Lattice Parameter Expansion Research Articles

Symmetry and lattice mismatch induced strain accommodation near and away from correlated perovskite interfaces

Distinct MnO6 octahedral distortions near and away from the La0.67Sr0.33MnO3/SrTiO3(001) (LSMO/STO) interface are quantified using synchrotron x-ray diffraction and dynamical x-ray diffraction simulations. Three structural regions of stress accommodation throughout the film thickness were resolved: near the LSMO/STO interface, intermediate region farther from the interface, and the main layer away from the interface. The results show that within the first two unit cells stress is accommodated by the suppression of octahedral rotations in the film, leading to the expansion of the c-axis lattice parameter. Farther from the interface film structure acquires octahedral tilts similar to thicker perovskite films under tensile stress, leading to a reduced c-axis parameter. We demonstrate that these regions are related to two different strain coupling mechanisms: symmetry mismatch at the interface and lattice mismatch in the rest of the film. The findings suggest new routes for strain engineering in correlated perovskite heterostructures.

In situ neutron diffraction analysis of stress-free d-spacing during solution heat treatment of modified 319 Al alloy engine blocks

Aluminium alloy engine blocks have successfully replaced ferrous materials in order to maximise weight savings and improve vehicle fuel efficiency. However, the development of an optimal heat treatment process is required to improve engine block casting integrity and prevent potential problems such as in-service cylinder distortion. Optimisation of heat treatment parameters requires an in-depth study to determine how residual stresses are relieved with time during solution heat treatment. In order to perform this analysis, however, in situ neutron diffraction must first be carried out on stress-free samples of the same composition and processing history as the engine blocks to account for factors such as thermal expansion and changes in lattice parameter due to dissolution of secondary phases. The results from this study suggest that thermal expansion caused the largest change in d0 spacing, while prolonged exposure at the solutionising temperature resulted in relatively small changes in {311} and {331} d0 spacing due to phase dissolution.

Orientation dependence of nitrogen supersaturation in austenitic stainless steel during low-temperature gas-phase nitriding

A hardened surface layer was produced on 316L austenitic stainless steel via low-temperature gas-phase nitriding. The effects of nitriding temperature, nitrogen activity and processing time were systematically studied. Concentration–depth profiling by Auger electron spectroscopy revealed very high levels (up to 25at.%) of interstitial nitrogen in solid solution. This causes a lattice parameter expansion of up to 10% at the alloy surface. X-ray diffractometry revealed that the expansion – and thus the level of nitrogen supersaturation – strongly depends on the crystallographic orientation. We attribute this effect to the elastic anisotropy of austenite, exacerbated by a nitrogen-induced paramagnetic-to-ferromagnetic transition.

(Invited) Three-Dimensional Epitaxial Si1-XGex, Ge and SiC Crystals on Deeply Patterned Si Substrates

The heteroepitaxial growth of layers onto substrates differing substantially in lattice parameter and thermal expansion coefficients continues to be a challenge because of the formation of crystal defects, wafer bowing or layer cracking. We have recently demonstrated for the example of Ge/Si(001) that these deficiencies can be avoided by combining deep substrate patterning with appropriately tuned surface diffusion lengths, resulting in dense arrays of highly perfect three-dimensional epitaxial crystals [1]. Here we discuss the extension of the method to layer/substrate combinations with lattice misfits ranging from zero for pure Si/Si(001) up to 20% for 3C-SiC/Si(001).As an example we show in Fig. 1 scanning electron microscopy images obtained on space-filling arrays of Si, Si0.6Ge0.4 and Ge crystals grown to a height of 8 µm onto 2 µm wide pillars separated by 2 µm wide trenches etched to a depth of 8 µm into Si(001). The surface diffusion lengths were kept approximately the same for the three arrays by keeping the deposition rate constant while lowering the substrate temperature from 810° C for Si, to 660° C for the alloy and finally to 485° C for Ge. This is reflected in the remarkably similar crystal morphology for the three cases, characterized by narrow gaps between neighboring crystals and closely similar facet structures. The unusual growth mode of Fig. 1 results mainly from the combination of short surface diffusion lengths below typical facet sizes and reactive flux shielding by neighboring substrate pillars or crystals. While the latter is essentially given by the substrate geometry, tuning of the diffusion lengths by means of substrate temperature may affect the deposition rate. Indeed, the structures of Fig. 1 have been obtained by low-energy plasma-enhanced chemical deposition [2], providing fast, nearly temperature independent deposition rates. The approach is applicable also to off-cut substrates and to other substrate orientations. Figure 2 shows an example of an array of 8 µm tall Ge0.9Si0.1crystals on Si(111) pillars.High-resolution X-ray diffraction with laboratory sources and scanning nano-diffraction by a focused synchrotron X-ray beam proves that the structures of Figs. 1 and 2 are entirely free from misfit and thermal strain [3]. Wafer bowing is virtually eliminated and layer cracks cannot arise.The short surface diffusion lengths required for the growth of 3D crystal arrays can more easily be attained for compound semiconductors. Here the ratio of anion and cation radical fluxes provides an additional control parameter such that molecular beam epitaxy and even chemical vapor deposition (CVD) can be used as deposition tools.We have applied the method outlined above to the growth of 3C-SiC on deeply patterned Si(001) by low pressure CVD. As an example we show in Fig. 3 a cross-section SEM image through 3C-SiC ridges which clearly exhibit the kind of self-limited lateral expansion visible also in Figs. 2 and 3. For high SiC ridges all stacking faults on {111} planes parallel to the ridges escape through the ridge sidewalls.Financial support by the Swiss federal program Nano-Tera through project NEXRAY, by Fondazione Cariplo through the MANDIS project, and by PileGrowth Tech is gratefully acknowledged.[1] C.V. Falub et al., Science 335, 1330 (2012).[2] C. Rosenblad et al., J. Vac. Sci. Technol. A 16, 2785 (1998).[3] C.V. Falub et al., Sci. Rep. 3, 2276 (2013).

Gadolinium-substitution induced effects on the structure and AC electrical properties of cobalt ferrite

We report on the frequency (f=20Hz–1MHz) and temperature (T=300–600K) dependent electrical properties of gadolinium (Gd) substituted cobalt ferrite (CoF2−xGdxO4 (CFGO); x=0.00–0.40). Gd-substituted cobalt ferrites crystallize in cubic inverse spinel phase. CFGO materials exhibit lattice parameter expansion from 8.373Å (x=0.0) to 8.422Å (x=0.4) due to the larger ionic radius of Gd3+ compared to Fe3+. The effect of Gd-substitution is significant on the electrical properties; electrical conductivity decreases with increasing Gd-concentration. A two-layer model consisting of semiconducting-CFGO-grains separated by insulating grain-boundaries was able to account for the observed temperature and frequency dependent electrical properties.

Thermal Expansion of HfO2 and ZrO2

The thermal expansion of a low symmetry crystal can be much more interesting than the lattice parameter expansion would suggest. Here, the complete thermal expansion tensors for monoclinic and tetragonal phases of ZrO2 and HfO2 have been measured in air, by high‐resolution, high‐temperature X‐ray diffraction. These results reveal the highly anisotropic nature of thermal expansion in the monoclinic phase as well as a cooperative movement of ions and the existence of a zero thermal expansion plane.

Thermal Expansion of Ln6WO12 (Ln = Y,Ho,Er,Yb) and Ln2WO6 (Ln = Gd,Dy,Ho) – an In Situ Synchrotron X‐ray Diffraction Study

The thermal expansion (TE) behavior of cubic and rhombohedral Ln6WO12 (Ln = Y, Ho, Er, Yb) and monoclinic Ln2WO6 (Ln = Gd, Dy, Ho) was investigated by synchrotron X‐ray diffraction from room temperature to approximately 1500°C. The volumetric and lattice parameter expansions were measured for all compositions in both systems, and the respective expansion coefficients were derived and fitted over the observed temperature range with a second‐order polynomial. The relative TE evolution along the unit cell edges in each phase was described from a crystallographic perspective, with the reasons for TE dynamics explained in terms of the fundamental constituent units of the structure. Analysis of the TE ellipsoid of the monoclinic Ln2WO6 revealed a continuous change in both its shape and orientation, with the latter effect strongly manifested in the (010) plane. A noticeable reversal of the relative expansion rates between a, and b and c lattice parameters was attributed to the rotation of the ellipsoid cross section in this plane, bringing the larger of the two eigenvectors closer to a, while the smaller one to c. Investigating the structural dynamics of the constituent layers in Ln2WO6 suggested that the bridging role of the Ln polyhedron centered on the only general position in the unit cell may be the reason for the rotating TE ellipsoid.

Mechanical-Electrochemical Coupling in Materials for Solid Oxide Fuel Cells: Insights from Computer Simulations

The coupling between the electrical, chemical and mechanical properties of materials, usually referred to as Electro-Chemo-Mechanics [1], has very important implications for energy related materials and devices. Indeed, this coupling can be beneficial, e.g. the ion conductivity enhancement observed in ceria and zirconia when these materials are strained [2], or detrimental, e.g. the lattice parameter expansion observed in ceria upon reduction [3]. For this reason a better understanding of this coupling is necessary in order to tailor the properties of these materials.Atomistic computer simulations represent a powerful tool to study the mechanical-electrochemical coupling, as they can provide information that is complementary to experiments. In this presentation, I will review some recent computational work in this field. First I will talk about chemical expansion in ceria, an example of chemo-mechanical coupling. I will show how, by combining Density Functional Theory and Molecular Dynamics Calculations with experimental data, we concluded that chemical expansion is caused by two competing processes, the formation of a vacancy (leading to a lattice contraction) and the cation radius change (leading to a lattice expansion). This information was then condensed in a simple analytical model, which was then used to predict materials compositions that minimize chemical expansion. Then I will present two more examples from my work: the first one on the study of co-doping strategies in ceria as a means to enhance its ionic conductivity (electro-chemical coupling) and the second one on the effects of dislocations in SrTiO3 on the defect chemistry and mobility of this material (electro-chemo-mechanical) coupling.

Tailoring of Lattice Parameter in Palladium By Alloying with Inert-Gases and Its Impact on Pd-H System

Metallic palladium is a commonly employed heterogeneous catalyst used in particular in reduction, hydrogenation and dehydrogenation reactions. The standard Gibbs energies of hydrogen chemisorption on palladium surface is strongly dependent on the lattice distortions <Δa/a> that have been demonstrated e.g. by the ccharacterization of pseudomorphic palladium layers deposited on foreign metals [1]; however, in such systems the strong chemical influence of the substrate by no means cannot be eliminate under experimental conditions. Similar conclusion can be drawn for bimetallic alloys, in which the charge transfer between both constituents affects their electronic structure [2]. Lattice contraction caused by the surface tension in palladium nanoparticles seems to be relatively easily achievable, however, also in this case the surface phenomena are hindered by the presence of the support and/or organic capping agents used for NPs stabilization so that the fundamental studies of adsorption processes are difficult.Here we report a method for the lattice parameter expansion achieved by means of ion implantation of inert gases, such as N2 and noble gases, in thin palladium layers (50-500 nm in thickness). By using this approach the lattice parameter can be tailored by changing the gas type, implantation ionic current or dose. By using noble gasses for implantation the chemical effects normally related to alloying was entirely eliminated. The nonmetallic element content in these alloys varied from 0.1 to 10 at. % depending on experimental conditions. Obtained layers were characterized by surprisingly good stability even after multiple cycles of hydrogen absorption and desorption [3]. Prepared Pd-X films were investigated by using Grazing Incidence X-ray Diffraction (GIXD). This method allowed us to get insight into depth-resolved material structure. After inert gases implementation we have observed diffraction lines from solid inert gases embedded into palladium structure most likely in form of nanoparticles. The studies of hydrogen absorption in those alloys were carried out using classical transient measurements and electrochemical impedance spectroscopy. The hydrogen insertion into the alloy was performed in an aqueous 0.1 M HClO4 solution and electrosorption isotherms were then determined. The results indicate that although the total amount of the hydrogen dissolved in those alloys is only slightly lower with an increase of the nonmetallic element content, the hydrogen insertion in the alpa-phase was enhanced nearly by two orders of magnitude for PdXe alloy with respect to pure palladium (Figure 1). This result indicate that lattice distortion is an extremely important factor in metal/hydrogen systems and quite crucial in heterogeneous catalysis, e.g. in hydrogenation reactions and/or hydrogen storage.Literature:[1] L.A. Kibler, A.M El-Aziz, R. Hoyer, D.M. Kolb, 2005, Angewandte Chemie – Int. Ed 44 (14) , pp. 2080-2084[2] J.A. Rodriguez, D.W. Goodman, Acc. Chem. Res. 28 (1995) 477[3] P. Połczyński, G. Dercz, R. Jurczakowski, manuscript in preparation.

Molecular dynamic study on thermal expansion of U1-xPuxO2

Molecular dynamic simulation is performed to investigate the thermal properties of U1-xPuxO2 (x=0.07, 0.15, 0.25, 0.5) using the potential of partially ionic model at temperatures ranging from 300 to 3000 K and pressures in a range of 0-1.5 GPa. The results indicate that the lattice parameters decrease linearly with Pu ratio increasing under different temperatures. The linear expansion coefficient increases with Pu ratio increasing. The isothermal compressibility decreases with Pu ratio decreasing. In addition, the experience functions of lattice parameter and linear expansion coefficient are also derived.

Development and characterization of 3CaO·P2O5-SiO2-MgO glass-ceramics with different crystallization degree

The CaO-P2O5-SiO2-MgO system presents several compounds used as biomaterials such as hydroxyapatite (HA), tricalcium phosphate (TCP) and TCP with magnesium substituting partial calcium (TCMP). The β-TCMP phase with whitlockite structure has interesting biological features and mechanical properties, meeting the requirements of a bioactive material for bone restoration. In this work, the production of Mg-doped TCP, β-TCMP, has been investigated by crystallization from a glass composed of 52.75 wt% 3CaO·P2O5, 30 wt% SiO2 and 17.25 wt% MgO (i.e., 31.7 mol% CaO, 10.6 mol% P2O5, 26.6 mol% MgO and 31.1 mol% SiO2) using heat treatments between 775 °C and 1100 °C for up to 8 h. The devitrification process of the glass has been accompanied by differential scanning calorimetry (DSC), high-resolution X-ray diffraction (HRXRD), relative density and bending strength measurements. The characterization by HRXRD and DSC revealed the occurrence of whitlockite soon after the bulk glass preparation, a transient non-cataloged silicate between 800 °C and 1100 °C, and the formation of diopside in samples treated at 1100 °C as crystalline phases. The overall crystalline fraction varied from 26% to 70% depending on the heat treatments. Furthermore, contraction of the a-axis lattice parameter and expansion of the c-axis lattice parameter of the whitlockite structure have been observed during the heat treatments, which were attributed to the β-TCMP formation with the partial substitution of Ca2+ by Mg2+. Relative densities near 99% and 97% for the glass and glass-ceramics respectively indicated a discrete reduction as a function of the devitrification treatment. Bending strengths of 70 MPa and 120 MPa were determined for the glass and glass-ceramic material crystallized at 975 °C for 4 h, respectively.

Hydrothermal Synthesis and Characterization of Nb&lt;sup&gt;5+&lt;/sup&gt;-Doped SrTiO&lt;sub&gt;3&lt;/sub&gt; Powders

Nb5+-doped SrTiO3 (STO) particles were synthesized by a simple hydrothermal reaction at 150 °C for 4h. It was found that the main diffraction peaks of Nb5+-doped STO samples with different dosage of dopants shifted gradually to low angles, indicating the little lattice parameter expansions which result from the partial substitution of Ti4+ (0.061 nm) by Nb5+ (0.064 nm) in perovskite structure. From the lattice parameters, the max Nb5+ dopant concentration is about 2 mol%, and the particles obtained were 200 nm-sized and monodispersed.

Electrical and Optical Properties of Sb-Doped BaSnO3

The electronic and optical properties of the cubic perovskite, BaSnO3, are compared with the well-known transparent conducting oxides (TCOs), SnO2 and In2O3. The optical band gaps of the undoped compounds, as measured by diffuse reflectance spectroscopy on powdered samples, are 3.1 eV for BaSnO3 and 3.8 eV for SnO2. Electronic structure calculations show that both compounds possess a large conduction band dispersion, which suggests that BaSnO3, like SnO2, should be a good TCO if it can be n-doped. To explore this possibility the properties of substitutionally doped, BaSn1–xSbxO3 samples were investigated. The electrical conductivity increases drastically for BaSn1–xSbxO3 samples with x ≤ 0.05, showing a transition from an insulating to a metallic state. For higher doping levels, 0.05 < x < 0.15, the conductivity saturates at 4 S cm–1. This is accompanied by saturation in the expansion of the cubic lattice parameter. The color of the pellets changed from white (x = 0) to bluish black (x = 0.15). This darkening originates from the formation of an intense and broad optical absorption band centered at 1200–1300 nm for the more highly doped samples. This absorption band spans both the visible and the near-infrared regions, resulting in a loss of transparency. Various spectroscopic techniques were used to elucidate the observed behavior. Mössbauer spectroscopy reveals the presence of mixed valent antimony, Sb3+(5s2)/Sb5+(5s0), as x increases. ESR spectra collected on a BaSn0.99Sb0.01O3 sample indicate that only ∼5% of unpaired electrons are present as delocalized carriers. The other 95% are localized to form a Sn3+ trapped electron center. To explain the tendency for carrier localization in doped BaSnO3 a mechanism based on strong electron–phonon interactions in perovskites containing cations with (n – 1)d10ns0 electronic configuration is proposed. This mechanism explains why BaSn1–xSbxO3 possesses relatively poor TCO characteristics, in sharp contrast to widely used TCO materials Sn1–xSbxO2 and In1–xSnxO1.5.

Significant enhancement of critical current density by effective carbon-doping in MgB2thin films

The pure and carbon (C)-doped <TEX>$MgB_2$</TEX> thin films were fabricated on <TEX>$Al_2O_3$</TEX> (0001) substrates at a temperature of <TEX>$650^{\circ}C$</TEX> by using hot-filament-assisted hybrid physical-chemical vapor deposition technique. The <TEX>$T_c$</TEX> value for pure <TEX>$MgB_2$</TEX> film is 38.5 K, while it is between 30 and 35 K for carbon-doped <TEX>$MgB_2$</TEX> films. Expansion in c-axis lattice parameter was observed with increase in carbon doping concentration which is in contrast to carbon-doped <TEX>$MgB_2$</TEX> single crystals. Significant enhancement in the critical current density was obtained for C-doped <TEX>$MgB_2$</TEX> films as compared to the undoped <TEX>$MgB_2$</TEX> film. This enhancement is most probably due to the incorporation of C into <TEX>$MgB_2$</TEX> and the high density of grain boundaries, both help in the pinning of vortices and result in improved superconducting performance.

Integration of GaAs on Ge/Si towers by MOVPE

ABSTRACTWe report on the maskless integration of micron-sized GaAs crystals on patterned Si substrates by metal organic vapor phase epitaxy. In order to adapt the mismatch between the lattice parameter and thermal expansion coefficient of GaAs and Si, 2 μm tall Ge crystals were first grown as virtual substrate by low energy plasma enhanced chemical vapor deposition. We investigate the morphological evolution of the GaAs structures grown on top of the Ge crystals at the transition towards full pyramids with energetically stable {111} facets. A substantial release of strain is shown in GaAs crystals with a height of 2 μm and lateral sizes up to 15×15 μm2 by both X-ray diffraction and photoluminescence.

Activity and Evolution of Vapor Deposited Pt-Pd Oxygen Reduction Catalysts for Solid Acid Fuel Cells

The performance of hydrogen fuel cells based on the crystalline solid proton conductor CsH2PO4 is circumscribed by the mass activity of platinum oxygen reduction catalysts in the cathode. Here we report on the first application of an alloy catalyst in a solid acid fuel cell, and demonstrate a mass activity 4.5 times greater than Pt at 0.8 V. This activity enhancement was obtained with platinum-palladium alloys that were vapor-deposited directly on CsH2PO4 at 210 °C. Catalyst mass activity peaks at a composition of 84 at% Pd, though smaller activity enhancements are observed for catalyst compositions exceeding 50 at% Pd. Prior to fuel cell testing, Pd-rich catalysts display lattice parameter expansions of up to 2% due to the presence of interstitial carbon. After fuel cell testing, a Pt-Pd solid solution absent of lattice dilatation and depleted in carbon is recovered. The structural evolution of the catalysts is correlated with catalyst de-activation.

Structural Parameters of Pr3MgNi14 during Hydrogen Absorption–Desorption Process

Structural parameters of Pr(3)MgNi(14) after a cyclic hydrogen absorption-desorption process were investigated by X-ray diffraction. Pr(3)MgNi(14) consisted of two phases: 80% Gd(2)Co(7)-type structure and 20% PuNi(3)-type structure. The pressure-composition (P-C) isotherm of Pr(3)MgNi(14) indicates a maximum hydrogen capacity of 1.12 H/M (1.61 mass %) at 298 K. The cyclic property of Pr(3)MgNi(14) up to 1000 cycles was measured at 313 K. The retention rate of the sample was 87.5% at 1000 cycles, which compares favorably with that of LaNi(5). After 1000 cycles, the expansions of lattice parameters a and c and the lengths along the c-axes of the PrNi(5) and PrMgNi(4) cells of the Gd(2)Co(7)-type structures were 0.20%, 1.26%, 0.47%, and 3.68%, respectively. The metal sublattice expanded anisotropically after the cyclic test. The isotropic and anisotropic lattice strains can be refined by Rietveld analysis. The anisotropic and isotropic lattice strains were almost saturated at the first activation process and reached values of 0.2% and 0.1%, respectively, after 1000 cycles. These values are smaller by 1 order of magnitude than those of LaNi(5).

Low-temperature selective catalytic reduction of NO with NH3 over V/ZrO2 prepared by flame-assisted spray pyrolysis: Structural and catalytic properties

A series of V/ZrO2 (V/Zr atomic ratio=0.05, 0.11, 0.17, 0.25, 0.33, 0.42), V-WOx(0.66)/ZrO2, and V-MoOx(0.66)/ZrO2 were synthesized by adopting a one-step flame spray pyrolysis technique and investigated for the low-temperature selective catalytic reduction (SCR) of NO with ammonia in the presence of excess oxygen. Our XRD results suggest that the vanadia species are in amorphous state as dominant surface monomeric VOx species on zirconia support in V/ZrO2 samples with V/Zr≤0.17. Further increase in vanadia content led to the formation of ZrV2O7 solid solution as a result of zirconia migration into the V2O5 crystallites. H2-TPR data results are highly consistent with the XRD results that the low temperature shifts in the reduction peaks of 15% V/ZrO2 catalyst attributed to the presence of more easily reducible dominant surface monomeric VOx species. The evolution of a new reduction peak at high temperature indicates the formation of dominantly isolated polymeric V oxides species in V/ZrO2 samples with V/Zr≥0.25. Our H2-TPR profiles for tungsten-promoted V/ZrO2 catalyst revealed the shift of (T1) peak position to lower temperatures, suggesting that the reduction potential of vanadium oxide species is increased compared to V/ZrO2 catalyst. This occurrence signifying that the addition of tungsten to V/ZrO2 promoted the catalyst for the formation of monomeric surface vanadia species, whereas the addition of Mo promoted the formation of polymeric VOx species and thus inhibit the SCR activity. An intense sharp band characteristic of coordinatively held NO2 species is evident at 1630cm−1, no gaseous N2O species were detected at 2224cm−1, 1286cm−1 in the in-situ FT-IR spectra of NO adsorbed over the V/ZrO2. Our in-situ FT-IR studies of NO+NH3 co-adsorption demonstrate that the strong signals at 1435 and 1714cm−1 (bending vibration of NH4+) have seen to decrease with respect to temperature. This observation reveals that the NH4+ species bound to Brönsted acid sites are responsible for the enhancement in the SCR reaction over the vanadia-zirconia surfaces. The low temperature NO catalytic reduction activity would indicate that an optimal dispersion of monomeric VOx species on zirconia is attained with the 15% of V in the V/ZrO2 catalyst. The introduction of Zr (seven fold coordination) into V2O5 may lead to the reduction of elemental number in crystal grain and deviation of adjacent oxygen atoms. The change in lattice parameter, crystal anisotropy and negative thermal expansion can block the release of labile oxygen, this seems to be the reason for the decrease in catalytic activity in V/ZrO2 catalysts with V/Zr≥0.25. The addition of tungsten has a strong influence on the NO conversion, since tungsten loading with the WOx/VOx atomic ratio=0.66 exhibits a maximum conversion of ∼98% in the temperature range 180–240°C, whereas the molybdenum loading showed an inhibition effect on the SCR activity of V/ZrO2 catalyst.

Wet Chemical Synthesis of Ni-Al Nanoparticles at Ambient Condition

The synthesis of intermetallic Ni-Al nanoparticles by co-reduction approach of several organometallic precursors with sodium naphthelide in non-aqueous solution was studied. The state of the art in nanoparticles synthesisation is the selection of suitable precursors and the adaption of colloid chemistry to non-aqueous media at the room temperature under inert atmosphere. The reduction of an organometallic precursor, nickel (II) acetylacetonate, Ni(Acac)2as a source of Ni element of the intermetallic, and aluminum trichloride, AlCl3in tetrahydrofuran (THF) solution gave a black particles. The powder X-ray diffraction spectroscopy (pXRD) result shows an expansion of lattice parameter for FCC-Ni indicating the cooperation of Al atoms in Ni structures. The estimation value of Al concentration using Scherrer’s equation is 10 at%. The particles were investigated in more detail by hard X-ray photoemission spectroscopy (HX-PES). The HX-PES spectrums confirmed that the black particles has binding energy consistent to standard materials of Ni3Al. The absence of organic residues shown by the Fourier-transform infrared, FTIR spectrometer indicates that the as prepared Ni-Al nanoparticles are free from by-products.

Defect structure and electrical conductivity in the pseudo-binary system Bi3TaO7–Bi3NbO7

A study of electrical and structural characteristics of compositions in the Bi3Ta1−xNbxO7 system, using X-ray and neutron powder diffraction and AC impedance spectroscopy, is presented. The electrical conductivity increases with increasing niobium content. A full solid solution is observed which adopts an incommensurately ordered pseudo-cubic fluorite structure (type II). Analysis of the defect structure of the x=0.50 composition shows chains of niobate/tantalate octahedra as a likely structural motif. A small degree of non-linearity in the thermal expansion of the cubic subcell lattice parameter is observed.