Sodium Doping Research Articles

Superconducting properties of sodium doped (Pb,Cd)-1212 type compounds

The effect of sodium doping (3–8 mol%) on the structural, thermal and superconducting properties of (Pb 0.5,Cd 0.5)Sr 2(Y 0.6,Ca 0.4)Cu 2O 7− δ has been studied. For 5 mol% NaNO 3 doping, relatively pure superconducting phase was formed without SrCuO 2 and Sr 5Pb 3CuO 12 impurities as observed in both 3% and 8% doped as well as undoped superconductors. The cell parameters and cell volumes are also found to be minimum for the 5% doped superconductor, but were slightly larger than for the undoped superconductor. Highest T c of 55 K was also observed for 5% doped sodium containing sample and the T c enhancement was 15 K above the sodium free superconductor. The effect of calcium content on the T c enhancement by 5% sodium addition was investigated for (Pb 0.5Cd 0.5)Sr 2(Y 1− x Ca x )Cu 2O 7− δ ( x=0.3, 0.5) superconductors. The sodium free superconductors show only onset of superconductivity ( T c,onset), which increases from 23 to 49 K with increasing calcium content. The resistivity behaviour before T c changes from semiconducting to metallic nature. Addition of sodium leads to the observation of zero resistance ( T c,zero) at 25 K only for x=0.5 sample, which is however lower than the T c,zero of 30 K exhibited by the superconductor with x=0.4 calcium content. The lowering of melting point and denser microstructure with larger grains were observed upon 5% sodium doping on (Pb 0.5,Cd 0.5)Sr 2(Y 0.6,Ca 0.4)Cu 2O 7− δ superconductor.

Effect of sodium and oxygen doping on the conductivity of CuInS2 thin films

Doping of Cu-poor CuInS2 thin films by sodium and oxygen species, such as O2 and O, was investigated by SIMS and conductivity measurements. Increased oxygen concentration is found for Na-doping. The SIMS signals of CuO and CuOS were detected. They coincide for O-doped films but differ for Na and O2 doped films. This is interpreted as due to grain boundary effects. Na doping leads to an increase in lateral conductivity. This finding supports the model previously proposed by L. Kronik, D. Cahen, H.W. Schoek, Adv. Mater. 10 (1998) 31] that oxygen plays a major role in Na doping. The presented results, furthermore, propose oxygen single doping for chalcopyrite films.

Comparison of superconductivity and structure for YBa2Cu3Oy with potassium and sodium doping

The nominal composition of YBa2−x M x Cu3O y (M = K, Na) cuprates with x ≤ 0.30 were synthesized by the standard solid-state reaction technique. X-ray diffraction (XRD) and the resistivity measurements were used to characterize the structure and the superconductivity of the doped cuprates. There was no impurity phase detected within the whole doping range. The structure of the main phase (“123”) has the orthorhombic with P mmm symmetry. With increasing the content of dopants, the lattice constants and some other structural parameters are almost unchanged for M = K, whereas they changed for M = Na. The refined contents of dopants are consistent with that of the nominal ones. The zero resistance temperature T c0 decreases sharply with the increase of the content of potassium in potassium-doped samples as x ≤ 0.20. For sodium-doped YBa2−z Na x Cu3O y cuprates, T c0 varies very little. The difference in superconductivity depression may result from the shift oxygen, which transfers conducting carriers from Cu-O chains to Cu-O2 sheets or the structural stress effect.

Hydrostatic Stress Induced Shifts of Tc for Cr3+ Doped Sodium Ammonium Sulphate Dihydrate

Hydrostatic Stress Induced Shifts of Tc for Cr3+ Doped Sodium Ammonium Sulphate Dihydrate

Hydrostatic Stress Induced Shifts of Tc for Cr3+ Doped Sodium Ammonium Sulphate Dihydrate

Hydrostatic Stress Induced Shifts of Tc for Cr3+ Doped Sodium Ammonium Sulphate Dihydrate

Effect of sodium doping on the oxygen distribution of Hg-1223 superconductors

Low-temperature oxygen annealing was performed on Na-doped and undoped Hg-1223 phases. It is argued that Na could perturb the electronic band structure of the material by changing the distribution of oxygen in the Hg–O layer, which then could affect the superconductivity of the material during the annealing process. It has been found that T c can be increased by more than 20 K using an annealing temperature of 300°C for 10 h, while annealing above 350°C leads to loss of superconductivity due to Hg loss. Normal state- ρ tends to decrease with increasing annealing temperatures up to 400°C. In addition, flattening in the normal state- ρ curves of doped samples indicated an increasingly insulating behavior.

Evidence of dynamic Jahn-Teller distortions in two-dimensional crystalline molecular films

The surface electronic structure in crystalline copolymer films of vinylidene fluoride (70%) with trifluoroethylene (30%) has been studied by photoemission and inverse photoemission as a function of alkali metal (sodium) doping. Sodium doping introduces at least two new states into the band (HOMO-LUMO) gap well away from the Fermi level. While the sodium-doped copolymer is observed to resemble an n-type semiconductor, the change in electronic structure with temperature suggests that dynamic distortions lead to a photoemission initial state splitting of the lower Hubbard-like bands. There is a decrease in the effective Debye temperature with sodium doping which may, in turn, enhance the dynamic Jahn-Teller distortion.

Electrochemistry of Sodium Sulfate Doped Glass Melts.

Redox behaviors of sulfur species in sodium borate, silicate and phosphate melts doped sodium sulfate were studied by means of differential pulse voltammetry. In the 10Na2O⋅90B2O3 melt, three reduction peaks are observed. The peak intensity at -400mV, which appeared as a shoulder of the peak at -300mV, decreases with the elapse of time. In the early stages of melting, noises are superimposed on the peak beyond -600mV. In the 30Na2O⋅70B2O3 melt, the profile of the voltammogram does not change much with time after 92h. The voltammograms of sodium metaphosphate melt at the initial stage of melting have large noises beyond -600mV. The peak at -400mV disappears after 23h. In the sodium borate melts, the intensity of the peak at -450mV decreases and its position shifts to the positive side with an increase in temperature, whereas the intensity of the peak at -600mV increases with an increase in temperature. In the 20Na2O⋅80B2O3⋅0.5Na2S melt, the peak position shifts to the positive side with an increase in heating time due to the oxidation of S2- to SO42-. By combination of the Raman signal at 988cm-1 and the IR signal at 630cm-1, which are assigned to the fundamental vibration of SO42-, the three peaks of the voltammogram are assigned to the successive reductions of SO42-, SO2 and S0 with the cathodic reduction process. The stability of SO42- increases with an increase in the basicity of the melts and with a decrease in temperature.

Effects of introduction of sodium and water on second-order nonlinearity in poled synthetic silica glass

Second harmonic generation (SHG) from silica glasses doped with sodium or water was investigated to clarify the effects of the impurities on the second-order nonlinearity. Sodium ions were introduced into pure silica glasses from a polymer coating containing a trace amount of sodium with electrical poling. The doping of sodium drastically increased the SHG intensity from the poled silica glasses. The nonlinearity localized in the anode surface region is suggested to be ascribed to a frozen electric field formed by the drift of sodium ions. Introduction of water molecules into silica glasses was performed by hydrothermal treatment in purified water using an autoclave. The SHG intensity from the electrically poled glasses also increased with the increasing content of water molecules. In this case, the SHG was emitted from the entire region of the sample plate. The origin of the nonlinearity is tentatively assumed to be due to a frozen electric field created by charge separation with protonic conduction.

Effect on the reaction between methanol and hydrogen sulphide of Na or Mo doping on zirconia and alumina

The effect of sodium doping on alumina and zirconia activity in methanethiol formation from hydrosulphurisation of methanol by H 2S was studied. It provoked an activity decrease and a selectivity increase in agreement with the catalysts basicity increase. By contrast, molybdenum doped zirconia samples presented a higher activity but a lower selectivity than pure zirconia, as expected from their higher acidity. Increase of the CH 3OH/H 2S ratio in the reaction mixture improved both activity and CH 3SH selectivity. It was found that zirconia loaded with small amounts of molybdenum working under H 2S excess shows good performances towards CH 3SH production.

Effect of sodium doping on thermoluminescence and optical properties of barium borate (BaB 2O 4) single crystals

Thermoluminescence (TL) emission from undoped and sodium doped α- and β-BaB 2O 4 (BBO) crystals has been investigated. A single TL glow peak is observed for the undoped crystals of both phases. The glow peak temperatures found for α- and β-BBO crystals over the temperature range 35–300°C are 104 and 80°C, respectively. The presence of minute amount of sodium ions in the lattice gives rise to a glow peak around 200°C. For impurity concentrations higher than 0.02% (by wt), additional glow peaks around 123 and 240°C are also observed. The ratio of the TL intensities corresponding to the first and 200°C peaks is observed to increase with impurity concentration. This fact provides an easy and sensitive method of detecting the presence of sodium ions in BBO lattice. The results also show that sodium ions go substitutionally into the lattice and act as charge traps. The optical absorption in the ultra violet region and the crystal hardness towards ionizing radiations are found to be adversely affected by the presence of this impurity.

Oxidative coupling of methane. The effect of strontium and sodium dopants on catalytic performance of Y 2O 3, a p-type semiconductor material

Oxidative coupling of methane to higher hydrocarbons was investigated using a p-type semiconductor catalyst, Y 2O 3, doped with Sr 2+ and Na + cations at 1 atm pressure. The ratio of methane partial pressure to oxygen partial pressure was changed from 6 to 40 and temperature was kept constant at 1023 K in the experiments conducted in a co-feed mode. Both C 2+ selectivities and % CH 4 conversion were substantially higher for the case of Sr/Y 2O 3 (1:10 mole ratio) catalyst as compared to the undoped Y 2O 3 catalyst at constant P CH 4 /P O 2 ratios. For the case of Na-doped Y 2O 3 catalysts, C 2H 4 selectivity was observed to be nearly zero. Ethane selectivities increased in the order of Y 2O 3<Sr/Y 2O 3 (1:10) < Na/Y 2O 3 (1:10) <Na/Y 2O 3 (1:1). SEM/EDX analyses of fresh catalysts also indicated incorporation of Sr 2+ and Na + cations into the lattice structure of Y 2O 3. Excess Sr was detected by XRD on the Sr/Y 2O 3 catalyst after experiment. For the fresh Na/Y 2O 3 (1:1) catalyst, excess Na 2CO 3 was clearly observed in SEM photographs; the enhancement in C 2H 6 selectivity seen in this catalyst could be ascribed to this excess Na 2CO 3.

Relaxation and IR spectroscopic properties of the CN− stretching mode in silver halides

Abstract The relaxation times of the CN−stretching mode in AgCl and AgBr at 1.7 K are found to be a few hundred microseconds. These times are shorter by more than two orders of magnitude than those for CN− in most alkali halides. High frequency local modes discovered in the silver halides are suggested to act as fast relaxation channels causing this difference. Reexamination of CN− doped sodium halides also reveals a local mode clearing up the previously found short times in these materials, too. An energy gap law fits all data.

Preparation of π-conjugated polythiazoles and their electrically conducting properties

Poly(thiazole-2,5-diyl) (PTz), poly(4-methylthiazole-2,5-diyl) (PMeTz) and poly(4,4′-dimethyl-2,2′-bithiazole-5,5′-diyl) (PMeBTz) are synthesized by dehalogenation polycondensation of the corresponding dibromothiazoles with zero-valent nickel complexes. PTz and PMeTz are soluble in formic acid and trifluoroacetic acid, whereas PMeBTz is soluble in trifluoroacetic acid. PTz and PMeBTz have weight-average molecular weights (Mw) of 5.9 × 104 and 3.2 × 103, respectively, as determined by a light scattering method. The UV-Vis spectra of PTz, PMeTz and PMeBTz show π-π∗ absorption peaks at 421 nm (in formic acid), 420 nm (in formic acid) and 425 nm (in trifluoroacetic acid), respectively. These absorption peaks are shifted to longer wavelength compared with that (λmax = 233 nm) of thiazole. Sodium doping of polythiazoles affords semiconducting materials with conductivity (σ) values of an order of 10−4 S cm−1.

Electronic structure of pristine and sodium-doped cyano-substituted poly(2,5-dihexyloxy-p-phenylenevinylene): A combined experimental and theoretical study

The electronic structure of cyano-substituted poly(2,5-dihexyloxy-p-phenylene-vinylene), or CN-PPV, has been studied in both pristine and doped states. Ultraviolet photoelectron spectroscopy (UPS) and x-ray photoelectron spectroscopy (XPS), as well as optical absorption spectroscopy have been carried out under ultrahigh vacuum (UHV) conditions, and the results have been interpreted with the help of quantum-chemical calculations. For the pristine polymer, the addition of cyano groups to the vinylene units does not affect the width of the π-bands closest to the Fermi level; however, the positions of the flat parts of the upper π-bands are shifted by approximately 0.4 eV towards higher binding energies relative to the Fermi energy, as compared with the corresponding bands of other alkoxy-substituted poly(p-phenylenevinylene)s. On the other hand, there are only marginal differences in the optical absorption spectra; the interband absorption onset is comparable to the values for alkoxy-substituted poly(p-phenylenevinylene)s. In the case of sodium doping, it is found experimentally that at saturation doping, there is about one sodium ion per phenylene vinylene unit; in that situation, two new states appear in the previously forbidden energy bandgap, which are consistent with the formation of bipolaron bands. These results are similar to those obtained for sodium-doping of poly(p-phenylenevinylene) (PPV). The peak-to-peak splitting of the bipolaron peaks in CN-PPV is 1.05 eV, compared with about 2.0 eV for sodium-doped PPV at saturation doping; this difference is related to the pinning of some of the transferred charges to the cyano vinylene groups and the phenylene rings that they are conjugated to in CN-PPV, causing a stronger confinement of the bipolaron charge carriers.

Solid state battery with pure and doped sodium yttrium fluoride as the solid electrolyte

Solid state batteries using pure and doped sodium yttrium fluoride as the solid electrolytes were fabricated at ambient temperature. The discharge characteristics of the cells for a load of 1 M Omega were studied. The cell with NaYF4:Dy as the solid electrolyte exhibited a larger plateau region compared with the other cells. Open circuit voltage and short circuit current of the cells range from 2.5 to 2.7 V and 7 mu A to 435 mu A respectively. The performances of the cells under varying loads for a constant voltage of 1.5 V were also investigated. Various cell parameters were evaluated.

Superconductivity in the (Yba2Cu3)1−xNaxO7−δ System

The (YBa2Cu3)1−xNaxO7–δ system in the range of x= 0–0.8 was investigated. Experimental data suggest that the sodium doping with x 0.26 does not affect the critical transition temperature Tc, and the crystal structure maintains the orthorhombic lattice with a slightly smaller unit cell. However, sodium doping increases the sintering and grain growth kinetics, resulting in a higher superconducting phase volume and an enhanced Meissner effect. It also lowers the processing temperaturel. The experimental data also suggest that the sodium atoms diffuse into the superconducting YBa2Cu3O7−δ crystallites, which stabilizes the orthorhombic phase. The transition temperature (ortho‐rhombic to tetragonal) in sodium‐doped materials increases with the increasing concentration of sodium.

The preparation and magnetic properties of sodium-modified iron oxide thin films by a solgel method

Spinel-type thin magnetic films consisting of sodium-modified iron oxide were prepared using a solgel method and a dip-coating technique. Iron(III) nitrate [Fe(NO 3) 3 . 9H 2O] and sodium methoxide [CH 3ONa] were dissolved in ethylene glycol and 2-methoxyethanol to form the starting solution. The thickness was controlled by the solution parameters and withdrawal speed. Magnetization values depended on the amount of sodium doping [c Na = 0−0.5, where c Na = Na ( Fe + Na) ], the temperature and the atmosphere during firing cycles. Films were characterized by means of X-ray diffraction measurement (cobalt anode), UV—VIS, SEM and magnetization measurements. Reasonable results were obtained for a sodium doping level of c Na = 0.2 at an annealing temperature of 430°C. The magnetization and coercive force were 188.5 × 10 3 T (150 emu/cm 3) and 4 × 10 3 A/m (50 Oe), respectively.

Spectroscopic measurements of Rosseland mean opacity

The first quantitative measurement of photoabsorption in the region determining Rosseland and Planck mean opacity, is obtained for an x-ray heated iron plasma, using novel techniques and instrumentation. The plasma density of 0.0113 ± 0.0013 g/cm 3 and temperature of 59 ± 3 eV are accurately constrained experimentally by imaging plasma expansion and observing and modeling absorption in sodium dopant ions. The measured iron absorption spectrum is compared with several newly developed opacity models. The data constrains Rosseland and Planck group means with of order 15% precision. This is the first quantitative experimental certification of opacity models germane to radiative transfer in LTE plasmas.

Structural and thermal properties of (YBa2Cu3)1−xNaxO7−δ materials

This letter discusses experimental data on thermal expansion and thermogravimetric analysis (TGA) to elucidate the structural and thermal characteristics of (YBa2Cu3)1−xNaxO7−δ materials. The experimental data reveal that the incorporation of sodium in the (YBa2Cu3)1−xNaxO7−δ materials stabilizes its orthorhombic structure and makes it less sensitive to oxygen resorption and desorption processes. In addition, the sodium doping was found to raise the orthorhombic↔tetragonal phase transformation temperature. Furthermore, the Auger electron spectroscopy (AES) data reveal that sodium selectively replaces yttrium in the crystal lattice.