eff of 29.67 cm2 s?1 which provides an efficient pathway for the photogenerated electrons with minimum electron recombination loss that increased the J sc and V oc in the DSSC. The obtained structural and electron transport analysis was proposed as a suitable benchmark for In2O3-MWCNTs-based dye-sensitized solar cell (DSSCs) application. Hence, this study suggests that the optimum temperature for In2O3-MWCNTs is at annealing temperature of 450 °C prepared via sol-gel method.  相似文献   

17.
Crystals of the KPb2Br5compound are investigated using polarized light microscopy and calorimetry. The birefringence and the angle of rotation of the optical indicatrix are measured in the temperature range 270–620 K. It is found that the KPb2Br5 crystal undergoes a first-order ferroelastic phase transition at temperatures T0↑ = 519.5 K and T0↓ = 518.5 K with a change in the enthalpy ΔH = 1300 ± 200 J/mol. This transition is accompanied by both twinning and the symmetry change mmm ? P21/c. It is revealed that the angle of rotation of the optical indicatrix exhibits an unusual behavior under variations in the temperature due to a strong temperature dependence of the birefringence.  相似文献   

18.
Tm x Cu3V4O12, a perovskite-like oxide (space group, Im-3; Z = 2; a = 7.279–7.293 Å) containing vacancies in its cationic sublattice, was obtained barothermally (P = 7.0–9.0 GPa, t = 1000–1100°C) for the first time. The temperature dependences on the electrical resistivity (10–300 K) and the magnetic susceptibility (0–300 K) were investigated. It was shown that the oxide Tm x Cu3V4O12 is characterized by metal-type conductivity and paramagnetic properties.  相似文献   

19.
Bi4Ti3O12 (BIT) nanoparticles with a narrow average particle size distribution in the range of 11–46 nm was synthesized via a metal-organic polymeric precursor process. The crystallite size and lattice parameter of BIT were determined by XRD analysis. At annealing temperatures >550 °C, the orthorhombic BIT compound with lattice parameters a = 5.4489 Å, b = 5.4147 Å, and c = 32.8362 Å was formed while at lower annealing temperatures orthorhombicity was absent. Reaction proceeded via the formation of an intermediate phase at 500 °C with a stoichiometry close to Bi2Ti2O7. The particle size and the agglomerates of the primary particles have been confirmed by FESEM and TEM. The decomposition of the polymeric gel was ascertained in order to evaluate the crystallization process from TG-DSC analysis. Raman spectroscopy was used to investigate the lattice dynamics in BIT nanoparticles. In addition, investigation of the dependence of the visible emission band around the blue–green color emission on annealing temperatures and grain sizes showed that the effect of grain size plays important roles, and that oxygen vacancies may act as the radiative centers responsible for the observed visible emission band.  相似文献   

20.
The structural, mechanical, electronic and thermoelectric properties of the low temperature orthorhombic perovskite phase of CH3NH3PbI3 have been investigated using density functional theory (DFT). Elastic parameters bulk modulus B, Young’s modulus E, shear modulus G, Poisson’s ratio ν and anisotropy value A have been calculated by the Voigt–Reuss–Hill averaging scheme. Phonon dispersions of the structure were investigated using a finite displacement method. The relaxed system is dynamically stable, and the equilibrium elastic constants satisfy all the mechanical stability criteria for orthorhombic crystals, showing stability against the influence of external forces. The lattice thermal conductivity was calculated within the single-mode relaxation-time approximation of the Boltzmann equation from first-principles anharmonic lattice dynamics calculations. Our results show that lattice thermal conductivity is anisotropic, and the corresponding lattice thermal conductivity at 150 K was found to be 0.189, 0.138, and 0.530 Wm?1K?1 in the a, b, and c directions. Electronic structure calculations demonstrate that this compound has a DFT direct band gap at the gamma point of about 1.57 eV. The electronic transport properties have been calculated by solving the semiclassical Boltzmann transport equation on top of DFT calculations, within the constant relaxation time approximation. The Seebeck coefficient S is almost constant from 50 to 150 K. At temperatures 100 and 150 K, the maximal figure of merit is found to be 0.06 and 0.122 in the direction of the c-axis, respectively.  相似文献   

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