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1.
Cu7PSe6 is a mixed conductor that crystallizes in the simple cubic structure at room temperature. Structural transitions above and below room temperature are accompanied by step-like changes in electrical conductivity. The substitution of Ag+ for Cu+ in Cu7PSe6 stabilized the simple cubic structure over a wider range of temperatures than is observed for the pure compound. A disproportionate decrease in electrical conductivity accompanies modest levels of silver substitution. The prominent step in electrical conductivity associated with the low-temperature crystallographic phase transition disappears in (AgxCu1−x)7PSe6 solid solutions for a composition parameter x=0.20, replaced by two distinct changes in the slope of conductivity below room temperature.  相似文献   

2.
The Ag6PS5Br and Ag6PS5I argyrodites crystallize in a face-centered-cubic lattice at room temperature. Both compounds exhibit purely Arrhenius behavior throughout the temperature range 150-400 K with similar activation energies of about 0.23 eV. Cu6PSe5Br and Cu6PSe5I also crystallize in a face-centered-cubic structure at room temperature. Cu6PSe5Br exhibits a distinctive anomaly in electrical conductivity near 286 K while Cu6PSe5I undergoes a first-order electrical phase transition near 265 K. Their activation energies above room temperature are 0.13 and 0.30 eV, respectively.  相似文献   

3.
The total electrical conductivities at room temperature of Ag6PSe5Cl, Ag6PSe5Br, and Ag6PSe5I were found to be 2.0×10−4, 5.6×10−4, and 6.8×10−4 S/cm, respectively. In the chloride and iodide compounds, the electronic contribution comprises approximately 1% of the total conductivity, although it exceeds 10% of the total conductivity in the bromide compound. Ag6PSe5Cl and Ag6PSe5Br exhibit purely Arrhenius behavior throughout the temperature range 150-300 K. Ag6PSe5I exhibits a second-order anomaly in electrical conductivity at 324 K.  相似文献   

4.
Electrical conductivity and fundamental absorption spectra of monocrystalline Cu7GeS5I were measured in the temperature ranges 95-370 and 77-373 K, respectively. A rather high electrical conductivity (σt=6.98×10−3Ω−1 cm−1 at 300 K) and low activation energy (ΔEa=0.183 eV) was found. The influence of different types of disordering on the Urbach absorption edge and electron-phonon interaction parameters were calculated, discussed and compared with the same parameters in Cu7GeS5I, Cu6PX5I (X=S,Se) and Ag7GeX5I (X=S,Se) compounds. We have concluded that the P→Ge and Cu→Ag cation substitution results in an increase of the electrical conductivity and a decrease of the activation energy. Besides, P→Ge substitution, results in complete smearing and disappearance of the exciton absorption bands and in blue shift of the Urbach absorption edge, an increase of the edge energy width and an electron-phonon-interaction enhancement.  相似文献   

5.
Structural, magnetic, heat capacity, electrical and thermal transport properties are reported on polycrystalline Ba8Ni6Ge40. Ba8Ni6Ge40 crystallizes in a cubic type I clathrate structure with unit cell a=10.5179 (4) Å. It is diamagnetic with susceptibility χdia=−1.71×10-6 emu/g Oe. An Einstein temperature 75 K and a Debye temperature 307 K are estimated from heat capacity data. It exhibits n-type conducting behavior below 300 K. It shows high Seebeck coefficients (−111×10-6 V/K), low thermal conductivity (2.25 W/K m), and low electrical resistivity (8.8 mΩ cm) at 300 K.  相似文献   

6.
Compositional behavior of Urbach absorption edge is studied as well as the effect of compositional disordering on the parameters of exciton-phonon interaction, phase transition temperatures and electric conductivity in Cu6P(S1−xSex)5Br1−yIy superionic solid solutions. The effect of different types of disordering on the optical absorption processes and specific features of compositional changes in the absorption edge spectra under S→Se and Br→I anion substitution in the mixed crystals are investigated. (x, T) phase diagrams for Cu6P(S1−xSex)5X (X=I, Br) solid solutions are studied.  相似文献   

7.
Series of polycrystalline samples of Zn2−xCuxBaFe16O27 were prepared by usual ceramic methods, where x=0.0, 0.4, 0.6, 0.8, 1.0, 1.4. X-ray analysis done at room temperature using CoKα with λ=1.790 Å confirms the presence of W-type hexaferrite phase structure. Saturation magnetization and hysteresis loops curves measurements at room temperature were studied as a function of Cu2+ substitution. It can be seen that the Cu2+ content slightly decreases the saturation magnetization from 25 to 20 emu g−1; all hysteresis loops are closed, which indicates low anisotropy field and low saturation magnetization field. The dc conductivity and thermoelectric power were measured in a range from room temperature up to T=750 K for all samples. The thermoelectric power decreases on increasing Cu2+ content, and the conductivity increases with temperature. The value of the charge-carrier concentration increases by increasing the temperature and Cu2+ content.  相似文献   

8.
Copper substituted bismuth vanadate films have been successfully deposited first time by spray pyrolysis technique on glass substrates suitable for low temperature solid oxide fuel cells. Desired phase formation of polycrystalline Bi2V0.9Cu0.1O5.35 (BICUVOX.10) was confirmed by X-ray diffraction technique. These films were further studied with EDAX and SEM techniques for their compositional and morphological characterization. Electrical conductivity of BICUVOX.10 is found to be 5.7 × 10−2 (Ω cm)−1 at 698 K, predicts the onset temperature for ionic contribution suitable for low temperature SOFC applications. Room temperature complex impedance plot reveals that electrical process arises due to contribution from the grain interior.  相似文献   

9.
Ion beam sputtering process was used to deposit n-type fine-grained Bi2Te3 thin films on BK7 glass substrates at room temperature. In order to enhance the thermoelectric properties, thin films are annealed at the temperatures ranging from 100 to 400 °C. X-ray diffraction (XRD) shows that the films have preferred orientations in the c-axis direction. It is confirmed that grain growth and crystallization along the c-axis are enhanced as the annealing temperature increased. However, broad impurity peaks related to some oxygen traces increase when the annealing temperature reached 400 °C. Thermoelectric properties of Bi2Te3 thin films were investigated at room temperature. The Bi2Te3 thin films, including as-deposited, exhibit the Seebeck coefficients of −90 to −168 μV K−1 and the electrical conductivities of 3.92×102-7.20×102 S cm−1 after annealing. The Bi2Te3 film with a maximum power factor of 1.10×10−3 Wm−1 K−2 is achieved when annealed at 300 °C. As a result, both structural and transport properties have been found to be strongly affected by annealing treatment. It was considered that the annealing conditions reduce the number of potential scattering sites at grain boundaries and defects, thus improving the thermoelectric properties.  相似文献   

10.
We prepared in-situ Au contacts on high-quality epitaxial YBa2Cu3O7 (YBCO) films. Very high specific contact resistivity values up to ∼10−2 Ω cm2 at 4.2 K were obtained on 12×5 μm2 contact areas. This resistivity value decreased by two orders of magnitude as the temperature was raised to room temperature. In the temperature range T<200 K, the contacts showed non-ohmic behavior suggesting the presence of a well-defined insulating native Y-Ba-Cu-O barrier between the two electrodes. The electrical transport in this barrier layer was analyzed in the limit of high temperatures and high voltages to follow Mott's variable-range hopping conduction mechanism with physically reasonable parameters describing the localized states in the barrier. The high-resistivity contacts were tested successfully in quasiparticles injection experiments where the critical current Ic of the YBCO microbridge could be strongly suppressed on injection of an additional current through the contact into the superconducting channel.  相似文献   

11.
The Bi0.9Sb0.1 powders were prepared by mechanical alloying and then pressed under 6 GPa at different pressing temperatures. X-ray diffraction spectra showed that the single phase was formed. The nanostructure of grain was observed by bright-field imaging. Electrical conductivity, Seebeck coefficient, and thermal conductivity had been investigated in the temperature range of 80-300 K. The absolute Seebeck coefficient value of 120.3 μV/K was measured at 130 K. The figure-of-merit reached a maximum value of 0.90×10−3 K−1 at 140 K.  相似文献   

12.
Inorganic-organic hybrid electrolytes were prepared by the mechanochemical method using the Li+ ion conductive 70Li2S·30P2S5 glass and various alkanediols. Local structure of the prepared electrolytes was analyzed by FT-IR and Raman spectroscopy. The effects of the proportion and chain length of alkanediols on conductivity of the hybrid electrolytes were investigated. The hybrid electrolyte with 2 mol.% of 1,4-butanediol exhibited the conductivity of 9.7 × 10− 5 S cm− 1 at room temperature and the unity of lithium ion transference number. The use of alkanediols with shorter chain length was effective in increasing conductivity of hybrid electrolytes. The electrolyte using ethyleneglycol showed the highest conductivity of 1.1 × 10− 4 S cm− 1 at room temperature. Lowering glass transition temperature by incorporation of alkanediols is responsible for the enhancement of conductivity of hybrid electrolytes.  相似文献   

13.
We report the results of an X-ray diffraction study of CdAl2Se4 and of Raman studies of HgAl2Se4 and ZnAl2Se4 at room temperature, and of CdAl2S4 and CdAl2Se4 at 80 K at high pressure. The ambient pressure phase of CdAl2Se4 is stable up to a pressure of 9.1 GPa above which a phase transition to a disordered rock salt phase is observed. A fit of the volume pressure data to a Birch-Murnaghan type equation of state yields a bulk modulus of 52.1 GPa. The relative volume change at the phase transition at ∼9 GPa is about 10%. The analysis of the Raman data of HgAl2Se4 and ZnAl2Se4 reveals a general trend observed for different defect chalcopyrite materials. The line widths of the Raman peaks change at intermediate pressures between 4 and 6 GPa as an indication of the pressure induced two stage order-disorder transition observed in these materials. In addition, we include results of a low temperature Raman study of CdAl2S4 and CdAl2Se4, which shows a very weak temperature dependence of the Raman-active phonon modes.  相似文献   

14.
High-quality LaCuO2, elaborated by solid-state reaction in sealed tube, crystallizes in the delafossite structure. The thermal analysis under reducing atmosphere (H2/N2: 1/9) revealed a stoichiometric composition LaCuO2.00. The oxide is a direct band-gap semiconductor with a forbidden band of 2.77 eV. The magnetic susceptibility follows a Curie-Weiss law from which a Cu2+ concentration of 1% has been determined. The oxygen insertion in the layered crystal lattice induces p-type conductivity. The electrical conduction occurs predominantly by small polaron hopping between mixed valences Cu+/2+ with an activation energy of 0.28 eV and a hole mobility (μ300 K=3.5×10−7 cm2 V−1 s−1), thermally activated. Most holes are trapped in surface-polaron states upon gap excitation. The photoelectrochemical study, reported for the first time, confirms the p-type conduction. The flat band potential (Vfb=0.15 VSCE) and the hole density (NA=5.8×1017 cm−3) were determined, respectively, by extrapolating the curve C−2 versus the potential to their intersection with C−2=0 and from the slope of the linear part in the Mott-Schottky plot. The valence band is made up of Cu-3d orbital, positioned at 4.9 eV below vacuum. An energy band diagram has been established predicting the possibility of the oxide to be used as hydrogen photocathode.  相似文献   

15.
Polycrystalline sample of Ca3Nb2O8 was prepared by a high-temperature solid-state reaction technique. X-ray diffraction (XRD) analysis confirms the formation of single-phase compound of hexagonal (rhombohedral) crystal structure at room temperature. Scanning electron micrograph of the material showed uniform grain distribution on the surface of the sample. Detailed studies of dielectric properties of the compound, studied in a wide frequency range (102-106 Hz) at different temperatures (25-500 °C), exhibit a dielectric anomaly suggesting phase transition of ferroelectric-paraelectric and structural type at 300 °C. Electrical properties of the material were analyzed using a complex impedance technique. The Nyquists plot showed the presence of bulk effect in the material in the studied temperature range. Studies of electrical conductivity over a wide temperature range suggest that the compound has negative temperature coefficient of resistance behavior.  相似文献   

16.
The crystal structure, the 13C NMR spectroscopy and the complex impedance have been carried out on [Cd3(SCN)2Br6(C2H9N2)2]n. Crystal structure shows a 2D polymeric network built up of two crystallographically independent cadmium atoms with two different octahedral coordinations. This compound exhibits a phase transition at (T=355±2 K) which has been characterized by differential scanning calorimetry (DSC), X-rays powder diffraction, AC conductivity and dielectric measurements. Examination of 13C CP/MAS line shapes shows indirect spin–spin coupling (14N and 13C) with a dipolar coupling constant of 1339 Hz. The AC conductivity of this compound has been carried out in the temperature range 325–376 K and the frequency range from 10−2 Hz to 10 MHz. The impedance data were well fitted to two equivalent electrical circuits. The results of the modulus study reveal the presence of two distinct relaxation processes. One, at low frequency side, is thermally activated due to the ionic conduction of the crystal and the other, at higher frequency side, gradually disappears when temperature reaches 355 K which is attributed to the localized dipoles in the crystal. Moreover, the temperature dependence of DC-conductivity in both phases follows the Arrhenius law and the frequency dependence of σ(ω,T) follows Jonscher's universal law. The near values of activation energies obtained from the conductivity data and impedance confirm that the transport is through the ion hopping mechanism.  相似文献   

17.
We carefully studied the nonsuperconducting sample of the magneto-superconducting RuSr2(Eu1−xCex)Cu2O10−δ series with composition RuSr2EuCeCu2O10−δ. This compound seems to exhibit a complex magnetic state as revealed by host of techniques like resistivity, thermopower, magnetic susceptibility, and MR measurements. The studied compound exhibited ferromagnetic like M(H) loops at 5, 20, and 50 K, and semiconductor like electrical conduction down to 5 K, with −MR7 T of up to 4% at low temperatures. The −MR7 T decreases fast above 150 K and monotonically becomes close to zero above say 230 K. Below, 150 K −MR7 T decreases to around 3% monotonically down to 75 K, with further increase to 4% at around 30 K and lastly having a slight decrease below this temperature. The thermopower S(T) behavior closely followed the −MR7 T steps in terms of d(S/T)/dT slopes. Further, both MR7 T steps and d(S/T)/dT slopes are found in close vicinity to various magnetic ordering temperatures (Tmag) of this compound.  相似文献   

18.
Field cooling (FC) poled/unpoled PMN-29%PT single crystal and room temperature (RT) poled/unpoled PMN-34.5%PT textured ceramic were investigated between ∼0 and 300 °C by thermal expansion, dielectric and Raman spectroscopy. New phase transitions are evidenced at 40, 91 and 180 °C in the case of FC PMN-29%PT as well as at 70 and 200 °C for RT PMN-34.5%PT and their order is discussed. The physical properties of the textured ceramics are rather similar to the ones observed for the single crystals that make them low-cost alternative for a wide range of applications. However, the temperatures and character of the phase transitions strongly depend on the kind of the poling conditions. Temperature dependences of the Raman line parameters show that the NbO6 octahedra remain stable during temperature increase, while TiO6 ones evolve quasi-continuously. The step transitions of the Pb2+ ion sublattice are evidenced. This suggests that the TiO6 and Pb2+ sublattices are especially coupled. The role of the TiO6 clusters on the structural phase transitions and dielectric properties of the PbMg1/3Nb2/3O3-xPbTiO3 (PMN-PT) system is discussed. The presence of the Raman modes above the maximum dielectric permittivity reveals that the local symmetry is lower than the cubic one (Pm3m). The decrease of the Raman line intensities vs. temperature indicates precisely the continuous evolution of the local symmetry towards the cubic one. The temperature evolution of the Rayleigh wing parameters appears sensitive to the phase transitions’ presence.  相似文献   

19.
Antiferromagnetic phase transition in two vanadium garnets AgCa2Co2V3O12 and AgCa2Ni2V3O12 has been found and investigated extensively. The heat capacity exhibits sharp peak due to the antiferromagnetic order with the Néel temperature TN=6.39 K for AgCa2Co2V3O12 and 7.21 K for AgCa2Ni2V3O12, respectively. The magnetic susceptibilities exhibit broad maximum, and these TN correspond to the inflection points of the magnetic susceptibility χ a little lower than T(χmax). The magnetic entropy changes from zero to 20 K per mol Co2+ and Ni2+ ions are 5.31 J K−1 mol-Co2+-ion−1 and 6.85 J K−1 mol-Ni2+-ion−1, indicating S=1/2 for Co2+ ion and S=1 for Ni2+ ion. The magnetic susceptibility of AgCa2Ni2V3O12 shows the Curie-Weiss behavior between 20 and 350 K with the effective magnetic moment μeff=3.23 μB Ni2+-ion−1 and the Weiss constant θ=−16.4 K (antiferromagnetic sign). Nevertheless, the simple Curie-Weiss law cannot be applicable for AgCa2Co2V3O12. The complex temperature dependence of magnetic susceptibility has been interpreted within the framework of Tanabe-Sugano energy diagram, which is analyzed on the basis of crystalline electric field. The ground state is the spin doublet state 2E(t26e) and the first excited state is spin quartet state 4T1(t25e2) which locates extremely close to the ground state. The low spin state S=1/2 for Co2+ ion is verified experimentally at least below 20 K which is in agreement with the result of the heat capacity.  相似文献   

20.
The nanocrystalline materials with the general formula Bi85Sb15−xNbx (x=0, 0.5, 1, 2, 3) were prepared by mechanical alloying and subsequent high-pressure sintering. Their transport properties involving electrical conductivity, Seebeck coefficient and thermal conductivity have been investigated in the temperature range of 80-300 K. The absolute value of Seebeck coefficient of Bi85Sb13Nb2 reaches a maximum of 161 μV/K at 105 K, which is 69% larger than that of Bi85Sb15 at the same temperature. The power factor and figure-of-merit are 4.45×10−3 WK−2m−1 at 220 K and 1.79×10−3 K−1 at 196 K, respectively. These results suggest that thermoelectric properties of Bi85Sb15 based material can be improved by Nb doping.  相似文献   

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