In situ neutron diffraction studies of a commercial, soft lead zirconate titanate ceramic: response to electric fields and mechanical stress

Structural changes in commercial lead zirconate titanate (PZT) ceramics (EC-65) under the application of electric fields and mechanical stress were measured using neutron diffraction instruments at the Australian Nuclear Science and Technology Organisation (ANSTO) and the Oak Ridge National Laboratory (ORNL). The structural changes during electric-field application were measured on the WOMBAT beamline at ANSTO and include non-180° domain switching, lattice strains and field-induced phase transformations. Using time-resolved data acquisition capabilities, lattice strains were measured under cyclic electric fields at times as short as 30 μs. Structural changes including the (002) and (200) lattice strains and non-180° domain switching were measured during uniaxial mechanical compression on the NRSF2 instrument at ORNL. Contraction of the crystallographic polarization axis, (002), and reorientation of non-180° domains occur at lowest stresses, followed by (200) elastic strains at higher stresses.     

X-ray diffraction and Mössbauer spectroscopy studies of cementite dissolution in cold-drawn pearlitic steel

Cementite dissolution in cold-drawn pearlitic steel (0.8 wt.% carbon) wires has been studied by quantitative X-ray diffraction (XRD) and Mössbauer spectroscopy up to drawing strain 1.4. Quantification of cementite-phase fraction by Rietveld analysis has confirmed more than 50% dissolution of cementite phase at drawing strain 1.4. It is found that the lattice parameter of the ferrite phase determined by Rietveld refinement procedure remains nearly unchanged even after cementite dissolution. This confirms that the carbon atoms released after cementite dissolution do not dissolve in the ferrite lattice as Fe-C interstitial solid solution. Detailed analysis of broadening of XRD line profiles for the ferrite phase shows high density of dislocations (～10¹⁵/m²) in the ferrite matrix at drawing strain 1.4. The results suggest a dominant role of ?1?1?1? screw dislocations in the cementite dissolution process. Post-deformation heat treatment leads to partial annihilation of dislocations and restoration of cementite phase. Based on these experimental observations, further supplemented by TEM studies, we have suggested an alternative thermodynamic mechanism of the dissolution process.     

Characterization of mineral phases of agricultural soil samples of Colombian coffee using M?ssbauer spectroscopy and X-ray diffraction

Friedreich ataxia is a disease that is associated with defects in the gene coding for a small protein frataxin. Several different roles have been proposed for the protein, including iron chaperoning and iron storage. M?ssbauer spectroscopy was used to probe these hypotheses. Iron accumulation in mutant mitochondria unable to assemble iron sulfur clusters proved to be insensitive to overexpression of frataxin, ruling out its potential involvement as an iron storage protein similar to ferritin. Rather, it was found that frataxin negatively regulates iron sulfur cluster assembly.     

Structural studies and impedance spectroscopy of sol–gel derived Bi0.9Pr0.1FeO3 nanoceramics

Nano-crystalline Bi_0.9Pr_0.1FeO₃ (BPFO) ceramics have been synthesized by a sol–gel technique. The Rietveld refinement of the room temperature powder X-ray diffraction pattern confirms that the BPFO crystallizes in the rhombohedral R3c space group symmetry. SEM image of the sintered BPFO ceramic shows particles with same shape and fine grain morphology with the average grain size of 53±12 nm. The electrical properties of the ceramic are analysed by impedance spectroscopy. Grain and grain-boundary effect is observed in the material at lower temperature range which has been confirmed by electric modulus formalism. The ac conductivity spectrum obeys the Johnscher's power law. The activation energy calculated from dc conductivity is found to be 0.373 eV, which represents the conduction of small polaron over barrier between two sites of the lattice.     

X-ray photoelectron spectroscopy analysis of (Ln1−xSrx)CoO3−δ (Ln: Pr,Nd and Sm)

The chemical states of the surface of (Ln_0.5Sr_0.5)CoO_3?δ (Ln (lanthanides) = Pr, Nd and Sm) used for cathode materials of intermediate temperature operating solid oxide fuel cells (IT-SOFCs) were investigated by X-ray photoelectron spectroscopy (XPS). Oxygen peaks comprised of lower binding energy (LBE) and higher binding energy (HBE) peaks from (Ln_0.5Sr_0.5)CoO_3?δ and Pr_0.3Sr_0.7CoO_3?δ (PSC37) showed that some merged oxygen peak behavior is a function of the Sr and lanthanide concentrations. By investigating the oxygen peaks, it was determined that more oxygen vacancies were generated on the surface of the cathodes when the lanthanides and Sr were substituted into perovskite oxides. When comparing the binding energies (BEs) of PSC37 with Pr_0.5Sr_0.5CoO_3?δ (PSC55), the LBE and HBE of the Sr peaks both increased when Sr was substituted at the A-site of a perovskite. Surface analysis of the Co peak on the surface of the cathode materials showed that the Co exists mainly as Co³⁺ and partially oxidized to Co⁴⁺ on the cathode materials. The partial existence of Co⁴⁺ can provide some polaron hopping providing electronic conduction for the solid oxide fuel cell.     

Study of phase transition on nanocrystalline (La, Sr)(Mn, Fe)O system using high-pressure Mössbauer spectroscopy and high-pressure X-ray diffraction

Pressure-induced structural changes on nano-crystalline La_0.8Sr_0.2Mn_0.8Fe_0.2O₃ were studied using high-pressure Mössbauer spectroscopy and high-pressure X-ray diffraction. Mössbauer measurements up to 10 GPa showed first order transition at 0.52 GPa indicating transformation of Fe^4?+? to high spin Fe^3?+?, followed by another subtle transition at 3.7 GPa due to the convergence of two different configurations of Fe into one. High-pressure X-ray diffraction measurements carried up to 4.3 GPa showed similar results at 0.6 GPa as well as 3.6 GPa. Attempts were made to explain the changes at 0.6 GPa by reorientation of grain/grain boundaries due to uniaxial stress generated on the application of pressure. Similarly variation at 3.6 GPa can be explained by orthorhombic to monoclinic transition.     

Ab initio and anion photoelectron studies of Rhn (n = 1 − 9) clusters

We present an analysis of Na-He collisional profiles at high density and very low temperature in a unified line shape semi-classical theory which contains the impact as well the quasistatic limits. Clearly understanding the variation of shape of the two fine-structure components of the 3s?3p line with increasing helium density allows us to understand experimental spectra of a Na atom attached to He nanodroplets. We compare our collisional approach to path integral Monte Carlo calculations using the same ab initio Na-He molecular potentials.     

Applicability of chemical derivatization – X-ray photoelectron spectroscopy (CD–XPS) to the characterization of complex matrices: case of electrosynthesized polypyrroles

Problems arising in the application of XPS coupled with derivatization reactions (CD-XPS) to the characterization of complex matrices are stressed by considering the case of polypyrroles electrosynthesized from aqueous solution. In these materials oxygen– and nitrogen–carbon functionalities are contemporaneously present, as well as acidic, basic, charged and reducible groups. The derivatizing agents titanium di-isopropoxide-bis(2,4-pentanedionate) (TAA), trifluoroethanol (TFE) and pentafluorophenylhydrazine (PFPH) were used to label the C–OH, COOH and CO groups, respectively, in the pristine (PPY) and in the overoxidized (PPYox) polymer. The case shows that, when real samples are analysed, only the correlation among the information present in all the available spectra can supply the key to the interpretation of CD-XPS data, such as the actual stoichiometry and secondary effects. In particular, it is showed that PFPH cannot be used as a reliable derivatizing agent for CO groups in PPYox, due to the competition of a side reaction (already reported for hydrazines) occurring on this particular substrate. This effect may be disregarded if a thorough control of the stoichiometry is not performed.     

X-ray photoelectron diffraction study of an oxidized PtCo(001) alloy surface: evidence for atomic scale rippling of the CoO overlayer

The overlayer of cobalt monoxide that forms upon low pressure oxidation of the (001) plane of a PtCo alloy was studied by X-ray photoelectron diffraction and other surface techniques. The analysis of the XPD data carried out using model calculations in the single scattering-plane wave approximation shows that the overlayer structure is similar to that of the (001) plane of fcc CoO, with the Co atoms displaced at different heights from the substrate in correspondence to the type of site occupied.     

Structural and bonding properties of ScSi_n~-(n=2～6) clusters:photoelectron spectroscopy and density functional calculations

Anion ion photoelectron spectroscopy and density functional theory (DFT) are used to investigate the electronic and structural properties of ScSi_n^- (n=2sim6) clusters and their neutrals. We find that the structures of ScSi_n^- are similar to those of Si_n+1^-. The most stable isomers of ScSi_n^- cluster anions and their neutrals are similar for n=2, 3 and 5 but different for n=4 and 6, indicating that the charge effect on geometry is size dependent for small scandium-silicon clusters. The low electron binding energy (EBE) tails observed in the spectra of ScSi_4,6^- can be explained by the existence of less stable isomers. A comparison between ScSi_n^- and VSi_n^- clusters shows the effects of metal size and electron configuration on cluster geometries.     

X-ray photoelectron and mössbauer spectroscopy studies of the valence state of transition metal ions in Co1–x Fe x Cr2O4 (x = 0.1, 0.2, 0.5) ceramics

The valence state of transition metal ions in the Co_1–x Fe _x Cr₂O₄ (x = 0.1, 0.2, 0.5) system has been investigated using X-ray photoelectron and Mössbauer spectroscopy. It has been shown that, in this system, there are Fe²⁺ and Fe³⁺ ions. The relative Fe³⁺/Fe²⁺ contents have been determined by fitting the experimental Fe 2p photoelectron spectra by a superposition of theoretical spectra of the Fe²⁺ and Fe³⁺ ions, as well as using Mössbauer spectroscopy.     

Preparation,surface state and band structure studies of SrTi(1 − x)Fe(x)O(3 − δ) (x = 0–1) perovskite-type nano structure by X-ray and ultraviolet photoelectron spectroscopy

In this report, SrTi_(1 ? x)Fe_(x)O_(3 ? δ) photocatalyst powder was synthesized by a high temperature solid state reaction method. The morphology, crystalline structures of obtained samples, was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscopy (TEM), respectively. The electronic properties and local structure of the perovskite STF_x (0 ≤ x ≤ 1) systems have been probed by extended X-ray absorption fine structure (EXAFS) spectroscopy. The effects of iron doping level x (x = 0–1) on the crystal structure and chemical state of the STF_x have been investigated by X-ray photoelectron spectroscopy and the valence band edges for electronic band gaps were obtained for STF_x by ultraviolet photoelectron spectroscopy (UPS). A single cubic perovskite phase of STF_x oxide was successfully obtained at 1200 °C for 24 h by the solid state reaction method. The XPS results showed that the iron present in the STF_x perovskite structure is composed of a mixture of Fe³⁺ and Fe⁴⁺ (SrTi_(1 ? x)[Fe³⁺, Fe⁴⁺]_(x)O_(3 ? δ)). When the content x of iron doping was increased, the amount of Fe³⁺ and Fe⁴⁺ increased significantly and the oxygen lattice decreased on the surface of STF_x oxide. The UPS data has confirmed that with more substitution of iron, the position of the valence band decreased.     

Surface electronic structure of single-domain Si( 001) 2 × 2-Al: an angle-resolved photoelectron spectroscopy study using synchrotron radiation

The electronic structure of a single-domain Si(001)2 × 2-Al surface has been studied by angle-resolved photoelectron spectroscopy (ARPES) using synchrotron radiation. Through detailed ARPES measurements along various symmetry axes of the surface Brillouin zone, the existence and dispersions of five surface states are identified, one at binding energies a little less than 1 eV and the others between 1 and 2 eV. The origin of the surface states are discussed in terms of the Al-dimer structures on Si(001).     

X-ray diffraction,electrical and magnetic studies of solid solution La0.6Sr0.4MnO3-δ□δ (0.0 ≤ δ ≤ 0.2)

Nonstoichiometric substituted lanthanum manganite powder has been synthesized by solid state reaction method. X-ray diffraction shows that the material exists in single phase having a perovskite structure. A structural phase transition separating a rhombohedral phase and an orthorhombic phase was observed at the rate δ ≈ 0.127 corresponding to a Mn³⁺ concentration of about 85 %. The material is ferromagnetic for 0 ≤ δ ≤ 0.127 and antiferromagnetic for 0.15 ≤ δ ≤ 0.20 The Curie temperature is very sensitive to the presence of vacancies. The investigation of electrical properties shows metallic behavior at low temperature for δ ≤ 0.10 and as insulator for 0.127 ≤ δ ≤ 0.20. The variation of activation energies with the rate of vacancies has been investigated.     

Proton transfer in water–hydroxyl mixed overlayers on Pt(1 1 1): Combined approach of laser desorption and spatially-resolved X-ray photoelectron spectroscopy

Proton transfer in water–hydroxyl mixed overlayers on a Pt(1 1 1) surface was studied by a combination of laser induced thermal desorption (LITD) method and spatially-resolved X-ray photoelectron spectroscopy (micro-XPS). The modulated pattern OH + H₂O/H₂O/OH + H₂O was initially prepared by the LITD method; vacant area with a 400 μm width was first formed in the mixed OH + H₂O overlayer by irradiation of focused laser pulses, and followed by refilling the vacant area with pure H₂O. Spatial distribution changes of OH and H₂O were measured as a function of time with the micro-XPS technique, which indicated that H₂O molecules in the central region flow into the OH + H₂O region. From quantitative analyses using a diffusion equation, we found that the proton transfer in the mixed overlayer consists of at least two pathways: direct proton transfer from H₂O to OH in the nearest site and the proton transfer to the next-nearest site via H₃O⁺ formation. The time scale of first and second path was estimated to be 5.2 ± 0.9 ns and 48 ± 12 ns at 140 K, respectively. In the presence of water capping layer, however, the rate of proton transfer is reduced by an order of magnitude, which would be explained by peripatetic behavior of proton into H₂O capping layer.