Ionic conductivity of Ag+ exchanged α-zirconium phosphate

The conductivity of silver ion in silver exchanged α-zirconium phosphate, Zr(AgPO₄)₂, was measured in the temperature range 80 to 330°C. The data were found to conform to an Arrehnius type behavior in this temperature range with an activation energy of 0.53eV and ⁰300°C = 1.94 × 10^?4 ohm^?1 cm^?1. The conductivity values for Ag⁺ are higher than the corresponding values obtained for Na⁺ and K⁺ conduction in their respective exchanged forms. This enhancement is attributed to the greater polarizibility of the silver ion.     

Investigation of the temperature dependence of electron and phonon Raman scattering in single crystal YBa2Cu3O6.952

Detailed Raman-scattering measurements have been performed on high-quality YBa₂Cu₃O_6.952 single crystal (T _c =93 K, ΔT _c =0.3 K). A sharp (FWHM 7.2 cm^?1 at 70 K and 10.0 cm^?1 at 110 K) 340 cm^?1phonon mode has been observed inB _1g polarization. An electronic scattering peak at 500 cm^?1 in theB _1g polarization extends down to 250 cm^?1. These FWHM values determine the upper limit of the homogeneous linewidth of the phonon and electronic excitations. The start of the electronic spectral function renormalization and of the 340 cm^?1 mode anomalies (frequency softening, linewidth sharpening, and intensity increase) have been observed to occur approximately 40 K aboveT _c . The 340 cm^?1 mode Fano shape analysis has been performed and the temperature dependences of the Fano shape parameters have been estimated. All 340 cm^?1 mode anomalies have been explained by the electronic spectral function renormalization.     

Fast ionic lithium conduction in solid lithium nitride chloride

Lithium nitride chloride (Li_1.8N_0.4Cl_0.6) crystallizes in a defect anti-fluorite structure with 10% of the lithium sites being vacant. Its electrical conductivity and thermodynamic stability have been investigated in the temperature range from 25 to 400° C. Lithium ions are the predominant charge carriers, yielding a conductivity temperature product of σ T = 7.456 × 10⁴ exp(?0.49₅ eV/kT) $\text{Ω}{}^{\mathrm{?1}}$ cm^?K. The electronic contribution to the total conductivity is smaller by a factor of less than 10^?4. The material is thermodynamically stable against pure metallic lithium and has a decomposition voltage larger than 2.5 V.     

On electrical transport in CoWO4 single crystals

CoWO₄ is a p-type semiconductor with conductivity in the range 10^–8 to 10^–3 ohm^–1 cm^–1. The solid exhibits extrinsic behaviour up to 750 K and intrinsic behaviour above 750 K. In this solid conduction by hopping of small polarons seems to be dominating up to 750 K and above 750 K conduction becomes band type. The energy band gap of the solid has been found to be 2.80 eV. The values of mobility and the mean free path are estimated. The variation of dielectric constant with temperature has been attributed to changes in atomic and ionic polarization and space charge polarization of thermally generated charge carriers.     

Electrical transport in copper chromite catalyst

The electrical conductivity, σ, and thermoelectric power, S, of copper chromite (CuCr₂O₄) are reported in the temperature range 295 to 815 K. A break (T _B) in the slope of the plot of log σ against T ^?1 was observed around 556 K. Apart from this break, the curves are linear, and their slopes correspond to activation energies of 0.60 eV (T _B<556 K) and 1.22 eV (T _B>556 K). A break (T′ _B) in the slope of the -S against T ^?1 plot was also observed round 556 K. Apart from the break at this temperature, the S against T ^?1 curves are linear. At T′ _B>556, S can be expressed by the relation $$S = - \left[ {\left( {\frac{{0.65 eV}}{{{\text{2}}eT}}} \right) + (0.42) mV K^{ - {\text{1}}} } \right]$$ The mechanism involved in the electrical transport is the hopping of holes from Cr⁴⁺ centres to neighbouring Cr³⁺ ions. The typical hopping mobility of the holes is of the order of 10⁶ m² V^?1 sec^?1. The mobility activation energy of the holes in CuCr₂O₄ decreases with temperature due to the smoothing of the potential barriers between Cr⁴⁺ and Cr³⁺ sites.     

A.C. proton conduction in hydrous oxides

A.C. proton conductivity measurements on poorly crystalline, electrically insulating hydrous oxides of Sb, Th, In, Cr, Al and Ga show a very wide range of values from 6 × 10^?8 ohm^?1 cm^?1 for A l (OH)₃·H₂O to 7.5 × 10^?3 ohm^?1 cm^?1 for Sb₂O₅·5.4H₂O at 293K. All the samples could be classified as particle hydrates, but the particles themselves appear to vary from oxides (e.g. ThO₂) to hydroxides (e.g. In(OH)₃) to a framework hydrate (e.g. (H₃O)₂Sb₂O₆·H₂O). They are all easily fabricated into dense pellets.     

Variable—Range hopping in Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-K<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript> glasses

The dc conductivity of the glasses in the Fe₂O₃-Bi₂O₃-K₂B₄O₇ system was studied at temperatures between 223 and 393 K. At temperatures from 300 to 223 K, T^–1/4 (T is temperature) dependence of the conductivity was found, however, both Mott variable-range hopping and Greaves intermediate range hopping models are found to be applicable. Mott and Greaves parameters analysis gave the density of states at Fermi level N (E_F) = 3.13 × 10²⁰–21.01 × 10²⁰ and 1.93 × 10²¹–16.39 × 10²¹ cm^–3eV^–1 at 240 K, respectively. The variable-range hopping conduction occurred in the temperature range T = 300–223 K, since W_D was found to be large (W_D = 0.08–0.14 eV for these glasses) and dominated the conduction at T < 300 K.     

Proton conducting membranes composed of hydronium alunite

High proton conductivity, of 3 × 10^?4 ohm^?1 cm^?1 at 20°C, has been found in hydrated pressed discs of hydronium alunite, of formula (H₃O)Al₃(SO₄)₂(OH)₆. The conduction occurs within the hydrated interparticle regions into which protons have been donated, probably from the H₃O⁺ groups exposed on the crystal surfaces. The general utility of the membranes is discussed.     

Electrical properties of electrochemically prepared thin polytetrahydrofuran films II: Characterization under D.C. conditions

The electrical characteristics of electrochemically prepared polytetrahydrofuran (poly-THF) films were studied under d.c. conditions. At low fields (?10⁵ V cm^?1) a phonon-assisted hopping conduction occurs in poly-THF films 2000 Å thick. The low temperature dependence of the conductivity (T< 243 K) is related to interchain hopping, whereas the high temperature dependence of the conductivity (>320 K) is ascribed to trap hopping. At high fields (E>10⁵ V cm^?1) and high temperatures (T>320 K) Schottky conduction is observed and the Schottky barrier height depends both on the electrode metal and on the field direction. At temperatures below 320 K, Poole-Frenkel conduction occurs and the current intensity is independent of the nature of the electrodes and of the field direction. At very low temperatures (T<100 K) and high fields (E>10⁶ V cm^?1), thermally assisted tunnel effect conduction (δj∞T²) is observed. These changes in conduction with the temperature and the field are ascribed to changes in the polymer structure.     

Electrical and optical properties of TiN thin films

TiN thin films have been grown by reactive magnetron sputtering. It has been shown that an Ohmic contact to TiN thin-film can be made from indium. The TiN thin films have been shown to be n-type semiconductors with a carrier concentration of 2.88 × 10²² cm^?3 and resistivity of ρ = 0.4 Ω cm at room temperature. The activation energy for conduction in the TiN films at temperatures in the range 295 K < T < 420 K is 0.15 eV. The optical properties of the TiN thin films have been investigated. The material of the TiN thin films has been shown to be a direct gap semiconductor with a band gap E _g = 3.4 eV.     

A study of the electrical characteristics,before electroforming,of thin SiOx films with laterally-spaced electrodes

The sample structure comprises two laterally-spaced electrodes joined by a thin dielectric film. The electrodes make a blocking contact to the dielectric with a barrier height ～ 0.75 eV. The voltage-current characteristic is studied between 213 to 413 K. Below room temperature the effect of hopping conduction on such contacts is explained. At room temperature and at high fields where hopping conduction is expected to be less effective, the conduction is controlled by the contact. Above room temperature and at low fields localized state conduction (hopping) becomes effective again with activation energy ～ 0.07 eV and an estimated charge carrier mobility of 1.3×10^?2cm²V^?1sec^?1. The density of ionizable impurities is estimated to be in the range 1 to 6×10¹⁸cm^?3 and the density of surface states is of the order of 1×10¹³cm^?2.     

Investigation of the temperature dependence of electron and phonon Raman scattering in single crystal YBa2Cu3O6.952

Detailed Raman-scattering measurements have been performed on high-quality YBa₂Cu₃O_6.952 single crystal (T _c =93 K, T _c =0.3 K). A sharp (FWHM 7.2 cm^–1 at 70 K and 10.0 cm^–1 at 110 K) 340 cm^–1phonon mode has been observed inB _1g polarization. An electronic scattering peak at 500 cm^–1 in theB _1g polarization extends down to 250 cm^–1. These FWHM values determine the upper limit of the homogeneous linewidth of the phonon and electronic excitations. The start of the electronic spectral function renormalization and of the 340 cm^–1 mode anomalies (frequency softening, linewidth sharpening, and intensity increase) have been observed to occur approximately 40 K aboveT _c . The 340 cm^–1 mode Fano shape analysis has been performed and the temperature dependences of the Fano shape parameters have been estimated. All 340 cm^–1 mode anomalies have been explained by the electronic spectral function renormalization.This work was supported by Swedish Natural Sciences Research Council (G.B. and L.B.) and by the National Science Foundation (DMR 91-20000) through the Science and Technology Center for Superconductivity (G.B. and M.V.K.).     

Electrical conduction in light rare-earth tungstates

This paper reports the results of electrical conductivity (σ) and thermoelectric power (H) of light rare-earth tungstates in the temperature range 600–1200K. Holes are the dominant charge carriers over the whole studied temperature range for Nd, Sm and Gd tungstates. However, in the case of La, Ce and Pr tungstates, the conduction is dominated by electrons at lower temperatures, but above 950K in La, 800K in Ce and 950K in Pr the dominant charge carriers become holes. A sharp break and change in the log σ vs 1/T slope occurs in La, Ce and Pr tungstates around the same temperature at which the dominant charge carrier changes from electrons to holes. In the case of Nd, the conductivity anomaly occurs around 1020K without any change in the nature of the charge carrier. The data have been analysed using band theory.     

Superconductivity,normal state electrical and structural properties of Nb/Al2O3 cermet films

Nb/Al₂O₃ cermet films were obtained by electron-gun evaporation from two independent sources. Films containing 71 wt.% Nb (particle size about 20 Å) have an activated type of conduction mechanism due to the hopping of the charge carriers between localized states. The activation energy decreases continously from 8.8 x 10^?3 eV (300°K) to 1 x 10^?6 eV (1.9°K), which indicates that the localized states lie close to the Fermi level of the system. These states can be associated with small Nb particles (below the resolution power of the electron microscope—10 Å) in the alumina matrix. Films containing more than 85wt.%Nb (mean particle size 32 Å) have a metallic-type conduction mechanism and show superconductive properties. The transition temperature is reduced to 4.5—5.2°K compared with the Nb bulk value of 9.2°K; this is presumably due to a decrease of the electronic interaction in the surface layer of the Nb particles.     

Constant-Volume Gas Thermometry with Different Helium-3 Gas Densities at NMIJ/AIST

Constant-volume gas thermometer (CVGT) measurements are conducted using ³He of three different densities as the working gas to obtain the thermodynamic temperature T _CVGT and the second virial coefficient of ³He, B, at temperatures down to 3 K, using the triple point of Ne as a reference temperature. Densities of 127 mol ?? m^?3 and 278 mol ?? m^?3 are used in addition to the density of 168 mol ?? m^?3 used in the measurement reported previously, where T _CVGT was obtained using the virial coefficient adopted by the International Temperature Scale of 1990 (ITS-90), B _ITS-90. T _CVGT is obtained by two methods, by the single- and multi-isotherm fitting of B to the three densities and by the method used in the previous work using one of the three densities and B _ITS-90. B obtained from the isotherm fitting agrees with B _ITS-90 within the uncertainty of the data used to derive B _ITS-90. Moreover, B obtained from a multi-isotherm fit agrees with that of recent theoretical ab initio calculations within 0.05?cm³ ?? mol^?1 at 5 K and above, and within 0.3?cm³ ?? mol^?1 down to 3 K. The values of T _CVGT obtained from the multi-isotherm fits assuming different forms for the temperature dependence of B agree with each other within 0.1?mK. T _CVGT obtained from the multi-isotherm fitting agrees with that obtained from the method in the previous report within 0.22?mK. The tendency of the difference between T _CVGT and the ITS-90 temperature reported in the previous work is confirmed in the present work.     

High ionic conductivity in densified polycrystalline lithium nitride

Pure polycrystalline Li₃N pellets densified by sintering at elevated temperatures have been found to have a conductivity of 4 × 10^?4 ohm^?1 cm^?1 at 25°C. The impedance of conductivity cells prepared from these pellets with lithium electrodes has been found to be essentially frequency independent. The d.c. conductivity was 2 × 10^?4 ohm^?1 cm^?1 at 25°C. Its use in solid state batteries must allow for the fact that it reacts with cathode-active materials under moderate conditions.     

Resonant Raman Study of Superconducting Gap and Electron-Phonon Coupling in YbBa2Cu3O7−δ

We investigate the electronic background as well as the 02-03 mode at 330 cm ^–1 of highly doped YbBa ₂ Cu ₃ O _7– in B _1g symmetry. Above the critical temperature T._c the spectra consist of an almost constant electronic background and superimposed phononic excitations. Below T _c the superconducting gap opens and the electronic background redistributes exhibiting a 2 peak at 320 cm ^–1 . We use a model that allows us to separate the background from the phonon. In this model the phonon intensity is assigned to the coupling of the phonon to inter- and intraband electronic excitations. For excitation energies between 1.96 eV and 2.71 eV the electronic background exhibits hardly any resonance. Accordingly, the intraband contribution to the phonon intensity is not affected. In contrast, the interband contribution vanishes below T _c at 1.96 eV while it remains almost unaffected at 2.71 eV.     

Fish-Tail Effect and Its Evolution Under Neutron Irradiation in Li-Doped YBa2Cu3O7−x

The evolution of the critical current density of Li-doped YBa₂Cu₃O_7?x polycrystalline samples submitted to neutron irradiation is investigated as function of magnetic field (0 ≤ B ≤ 6 T) temperature (5 ≤ T ≤ 85 K) and neutron fluence (0 ≤ Φ ≤ 9.98 × 10¹⁷ cm^?2). At fluences lower than 10¹⁷ cm^?2, a second peak in j _s vs. B dependence is present (fish-tail effect). Its magnitude decreases with increasing the fluence. Above 10¹⁷ cm^?2, the second peak of current density completely disappears; instead, the logarithmic susceptibility shows a second peak at a certain field B _infl. A dependence of B _infl on fluence is proposed.     

Rapid H+ conductivity in hydrogen uranyl phosphate-A solid H+ electrolyte

We have found that the layered hydrate HUO₂PO₄. 4H₂O is a rapid proton conductor. The room temperature conductivity of 4 × 10^?3ohm^?1cm^?1 is higher than that of Na⁺ in β alumina. The activation energy is 30± 3 kJ mol^?1. The material is insoluble, and presses into transluscent discs suitable for solid electrolyte applications.     

The incommensurate solid solution phase Na5−4x Zr1+x(PO4)3:0.04 <x <0.15

The orthophosphate solid solution phase, Na_5?4x Zr_1+x(PO₄)₃:0.04 ? x ? 0.15 has trigonal symmetry with an apparent one dimensional incommensurate superstructure parallel to c_HEX. Using selected area electron diffraction patterns as a guide, an indexing scheme for the powder X-ray data has been devised. The parameter $\text{k = c}{}_{\mathrm{<mtext>supercell</mtext>}}\text{c}{}_{\mathrm{<mtext>subcell</mtext>}}$ varies smoothly with composition from ～ 10.4 at x = 0.04 to ～4.4 at x = 0.11 and is believed to originate in ordering of the extra interstitial Zr⁴⁺ ions. The Na⁺ ion conductivity increases gradually with x and for x = 0.108 varies from ～5×10^?8 ohm^?1 cm^?1 at 25°C to ～1×10^?3 ohm^?1 cm^?1 at 300°C.