High-purity Specimens Research Articles

New hybrid materials for organic light-emitting diode devices

The regularities of polymorphism in high-purity crystalline tris(8-hydroxyquinoline) aluminum, gallium, and indium (Meq3) have been studied in the temperature range of 300–712 K. From the results of an analysis of photoluminescence and Raman spectra and X-ray diffraction data, a generalized picture has been produced, according to which, for all the studied compounds, a series of polymorphic transitions is the same: β → α → δ → γ → ɛ. Based on high-purity single-phase specimens of the investigated metal complexes and boron oxide, new hybrid materials have been synthesized: bulk samples (alloying technique) and thin films (vacuum thermal evaporation). The photo- and electroluminescent properties of the hybrid materials at room temperature have been investigated. It has been established that, as the synthesis duration of the bulk hybrid materials increases from 5 to 60 min, a photoluminescence maximum shifts to a short-wavelength domain from the value typical of pure δ(γ)-Meq3 by 40, 15, and 10 nm for Alq3, Gaq3, and Inq3, respectively.

Observation of an unusual case of triple-line instability

Bi vapors penetrate along the triple lines in electrodeposited Ni specimens to form open channels at 800 and 900 °C. This triple-line instability can be interpreted as a case of triple-line wetting by a gas phase. Further controlled experiments using high-purity Ni specimens suggest that the presence of S impurities is essential. This unusual wetting phenomenon is related to the formation of a bilayer complexion in Ni–Bi and its occurrence can significantly affect microstructural stability and corrosion resistance.

High purity specimens of URu2Si2 produced by a molten metal flux technique

We report a molten metal flux technique to produce high purity specimens of URuSi. Magnetic susceptibility (), heat capacity () and electrical resistivity () measurements show that the bulk properties of these crystals are similar to those that are produced by the Czochralski technique followed by solid-state electro-transport. In particular, we find residual resistivity ratios RRR / as large as 220.

High temperature thermoelectric properties of p-type skutterudites BaxYbyCo4-zFezSb12

Several polycrystalline p-type skutterudites with compositions BaxYbyCo4−zFezSb12, with varying filler concentrations x and y, and z = 1 to 2, were synthesized by reacting the constituents and subsequent solid state annealing, followed by densification by hot-pressing. Their thermoelectric properties were evaluated from 300 to 820 K. The Yb filling fraction increased with Fe content while the amount of Fe substitution had little influence on the Ba filling fraction. High purity specimens were obtained when the Fe content was low. Bipolar conduction contributed to the thermal conductivity at elevated temperatures. A maximum ZT value of 0.7 was obtained at 750 K for the specimen with the highest Fe content and filling fraction. The potential for thermoelectric applications is also discussed.

Preparation and characterization of laser-irradiation induced amorphous for Ge2Sb2Te5 phase-change materials

It has been a challenge to fully understand the structural characteristics of laser-irradiation induced amorphous (L-a) Ge2Sb2Te5 (GST) alloy due to the difficulties of collecting diffraction data from high purity specimens. In this paper, by fabricating GST thin films on different substrates, we exhibit an effective way of preparing L-a GST dots in submicron scale on various types of specially designed transmission electron microscope (TEM) grids. The structural characteristics of L-a GST in the form of pair distribution functions (PDF) can be achieved on single dots of L-a GST via selected area electron diffraction (SAED). This general approach would be convenient for precisely producing laser-irradiation induced materials in submicron scale for structural investigation.

Spin-glass characteristics in the quaternary spinel-type Ag(Cr1-xSnx)2S4

A few spinel compounds exist with the occupation of Ag atom on tetrahedral (or A) sites and have been less extensively studied. It is hard to synthesize high purity specimens of Ag-based thiospinels. The substituted quaternary spinel compounds Ag(Cr1-xSnx)2S4 (x = 0.50, 0.60, and 0.70) have been successfully prepared. These compounds exhibit the spin-glass nature with the freezing temperature Tg = 18.0, 15.4, and 11.4 K, respectively, where the irreversibility arises between ZFC (zero-field-cooled) and FC (field-cooled) magnetization with decreasing temperature. The asymptotic Weiss temperature θ has small value, which indicates a spin-glass magnetic property. The effective moment peff per Cr-atom is close to the spin only value for Cr3+ ion. These values are θ = – 0.90 K, peff = 3.92 Cr-atom-1 for x = 0.50; θ = 1.96 K, peff = 3.90 Cr-atom-1 for x = 0.60; and 8 = – 4.07 K, peff = 3.87 Cr-atom-1 for x = 0.70. The random distribution of Cr and Sn atoms on octahedral (or B) sites can introduce magnetic frustration. The spin frustration is due to the competition between ferromagnetic and antiferromagnetic interactions. A collinear spin alignment is inhibited in Ag(Cr1-xSnx)2S4.

Effects of Solute Segregation on Precipitation Phenomena and Age Hardening Response of High-Purity and Commercial AZ91 Magnesium Alloys

In the present study, the continuous and discontinuous precipitation behavior of the commercial AZ91 alloy containing manganese and the AZ91 alloy produced from high-purity elemental components with no manganese addition has been investigated. It was found that for the commercial alloy, the solute manganese segregated within the primary α-Mg dendrites during solidification and played a major role in the initiation of non-uniform distribution of β-precipitates within the matrix grains. In addition, the solute manganese significantly suppressed the growth of discontinuous (lamellar) precipitates. The high-purity alloy also exhibited non-uniform precipitation. However, the precipitation patterns differed from those observed in the commercial alloy due to the inhomogeneous distribution of aluminum, the origin of which was rooted in the solute segregation within the interdendritic regions of the solidification structure. These differences in the precipitation mode caused by the presence or absence of manganese influenced the age hardening of the alloys. The high-purity specimens aged at lower temperatures attained higher peak-hardness owing to greater area fractions of discontinuous precipitation cells.

Synthesis and crystallographic studies of garnet-related lithium-ion conductors Li 6CaLa 2Ta 2O 12 and Li 6BaLa 2Ta 2O 12

High-purity specimens of Li 6CaLa 2Ta 2O 12 and Li 6BaLa 2Ta 2O 12 have been successfully synthesized by solid-state reactions. The analytical chemical compositions of these samples were in good agreement with the nominal compositions of Li 6CaLa 2Ta 2O 12 and Li 6BaLa 2Ta 2O 12. The Rietveld refinements verified that these compounds have the garnet-type framework structure with the lattice constants of a = 12.725(2) Å for Li 6CaLa 2Ta 2O 12 and a = 13.001(4) Å for Li 6BaLa 2Ta 2O 12. All of the diffraction peaks of X-ray powder diffraction patterns were well indexed on the basis of cubic symmetry with space group Ia-3 d. To make a search for Li sites, the electron density distributions were precisely examined by using the maximum entropy method. Li + ions occupy partially two types of crystallographic site in these compounds: (i) tetrahedral 24d sites, and (ii) distorted octahedral 96h sites, the latter of which are the vacant sites of the ideal garnet-type structure. The present Li 6CaLa 2Ta 2O 12 and Li 6BaLa 2Ta 2O 12 samples exhibit the conductivity σ = 2.2 × 10 − 6 S cm − 1 at 27 °C ( E a = 0.50 eV) and σ = 1.3 × 10 − 5 S cm − 1 at 25 °C ( E a = 0.44 eV), respectively.

Effects of impurities on one-dimensional migration of interstitial clusters in iron under electron irradiation

One-dimensional (1D) migration of small interstitial-type dislocation loops was studied for Fe specimens of different purities at room temperature under electron irradiation using a high-voltage electron microscope. Most 1D migration appeared as discrete jumps (stepwise positional changes) at irregular intervals, and sometimes involved back and forth motion between certain points. The distribution of jump distances extended to over $100\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ in high-purity specimens; it was less than $30\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ in low-purity specimens. Jump frequency was almost proportional to electron beam intensity and was on the same order as the rate of atomic displacement by electron irradiation. Molecular dynamics simulation suggested the suppression of 1D migration of an interstitial cluster (7i) by an oversized solute Cu atom located in the dilatational strain field of the cluster. We proposed that the 1D jump process occurs in the following sequence: (1) interstitial clusters are in a stationary state due to trapping effect by impurity atoms, (2) incident electrons hit and displace impurity atom to cause detrapping, (3) liberated clusters cause fast 1D migration at low activation energy, and (4) the cluster is trapped again by another impurity. Experimental results were analyzed and discussed in terms of the proposed model.

Structural and electrochemical properties of Li 0.44+ xMn 1− yTi yO 2 as a novel 4 V positive electrode material

The specific capacity of Li 0.44Mn 1− y Ti y O 2 (0 < y < 0.22) positive electrode materials has been improved by an additional lithium-insertion treatment in molten LiNO 3–LiOH salt at a low temperature. High-purity specimens of the lithium-inserted Li 0.44+ x Mn 1− y Ti y O 2 have been successfully prepared. We have conducted a systematic experimental study of the structural and electrochemical properties of these compounds. The inserted lithium content, x, in Li 0.44+ x Mn 1− y Ti y O 2 increases together with the substituted Ti content, y. The initial charge capacity increases from 130 mAh g −1 ( y = 0) to 145 mAh g −1 ( y = 0.22) for the Li 0.44+ x Mn 1− y Ti y O 2 compounds. The maximum discharge capacity that has been achieved is 180 mAh g −1 in the case of Li 0.72Mn 0.78Ti 0.22O 2 between 2.5 and 4.8 V with a fixed current density of 30 mA g −1 ( C/6) at 30 °C. The discharge capacity at the 4 V plateau region (about 100 mAh g −1) in the lithium-inserted Li 0.55MnO 2 has been improved to twice that in as-prepared Li 0.44MnO 2 (about 50 mAh g −1). The structural differences between Li 0.44MnO 2 and Li 0.55MnO 2 are discussed based on XRD Rietveld analysis results.

The diffusion behaviors of interstitial impurities in V–4Cr–4Ti alloys under ion irradiation

NIFS HEAT-1 and four types of the V–4Cr–4Ti alloys with different oxygen and nitrogen content were irradiated with Cu 2+ ions at 973 K up to dose of 10 dpa. In this irradiation condition, the flux of oxygen, which through the surface is estimated about 2–4 × 10 16 (s m 2) −1, and the oxygen levels in specimens are calculated by finite difference method. In the cases of high purity specimens, oxygen diffused from the surface into the irradiated region. Moreover, oxygen diffused from the back of the irradiated surface into the irradiated region and enhanced the precipitations at the irradiated region. It is shown that the initial impurity level and flux of oxygen, which diffused from the atmosphere, essentially limited the precipitation behavior.

Direct reaction synthesis of Mg2B14 from elemental precursors

Abstract Mg2B14 prepared by reaction of high-purity Mg and B was analyzed by X-ray diffraction and Rietveld analysis. The structure refinement for space group Imam resulted in residuals Rp = 6.95% and RBragg = 3.72% with lattice parameters a = 5.9738(3) A, b = 8.1255(4) A, and c = 10.4809(5) A. AlMgB14 produced by the same method did not yield high-purity specimens.

Magnetization, electrical resistivity and specific heat measurements of Na Co2O4

DC magnetic susceptibility (χ), electrical resistivity (ρ) and specific heat (C) have been investigated for layered compound NaxCo2O4 as a function of temperature (T) using high purity specimens melted and grown in a floating-zone furnace. A broad maximum of χ(T) at ∼14K, a behavior of ρ(T) obeying ρ(T)=ρ0+AT2 at low temperatures and a large γ(=C/T) value of ∼60mJ/molK2 at 2K are found. These behaviors are qualitatively similar to those of a d-electron heavy fermion compound LiV2O4.

Complexes of platinum and hydrogen in silicon observed by optical absorption and electron spin resonance

Complexes of hydrogen (H) and platinum (Pt), especially the ${\mathrm{PtH}}_{3}$ and ${\mathrm{PtH}}_{4}$ complexes in Si, were studied by measurements of their optical absorption at 5 K and by electron-spin resonance (ESR) at temperatures 10 K. Floating-zone Si was separately doped with Pt and H, with heating at 1000 \ifmmode^\circ\else\textdegree\fi{}C--1360 \ifmmode^\circ\else\textdegree\fi{}C followed by quenching in water. In the case of high-purity n-type specimens with a lower concentration of Pt than that of H, optical-absorption peaks at 1909.1, 1910.3, and 1930.4 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ were observed in addition to the peaks due to the PtH and ${\mathrm{PtH}}_{2}$ complexes. Furthermore, we observed two strong peaks at about 1898.5 and 1921.9 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, especially, in n-type specimens. Based on the results of annealing, the dependencies of peaks on the position of the Fermi level, peak splitting by codoping of H and deuterium, and photo-ESR measurements, the peaks observed at 1910.3 and 1930.4 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ are attributed to the ${\mathrm{PtH}}_{3}$ complex with a neutral charge state and those observed at about 1898.5 and 1921.9 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ are due to the ${\mathrm{PtH}}_{3}$ complex with a negative charge state. We also assigned the peak observed at 1909.1 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ to the ${\mathrm{PtH}}_{4}$ complex.

Low-Temperature Acoustic and Thermal Properties of Plastically Deformed, High-Purity Crystalline Specimens of Al, Nb and Ta

Low-Temperature Acoustic and Thermal Properties of Plastically Deformed, High-Purity Crystalline Specimens of Al, Nb and Ta

Energy Dispersive Spectrometry Calibration of Fe and Co

Energy Dispersive Spectrometry (EDS) is an ubiquitous method of elemental analysis for SEM, TEM, and STEM applications. The elements of interest are generally quantified without standards using theoretical calculations or by using standards that are high purity specimens of the elements measured. However, EDS is often used to determine a small percentage of an element in a matrix. The accuracy and limit of detection of these low concentration measurements has not been established. An earlier report proved the concept that a cross section high dose BF2implanted specimen could provide a standard for EDS measurement of F. This study extends this quantification approach to transition elements of importance to the semiconductor industry.The Fe and Co standards were created by high dose ion implantation. For ions implanted into silicon, a dose of lxl016atoms/cm2results in a peak concentration of approximately lxl021atoms/cm3or 2% atomic. The exact concentration can be determined using methods such as Rutherford Backscattering Spectrometry (RBS) and Secondary Ion Mass Spectrometry (SIMS).

Low-Temperature Thermal Conductivity of High-Purity and Doped Tantalum Single Crystals after Plastic Deformation

The thermal conductivity of plastically deformed, high-purity and doped tantalum single crystals was measured in the temperature range between 50 mK and about 2 K. The deformation was performed in such a way that comparable dislocation arrangements and dislocation densities are produced for both, high-purity and doped specimens. Surprisingly, the thermal resistivity Wd due to plastic deformation depends strongly on the purity of the crystals and the deformation temperature. In the high-purity specimens a thermal resistivity is observed which is much larger than in the case of doped specimens. This additional thermal resistivity is larger after deformation at intermediate temperature than after deformation at low temperatures and has to be attributed to a dynamic interaction between phonons and non-screw dislocations. In the present paper the scattering mechanism is related to oscillations of geometrical kinks in non-screw dislocations.

The influence of trace impurities on the mechanical characteristics of a superplastic 2 mol% yttria stabilized zirconia

In contrast to metallic alloys, the mechanical characteristics of superplastic ceramics are very sensitive to minor changes in levels of trace impurities. In the present study, the mechanical behavior of a 2 mol% yttria stabilized tetragonal zirconia was studied in tension and compression in two batches of material, with small variations in levels of trace impurities, to examine the influence of stress axis and impurity content on the deformation behavior. The mechanical properties of the material were characterized in terms of the expression: ε ̇ ∝σ n where ε ̇ is the strain rate, σ is the stress and n is termed the stress exponent. The mechanical behavior of the ceramic was identical in tension and compression, for a material with a given level of impurity. The high purity specimens exhibited a transition from a stress exponent of ∼3 to ∼2 with an increase in stress, whereas the low purity material displayed only n∼2 behavior over the entire stress range studied. Detailed high resolution and analytical electron microscopy studies revealed that there was no amorphous phase at interfaces in both batches of material; however, segregation of Al at interfaces was detected only in the low purity material. The observed transition in stress exponents can be rationalized in terms of two sequential mechanisms: grain boundary sliding with n∼2 and interface reaction controlled grain boundary sliding with n∼3. The transition from n∼3 to ∼2 occurred at lower stresses with an increase in the grain size and a decrease in the purity level.

The anisotropy of Hf diffusion in α-Zr

Hf diffusion coefficients (D) have been measured (∼ 870–1100 K) in directions parallel (Dpa)and perpendicular (Dpe) to the c-axis of double-faced, single-crystal specimens of both high purity (HP) and nominally pure (NP) α-Zr. The diffusion profiles were measured by secondary ion mass spectrometry. Hf diffusion in HP α-Zr is characterised by an activation energy of about 3.0 eV and a pre-exponential factor of about 10−5 m2/s The anisotropy ratio, Dpa/Dpe, is ∼ < 1.0 for the HP specimens and mostly > 1.0 for the NP specimens. A dependence of D on diffusion time/depth is indicated for some experiments on NP Zr.

Effect of Glass Additions on the Indentation‐Strength Behavior of Alumina

The effect of small calcium aluminosilicate (CAS) glass additions on the microstructure and flaw tolerance of alumina ceramics is investigated, and the results compared to a high‐purity alumina. The high‐purity alumina specimens were dense with microstructures consisting of a uniform grain size distribution and equiaxed grain morphology. Additions of only 1 wt% glass phase resulted in a bimodal grain size distribution containing large, elongated grains within a fine‐grain matrix. Indentation‐strength tests indicated enhanced flaw tolerance with the bimodal microstructure, even though both materials had nominally the same average grain size. The strength of unindented specimens was also observed to decrease with glass additions. Observations of crack paths show a greater propensity for bridging in the glass‐containing alumina due to the presence of coarse, elongated grains and perhaps a lower grain boundary toughness. However, crack extension occurs transgranularly when the size of the coarsest grains becomes too large. This suggests that an optimum in flaw tolerance will be achieved with an elongated grain morphology and intermediate grain size.