X-ray Lattice Parameter Research Articles

Influence of Deposition Parameters on the Properties of Titanium Nitride Films Formed by Ion Beam Assisted Evaporation

An IBAD system comprising a resistance heated linear evaporation source and a r.f. ion source providing a ribbon-shaped N + /N 2 + -ion beam was employed for the deposition of TiN x -films onto Si(100)-substrates. The ion energy E ion and the flux density ratio J ion /J Ti ; of the nitrogen ions and the evaporated Ti could be varied independently. Their influence on the film properties was studied for J ion /J Ti -values from 0.13 to 0.73 at a fixed E ion of 540 eV, and for E ion values from 140 eV to 1040 eV at a fixed J ion /J Ti -ratio of 0.27. The flux density ratio strongly influences the chemical composition of the TiN x -layers with x varying from 0.5 to 1.4. X-ray lattice parameter measurements point to empty nitrogen sites in the cubic 6-TiN lattice for the understoichiometric range, and surplus nitrogen atoms incorporated as interstitials for x>1. The increase of the flux density ratio causes a transition from a columnar structure with tensile stress (zone 1 in the structure zone model) to a compressively stressed dense structure (zone T). Simultaneously, the crystallite orientation of the cubic 6-TiN-phase changes from a (111)-to a (100)-fibre texture. The ion energy variation at a constant flux density ratio causes again a transition from a columnar film structure (zone 1) to a T-zone structure, accompanied by a change from a (110)-ideal layer texture to a (110)-fiber texture. Film density and average grain size increase from zone 1 to zone T. The development of the microstructural film properties are discussed in terms of the energy input by the N + /N 2 + -bombardment, and of the total free energy of the films. The behaviour of the grain size and the film hardness is referred to the predictions form the Hall-Petch relation.

The influence of vacancy concentration on the mechanical behavior of Fe-40Al

Abstract In order to investigate the effect of vacancies on mechanical behavior room-temperature compression tests have been performed on polycrystals and single-slip oriented single crystals of Fe-40 at% Al annealed at different temperatures and quenched. Vacancy concentrations were determined using a combination of X-ray lattice parameter measurements and dilatometry. Both polycrystals and single crystals displayed a rapid initial increase in yield stress with increasing vacancy concentration (when [111] slip occurred on (101) and (110) in the single crystals), followed by a much slower increase at high vacancy concentrations (> 4 × 10 −3 ). This slower increase corresponded to the activation of (211) slip in the single crystals. The effects of vacancies on the yield strength are consistent with a frictional strengthening mechanism. In contrast, the work-hardening rate of both polycrystals and single crystals was only weakly dependent on the vacancy concentration. Dislocation pinning points, debris and loops were produced through the interactions between gliding dislocations and the quenched-in vacancies.

Gas atomized powders of hydride-forming alloys and their application in rechargeable batteries

Gas atomized powders of LaNi 4.5Al 0.5 and LaNi 2.5Co 2.4Al 0.1 alloys were prepared and separated into fractions with different particle sizes. The dependence of morphology, oxygen content and crystal structure of the powders on particle size have been analyzed by means of XRD, SEM and EDS. The hydriding and electrochemical properties of different fractions were also evaluated. All fractions had a similar particle morphology and X-ray lattice parameters. EDS of the gas atomized alloys indicated that the surface of the smaller particles was less contaminated by oxygen than course particles. At the same time the fractions with particle sizes below 50 μm had poor activity both for gas hydrogenation and electrochemical charging. On the DTA curve of the small particles fraction an additional exothermal peak was observed, which may be attributed to a thermal-induced crystallization of the more developed amorphous component of the small particles structure. Gas atomized powders having large particle sizes display hydrogen and electrochemical capacity similar to those of arc-melted alloys.

Cellular structure in LEC ternary Ga 1 − xIn xAs crystals

Bulk Ga 1 − x In x As single crystals with In composition ranging from x = 0.02 to 0.1 have been grown by the LEC method from melt compositions of 26.3 to 55 mol% In. Due to segregation effects, the In content in the melt increases during growth. Crystals grown from different initial melt compositions exhibited cellular structure followed by polycrystallinity when the melt composition had reached a unique critical value of In concentration for a particular set of growth conditions. The point at which cellular structure occurs has been evaluated for a variety of growth parameters. These parameters include initial melt compositions, thermal gradients in the melt, crystal rotation and pull speed. Applying the knowledge of the conditions for the onset of cellular structure has maximized the successful growth of single-crystal ternary material and has been instrumental in increasing indium content. The AB and KOH etches were used to highlight growth striations, view onset of cellular structure and examine dislocation density. The In composition in the crystal was determined by low-temperature PL, X-ray lattice parameter measurement, absorption edge position and WDX.

Crystal growth of iron-based compounds by the cold-crucible Czochralski technique

Bulk single crystals of NbFe2, HoFe2 and (TbDy)Fe2 have been grown from a melt with a cold-crucible Czochralski technique. The as-grown crystals were characterised by X-ray diffraction, optical and scanning electron microscopy. The microstructural defects of the pseudo-binary (TbDy)Fe2 crystals have been studied by transmission electron microscopy. The as-grown NbFe2 crystals with C14 hexagonal structure contain many thermal cracks, but no secondary phases. Both X-ray lattice parameter measurement and EDX/SEM analysis show consistent stoichiometric composition. However, both HoFe2 and (TbDy)Fe2 have C15 cubic Laves phase structure and form by peritectic reactions with a narrow separation between the liquidus and solidus lines. By adopting a slow growth rate, a planar growth front has been maintained and bulk single crystals have been achieved. The as-grown crystals of (TbDy)Fe2 contain many needle-shaped Widmanstatten precipitates formed by a solid state reaction. Microstructural study by transmission electron microscopy revealed the presence of many {111} plane stacking faults and a few twin boundaries. A large number of interfacial dislocation networks have been observed on the Widmanstatten precipitates. The presence of thermal cracks, microstructural defects and Widmanstatten precipitates in the Laves phase compounds will strongly affect the measurement of the magnetic properties of the crystals.

The formation of mullite from kaolinite under various reaction atmospheres

In addition to its importance as a high-technology ceramic, mullite is also an intermediate phase in the formation of non-oxide ceramics (sialons) by carbothermal reduction of clay minerals. This reaction involved the formation of mullite under non-oxidizing atmospheres and in the presence of carbon. The effect of eight different reaction atmospheres on mullite formation from kaolinite in the presence and absence of carbon was studied by X-ray diffraction, 27Al and 29Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. Generally, a greater amount of mullite is formed at 1200 °C under vacuum and reducing atmospheres, which also produce mullites that are slightly more silica-rich (as deduced from X-ray lattice parameter measurements) but contain higher proportions of tetrahedral 27Al NMR resonance at ≈ 46 ppm, probably associated with Al ∗ sites. Reaction systems containing either nitrogen or ammonia in the presence of carbon show NMR evidence of previously unreported early stage formation of SiON bonds. Thermodynamic calculations are presented which suggest that the formation of SiO is an important factor in the complex interactions between the various solid and gaseous reactants.

Investigation of the composition of vapour-grown Pb 1- xSn xSe crystals ( x ≤ 0.4) by means of lattice parameter measurements

Experiments on the crystal growth of pseudobinary lead-tin selenide from the vapour were performed under near-equilibrium conditions for SnSe molar fractions of 0 ≤ x ≤ 0.4, where the rocksalt structure exists. Precise X-ray lattice parameter measurements were carried out on single crystals by means of the Soller-slit method. A difference of 0.01 in x between the crystal and the remainders of the source was found for average x = 0.35, but for x = 0.15 it was barely significant. The compositional uniformity allowed applying the single crystals for determination of a linear dependence of the lattice parameter on the SnSe molar fraction. The dependence is valid for Pb 1- x Sn x Se solid solutions displaying metal excess (n-type conductivity).

Cation nonstoichiometry in (Bi, Pb) 2Sr 2Ca 2Cu 3O 10+δ

X-ray lattice parameter measurements of the (Bi, Pb) 2- x Sr 2- y Ca 2- z Cu 3O 10+δ system show that a continuously varying solid-solution cation nonstoichiometry exists within -0.1< x<0.1, 0< y<0.3, and 0< z<0.3. However, the system cannot incorporate any defect at its Cu site. The oxygen content determined by titration decreases linearly with increasing cation-vacancy concentration. The critical temperature, T c, shows a maximum value at the stoichiometric cation composition and decreases to a lower constant value across the nonstoichiometric composition region with increasing alkaline-earth deficiency. Flux pinning in this system is increased by the cation-vacancy concentration only in the low-temperature range, while it decreased in the high-temperature range. The flux-pinning behavior is discussed in view of its two-dimensionality in the superconductivity for this system.

High-temperature phase equilibria in Cr-Cr3Si two-phase alloys

Phase equilibria in two-phase Cr-Cr3Si alloys have been investigated using metallography, XRD, and electron microprobe analysis. Cr-Si alloys with compositions of up to 15.0% Si were directionally solidified using cold crucible Czochralski crystal growth and equilibrated chemically at either 1200,1400, or 1600 °C. Measured Si concentrations of the Cr and the Cr3Si phases were found to be significantly lower than those given by the most recent assessment of the Cr-Si phase diagram, particularly at temperatures above 1200 °C. This explains why the volume fraction of Cr3Si in the directionally solidified eutectic is lower than that predicted by the assessed phase diagram. X-ray lattice parameter data for both Cr and Cr3Si are also reported.

A high temperature lattice parameter and dilatometer study of the defect structure of nonstoichiometric cerium dioxide

The defect structure of CeO 2− x has been investigated over the composition range from CeO 2 to CeO 1.8 and 900°C using the combined techniques of high temperature dilatometric length change and X-ray lattice parameter measurements. The oxygen partial pressure associated with the nonstoichiometric composition was controlled by passing different ratios of H 2/He mixtures through a constant temperature water bubbler and was monitored constantly with a YSZ oxygen sensor. The difference between the percent expansion for the dilatometric and X-ray lattice parameter measurements was zero, which indicated that the predominant defects of the CeO 2- x are oxygen vacancies.

Optical fluorescence from chromium ions in sapphire: A probe of the image stress

The concentration dependent frequency shift of the fluorescence from chromium ions in sapphire is shown to be a direct probe of the image stress produced by the chromium substituting for the smaller aluminium ions in sapphire. Our analysis is based on a comparison of the frequency shift produced when the volume of a sapphire crystal is changed by an external pressure to that produced by a concentration of substitutional solute. The volumetric strain sensed by the fluorescing chromium ion when the lattice is expanded by substitutional solute is approximately one-third of that determined from X-ray lattice parameter measurements, in accord with the Eshelby analysis of the strain field due to a concentration of elastic defects in a finite body.

The hydrolysis reaction of some cubic and tetragonal lanthanide dicarbide solid solutions

Two series of solid solution dicarbides made from a light and a heavy dicarbide, Er 1- x Ce x C 2 and Lu 1- x La x C 2, have been made and the change in X-ray lattice parameters across the series of tetragonal and cubic phases determined. Deviations from Vegard's law behaviour are discussed. Both series have been hydrolysed in water vapour at 11.0 × 10 2Nm −2 pressure and 14.5 °C and the rate constants for the linear reaction determined. The reaction rates for the Lu 1- x La x C 2 samples with water have been measured together with four cubic phases, Lu 0.5La 0.5C 2, Lu 0.5Ce 0.5C 2, Lu 0.5Pr 0.5C 2 and Lu 0.5Nd 0.5C 2. The changes in linear reaction rate constants for these samples, together with those of CeC 2 and LuC 2, are discussed in terms of CC bond lengths and f character of the metal band electrons which contribute to the MC 2 covalent bond. The reactivity sequence CeC 2 > Ce 0.5 Lu 0.5 C 2 ⪢ LuC 2 is explained.

Upper critical field of gold-doped YBa2Cu3O7- delta.

Specimens of YBa 2 Cu 3 O 7-δ containing 2.2 at. % Au were prepared using a zone-melting technique. Optical microscopy, x-ray lattice parameter, and fluorescence measurements were used to characterize the morphology and gold content of the specimens. A comparison of the values of the reversible magnetization leads to the conclusion that the upper critical field in the Au-doped specimens is significantly lower than in undoped samples prepared in an identical fashion

Growth kinetics of sintered NiO/ZrO2 (5 mol.% Y2O3) composites

This work uses X-ray diffraction and scanning electron microscopy to investigate the solution of NiO in ZrO 2 (with 5 mol% Y 2 O 3 , mainly in a metastable t′ phase as plasma sprayed powders) and the resultant growth kinetics of the NiO/ZrO 2 composite at 1600 °C. The tt́-ZrO 2 transforms into cubic (c-) ZrO 2 within 1 h upon firing, and room temperature X-ray lattice parameter results indicate that the solubility of NiO in c-ZrO 2 is about 3 mol%. Within the solubility limit, both sintering and growth of c-ZrO 2 grains were enhanced by NiO addition. A further increase in the NiO content results in the formation of NiO particles which hinder the grain growth of c-ZrO 2 . For specimens with 10 mol% NiO the c-ZrO 2 grains were found to follow the t 1 3 growth kinetics, i.e. bulk diffusion controlled, while the intergranular and intragranular NiO particles coarsen according to t 1 4 and t 1 5 laws respectively. The interfacial energy of NiO/c-ZrO 2 is about 0.48 ± 0.1 J m 2 , inferred from the geometry of the NiO particles at the grain boundary.

Investigation of the equilibrium concentration of lattice vacancies in silver and dilute silver-tin alloys with a differential dilatometer

The difference between relative changes in macroscopic length Delta L/L and X-ray lattice parameter Delta a/a has been measured over a wide temperature range from room temperature to 25 K below the respective melting point in pure silver and in some dilute silver-tin alloys between 0.25 and 8.60 at.% Sn. At higher temperatures, Delta L/L- Delta a/a increases, showing an Arrhenius behaviour due to vacancy formation. The absolute vacancy concentration at the melting point increases continuously from 5.2*10-4 for pure silver to 2.5*10-3 for a Ag-8.6 at.% Sn alloy. The vacancy formation enthalpy decreases from 1.05 to 0.74 eV simultaneously. The binding enthalpy and entropy for the first vacancy-impurity complex were found to be hBI=0.15+or-0.02 eV and sBI=-(0.5+or-0.2)kB. The impurity-impurity interaction is repulsive and of the order of 1/10 eV, similar to other noble metal alloys with positive excess charge. The binding Gibbs free energy of the first complex was determined as gBI=0.20+or-0.02 eV in good agreement with earlier measurements of resistivity and silver self-diffusion enhancement in silver-tin alloys but without some of their constraints since the vacancy concentration has been determined directly. All results can be interpreted within the framework of the model of Berces and Kovacs (1983).

Phase transformation and microstructure in (Mg,Ti)-PSZ

Phase transformation and microstructure in Mg-PSZ (8 mol% MgO), sintered (1600°C, 6 h) with 0 to 15 mol% additions of TiO2 (designated as 0T to 15T specimens), were studied by X-ray diffraction and electron microscopy. According to the room-temperature X-ray lattice parameter, the saturation of TiO2 in the cubic (c-) zirconia was reached at a total TiO2 addition of ca. 6 mol% at 1600°C, whereas the solubility limit in tetragonal (t-) zirconia was not reached in the composition range studied. The amount of t-zirconia increases with increasing TiO2 content at 1600°C, as indicated by the monoclinic (m-) zirconia content in the furnace-cooled specimens. Regardless of the modification of the lattice misfit strain by TiO2 dissolution, the precipitates of t-phase in the c-matrix remain lenticular with {1 0 0} habit plane. Loops, due probably to condensation of the structural vacancies, were found in the m-phase of 9T, but not in 1T and 6T specimens.

Preparation and characterization of lithium, manganese, cobalt and copper vermiculites

Lithium, manganese, cobalt and copper vermiculites were synthesized by ion-exchange from hydrogen vermiculite. The ionic conductivity was determined using impedance spectroscopy for these single crystals, and x-ray powder diffraction was used to characterize the samples. Measurements of the ionic conductivity and x-ray lattice parameters suggest that there is a strong relationship between the ionic mobility and the size of the hydrated cations, as measured by the lattice separation of the vermiculite's aluminosilicate layers.

Study of temperature dependent structural changes in molecular-beam epitaxy grown Hg1−xCdxTe by x-ray lattice parameter measurements and extended x-ray absorption fine structure

Infrared detectors fabricated from Hg1−xCdxTe typically operate in the 60 to 160 K range. The temperature dependence of the atomic structure of HgCdTe may influence device performance. We present the first detailed study of the x-ray diffraction lattice parameters of molecular-beam epitaxy grown Hg1−xCdxTe epilayers between 15 and 300 K. The epilayers were grown on (100) oriented CdTe substrates, and varied in thickness (6 to 11-μm) and composition (x=0–0.172). The (400) reflection was measured to determine the lattice parameter a⊥ normal to the film. HgTe (x=0) exhibited normal lattice contraction (α=4.7×10−6±0.3 K−1 at 300 K), with a minimum in a⊥ at 60 K, and an expansion of a⊥ below 60 K. In addition to showing a minimum in a⊥ at 60 K, some of the Hg1−xCdxTe (x≠0) epilayers (10 μm thick) exhibited anomalous behavior with varying degrees of thermal hysteresis in a⊥. The average contraction of a⊥ for these epilayers from 300 to 60 K is 0.006 Å. This is compared with results we have obtained from a temperature dependent extended x-ray absorption fine structure study of these HgCdTe epilayers: whereas HgTe exhibited a normal thermal contraction of the Hg–Te bond length consistent with the lattice parameter results, in the HgCdTe epilayers this bond contracts 0.02 to 0.03 Å on cooling from 300 to 10 K. We also present lattice parameter measurements for a thin cap layer of CdTe on HgCdTe. An increase of 0.0134 Å in a⊥ relative to the bulk was observed for a 1000 Å layer of CdTe on HgCdTe at 300 K.

Colour centres in neutron irradiated aluminium oxy-nitride

Aluminium oxy-nitride (9Al2O3.5AlN) has been neutron irradiated to fluences varying from 1018-1024 n m-2 (En>1 MeV) at 60 degrees C. The defect structures were studied by X-ray lattice parameter measurements and optical spectroscopy. The lowest neutron doses produced an anomalous volume expansion of 0.17% which was also reflected in a shift of the absorption edge to longer wavelengths. The exponential variation of the absorption edge with photon energy suggests that the 'edge' is the long wavelength side of an exciton band. The identification of two V bands with the intrinsic octahedral aluminium vacancy (2.225 eV) and the tetrahedral aluminium vacancy (3.15 eV), and their relative strengths after low neutron doses, suggested that the volume expansion may be associated with the octahedral aluminium vacancy centre. The oscillator strength of the two V bands was calculated to be 3*10-5. At higher neutron fluences the increase in lattice parameter and anion vacancy concentration showed good agreement with those found for equivalent doses in Al2O3. Comparison with the absorption spectrum of irradiated Al2O3 leads to the following assignment of anion vacancy centres to absorption bands in AlON:F-5.46 eV, F+-5.00 eV, FA-4.6 eV, F2-4.1 eV, F2+-3.68 eV.

Ion Transport in Single Crystals of the Clay-Like Aluminosilicate, Vermiculite

AbstractWe have made an investigation of the ion transport properties of single crystals of the naturally occurring clay vermiculite in order to elucidate the mechanism of conductivity including the predominant charge carrier. Measurements of the ion conductivity, magnetic susceptibility and x-ray lattice parameters of ion-exchanged samples strongly suggest that the native cations and not protons are the major current carriers. We have synthesized the hydrogen form and found that it is a much preferred precursor for ion-exchange by other cations allowing the time necessary for ion-exchange to be reduced from several months to around a week.