The Li2BaP2O7 compound has been obtained by the conventional solid-state reaction and characterized by X-ray powder diffraction. The title material crystallizes in the monoclinic system with C2/c space group. Electrical properties of the compound have been studied using complex impedance spectroscopy in the frequency range 200 Hz–5 MHz and temperature range 589–724 K. Temperature dependence of the DC conductivity and modulus was found to obey the Arrhenius law. The obtained values of activation energy are different which confirms that transport in the titled compound is not due to a simple hopping mechanism. AC conductivity measured follows the power-law dependence σAC?~?ωs typical for charge transport. Therefore, the experimental results are analyzed with various theoretical models. Temperature dependence of the power law exponent s strongly suggests that tunneling of large polarons is the dominant transport process. 相似文献
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
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, σac(ω)?=?σo? +?Aωα. 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
A few compositions in the system Ba1???xLaxSnO3 (x?=?0.00, 0.01, 0.05, and 0.10) have been synthesized via the solid state ceramic route. The synthesized powders have been characterized using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis, Raman spectroscopy, Fourier transformation infrared, thermogravimetrical analysis, and differential thermal analysis techniques. The powder X-ray diffraction pattern of the samples confirms the formation of a single-phase solid solution only up to 0.50?≤?x. It was found that all the samples have a cubic crystal structure. The electrical properties of La-modified BaSnO3 were studied using ac impedance spectroscopy technique over a wide range of temperatures (50–650 °C) in the frequency range of 10 Hz–13 MHz. The complex impedance plots above 300 °C show that total impedance is due to the contributions of grain and grain boundaries. The resistance of these contributions has been determined. Variation of these resistances with temperature shows the presence of two different regions with different slopes. The nature of the variation of conductivity of the grain and grain boundaries is different in different regions. Based on the value of activation energy, it is proposed that conduction via hopping of doubly ionized oxygen vacancies (VO??) is taking place in the temperature region of 300–450 °C, whereas in the temperature region of 450–650 °C, it is due to proton, i.e., OH? ions, hopping. 相似文献
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
Samples of the composition TlNiS2 in the hexagonal system with the unit cell parameters a=12.28 Å, c=19.32 Å, and ρ=6.90 g/cm3 are synthesized. The results of the investigation into the electrical and thermoelectrical properties of TlNiS2 samples in the temperature range 80–300 K indicate that TlNiS2 is a p-type semiconductor. It is found that, at temperatures ranging from 110 to 240 K, TlNiS2 samples in a dc electric field possess variable-range-hopping conduction at the states localized in the vicinity of the Fermi level. The density of localized states near the Fermi level is determined to be NF=9×1020 eV?1 cm?3, and the scatter of the states is estimated as J≈2×10?2 eV. In the temperature range 80–110 K, TlNiS2 exhibits activationless hopping conduction. At low temperatures (80–240 K), the thermopower of TlNiS2 is adequately described by the relationship α(T)=A+BT, which is characteristic of the hopping mechanism of charge transfer. In the case when the temperature increases to the temperature of the onset of intrinsic conduction with the activation energy ΔE=1.0 eV, there arise majority intrinsic charge carriers of both signs. This leads to an increase in the electrical conductivity σ and, at the same time, to a drastic decrease in the thermopower α; in this case, the thermopower is virtually independent of the temperature. 相似文献
The characteristics of Li+-ion conductivity σdc of structural γ modifications of Li3R2(PO4)3 compounds (R = Fe, Sc) existing in the superionic state have been investigated by impedance spectroscopy. The type of structural framework [R2P3O12]∞3- affects the σdc value and the σdc activation enthalpy in these compounds. The ion transport activation enthalpy in γ-Li3R2(PO4)3 (ΔHσ = 0.31 ± 0.03 eV) is lower than in γ-Li3Fe2(PO4)3 (ΔHσ = 0.36 ± 0.03 eV). The conductivity of γ-Li3Fe2(PO4)3 (σdc = 0.02 S/cm at 573 K) is twice as high as that of γ-Li3R2(PO4)3. A decrease in temperature causes a structural transformation of Li3R2(PO4)3 from the superionic γ modification (space group Pcan) through the intermediate metastable β modification (space group P21/n) into the “dielectric” α modification (space group P21/n). Upon cooling, σdc for both phosphates decreases by a factor of about 100 at the superionic TSIC transition. In Li3Fe2(PO4)3 σdc gradually decreases in the temperature range TSIC = 430–540 K, whereas in Li3R2(PO4)3 σdc undergoes a jump at TSIC = 540 ± 25 K. Possible crystallochemical factors responsible for the difference in the σdc and ΔHσ values and the thermodynamics and kinetics of the superionic transition for Li3R2(PO4)3 are discussed. 相似文献
Sodium silicate glasses doped with CuO and mixed with different contents of Bi2O3 (ranging from 4 to 16 mol%) were prepared. D.C. conductivity studies over a range of temperature from 225 to 325 K have been carried out. The conductivity is observed to decrease linearly with increase of Bi2O3 concentration. The results are analyzed using optical absorption, ESR, and IR spectral data. The spectroscopic studies have indicated that there is a gradual reduction divalent copper ions to monovalent ions with increase of Bi2O3 concentration. These studies have also indicated that such Cu+ ions participate in the glasses network forming and increase the polymerization of the glass network. The analysis of the results of D.C. conductivity indicated that in temperature region T > θD/2, the small polaron hoping model is valid, and the conduction is predicted to be adiabatic type. The analysis of the results has further revealed that there is a gradual change over of conduction mechanism from ionic to electronic with increase of Bi2O3 concentration. The low temperature part of D.C. conductivity is explained using variable range hopping (VRH) model. 相似文献
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
High-frequency (HF) conductivity in systems with a dense (with a density of n = 3 × 1011 cm?2) array of self-organized Ge0.7Si0.3 quantum dots in silicon with different boron concentrations nB is determined by acoustic methods. The measurements of the absorption coefficient and the velocity of surface acoustic waves (SAWs) with frequencies of 30–300 MHz that interact with holes localized in quantum dots are carried out in magnetic fields of up to 18 T in the temperature interval from 1 to 20 K. Using one of the samples (nB = 8.2 × 1011 cm?2), it is shown that, at temperatures T ≤ 4 K, the HF conductivity is realized by the hopping of holes between the states localized in different quantum dots and can be explained within a two-site model in the case of
, where ω is the SAW frequency and τ0 is the relaxation time of the populations of the sites (quantum dots). For T > 7 K, the HF conductivity has an activation character associated with the diffusion over the states at the mobility threshold. In the interval 4 K < T < 7 K, the HF conductivity is determined by a combination of the hopping and activation mechanisms. The contributions of these mechanisms are distinguished; it is found that the temperature dependence of the hopping HF conductivity approaches saturation at T* ≈ 4.5 K, which points to a τ0 ≤ 1. A value of τ0(T*) ≈ 5 × 10?9 s is determined from the condition ωτ0(T*) ≈ 1.
Spectral and kinetic characteristics of the luminescence and luminescence excitation spectra of polycrystalline SrB4O7:Pr (1%) and SrB6O10:Pr (1%) samples are studied at 150–170 K. The samples show an intense luminescence band in the vicinity of 405 nm (1S0→1I6 transitions of Pr3+) and shorter wavelength bands also assigned to transitions from the 1S0 level. The main luminescence decay constant is ~2×10?7 s. The excitation spectra of the 1S0 luminescence in these crystals are significantly different. The SrB4O7:Pr crystal shows three well-resolved bands at 6.14, 6.55, and 6.91 eV in the region of the 4f2→4f15d transitions and a complex structure in the region of interband transitions (7.1–20 eV), whereas the SrB6O10:Pr crystal shows a weakly structured band at 6.31 eV and no excitation in the region of the interband transitions. The physical mechanisms that may be responsible for the observed features of the spectra are discussed. 相似文献
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 Rp and constant phase elements. 相似文献
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
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
The luminescence spectra of a KZnF3: Tl+ crystal are investigated in the energy range from 4.75 to 5.9 eV at temperatures of 10–300 K upon excitation into the A absorption band (5.7–6.3 eV). At T=300 K, the luminescence spectra exhibit an intense band with a maximum at 5.45 eV, which is attributed to single Tl+ ions substituted for K+ ions. The 5.723-eV intense narrow band observed at T<20 K is assigned to the 3Γ1u-1Γ1g zero-phonon transition, which is weakly allowed by the hyperfine interaction. The luminescence decay is studied as a function of temperature. The main characteristics of the luminescence spectra are adequately described in terms of the semiclassical theory based on the Franck-Condon principle and the Jahn-Teller effect for an excited sp configuration of the Tl+ ion with the use of the parameters obtained earlier from analyzing the absorption spectra of the system under investigation. 相似文献
Dc and ac electrical conductivity of lead molybdate crystals is studied in the temperature range 300–550 K. The electrical conductivity was shown to have electronic (hole) impurity character. The I–V characteristics are typical of a space charge-limited current. The carrier mobility was estimated to be 10?5 cm2 V?1 sat T=300 K. The results of the study suggest the hopping mechanism of conduction in PbMoO4 crystals. 相似文献
The Rb3(HSeO4)2.5(H2PO4)0.5 compound was prepared and its thermal behavior and electric properties were investigated. The thermogravimetry (TGA) analysis and the differential scanning calorimetric (DSC) show the presence of a structural phase transition of the title compounds at 374 K which is confirmed by the variation of fp and σdc as a function of temperature. The complex impedance of the Rb3(HSeO4)2.5(H2PO4)0.5 compound has been investigated in the temperature range of 295–453 K and in the frequency range 209 Hz–1 MHz. The impedance plots show 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 Rp and constant phase elements CPE1 in series with fractal capacity CPE2. The frequency dependence of the conductivity is interpreted in terms of Jonscher’s law. The conductivity dc follows the Arrhenius relation. The near value of activation energies obtained from the analysis of modulus, conductivity data, and circuit equivalent confirm that the transport is through the ion hopping mechanism, dominated by the motion of the H+ proton in the structure of the investigated materials. 相似文献
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
The frequency (ν = 10?1–107 Hz) dependences σ(ν) of the conductivity of single crystals of the Pb0.67Cd0.33F2 superionic conductor with the fluorite-type structure (CaF2) in the temperature range of 132–395 K have been studied. The dependences σ(ν) have been discussed in the framework of the hopping relaxation of ionic carriers, which are mobile anions F?. From experimental curves σ(ν), the direct-current (dc) conductivity σdc and the average charge carrier hopping frequency νh have been determined. This has made it possible to calculate the charge carrier mobility μmob and charge carrier concentration nmob in these crystals. At room temperature (293 K), the electrical parameters are σdc = 1.6 × 10?4 S/cm, νh = 2.7 × 107 Hz, μmob = 2.0 × 10?7 cm2/(s V), and nmob = 5.1 × 1021 cm?3. 相似文献