Structural relaxation in the CoP-CoNiP system upon low-temperature annealing

The atomic structure of alloys in the CoP-CoNiP system in the initial state and its behavior upon low-temperature annealing is investigated. It is shown that structural relaxation starts at temperatures of 150–200°C and results in local atomic ordering at the network boundaries. Crystals 2–5 nm in size start to undergo nucleation at the boundaries of structural heterogeneities when heated further to 250–300°C. The nanocrystal structure corresponds to the metastable phase delta-Co (ICSD 42684) and the unknown phase Co_{1 ? x} P _x . The estimated diffusion coefficient for CoP alloy is 10^?14 m² s^?1, according to the experimental data.     

Heterodiffusion of chromium and cobalt in liquid iron

The heterodiffusion has been studied by the method of stationary diffusion source. In that method the saturated radioactive vapour of the diffusing element comes into contact with the liquid in which diffusion is being studied. Two variants of that method were applied and the diffusion coefficients of chromium and cobalt in liquid iron were determined, i.e.D _{(Cr→Fe, 1860K)}= =4·9×10^?5cm²/s andD _{(Co→Fe, 1820K)}=5×10^?5cm²/s, respectively. The values of maximum concentration of chromium in Fe-samples after diffusion were of the order of 10^?1 to 10^?2 wt-%, those of cobalt of 10^?4 wt-%. This experimental method is rather simple and the results obtained are in good conformity with other measurements.     

Diffusion of hydrogen and deuterium on the (111) plane of tungsten

The diffusion of ¹H and ²H on the (111) plane of a W field emitter has been studied by the fluctuation method at various coverages. Both activated and unactivated diffusion is observed; the latter shows very little isotope effect, suggesting that coupling to the substrate is so strong that mass renormalization makes the effective masses of ¹H and ²H nearly identical. Values of D in the tunneling, i.e. temperature independent, regime are 10^?13?5 × 10^?14 cm²/s depending on coverage. For activated diffusion at high coverages, corresponding to population of the β₁ state E = 2.4?3.2 kcal/mol and D₀ = 2 × 10^?8 ?5 × 10^?7 cm²/s, depending on coverage. For lower coverages, corresponding to β₂ population, E = 7–9 kcal/mol, D₀ = 9 × 10^?6 ?2 × 10^?3 cm²/s, again depending on coverage. Similar values are obtained for ²H, with E and D₀ values slightly reduced. An exponentially decaying correlation signal for clean W was also seen and interpreted in terms of flip-flop of W atoms.     

Pressure dependence of the absorption edge for Cd1-xMnxTe

The effect of pressure on the optical absorption edge of mixed crystals Cd_1-xMn_xTe with different manganese concentrations is reported. The observed absorption edge shifts to higher energy with increasing pressure at a rate of α=7?8×10^?3 eV/kbar and a second order coefficient of β=-4×10^?5 eV/kbar² for x<0.5, to lower energy with increasing pressure at a rate of α=-5.0 ×10^?3 eV/kbar for x?0.5. A phase transition occurs for all the samples studied. The absorption edge of the new phase is outside the wavenumber range of the instrument. The physical origins of different pressure coefficients are discussed in the light of the deformation potentials of energy band states and the hybridization of the Mn²⁺ 3d levels with the p-like states in the valence band.     

Study of sensitization of Cr4+ ions by Yb3+ ions in yttrium-aluminum garnet crystals

The possibility of using ytterbium ions as sensitizers of luminescence of tetravalent chromium in yttrium-aluminum garnet single crystals is studied. It is found that average values of the microparameters of electronic energy transfer between ytterbium and chromium ions are C _DA=7.05×10^?36 cm⁶/s and C _DD=4.55×10^?43 cm⁶/s.     

Nuclear magnetic resonance of intermetallic compounds Gd2Ni17−xAlx

²⁷Al Knight shifts vs temperature and magnetic susceptibility for the intermetallic compounds Gd₂Ni_17?xAl_x (x = 17; 16.2; 16; 15) are presented. The results are discussed in terms of the uniform polarization model fo the conduction electrons by the 4f and 3d spins localized on the Gd and Ni ions. The phenomenological exchange constants J_sf and J_sd range between ?1.80×10^?3 and 1.19×10^?3 eV and ?0.63×10^?3 and ?0.52×10^?3 eV, respectively.     

Localization of conduction electrons in the ferromagnetic clusters AuFe

The optical-conductivity spectra of concentrated solutions Au_{1 ? x} Fe _x with x = 17 and 22 at % have been measured in a frequency range of (10–33) × 10³ cm^?1 at room temperature. The results are analyzed together with previous optical data obtained for compounds with x = 4–12 at %. It is found that the magnetic contributions σ_magn = σ_AuFe ? σ_Au to dc and low-frequency(10 cm^?1) conductivities for an Fe concentration below 4 at % are almost equal, while the low-frequency magnetic contribution for larger concentrations is significantly larger than the dc one. An absorption band at frequencies of 1000–3000 cm^?1 has been found for samples with concentrations x = 6–22 at %. The observed phenomena are attributed to the localization of electrons inside clusters containing ferromagnetically ordered iron ions.     

Hyperfine and nuclear quadrupole interactions in copper-doped cadmium oxalate trihydrate single crystals

Electron spin resonance experiments on Cu²⁺ doped in a single crystal of cadmium oxalate trihydrate grown by a slow diffusion technique have been carried out at 77 K. The major features of the ESR spectra can be attributed to divalent copper (3d⁹) in substitutional Cd²⁺ sites. Information has been gained about the hyperfine and quadrupole interactions concerning the ion. The spin-Hamiltonian parameters in the $\text{S =}\text{1}\text{2}$, $\text{I =}\text{3}\text{2}$ manifold are: g_x = 2.0211; g_y = 2.2249; g_z = 2.4536; A_x = +84.5 × 10^?4cm^?1; A_y = +16.8 × 10^?4cm^?1; $\text{A}{}_{\mathrm{z}}\text{= ?40.8 × 10 ×}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$; P_x = ?7.4 × 10^?4cm^?1; P_y = ?0.4 × 10^?4cm^?1; and P_z = +7.8 × 10^?4cm^?1. An evaluation of the asymmetry and quadrupole coupling parameters revealed that the ground state of the guest ion in Cd(COO)₂ · 3H₂O is 0.97|x² ?y₂ > +0.24 |3z² ? r² >.     

Specific heat of NaNO2 near its transition points

Using an a.c. technique, the specific heat of NaNO₂ was measured as a function of temperature near its antiferroelectric-to-paraelectric phase transition point (T_N). The transition was found to be of the second order. The critical exponents are; α = 0·38 for ? = 2 × 10^?4 ～ 1 × 10^?1, and α′ = 0·18 for ? = ?2 × 10^?4 ～ ?3 × 10^?3. The critical exponents deduced from the scaling-law relations are roughly close to the values obtained from a random phase approximation for a system with an isotropic interaction. However, a difference was recognized between the observed exponent for the specific heat and the values theoretically given for T > T_N by the random phase approximation for a system with a short-range interaction or for a system with a long-range dipolar interaction. A thermodynamical analysis was made by using the generalized Pippard relation, and the present result was found to be consistent with the pressure dependence of the antiferroelectric transition point.     

Effects of damage rate on Cu precipitation in Fe–Cu model alloys under neutron irradiation

The formation of Cu precipitates and point defect clusters was investigated in two Fe–Cu binary model alloys, Fe–0.3Cu and Fe–0.6Cu, irradiated at 573?K at three different damage rates, namely 3.8?×?10^?10, 1.5?×?10^?8 and 5?×?10^?8?dpa (displacements per atom)/s, up to about 1.6?×?10^?2?dpa. Results of positron annihilation experiments indicated that Cu precipitates were formed in these irradiations with different damage rates. The growth of Cu precipitates does not increase monotonously with increasing irradiation dose, but it rather depends on the nucleation and growth of microvoids. It is also clear that the nucleation and growth of microvoids are influenced by the irradiation dose rate.     

Ionic conductivity of Zr1−xIn2xO2−x

As x in Zr(In)O_2?x is increased from 0.08 to 0.16 (9–19 mole per cent In₂O₃) the activation energy E(x) for ionic conduction increases from 1.05 to 1.51 eV; the concuctivity decreases from 2 × 10^?5 to 3 × 10^?6Ω^?1cm^?1at 400°C, is composition-independent at about 580°C, and increases from 1 × 10^?2 to 4 × 10^?2Ω^?1cm^?1 at 800°C. The pre-exponential term of the Boltzmann-type conductivity equation depends exponentially on E(x), a much stronger dependence on x than theoretically expected with a model for ionic conductivity that includes nearest-neighbor defect interactions. Analysis of reported conductivity data for Zr(M)O_2?x (M = Sc, Y, Ca and rare earth metals) and other doped oxide electrolytes with fluorite-type structure reveals that the same relationship is observed with these materials when x γ0.08. It is shown that ionic conduction in these oxides is consistent with nearest neighbor vacancy-cation defect interaction forx < 0.08 but that an additional complex interaction with composition-dependent free energy ΔG(x) occurs when xγ 0.08.The lattice constant of Zr(In)O_2?x with the cubic fluorite-type structure is independent of composition, 5.114 ± 0.002 Å, in agreement with ionic size considerations.     

The ionic conductivity of Li6BaLa2M2O12 with coexisting Nb and Ta on the M sites

In a view to balancing cost and lithium ion conductivity, Li₆BaLa₂Nb _x Ta_2???x O₁₂ (x?=?0–2) was prepared by solid-state reaction, and its corresponding AC impedances were tested at temperatures ranging from 20 to 250 °C in air. Li₆BaLa₂Ta₂O₁₂ exhibits the highest conductivity, 8.77?×?10^?6?S/cm, and the second highest is Li₆BaLa₂Nb₂O₁₂ with 6.69?×?10^?6?S/cm. Partial replacement of Ta with Nb cannot bestow the advantages of cost saving or the enhancement of lithium ion conductivity. X-ray diffraction patterns revealed a gradual change as an increasing amount of Nb replaces Ta in Li₆BaLa₂Nb _x Ta_2???x O₁₂ (x?=?0–2), and it is thought that the trending of Nb and Ta to rest on the crystallographic planes is different.     

Na+ ion conductivity and crystallographic cell characterization in the Hf-nasicon system Na1+xHf2SixP3−xO12

We have measured the effect of varying the mobile ion concentration on the sodium ion conductivity in the Hf-Nasicon system, Na_1+xHf₂Si_xP_3-xO₁₂, for 1.4 ? x ? 2.8. The conductivity is greatest for Na_3.2Hf₂Si_2.2 P_0.8O₁₂: σ_25°C = 2.3 × 10^?3 (ω cm)^?1, and σ_250°C = 1.7 × 10^?1 (ω cm)^?1. These values are approximately 50% greater and worse, respectively, than the values reported for the best Zr-Nasicon. We have characterized the variation of lattice parameters with composition and found the behavior to be similar to that of Zr-Nasicon. A small distortion from rhombohedral to monoclinic symmetry occurs for compositions 1.8 ? x ? 2.2.     

dc ionic conductivity measurements on the mixed conductor Cu2−xSe

A brief review and some remarks on the theory and practice of the four point dc ionic conductivity measurement in a mixed conductor are presented. Measurements were made on Cu_2?xSe which has the electronic to ionic conductivity ratio of 2×10³–2×10⁵. The transients which appear on the voltage probes when a constant current is sent through the sample were found in complete agreement with the dependence predicted from the solution of the diffusion equation. Temperature dependence of σ_i of Cu_1.99Se in the range between 40°C and 180°C confirms the expected behaviour in the low- and high-temperature and intermediate phase. Composition dependence of σ_i of Cu_2?xSe in the high-temperature phase is not linear in x.     

Field ion microscopy of cascades of atomic displacements in metals and alloys after various types of irradiation

Experimental results on atomic-spatial investigation of radiative defect formation in surface layers of materials, initiated by neutron bombardment (of Pt, E > 0.1 MeV) and ion implantation (in Cu₃Au: E = 40 keV, F = 10¹⁶ ion/m², j = 10^?3 A/cm²), are considered. Quantitative estimates are obtained for the size, shape, and volume fraction of cascades of atomic displacements formed under various types of irradiation in the surface layers of the materials. It is shown that the average size of radiation clusters after irradiation of platinum to a fast neutron fluence of 6.7 × 10²² m^?2 (E > 0.1 MeV) is about 3.8 nm. The experimentally established average size of a radiation cluster (disordered zone) in the alloy after ion bombardment is 4 × 4 × 1.5 nm.     

Effect of homovalent (I−Br−) ion substitution on the ionic conductivity of LiI1−x Brx systems

The study of electric conductivity in the whole range of compositions of mixed LiI_1?x Br_x crystals has shown that doping of pure lithium halide (LiI or LiBr) by homovalent substitution leads to an increase in conductivity. This enhancement is essentially pronounced in the solid solution domains near the compositions of pure compounds (x < 0.15 and x > 0.90). Maximum conductivity is attained for the two phase composition LiI_0.75Br_0.25 (5 × 10^?7 S cm^?1 at 293 K) compared to those of starting compounds (4 × 10^?8: LiI and 9 × 10^?9: LiBr at 293 K). An Arrhenius behaviour of the conductivity evolution versus the inverse of the temperature shows that variations in conductivity are related to those of the activation energy whose minimum is close to 8.7 Kcal mole^?1. Lattice strain involved by substituting anions of different raddi could be the factor which increase the defect population.     

Stability and surface properties of GeSi alloy films on Si(111) substrate

Several GeSi alloy films with different surface properties were prepared from a 500 Å thick Ge film that had previously been grown on a Si(111)-7×7 substrate by molecular beam epitaxy. The films were prepared by combinations of sputtering, annealing and Ge deposition from an evaporator. The surface properties were studied by Auger electron spectroscopy (AES) and by low energy electron diffraction (LEED). A novel LEED system employing position-sensitive detection was used. The Ge film surface gave a superposition of 7×7 and c(2×8) LEED patterns. A 7×7 → 1×1 phase transition was observed at 425±10°C. An irreversible 7×7 → c(2×8) transition was observed when the sample was heated above 500°C. The Ge film melted at 750±30°C and formed a Ge_xSi_1−x (x = 0.85±0.05) alloy whose surface gave a 7×7 LEED pattern. A 7×7 → 1×1 phase transition was observed at 600±0.15°C. Prolonged sputtering and annealing resulted in a Ge_xSi_1−x (x = 0.53±0.05) alloy whose surface gave a 5×5 LEED pattern. An apparent 5×5 → 1×1 phase transition was observed at 870±10°C but at that temperature the film was converted irreversibly to one with a much lower Ge atom fraction (x = 0.025±0.005) whose surface gave a 7×7 LEED pattern. A surface with a 5×5 pattern identical to that for the x = 0.53 alloy was prepared by deposition or Ge on Si. A similar 5×5 surface was prepared by deposition of Ge on a facetted GeSi alloy surface originally showing a superposition of 5×5 and 7×7 patterns. The intensity distributions in all of the 7×7 LEED pattern were found to be similar to those for Si(111)-7×7 at nearly the same electron energies. The characteristics of the 7×7 → 1×1 phase transitions were discussed in direct comparison with those of the Si(111)7×7 → 1×1 and Ge(111)-c(2×8) → 1×1 transitions observed with the same LEED system.     

A LEED study of adsorbed neon on graphite

Neon monolayers on graphite have been investigated by high resolution LEED in the range 14.5 < T < 7.5 K and 10^?8 < p < 10^?4 Torr. The fluid-solid transition line has the form ln$\text{(}\text{p}\text{Torr}\text{)= ?}\text{A}\text{T + B}\text{,}\text{with}\text{A = 740 ± 45}\text{K and}\text{B = 31.0 ± 2.8}$. The solid is an incommensurate rotated phase whose lattice parameter decreases and rotation angle increases away from the transition line. Comparison is made with other thermodynamic and diffraction studies, and a preliminary phase diagram is constructed. Extrapolation of these data to higher temperatures and pressure suggests that this rotated solid monolayer is stable up to 23–25 K (P = 3?10 Torr) at coverage x = 1, and is stable over the range 0.88 < x < 1.0 at T = 16 K (2 × 10^?7 < p 1.5 × 10^?2 Torr). Extrapolation to lower temperatures gives the 2D triple point pressure in the range p = (0.3?3) × 10^?10 Torr. The steep slope of the fluid-solid transition line is consistent with the fluid phase having a high density (x?0.80) in the temperature range studied.     

Optical and structural properties of Zn1−x Mg x O ceramic materials

This paper reports structural, optical and cathodoluminescence characterizations of sintered Zn_1?x Mg _x O composite materials. The effects of MgO composition on these film properties have been analyzed. X-ray diffraction (XRD) confirms that all composites are polycrystalline with prominent hexagonal wurtzite structure along two preferred orientations (002) and (101) for the crystallite growth. Above doping content x = 10 %, the formation of the hexagonal ZnMgO alloy phase and the segregation of the cubic MgO phase start. From reflectance and absorption measurements, we determined the band gap energy which tends to increase from 3.287 to 3.827 eV as the doping content increases. This widening of the optical band gap is explained by the Burstein–Moss effect which causes a significant increase of electron concentration (2.89 × 10¹⁸?5.19 × 10²⁰ cm^?3). The luminescent properties of the Zn_1?x Mg _x O pellets are studied by cathodoluminescence (CL) at room and liquid nitrogen temperatures under different electron beam excitations. At room temperature, the CL spectra of the Zn_1?x Mg _x O composites exhibit a dominant broad yellow-green light band at 2.38 eV and two ultraviolet emission peaks at 3.24 and 3.45 eV corresponding to the luminescence of the hexagonal ZnO and ZnMgO structures, respectively. For the doped ZnO samples, it reveals also new red peaks at 1.72 and 1.77 eV assigned to impurities’ emissions. However, the CL spectra recorded at 77 K show the presence of excitonic emission peaks related to recombination of free exciton (X _A), neutral donor-bound excitons (D⁰X) and their phonon replicas. The CL intensity and energy position of the green, red and ultraviolet emission peaks are found to depend strongly on the MgO doping content. The CL intensity of the UV and red emissions is more enhanced than the green light when the MgO content increases. CL imaging analysis shows that the repartition of the emitting centers in Zn_1?x Mg _x O composites is intimately connected to the film composition and surface morphology.     

Diffusion of titanium in slightly reduced rutile

The self-diffusion of ⁴⁴Ti in slightly reduced rutile. TiO_2?δ, was measured along the c axis over the temperature range of 1000–1100°C between 0.2 and 1 × 10^?18atm. oxygen pressure. These measurements enabled the determination of the defect structure of TiO_2-δ for 0.02 ?gd ? 0.001. For oxygen pressures between 1 × 10^?13 and 1 × 10^?16atm. at 1058.4°C random tetravalent titanium atoms are the predominant defects evident from self-diffusion. The enthalpy of motion was determined as ΔH_m = 57.03 ± 4.9% kcal/mole. From the activation energy at 1.69 × 10^?16atm., the enthalpy of formation for tetravalent titanium interstitials was determined as ΔH_f = 276 ± 15.6% kcal/mole.For oxygen pressures less than 1 × 10^?16atm. at 1058.4°C, the tracer diffusion coefficient shows a continuous decline as the oxygen pressure is lowered. Comparisons with thermogravimetric studies and consideration of the similarity in structure between nonstoichiometric point defect phases and the first homologous series phase indicate that the order-disorder transition retains a considerable degree of short range order below the critical concentration in the form of Wadsley defects.