Superconducting and electrical properties of rhenium nitride and amorphous rhenium prepared by ion implantation

Different rhenium nitrides were prepared by homogeneous implantation of nitrogen ions into rhenium thin films at various temperatures as a function of N concentration. At 9 at % N new x-ray lines appeared in addition to the hcp rhenium phase. The formation of this phase, which could not be identified, was accompanied by a large increase in stress, of the order of 10¹¹ dynes/cm². Rhenium nitride with fcc structure was formed between 13 and 50 at %. For ReN a lattice parameter of 4.021±0.002 Å, a maximumT _cvalue of 4.5–5.0 K, and a resistivity ρ_RT of 250 µΩ-cm were obtained. Both rhenium nitride phases decomposed above 645 K. An x-ray amorphous phase was obtained after implantation of 40 at % N at LNT. This amorphous phase had aT _cvalue of 6.0 K and a ρ_RT value of 300 µΩ-cm. Transformation into an amorphous Re phase was also observed after implantation of 20 at % P. The maximumT _cvalue of this phase was 7 K. This phase decomposed at about 925 K.     

W、Mo、Re基体熔盐电沉积Ir涂层初探

采用熔盐电沉积法在W、Mo、Re基体表面分别制备了Ir涂层,通过扫描电镜和能谱分析了涂层的形貌和成分,对比研究了W、Mo、Re在熔盐电沉积Ir涂层过程中的性质。结果表明：W和Mo在氯化物熔盐体系中腐蚀严重,电沉积后在基体和涂层之间形成了含有腐蚀产物的夹盐层,大大降低了涂层和基体之间的结合力,在热应力和外力的作用下涂层易...     

Substrate heating rates for planar and cylindrical-post magnetron sputtering sources

Substrate heating energies per atom deposited are reported for planar magnetron sputtering of aluminum, chromium, nickel, copper, molybdenum, indium, tantalum, tungsten and platinum in argon as well as for aluminum and chromium sputtered in O₂. Data are also reported for cylindrical magnetron sputtering of niobium, silver, tantalum, tungsten and Pb-Sn in argon as well as for molybdenum sputtered in neon, argon, krypton and xenon. The planar and cylindrical magnetron heating rates were comparable. The heating energies for argon sputtering ranged from 10–15 eV per deposited atom for the light metals to almost 100 eV atom^-1 for tantalum and tungsten. The implied reactive sputtering heating energies were about 500 eV molecule^-1 for Cr₂O₃ and 1150 eV molecule^-1 for Al₂O₃. Special experiments were conducted to examine the contributions to the substrate heating of plasma species and ion neutralization and reflection at the cathode. The data indicate that charged plasma species do not contribute significantly to the heating but that neutralized and reflected ions play a significant role in the planar as well as the cylindrical cases despite the differences in cathode geometry.     

Phase relationships in the ternary systems (V,Cr, Mo,W, Mn,Re)-Al-N

Phase equilibria in the ternary systems of aluminum and nitrogen with vanadium, chromium, molybdenum, tungsten, manganese and rhenium are investigated by X-ray diffraction of sintered alloys. No ternary phase is observed. AIN does not show solubility for these metals, and coexists either with the solid solution of these metals with aluminium (in the case of vanadium, chromium and manganese) or with the pure metal (for molybdenum, tungsten and rhenium). Isothermal sections are presented for 1073 K (Mn-Al-N), 1273 K (V-Al-N, Cr-Al-N, Mn-Al-N and Re-Al-N), 1573 K (V-Al-N) and 1773 K (Mo-Al-N, W-Al-N and Re-Al-N).     

Effects of substitution of X (X=rhenium,chromium and zirconium) on the properties of Co7Mo6 μ phase: A first‐principles study

The effects of three typical refractory elements (rhenium, chromium and zirconium) substituting the molybdenum atom in Co₇Mo₆ μ phase were investigated using first‐principles calculations based on the density functional theory (DFT). Energy (including binding energy and defect energy) and electronic structures (including density of states and charge density) of Co₇Mo₅X (X=rhenium, chromium and zirconium) were calculated. The optimized lattice structure of Co₇Mo₆ agrees well with the experimental data. The calculated results show the bonding between doped rhenium atom and its nearest neighbor molybdenum and cobalt atoms gets visibly stronger, contributing to the good stability of the unit cell. Neverthless, the bonding between chromium and its nearest neighbor molybdenum and cobalt is weaker, and the zirconium‐molybdenum and zirconium‐cobalt bonds are much weaker. The results reveal rhenium tends to participate in the formation of μ phase, but zirconium and chromium atoms are not prone to concentrate in μ phase.     

Crystal structure and thermal annealing behaviors of high d 33 Aurivillius-phase ceramics Li0.04Ce0.04Na(0.46−x/2)Bi(4.46+x/2)Ti(4−x)Sc x O15 with the Sc3+/Bi3+ co-substitution

Modified Aurivillius-type-structured piezoelectric ceramics, Li_0.04Ce_0.04Na_(0.46?x/2)Bi_(4.46+x/2)Ti_(4?x)Sc _x O₁₅ (LiCe–NBT–Sc?x, x = 0, 0.025, 0.075, 0.125, 0.15, 0.175) were synthesized by using conventional solid-state reaction process. Rietveld refinement for the x = 0.125 modified sample was carried out by using powder X-ray diffraction and LiCe–NBT–Sc?0.125 was confirmed to be a four-layer Aurivillius oxide with orthorhombic space group A2 ₁ am [a = 5.45814(7) Å, b = 5.43029(7) Å, c = 40.8547(4) Å and V = 1,210.902(26) Å³; Z = 4], at room temperature. The Sc³⁺/Bi³⁺ substitution led to an increase in Curie temperatures (T _c) and an enhancement in piezoelectric property, and the LiCe–NBT–Sc?0.125 ceramic with a T _c of 675 °C had a high piezoelectric activity (d ₃₃) of 32 pC/N. Variable thermal-annealing d ₃₃ and resistivity (ρ) of the LiCe–NBT–Sc?0.125 ceramic were investigated; the d ₃₃ of the O₂ annealed sample reached up to 37 pC/N, and its resistivity was about 6.8 × 10⁶ Ω cm at 575 °C and about 6.5 × 10⁵ Ω cm at 650 °C.     

Electrical properties of exchange-enhanced systems: Co in (Pd95Rh5)

The electrical resistivity of several (Pd₉₅Rh₅)-based alloys containing between 1.1 and 2.6 at % Co has been measured up to 300K. In alloys containing between 1.4 and 2.6 at % Co the incremental resistivity δ?(T) is found to contain a Tsu2 term at low temperatures, as previously found for comparable amounts of Fe in the same host, and from which it is inferred that the restoration or removal of wave vector conservation for electron-magnon scattering in this type of system is not a mean-free-path effect. Estimates of the acoustic spin-wave stiffness are derived from the measured Tsu2 terms. These resistivity data also enable the magnetic ordering temperatures T _c and the s-electron- and d-electron-local moment exchange couplings J _s-local and J _d-local to be estimated. Differences in the behavior of the incremental resistivity δ?(T) in the paramagnetic regime of (Pd₉₅Rh₅)Fe and (Pd₉₅Rh₅)Co systems are tentatively discussed in terms of the possibility of localized spin fluctuations at the Co sites.     

Thermophysical measurements on tungsten-3 (wt %) rhenium alloy in the range 1500–3600 K by a pulse heating technique

Simultaneous measurements of the specific heat capacity, c _p, electrical resistivity, ρ, and hemispherical total emittance, ε, of tungsten-3 (wt%) rhenium alloy in the temperature range 1500–3600 K by a subsecond-duration pulse heating technique are described. The results are expressed by the relations $$\begin{gathered} c_{\text{P}} = 0.30332 - 2.8727 \times 10^{ - 4} {\text{ }}T + 1.9783 \times 10^{ - 7} {\text{ }}T^2 \hfill \\ {\text{ }} - 5.6672 \times 10^{ - 11} {\text{ }}T^3 + 6.5628 \times 10^{ - 15} {\text{ }}T^4 , \hfill \\ \rho = - 24.261 + 8.1924 \times 10^{ - 2} {\text{ }}T - 3.7656 \times 10^{ - 5} {\text{ }}T^2 \hfill \\ {\text{ + 1}}{\text{.1850}} \times {\text{10}}^{ - 8} {\text{ }}T^3 - 1.3229 \times 10^{ - 12} {\text{ }}T^4 , \hfill \\ \varepsilon = 0.1945 + 5.881 \times 10^{ - 5} {\text{ }}T, \hfill \\ \end{gathered} $$ where T is in K, c_p is in J·g^?1·K^?1, and ρ is in μΩ·cm. The melting temperature (solidus temperature) was also measured and was determined to be 3645 K. Uncertainties of the measured properties are estimated to be not more than ±3 % for specific heat capacity, ±1 % for electrical resistivity, ± 5 % for hemispherical total emittance, and ±20 K for the melting temperature.     

Optical study of localization in theab-plane conductivity of single crystals of YBa2Cu3O6.95 induced by ion damage

We studied the changes in the dc resistivity, Raman scattering, and IR conductivity of single crystals of YBa₂Cu₃O_6.95 induced by damage from low-energy He⁺ ion bombardment. It appears thatT _c , transport properties, and optical conductivity are strongly affected by modest irradiation doses whereas the chemical composition of the sample is not modified. Carrier localization is evidenced by the frequency dependence of the optical conductivity in the strongly damaged crystal and is used to explain the suppression of both the superfluid density andT _c upon irradiation. The temperature dependence of the superfluid density is in agreement with the theoretical predictions for ad-wave superconductor. We also show that the intrinsic residual losses in the FIR are dramatically reduced in the disordered crystal.     

Electrical properties of exchange-enhanced systems: Fe in (Pd95Rh5)

The electrical resistivity of the giant moment system Pd₉₅Rh₅ containing between 0.8 and 1.85 at % Fe has been measured from 1.4 to 300 K. The incremental resistivity in alloys containing more than 1.25 at % Fe is found to exhibit aT ² limiting low-temperature form; however for the 0.8 and 1.1 at % Fe alloys such aT ² form is not clearly discernible, with (T) exhibiting a temperature dependence intermediate betweenT ² andT ^3/2. The former result is predicted from conduction electron-magnon scattering for which wave vector conservation holds, from which it is inferred that the criterion for wave vector conservation in this type of alloy isnot determined by mean free path effects. Estimates of the acoustic spin-wave stiffnessD are derived from the measuredT ² coefficients. These resistivity data also enable estimates of the exchange coupling parameterJ _s-local to be made. The magnetic ordering temperatureT _c is considerably less discernible than in single-component hosts but approximate values have been derived for the various alloys, from which estimates of the exchange coupling parameterJ _d-local have been made. In the disordered phase the measured incremental resistivity is found to contain a term which decreases approximately linearly with increasing temperature, at a rate of –(1.1±0.45)10^–3 µ cm/K at % Fe. Using existing pressure data on both Pd- and PdRh-based alloys, it is shown that both the sign and magnitude of this term can be accounted for in terms of the volume dependence of the potential and exchange terms, in conjunction with a large coefficient of thermal expansion.This work has been supported in part by the Defence Research Board under Grant No. 9510-100.     

Effect of Co partial substitution on the valence state of Ru in the Gd<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ru<Subscript>2</Subscript>O<Subscript>7</Subscript> pyrochlore

Polycrystalline samples of Gd_2?xCo _x Ru₂O₇ with x = 0.0, 0.1 and 0.4 were synthesized by the molten salt method. The samples were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrical resistivity measurements. Rietveld refinements of the XRD patterns and XPS measurements showed that the Co²⁺ ion replaces Gd³⁺ sites. As a result, the lattice parameter a and the Ru–O bond length decrease; then, the Ru–O–Ru bond angle increases. Those changes induce a charge compensation which was detected by XPS measurements. The analysis of these results shows that the Ru 3d_5/2 core level could be fitted assuming the contribution of two different chemical states of the Ru. The Ru 3d_5/2 core level is localized at 280.7 and 281.6 eV, which corresponds to Ru⁴⁺ and Ru⁵⁺. The valence band XPS spectra show an increase in Co 3d states at the Fermi level as the Co content increases, which contribute to the decrease in the electrical resistivity.     

Kondo effect and impurity interactions in the resistivity of diluteZnMn alloys

The electrical resistivity of diluteZnMn alloys (c=1.7–2400 ppm Mn) has been investigated in the temperature range from 0.05 to 14 K. For the most dilute sample, single-impurity Kondo behavior is found, well described by the Hamann formula withT _K=0.9 K,S=3/2. ForT<50 mK, aT ² law with _R =0.3 K is expected. In the dilute limit the Kondo slope is –(1/c)d()/d(logT)=3.7±0.2 µ-cm/at % dec. In the more highly concentrated alloys, the slope decreases with increasing c and the lnT-like variation of the Kondo resistivity roughly terminates near a temperatureT _W(c),T _W being related to the average Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction strength between the Mn impurities. For 20 ppm c 1000 ppm, the resistivity slightly decreases at low temperatures and a broad resistivity maximum is observed atT _m (c), withT _m c ^0.7. ForT 2 _m, the resistivity dependence is linear inT, and for the most concentrated alloy aT ^3/2 orT ² dependence is measured at the lowest temperatures attainable. The investigation of the transition temperatureT _c (c) to superconductivity ofZnMn results in a critical concentrationc _cr=18 ppm Mn. The concentration dependence ofT _c below 0.3 K suggests the presence of the Kondo effect, although impurity interactions may also influenceT _c in this temperature range.Supported by Deutsche Forschungsgemeinschaft.     

Oxidation of chromia forming molybdenum-tungsten based alloys

The oxidation behaviour of tungsten and molybdenum based, chromia-forming alloys prepared by powder sintering activated with group VIII metals has been investigated. The influences of the alloy composition, nature of the sintering agent and oxidation temperature have been studied. A good oxidation resistance is observed with palladium as sintering agent. This metal is rejected at the grain boundaries and allows a fast diffusion of chromium to the metal-oxide interface. Contrary to palladium, nickel leads to a catastrophic oxidation of the sample. The formation of a two-phase interface enriched in nickel leads to a non-protective oxide layer constituted with Cr₂O₃ and NiWO₄.Catastrophic oxidation is observed when the refractory metals are oxidised into volatile oxides, i.e. in the case of the alloys with a high molybdenum content. Contrary to molybdenum, a high tungsten level leads to high oxidation resistance, even at temperature as high as 1300°C. In this latter case, alloys are two-phase: this result has led to the investigation of the ternary section of the Cr-Mo-W system at 1300°C.     

Influence of aluminum and vanadium alloying elements on the resistivity of titanium

The experimental data on the resistivity of titanium-aluminum and titanium-vanadium alloys in the temperature ranges of 77–1700 and 77–350 K, respectively, at alloying component concentrations below 10 at % are generalized. At these concentrations, the isotherms of the dependences ρ(c) are linear in the temperature range of the α phase (77–500 K) and in the β phase. The numerical values of the concentration angular coefficients (dρ/dc) _T = b were obtained for the Ti-Al and Ti-V systems at temperatures of 77 and 300 K and Ti-Al alloys in the β phase at T = 1400 K. The temperature derivatives (dρ/dT) _T = b _T for the α phase near the Debye temperature and the β phase, where the dependences ρ(T) are close to linear, have been calculated for Ti-Al alloys. In both cases the concentration dependences of the temperature angular coefficients b _T (c) decrease with an increase in the Al concentration; however, their magnitudes differ by an order of magnitude.     

Hochschmelzende Metalle und ihre Legierungen

Refractory metals and alloys. The application of refractory metals such as niobium, tantalum, molybdenum, tungsten, chromium and rhenium at high temperatures is discussed on the basis of a compilation of their physical, chemical and technological properties. The present state of knowledge in this field indicates, that the high temperature strength needed can be obtained with some of the refractory alloys also at temperatures much higher than 1000°C. However, at present, the oxydation resistance has not yet been improved far enough to allow the use of these materials in air.     

Preparation and properties of the (TlInSe2)0.96Se0.04 solid solution

TlInSe₂-rich TlInSe₂-Se alloys (0?C10 mol % Se) have been studied by X-ray diffraction. In the composition range 2.0?C6.0 mol % Se, the TlInSe₂-based ??-solid solutions decompose by a peritectoid reaction at 363 K. The space group of the (TlInSe₂)_0.96Se_0.04 solid solution is P222, and its lattice parameters are a = 6.575 ± 0.001 ?, b = 10.080 ± 0.001 ?, and c = 11.280 ± 0.001 ?. The electrical conductivity of singlecrystal samples of this solid solution is (0.5?C3.0) × 10^?3 S/cm at room temperature and varies little at temperatures from 85 to 280 K.     

Influence of Zr substitution on superconductivity of YBa2Cu3O7 − δ

We report on the successful synthesis of single-phase Zr-substituted YBa₂(Cu_1?x Zr _x )₃O_{7 ? δ} superconductors up to 5 at.% (x=0.0–0.05) and characterized them according to resistivity and ac susceptibility measurements. We did not observe any significant change in orthorhombicity and inT _c similar to Ni²⁺- and Nb⁵⁺-doped systems.     

Quantitative analysis of microstructural effects on fatigue crack growth in widmanstätten Ti-6A1-4V and Ti-8Al-1Mo-1V

Analysis of fatigue crack growth behavior of five beta-annealed alloys indicates significant effects of microstructure upon the logarithmic plot of fatigue crack growth rate (da/dN) vs stress-intensity range (ΔK). Each plot exhibits a bilinear form with a transition at ΔK_T, the position of which lies between $\text{18}\text{and}\text{31}\text{MPa}\text{·}\text{m}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ for the five alloys. Comparison of mean Widmanstätten packet size to cyclic plastic zone size, as analyzed on the basis of different models, indicates their equality at ΔK_T. Greater clustering of the packet size distribution about the mean value effects a decrease in hypertransitional exponent (m_A) in the power law, da/dN = C(ΔK)^m, and a simulataneous increase in the sharpness of transition. Hypertransitional exponents for the five alloys lie between 2.9 ≤ m_A ≤ 4.7, whereas hypotransitional exponents lie between 5.9 ≤ m_B ≤ 7.6. Hypotransitional growth rates vary inversely with mean packet size, with a 20-fold reduction in da/dN observed for a 3.5-fold increase in mean packet size.