Electrical conductivity of metastable κ-CeZrO4 phase possessing ordered arrangement of Ce and Zr ions

Electrical conductivity σ_t of metastable κ-CeZrO₄ possessing ordered arrangement of Ce and Zr ions in a manner similar to a pyrochlore-type was measured as a function of temperature and time, and compared with tetragonal metastable t′-(Ce_0.5Zr_0.5)O₂ and t′_meta-(Ce_0.5Zr_0.5)O₂ phases possessing random arrangement of the cations. The κ disk was prepared by reoxidizing a pyrochlore-type precursor in O₂ gas at 873 K. The σ_t as measured for the κ-CeZrO₄ was reproducible as a function of temperatures between 957 and 1190 K. At increasing temperatures above 1233 K, the σ_t decreased gradually with time due to the phase transition: κ→t′, and became consistent with the t′. Although the κ-CeZrO₄ phase is thermodynamically less stable than the t′-(Ce_0.5Zr_0.5)O₂, it was virtually stable up to around 1233 K. It was found from the change in the σ_t due to the phase transition that the σ_t for the metastable κ-CeZrO₄ was an order of magnitude higher than that for the t′ and was similar to that for the t′_meta. It was previously reported that a phase transition, t′_meta→t′, occurred above 1143 K. The phase transition, κ→t′, accompanied by redistribution of the cations appeared to occur at higher temperatures than that for t′_meta→t′ leaving random cation arrangement.     

X-ray diffraction studies of Bi2O3 films prepared by reactive and activated reactive evaporation

Bi₂O₃ films were prepared by reactive evaporation and by activated reactive evaporation. The various phases obtained were studied using X-ray diffraction. Reactive evaporation always produced β-Bi₂O₃ films. For a given substrate temperature, low rates of deposition (less than 20 Å s^-1) always produced β-Bi₂O₃ films, whereas high rates of deposition (greater than 35 Å s^-1) produced α-Bi₂O₃ films when the oxygen partial pressure inside the chamber was kept constant. Films prepared by both reactive evaporation and activated reactive evaporation at substrate temperatures below 400 K were amorphous in nature and at higher substrate temperatures polycrystalline films were produced. The results obtained on annealing these films in high vacuum and in air are also reported.     

Thermodynamic and neutron diffraction studies of the nucleation of solid4He on graphite

The nucleation of solid layers of⁴He on the surface of exfoliated graphite (Grafoil) was investigated by thermodynamic and neutron diffraction measurements. The thermodynamic measurements consisted of recording isopycnals in the vicinity of the melting curve. The isopycnals show a rounding in comparison to the bulk ones, which can be explained by a continuous solidification of⁴He on the surface of graphite in a layer-by-layer mode in the van der Waals field of the substrate. Moreover, we found a hysteresis behavior of the isopycnals, probably due to defect states in the solidified film. The thickness of the solid film is estimated by means of a simple solidification model. The neutron diffraction results reveal microscopic details of the continuous nucleation process. It turns out that⁴He always condenses in hcp structure on the surface of graphite even in that region of the phase diagram where the equilibrium bulk phase is the bcc structure. An analysis of the linewidths and the intensities of the Bragg reflections gives information on the mean diameters, the thickness, and the orientation of the surface solid crystallites. Where comparable, the neutron diffraction data are in very good agreement with the thermodynamic results.This research was partially supported by the Bundesministerium für Forschung und Technologie (BMFT) of West Germany.     

X-ray diffraction study of epitaxial zinc and cadmium films prepared by hot-wall technique

Hot-wall technique greatly improves the quality of zinc and cadmium films deposited on glass substrate. At substrate temperature the growth of such films is well ordered, showing highly preferred orientation along c-axis. However, if the substrate temperature is increased beyond certain limit, we get polycrystalline growth of the films. This shows that the growth of zinc and cadmium films on glass substrate strongly depends on the substrate temperature.     

Mössbauer effect studies and X-ray diffraction analysis of cobalt ferrite prepared in powder form by thermal decomposition method

Cobalt ferrite (Co_xFe_3?xO₄) is prepared in powder form by thermal decomposition of iron and cobalt salts and is analysed by X-ray diffraction and Mössbauer spectroscopic techniques. The variation of Mössbauer parameters, lattice parameters and crystallite size of the products formed with variation in the composition of Fe and Co ratios are studied. The studies confirm the formation of nano-size cobalt ferrite particles with defect structure and it is found to be maximum for the Fe : Co = 60 : 40 ratio of the initial precursor oxides.     

X-ray diffraction and fourier transform infrared analysis of nanophase apatite coatings prepared by electrocrystallization

The concept of biological fixation of artificial joint prosthesis by using bioactive calcium phosphate coatings has generated considerable interest in recent years. This paper reports an electrocrystallization process for fabricating stoichiometric and non-stoichiometric hydroxyapatite (HA) coatings with nanometer size crystals similar to biogenic apatite. X-ray diffraction and Fourier Transform Infrared (FTIR) spectroscopy were used to characterize the structure and chemical composition of the HA coatings.As-deposited coatings at 65°C were poorly crystalline, Ca-deficient HA with a crystallite size of about 35 nm and exhibited apatitic characteristics similar to bone apatite. Post-treatment of coatings in steam at 125°C followed by calcining at 425°C resulted in the transformation of the initial phase to a well-defined stoichiometric HA with a crystallite size of about 100 nm.     

X-ray diffraction and Raman scattering studies in 10B+-implanted Cd0.96Zn0.04Te thin films prepared by vacuum evaporation

Polycrystalline Cd_0.96Zn_0.04Te thin films prepared by vacuum evaporation onto thoroughly cleaned glass substrates kept at room temperature were implanted with mass-analyzed beams of 100 keV boron ions (¹⁰B⁺) at various doses ranging from 10¹² to 10¹⁴ ions cm^–2. The X-ray diffraction pattern of the as-deposited film shows zinc blende structure with a predominant orientation along the 1 1 1 plane. The implanted films show a decrease in the 1 1 1 peak intensity and increase in the full-width at half-maximum (FWHM) with implantation dose. The surface roughness (rms) of the as-deposited film evaluated by atomic force microscopy is 3.7 nm and the value of roughness is found to increase with implantation dose. Raman spectra of the as-deposited films show longitudinal optic (LO) and transverse optic (TO) modes, which arise from CdTe-and ZnTe-like vibrations. There is no significant change in the Raman peak position due to implantation but the FWHM is found to be increased. This is probably due to the implantation-induced lattice disorder. The relative intensity of the Raman peaks and the area under the peaks were found to increase with implantation dose. These results are explained on the basis of the implantation-induced surface roughness and lattice disorder.     

Structural investigation of bismuth borate glass ceramics containing gadolinium ions by X-ray diffraction and FTIR spectroscopy

X-ray diffraction and FTIR spectroscopy measurements have been employed to investigate the xGd₂O₃ · (100 − x)[2Bi₂O₃ · B₂O₃] glass ceramics system, with 0  ≤ x ≤ 20 mol%. Heat treatment of glass samples at 625 °C for 24 h led to the formation of two crystalline phases. One crystalline phase is for the sample without gadolinium ions which belongs to the cubic system and another one is for the sample containing 20 mol% Gd₂O₃ which is orthorhombic with two unit cell parameters very close to each other. Between x = 0 mol% and x = 20 mol% there is a mixture of these crystalline phases. FTIR spectroscopy data suggest that the gadolinium ions play the network modifier role in the studied glasses. These data show that the glass structure consists of the BiO₃, BiO₆, BO₃, and BO₄ structural units, and the conversion among these units mainly depends on the Gd₂O₃ content.     

X-ray diffraction and compositional studies of AgInS2 thin films obtained by spray pyrolysis

Silver indium sulfide (AgInS₂) thin films have been prepared by the spray pyrolysis technique using silver acetate, indium acetate, and N,N-dimethylthiourea as precursor compounds. Depending on the film preparation conditions, AgInS₂ thin films are obtained which could be candidates to be used in photovoltaic devices. X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) compositional studies were done on films formed at different substrate temperatures (T _s) and Ag:In:S ratios in the starting solutions. When Ag:In:S ratios are 1:1:1, 1:0.25:2, and 1:1:2, XRD patterns of the thin films indicated that the crystallographic structure is mainly chalcopyrite AgInS₂. An additional phase, acanthite Ag₂S, appeared when the depositions where done at low T _s. EDS analysis showed that AgInS₂ films near stoichiometric composition were obtained by using an atomic ratio of Ag:In:S = 1:1:2 in the starting solution and T _s = 400 °C.     

X-ray diffraction studies of phase transformations between tetragonal and cubic phases in the BaSnxTi1−xO3 system

X-ray powder diffraction has been used to investigate the cubic–tetragonal phase transformation and lattice constant in a BaSnxTi1–xO3 system (x=0.0–0.2) at room temperature. The existing regions of tetragonal phase were strongly influenced by the amounts of tin (from x=0.0–0.1). The mass fraction of the tetragonal phase decreases as substitution of tin for titanium increases until x=0.1, while the mass fraction of the cubic phase increases simultaneously. The lattice constant of cubic phase and the cube roots of the unit-cell volumes of tetragonal phases indicate linear relations with the amounts of tin. © 1998 Chapman & Hall     

X-ray and neutron diffraction studies of the incommensurate structural transition in β-ThBr4

As first shown by Raman scattering, tetragonal β-ThBr₄ undergoes a phase transition at 92 K, in which the fourfold axis is preserved. In fact, low temperature powder X-ray and neutron diffraction revealed very weak extra lines, which could not be indexed satisfactorily. On the other hand, neutron diffraction and inelastic scattering on single crystals can be interpreted as a tripling of the cell along the fourfold axis with an incommensurate modulation in this direction.     

Photoluminescence and Raman studies of graphene thin films prepared by reduction of graphene oxide

Photoluminescence (PL) and Raman studies have been performed to investigate the optical properties of graphene thin films prepared by chemical and thermal reductions of graphene oxide (GO). The G peak in Raman spectra red-shifted after reduction of GO. Thermal reduction resulted in a more red-shift of the G peak than chemical reduction. A strong intensity of the D peak indicated that the prepared graphene films have significant structural disorders. A blue-shifted emission in PL spectra suggested that sp² clusters are embedded in a sp³ matrix that acts as a tunnel barrier, causing a strong fluctuation in the local band gap.     

Textural features of highly ordered Al-MCM-41 molecular sieve studied by X-ray diffraction,nitrogen adsorption and transmission electron microscopy

The preparation of a Al-MCM-41 mesoporous materials has been carried out using silica-gel and pseudoboehmite as silica and aluminum sources, respectively, and surfactant cetyltrimethylammonium bromide as structure template. The textural properties of the calcined Al-MCM-41 were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and N₂ isothermal adsorption measurements. The hexagonal structure parameter a_o was calculated based on d₍₁₀₀₎ XRD reflection as 4.75 nm. TEM images revealed the formation of a well-ordered Al-MCM-41. Accordingly, nitrogen adsorption measurements (BJH) showed a material with very narrow distribution and medium pore diameter of 3.14 nm. Mesopore volume based on adsorbed nitrogen was 0.51 cm³ g^− 1. Through a combination of XRD and N₂ adsorption data, the thickness of the channel walls of 1.61 nm could be calculated.     

X-ray diffraction and leaching of CsAlSi5O12 and CsZr2(PO4)3 irradiated by argon (3 MeV) ions

Metamict damage cross-sections for the candidate nuclear fuel waste immobilization materials CsAlSi₅O₁₂ and CsZr₂(PO₄)₃ irradiated with 3 MeV argon ions were found to be 0.6±0.2 nm² and 0.7±0.3 nm², respectively, from powder X-ray diffraction measurements. Based on caesium extraction into solution, heavy irradiation produced increases of up to a factor of 25 in the dissolution rates of the materials in deionized water and a brine at 100° C.     

Quantitative phase analysis by X-ray diffraction of martensite and austenite in strongly oriented orthodontic stainless steel wires

A method is described for measuring the volume fractions and textures of martensite and austenite in strongly textured stainless steel orthodontic wires using a conventional X-ray diffractometer. These wires display a classic fibre texture with the 111 of the FCC austenite phase and the 110 of the BCC martensite phase aligned parallel to the wire axis. The samples analysed consisted of wire cross-sections bundled together and chemically polished in an epoxy disc. In this form the dominant lines in the XRD patterns are the austenite (111) and the martensite (110). On the basis of X-ray diffraction results from these two lines only, procedures are described for, (a) correcting the X-ray intensity data for both the finite size and irregular cross-sectional shape of the specimens in relation to the X-ray beam footprint, (b) separately measuring the texture of the austenite and martensite phases and, (c) correcting the 111 and 110 integrated intensities for texture. These procedures are illustrated using X-ray data from four different orthodontic wires. The factors limiting the accuracy of the phase analysis are discussed.