Crystal Lattice Strain Research Articles

Quantitative Imaging of Crystalline Structural Information by Pulsed Neutron Transmission

Bragg edge transmission imaging using pulsed neutrons is expected as a new evaluation tool for engineering materials because it can non-destructively examine crystalline structural information inside the bulk with high spatial resolution over wide area simultaneously. Methodology of quantitative imaging of crystal lattice strain was developed at ISIS. However, crystallographic texture and microstructure could not be quantitatively visualized although these are important factors for controlling strength, workability and electromagnetic properties of a material. Therefore, we developed the Rietveld-based comprehensive analysis code, RITS, for neutron transmission data. Furthermore, we successfully evaluated not only strain but also texture and crystallite size owing to the RITS code, and also carried out the verification experiment with a neutron powder diffractometer. In this article, the quantitative visualization of texture and crystallite size by the RITS code is mainly presented.

Study of KDP crystal lattice strain and stress by high resolution X-ray diffraction

The lattice strain of large-scale KDP crystal is characterized by using high resolution X-ray diffraction technique, and the lattice stress is analysed quantitatively in detail. The results indicate that KDP crystal may cleave easily along the [001] direction, which corresponds to the cracking phenomenon in the practical work. The major factors of introducing the internal stress and causing crack in the crystal growth process are summarized. Those conclusions provide important theoretical basis for proposing crack control measures of the large-scale KDP crystals.

Effect of hydrogen absorption/desorption cycling on hydrogen storage properties of a LaNi3.8Al1.0Mn0.2 alloy

The effect of long-term hydrogen absorption/desorption cycling up to 3500 cycles on the hydrogen storage properties of LaNi3.8Al1.0Mn0.2 alloy was investigated. The pressure-composition (PC) isotherms for absorption/desorption and the absorption kinetics were measured at 433 K, 453 K and 473 K. X-ray diffraction analysis revealed that the alloy had a homogeneous hexagonal CaCu5 type structure and kept this structure even after 3500 cycles, but the diffraction peaks were broadened. The degree of peak broadening was increased with increase of the cycle number, but exhibiting a maximum after initial activation. The shapes of PCT curves after 300, 2000 and 3500 cycles were similar to that after initial activation. It was found that the alloy subjected to 300 cycles did not exhibit significant changes in hydrogen storage capacity, but the long-term cycling up to 2000 and 3500 cycles resulted in obvious decrease in hydrogen storage capacity. The degradation of the hydrogen capacity might be resulted from the formation of the irreversible sites and more stable hydride phase, though no new phase was found after absorption/desorption cycling from XRD pattern as shown in Fig. 6 because of the limitation of XRD analysis sensibility. The hydrogen absorption kinetics after 300 cycles was deteriorated but improved again after 2000 and 3500 cycles compared with that of after initial activation. The changes in hydrogenation properties of the alloy induced by cycling were discussed by considering the crystal structure, lattice strain and pulverization of the sample.

Trace element partitioning between ilmenite, armalcolite and anhydrous silicate melt: Implications for the formation of lunar high-Ti mare basalts

We performed a series of experiments at high pressures and temperatures to determine the partitioning of a wide range of trace elements between ilmenite (Ilm), armalcolite (Arm) and anhydrous lunar silicate melt, to constrain geochemical models of the formation of titanium-rich melts in the Moon. Experiments were performed in graphite-lined platinum capsules at pressures and temperatures ranging from 1.1 to 2.3 GPa and 1300–1400 °C using a synthetic Ti-enriched Apollo ‘black glass’ composition in the CaO–FeO–MgO–Al 2O 3–TiO 2–SiO 2 system. Ilmenite–melt and armalcolite–melt partition coefficients ( D) show highly incompatible values for the rare earth elements (REE) with the light REE more incompatible compared to the heavy REE ( D La Ilm – melt 0.0020 ± 0.0010 to D Lu Ilm – melt 0.069 ± 0.010 for ilmenite; D La Arm – melt 0.0048 ± 0.0023 to D Lu Arm – melt 0.041 ± 0.008 for armalcolite). D values for the high field strength elements vary from highly incompatible for Th, U and to a lesser extent W (for ilmenite: D Th Ilm – melt 0.0013 ± 0.0008, D U Ilm – melt 0.0035 ± 0.0015 and D W Ilm – melt 0.039 ± 0.005, and for armalcolite D Th Arm – melt 0.008 ± 0.003, D U Arm – melt 0.0048 ± 0.0022 and D W Arm – melt 0.062 ± 0.03), to mildly incompatible for Nb, Ta, Zr, and Hf (e.g. D Hf Ilm – melt 0.28 ± 0.05 and : D Hf Arm – melt 0.76 ± 0.07). Both minerals fractionate the high field strength elements with D Ta/ D Nb and D Hf/ D Zr between 1.3 and 1.6 for ilmenite and 1.3 and 1.4 for armalcolite. Armalcolite is slightly more efficient at fractionating Hf from W during lunar magma ocean crystallisation, with D Hf /D W = 12–13 compared to 6.7–7.5 for ilmenite. The transition metals vary from mildly incompatible to compatible, with the highest compatibilities for Cr in ilmenite ( D ∼ 7.5) and V in armalcolite ( D ∼ 8.1). D values show no clear variation with pressure in the small range covered. Crystal lattice strain modelling of D values for di-, tri- and tetravalent trace elements shows that in ilmenite, divalent elements prefer to substitute for Fe while armalcolite data suggest REE replacing Mg. Tetravalent cations appear to preferentially substitute for Ti in both minerals, with the exception of Th and U that likely substitute for the larger Fe or Mg cations. Crystal lattice strain modelling is also used to identify and correct for very small (∼0.3 wt.%) melt contamination of trace element concentration determinations in crystals. Our results are used to model the Lu–Hf–Ti concentrations of lunar high-Ti mare basalts. The combination of their subchondritic Lu/Hf ratios and high TiO 2 contents requires preferential dissolution of ilmenite or armalcolite from late-stage, lunar magma ocean cumulates into low-Ti partial melts of deeper pyroxene-rich cumulates.

X-ray study of dopant state in highly doped semiconductor single crystals

Using Si(As, P, B) and GaSb(Si) study, possibilities of X-ray diffraction methods for diagnostics of highly doped semiconductor crystals in characterization of dopant state - whether it is in the crystals in the form of solid solution or under various stages of its decomposition - are shown. The combination of techniques of X-ray diffraction topography and high resolution X-ray diffractometry, higher sensitive to the crystal lattice strain than that traditionally used is taken as the basis for investigating the crystals with slight and strong absorption of X-rays. These methods were supplemented with digital processing of the topographic images of growth striations and electrical measurements.

Evolution of structural and optical properties in the course of thermal evolution of sol–gel derived cobalt-doped gahnite

Thermal evolution of sol–gel derived gahnite (ZnAl 2O 4) with 4, 8 and 12 at.% of Zn replaced with Co was studied by thermal analysis techniques (DTA/TGA), X-ray diffraction (XRD) and UV–vis diffuse reflectance spectroscopy (DRS). Zinc–cobalt spinel powders were produced by gel heat treatment at temperatures as low as 400 °C. Crystal structure was characterized using Rietveld refinement of X-ray diffraction patterns for the samples annealed at 800 °C, simultaneously with the analysis of diffraction line broadening. It was found out that the distribution of Co 2+ ions in tetrahedral and octahedral sites of zinc cobalt aluminate crystal lattice, crystallite size and lattice strain depend on Co loading. The green color of samples thermally treated at T < 800 °C has been explained as a consequence of partial oxidation of Co 2+ ions at lower temperatures and accommodation of Co 3+ ions in octahedral sites. Thermal treatment at higher temperatures promote gradual change of color from green to blue, characteristic for tetrahedrally coordinated Co 2+ ions. The spectra evolution could be interpreted as a progressive reduction of Co 3+ to Co 2+ ions at higher temperatures.

Observation of Lattice Plane Bending during SiC PVT Bulk Growth Using &lt;i&gt;In Situ&lt;/i&gt; High Energy X-Ray Diffraction

We have investigated thermally induced strain in the SiC crystal lattice during physical vapor transport bulk growth. Using high energy x-ray diffraction lattice plane bending was observed in-situ during growth. With increasing growth rate increasing lattice plane bending and, hence, strain was observed. A comparison with numerical modeling of the growth process shows that the latter is related to the heat of crystallization which needs to be dissipated from the crystal growth front. The related temperature gradient as driving force for the dissipation of the heat of crystallization causes lattice plane bending. Optimization of the growth process needs to consider such effects.

Relationship between changes in the crystal lattice strain and thermal conductivity of high burnup UO2 pellets

Abstract Two kinds of disk-shaped UO2 samples (4 mm in diameter and 1 mm in thickness) were irradiated in a test reactor up to about 60 and 130 GWd/t, respectively. The microstructures of the samples were investigated by means of optical microscopy, scanning electron microscopy/ electron probe micro-analysis (SEM/EPMA) and micro-X-ray diffractometry. The measured lattice parameters tended to be considerably smaller than the reported values, and the typical cauliflower structure which is often observed in high burnup fuel pellet is hardly seen in these samples. Thermal diffusivities of the samples were also measured by using a laser flash method, and their thermal conductivities were evaluated by multiplying the heat capacity of unirradiated UO2 and sample densities. While the thermal conductivities of sample 2 showed recovery after being annealed at 1500 K, those of sample 4 were not clearly observed even after being annealed at 1500 K. These trends suggest that the amount of accumulated irradiation-induced defects depends on the irradiation condition of each sample. From the comparison of the changes in the lattice parameter and strain energy density before and after the thermal diffusivity measurements, it is likely that the thermal conductivity recovery in the temperature region from 1200 to 1500 K is related to the migration of dislocation.

High Temperature Crystal Chemistry and Oxygen Permeation Properties of the Mixed Ionic–Electronic Conductors LnBaCo2O5 + δ ( Ln = Lanthanide )

The high temperature crystal chemistry and oxygen permeation properties of the cation-ordered perovskite oxides [lanthanide , Nd, and Sm] have been investigated in comparison with the cation-disordered perovskite. The (, Nd, and Sm) oxides exhibit a metal-insulator transition at , as evidenced by total conductivity measurements and high temperature X-ray diffraction data and an oxygen vacancy order–disorder transition at in air, as evidenced by an orthorhombic to tetragonal transition. At a given temperature, the oxygen permeation flux decreases from to Nd to Sm due to the changes in crystal symmetry and lattice strain. The oxygen permeation mechanism in the is bulk-diffusion-limited rather than surface-exchange-limited for membrane thickness .

Minor element partitioning between fcc Fe metal and Fe–S liquid at high pressure: The role of crystal lattice strain

We present a new approach to model element distribution between solid and liquid metal phases, based on experimentally determined data for the partitioning of P, S, selected transition metals, and chalcophile elements between face-centred cubic (fcc) Fe and Fe–S liquid at pressures of 9, 15 and 23 GPa and temperatures between 1523 and 1773 K. Solid/liquid partition coefficients ( D) for the transition metals V, Cr, Mn, Fe, Co, and Ni range from a minimum D of 0.16–0.64 for V to a maximum D of 1.1–1.2 for Co, indicating modest but significant fractionation. D for the chalcophile elements Cu, Zn, Ga, Sn, and Pb varies from 0.029–0.051 for D Pb up to 1.6–2.4 for D Ga and for non-metals from 0.02–0.04 for S to 0.23–0.66 for P. A modified lattice strain model (as in common use for silicate mineral-melt partitioning) describes the variations in D values for the first row transition metals through the deviance in metal radius from the ideal site radius of Fe in solid metal, indicating that these metals all substitute into the iron site of the solid phase. Variations in D values for the chalcophile elements can also be rationalized using a lattice strain model, but chalcophiles occupy a different site in the solid metal, probably related to the presence of sulphur defects. We show that the lattice strain model can be applied to previously published low pressure experimental data, as well as to third-row transition metals as to first-row transition metals and chalcophiles. The fact that solid–liquid metal D values are amenable to interpretation using lattice strain models paves the way for the development of a new class of element partitioning models applicable to metallic core crystallization processes.

The effects of irradiation condition and microstructural change on lattice parameter, crystal lattice strain and crystallite size in high burnup UO 2 pellet

Pellet samples (average burnup: 37–62 GWd/t) were prepared from three kinds of fuel rods which were irradiated in the Halden Heavy Water Reactor in Norway, and microstructural changes in the pellet samples were investigated by means of optical microscopy, SEM/EPMA and micro-X-ray diffractometry. The measured lattice parameters tended to be smaller than the values reported previously, and it is likely that the measured lattice parameters were affected by the temperature conditions during the irradiation tests and the microstructural changes which occurred in the samples. Considering the burnup dependence of uniform and non-uniform strains, the following things are suggested: the interstitial atoms which cause uniform strain begin firstly to form dislocations as a recovery process of irradiation defect and the dislocation density increases. With increasing burnup, the accumulation of dislocations in the crystallite saturates and the migration of dislocations becomes dominant as a recovery process of irradiation defects in the crystallite.

Morin transition in hematite: Size dependence and thermal hysteresis

Hematite is a frequently used mineral in paleomagnetic and environmental magnetic studies. Just below room temperature, it undergoes a magnetic phase transition, the Morin transition, whose nature is an important part of our basic understanding of hematite's magnetism and magnetic memory. We have determined the temperature TM of the Morin transition from saturation remanence warming curves to be 250–261 K for 0.5–6 mm hematite natural single crystals, 257–260 K for 45–600 μm sieved crystal fractions, and 241–256 K for submicron synthetic hematites with grain sizes between 120 and 520 nm. The variation must be due to differences in crystal morphology, lattice strain, and crystal defects common in both synthetic and natural crystals. Our results are compatible with published data for 100 nm to 10 mm hematites and show that TM is nearly size independent, decreasing very gradually as particle size decreases over this broad range, which includes both multidomain (MD) and single‐domain (SD) structures. However, TM decreases sharply between 90 and 30 nm. Below 20 nm, the transition disappears entirely as near‐surface spins deviate strongly from the antiferromagnetic easy axis. Our SD and MD hematites exhibit a thermal hysteresis in the Morin transition: the values of TM in cooling and in heating are different. For the same cooling/warming rate, ΔTM is much greater for submicron hematites than for larger crystals. We attribute the lag in the transition in both cooling and heating to crystal imperfections and resulting internal stresses, and speculate that defects may serve to pin and stabilize surface spins. Preventing spin rotation in a region large enough to trigger the phase transition would inhibit destabilization of the weakly ferromagnetic phase in cooling and the antiferromagnetic phase in heating. The wide distribution of particle sizes in our submicron samples may also play a role.

Effects of Helium and Oxygen Common Implantation in Silicon Wafer

Defect engineering for SiO2 precipitation is investigated using He-ion implantation as the first stage of separation by implanted oxygen (SIMOX). Cavities are created in Si by implantation with helium ions. After thermal annealing at different temperatures, the sample is implanted with 120keV 8.0 × 1016 cm-2 O ions. The O ion energy is chosen such that the peak of the concentration distribution is centred at the cavity band. For comparison, another sample is implanted with O ions alone. Cross-sectional transmission electron microscopy (XTEM), Fourier transform infrared absorbance spectrometry (FTIR) and atomic force microscopy (AFM) measurements are used to investigate the samples. The results show that a narrow nano-cavity layer is found to be excellent nucleation sites that effectively assisted SiO2 formation and released crystal lattice strain associated with silicon oxidation.

Control of the crystal lattice strain gradient caused by low-frequency ultrasound

The opportunities of dynamic control of the ultrasound-induced strain gradient in germanium crystal lattice have been studied. Two methods of gradient strain control are offered, which are based on variation in the (i) frequency and (ii) amplitude of ultrasonic vibrations. Both methods have been experimentally implemented.

Effects of high-concentration phosphorus doping on crystal quality and lattice strain in SiGe HBTs

A high-concentration in-situ phosphorus-doping technique for silicon low-temperature epitaxial growth with Si 2H 6 has been developed. Growth temperature has an impact on the crystal quality and on lattice strain of phosphorus-doped silicon layers. Resistivity, micro-Raman spectroscopy, and high-resolution X-ray diffraction indicated that good crystal quality was achieved at a growth temperature of 525 °C. On the other hand, growth pressure has little influence on crystal quality or on lattice strain except for surface morphology. By optimizing epitaxial growth conditions, an extremely high concentration of phosphorous doping was achieved without a high-temperature activation annealing, and the resultant good crystal quality of the phosphorus-doped silicon layer gave a very low resistivity. Accordingly, the high-concentration in-situ phosphorus doping is a powerful technique to fabricate future ultra-high-speed SiGe HBTs.

Measurements of Crystal Lattice Strain and Crystallite Size in Irradiated UO2 Pellet by X-ray Diffractometry

Lattice parameters, crystallite sizes, and nonuniform strains of high-burnup UO2 fuel samples were measured using micro-X-ray diffractometry in order to investigate the effects of grain subdivision and strain distribution between crystallites on the microstructural changes, so-called rim structure formation, in UO2 pellets. The samples were prepared from fuel rods irradiated in commercial reactors, and pelletaveraged burnups of the samples were in the range from 41 to 61GWd/t. While the lattice parameters of the samples increased linearly in the burnup region up to approximately 70 GWd/t, the lattice parameters slightly decreased and tended to level off above 70GWd/t. The measured crystallite sizes were in the range from 100 to 200 nm and these were nearly the same as those of the “recrystalized grains” in the rim structure. The elastic strain energy densities, which were evaluated from the lattice parameters and nonuniform strains, tended to increase with burnup and show two plateaus at burnups of approximately 50 and 70GWd/t, respectively. The saturation of the measured strain energy density at approximately 50GWd/t can be attributed to the tangle of accumulated dislocations, and the increase in the strain energy density above 60GWd/t can be explained by the strain caused by crystallite rotation under the restraint conditions between crystallites.

Measurements of Crystal Lattice Strain and Crystallite Size in Irradiated UO2 Pellet by X-ray Diffractometry

Lattice parameters, crystallite sizes, and nonuniform strains of high-burnup UO2 fuel samples were measured using micro-X-ray diffractometry in order to investigate the effects of grain subdivision and strain distribution between crystallites on the microstructural changes, so-called rim structure formation, in UO2 pellets. The samples were prepared from fuel rods irradiated in commercial reactors, and pelletaveraged burnups of the samples were in the range from 41 to 61GWd/t. While the lattice parameters of the samples increased linearly in the burnup region up to approximately 70 GWd/t, the lattice parameters slightly decreased and tended to level off above 70GWd/t. The measured crystallite sizes were in the range from 100 to 200 nm and these were nearly the same as those of the “recrystalized grains” in the rim structure. The elastic strain energy densities, which were evaluated from the lattice parameters and nonuniform strains, tended to increase with burnup and show two plateaus at burnups of approximately 50 and 70GWd/t, respectively. The saturation of the measured strain energy density at approximately 50GWd/t can be attributed to the tangle of accumulated dislocations, and the increase in the strain energy density above 60GWd/t can be explained by the strain caused by crystallite rotation under the restraint conditions between crystallites.

Crystal texture selection in epitaxies of orthorhombic antiferromagnetic YMnO 3 films

The orthorhombic phase of YMnO 3 has been epitaxially stabilized on SrTiO 3 single crystal substrates. Changing the substrate orientation, the out-of-plane orientation of the epitaxial films can be tuned to (001), (101), or (100). Depending on the orientation, the films present varied crystal domain structures and lattice strains. Single domain YMnO 3(100) films have been grown on SrTiO 3(110) substrates, whereas they present two and three crystal variants on SrTiO 3(001) and SrTiO 3(111), respectively. Epitaxial stress in each domain is anisotropic, tensile in one direction and compressive in the other. It has consequences in the texture selection when domains with different out-of-plane orientation can grow epitaxially. Antiferromagnetism of YMnO 3 films has been confirmed by measuring the exchange bias field induced in an underlying ferromagnetic SrRuO 3 layer.

Sputtering growth and characterization of CoFe 2O 4–BaTiO 3 nanostructures

We report on the sputtering growth and characterization of nanostructures formed by a ferrimagnetic spinel (CoFe 2O 4) and a ferroelectric perovskite (BaTiO 3) on (0 0 1) and (1 1 1) oriented SrTiO 3 substrates. We present analysis of the crystal structure (crystal phases and lattice strain) and the surface morphology by X-ray diffractometry and by atomic force microscopy, respectively. Films grown on both substrates display phase segregation, being textured (either (0 0 1) or (1 1 1)) the films deposited at 700 °C and polycrystalline the ones grown at the highest deposition temperature (800 °C). The magnetic easy axis of films grown on SrTiO 3(0 0 1) is out-of-plane. It is found that phase separation and island size are depending on the growth conditions and the role of adatom supersaturation during growth is discussed.

Transformation of X-ray Server from a set of WWW-accessed programs into WWW-based library for remote calls from X-ray data analysis software

X-ray Server [x-server.gmca.aps.anl.gov] is a public project providing a collection of online software tools for modeling data in the fields of surface X-ray scattering and grazing-incidence X-ray diffraction from thin solid films and multilayers with account for the effects of crystal lattice strains, magnetization and interface roughness. This paper reports on recent developments that are addressing numerous requests to expand the Server access beyond plain web browser sessions and facilitate batch processing, remote fitting and integration of Server programs into users’ data analysis software.