Diffuse X-ray scattering by ice in the vicinity of the melting point

The X-ray pattern of ice recorded at −10°C reveals, along with the reflexes of a hexagonal phase, intense diffuse X-ray scattering, testifying to the presence of a noncrystalline phase in the sample. Heating of ice to a temperature close to the melting point leads to almost complete decomposition of the crystalline phase. As this takes place, intense diffuse X-ray scattering with a maximum at 2Θ of 23°C appears in the diffraction pattern, which is typical for a metastable amorphous phase. The first maximums of the radial distribution function for the metastable amorphous phase of ice appear to be close in their positions to the first radii of the hexagonal phase coordination spheres.     

Phase transitions in the atomic, electronic, and magnetic subsystems of LaSrMnO films versus the synthesis temperature

The evolution of the cluster structure in amorphous LaSrMnO films as synthesis temperature T _s increases from 20 to 300°C is considered. Two order-disorder phase transitions with different scale parameters are observed. One of them, the aggregation of disordered atoms into small (～20 Å) amorphous clusters at T _s = 100°C, shows up as a sharp increase in the intensity of diffuse X-ray scattering (diffuse halo 1) with a simultaneous suppression of incoherent (background) scattering. At T _s > 150°C, disordering dominates (I _incoh = I _max) until the next stage of ordering sets in at T _s = 250?300°C. At this stage, the crystalline phase forms from large (>100 Å) crystalline clusters. This amorphous-crystalline phase transition is characterized by the appearance of Debye lines and a reduction of the halo intensity. The structural phase transition to long-range order is accompanied by a decrease in the LaSrMnO resistivity from 10¹⁰ to 10 Ω cm and a change from the tunneling mechanism of conductivity involving metallic clusters (which is typical of granulated systems) to the hopping mechanism with a hop variable length following the Mott law ρ ～ exp(T ^?1/4). In the magnetic subsystem, the paramagnetic-ferromagnetic phase transition occurs.     

Spinodal ordering in Cu3Au

Results from, X-ray diffuse scattering and inelastic neutron scattering demonstrate the presence of long-lived fluctuations in order up to 5.0°C above the first-order phase transition, T_c = 383.2°C. The temperature for continuous ordering has been determined to be 358.2°C. The coherent phase boundary is 3–13°C below T_c.     

Effects of charge density waves on bragg peak intensities

The theory of diffraction from a modulated lattice predicts, in addition to satellite formation, that the main reflections themselves are affected. We observed this effect in TaS₂, across the polymorphic transition 1T₁ ? 1T₂ at T₀ = 80° C.     

The discovery of a 2H–6H solid state transformation in ZnxCd1−xS single crystals

Single crystals of Zn_xCd_1?xS have been grown from the vapour phase at 1100°C in the presence of H₂S gas. X-ray diffraction studies of the as-grown crystals show that polytypism and stscking faults occur in Zn_xCd_1?xS crystals for x ? 0.94. It is observed that for 0.92 < x < 0.98 the 2H structure of Zn_xCd_1?xS crystals transforms to a disordered 6H structure on annealing in vacuum around 600°C. For 0.95 < x < 0.98 this 6H structure finally transforms to a disordered 3C structure on annealing further at higher temperatures around 800°C. The structural transformations occur through a non-random insertion of stacking faults, as revealed by the diffuse streak joining the X-ray diffraction maxima along the 10.L reciprocal lattice row. Experimental investigation of the diffuse intensity distribution, as recorded on a single crystal diffractometer from partially transformed single crystals, reveals that the mechanism of the transformation is very different from that reported for the same transformation in silicon carbide and cannot be described in terms of a single-parameter model of non-random deformation faulting.     

Inhomogeneous lattice distortions in a Zn1 − x CrxSe crystal

The structure of a Zn_1?x Cr_xSe semiconductor crystal with x = 0.0029 was studied using thermal neutron diffraction. It was detected that the diffraction patterns of the crystal contain regions of diffuse scattering concentrated in the vicinity of the strong Bragg reflections. It was shown that the diffuse scattering was caused by transverse displacements of lattice atoms induced by chromium impurities, which undergo static tetragonal Jahn-Teller distortions in ZnSe.     

Metal atom-induced diffuse scattering from short-range order among deuterium atoms in single crystal α-phase V2D

X-ray scattering has been studied above the critical ordering temperature, T_c (133°C), in b.c.c. α-phase V₂D. At 140 and 200°C quite weak diffuse intensity was observed centered on the reciprocal lattice points of the ordered superlattice. This intensity is due to short-range order among deuterium atoms which induces a local or short-range modulation of the parent vanadium lattice and suggests the possibility of local octahedral D—D fluctuations building up well above T_c.     

Structural deformations of the cubic lattice of the Zn1 ? x Fe x Se (x = 0.001) crystal

The structural state of a Zn_{1 ? x} Fe _x Se (x = 0.001) crystal has been studied using thermal neutron diffraction. The diffraction patterns of the cubic crystal have been found to contain diffuse scattering regions concentrated in the vicinity of the strong Bragg reflections. It has been shown that the diffuse scattering effects are due to local transverse displacements of the crystal lattice atoms, and these displacements are induced by iron ions that demonstrate the static Jahn-Teller effect of the tetragonal type in the ZnSe compound.     

Inelastic neutron scattering study in cubic NaNbO3

Inelastic neutron scattering measurements performed on NaNbO₃ close to the cubic to tetragonal phase transition show that the 2D fluctuations earlier revealed by X-ray diffuse scattering correspond to an overdamped type dynamics. The sharp decrease in the spectral width observed at T-T_c =10° is interpreted in terms of the increase in correlation lengths and the cross-over between 2D and 3D behaviour of the fluctuations.     

Structural and magnetic properties of thin epitaxial Fe films on (1 1 0) GaAs prepared by metalorganic chemical vapor deposition

Iron films have been grown on (1 1 0) GaAs substrates by atmospheric pressure metalorganic chemical vapor deposition at substrate temperatures (T_s) between 135°C and 400°C. X-ray diffraction (XRD) analysis showed that the Fe films grown at T_s between 200°C and 330°C were single crystals. Amorphous films were observed at T_s below 200°C and it was not possible to deposit films at T_s above 330°C. The full-width at half-maximum of the rocking curves showed that crystalline qualities were improved at T_s above 270°C. Single crystalline Fe films grown at different substrate temperature showed different structural behaviors in XRD measurements. Iron films grown at T_s between 200°C and 300°C showed bulk α-Fe like behavior regardless of film thickness (100–6400 Å). Meanwhile, Fe films grown at 330°C (144 and 300 Å) showed a biaxially compressed strain between substrate and epilayer, resulting in an expanded inter-planar spacing along the growth direction. Magnetization measurements showed that Fe films (>200 Å) grown at 280°C and 330°C were ferromagnetic with the in-plane easy axis along the [1 1 0] direction. For the thinner Fe films (⩽200 Å) regardless of growth temperature, square loops along the [1 0 0] easy axis were very weak and broad.     

Phase transitions in PbSc0.5Ta0.5O3

Ordered and partially ordered PbSc_0.5Ta_0.5O₃ ferroelectric single crystals are studied by diffraction, electrophysical, and optical methods. X-ray diffraction and electrophysical methods indicate the presence of a phase transition in the low-temperature range (at T = ?40°C).     

Thermal conductivity of the amorphous and nanocrystalline phases of the beech wood biocarbon nanocomposite

Natural composites (biocarbons) obtained by carbonization of beech wood at different carbonization temperatures T _carb in the range of 800–2400°C have been studied using X-ray diffraction. The composites consist of an amorphous matrix and nanocrystallites of graphite and graphene. The volume fractions of the amorphous and nanocrystalline phases as functions of T _carb have been determined. Temperature dependences of the phonon thermal conductivity κ(T) of the biocarbons with different temperatures T _carb (1000 and 2400°C) have been analyzed in the range of 5–300 K. It has been shown that the behavior of κ(T) of the biocarbon with T _carb = 1000°C is controlled by the amorphous phase in the range of 5–50 K and by the nanocrystalline phase in the range of 100–300 K. The character of κ(T) of the biocarbon with T _carb = 2400°C is determined by the heat transfer (scattering) in the nanocrystalline phase over the entire temperature range of 5–300 K.     

Defect characterization in CeO2−x at elevated temperatures—I: X-Ray diffraction

The atomic defect structure of nonstoichiometric ceria was studied by means of X-ray diffraction. Polycrystalline samples of CeO_2?x (0?x?0.21) have been examined at 900 and 1000°C, with the stoichiometry controlled by adjusting the oxygen partial pressure between 1 and 10^?21 atm. It was observed that the lattice expands as a function of increasing defect concentration and exhibits only fluorite-like diffraction peaks. The integrated intensities of the Bragg reflections were analyzed for CeO₂ and CeO_1.91, at 900°C by difference electron-density techniques. It was concluded that the cation sublattice is essentially intact, and that the oxygen sublattice must be defective in nonstoichiometric ceria. Least-squares analyses on CeO_2?x (0?x? 0.21) at 900 and 1000°C supported the electron-density results and also showed that the temperature factors of both cations and anions increase with an increase in defect concentration, implying greater mean-square displacement of the atoms from their equilibrium positions.     

Surface nanostructure effects on optical properties of Pb(Zr x Ti1−x )O3 thin films

Optical scattering properties of nanostructured matter have crucial impact on performance efficiency of various photonic components, such as waveguides, display elements, and solar cells. In this paper, diffuse transmission properties of nanocrystalline Pb(Zr _x Ti_1?x )O₃ thin films with a high refractive index of ~2.5 and optical transmittance are presented. Thin films with a thicknesses ranging from 50 to 500 nm were studied using integrating sphere technique and results were compared to simulations performed by a scalar scattering theory. Thin films were deposited by pulsed laser deposition at room temperature on MgO(100) substrates and post-annealed at a temperature of 800 °C. Structural phase evolution-induced surface effects, which introduced periodicity on the film surface, cause the definite diffuse elements in transmission spectra of the films. Low and evenly distributed scattering amplitudes in k-space were seen for highly tetragonal- or trigonal-oriented films with non-textured surfaces, which led to low diffuse transmission values (T _D ≈ 5 %), while confined and increased scattering amplitudes in k-space were seen for tetragonal–trigonal-oriented films, with phase co-existence, which led to microstructure-induced textured surfaces and increased diffuse transmission values (T _D ≈ 50 %). For highly textured surfaces, scattering amplitudes distributed in tilted ellipsoid shape in k-space was observed. Difference between modeled and measured values was 3.8 % in maximum.     

Influence of a strontium-enriched intergranular cluster network on the electrical conductivity of In2O3-SrO ceramics

A metastable hexagonal R-phase is revealed in polycrystalline In₂O₃-SrO samples, which has the form of a network made up of mesoscopic clusters (60–180 Å in size). The clusters arise from strontium-enriched regions near grain boundaries in the main cubic structure of indium oxide. It is shown that annealing in oxygen at T _a ? 300°C saturates dangling bonds between the R-phase and the matrix and makes the system metastable. This state shows up in the presence of (i) solitary diffuse maxima from the R-phase imposed on Debye lines from the main phase in the X-ray diffraction pattern and (ii) the electron cyclotron resonance (ECR) line with g = 1.875. In addition, the sample in this state acquires a high resistivity (ρ ～ 10⁶ Ω cm). Relaxation at T ? 300°C after annealing at T _a > 300°C disrupts bonds between the strontium-enriched clusters of the R-phase and the indium oxide matrix. This causes spatial separation of the clusters, disruption of their coherent bonds with the matrix structure, and escape of excess oxygen from the sample along grain boundaries. As a result, a new stable state forms, which is characterized by (i) a series of diffuse maxima from the R-phase imposed on lines assigned to the main phase, (ii) the presence of the ECR line with g = 2 with the line with g = 1.875 retained, and (iii) the transition of the sample to a low-resistivity state (ρ ～ 100 Ω cm).     

Relaxation phenomena of poly-γ-benzyl-L-glutamate,poly-γ-methyl-L-glutamate,and copoly(γ-methyl-L-glutamate, γ-benzyl-L-glutamate)

Relaxation phenomena of poly-α-amino acids in the solid state have been investigated using poly-γ-benzyl-L-glutamate (PBLG), poly-γ-methyl-L-glutamate (PMLG), and copoly (γ-methyl-L-glutamate, γ-benzyl-L-glutamate) (PMBG) by means of dielectric, dynamic mechanical, NMR, dilatometric, and X-ray diffraction measurements at temperatures between ?196 and 180°C.

Each of the samples exhibits two relaxation regions, one at room temperature (β-relaxation) and the other in the range from ?150 to ?100°C (γ-relaxation). The γ-relaxation is attributed to motion of the side chains with small amplitude. The β-relaxation is due to large-scale motion of the side chain. It has been found that the β-relaxation is well described by the WLF-equation.

The intensity of the X-ray diffraction peak at 2θ = 7° for PBLG increases with increasing temperature, which is similar to results obtained in small-angle X-ray scattering for polymer crystals consisting of two phases, amorphous and crystalline. A break point is observed at 18°C where the specific volumetemperature curve also shows a break point.

It is concluded that the side chains of these polymers are almost amorphous, and that they undergo a glass-like transition while the backbones keep an α-helical conformation.     

Diffuse scattering and lattice dynamics of superionic copper chalcogenides

The energy-resolved neutron diffraction and inelastic neutron scattering study of diffuse scattering in copper chalcogenides was performed in order to clarify the role of static disorder versus low-energy phonons. Neutron diffraction patterns taken from Cu_1.75Se, Cu_1.98Se and Ag_0.25Cu_1.75Se powders in superionic phase show a broad maximum related to diffuse scattering. This diffuse background is suppressed in the energy-resolved experiment which indicates a strong contribution from inelastic scattering coming from correlated thermal displacements of the ions in the superionic phase. Diffraction experiments on a single crystal of α-Cu_1.8Se have revealed an ordered structure with superstructure reflections at the G ± 1/2 <111> and G ± 1/3 <220> positions of reciprocal space at room temperature. In addition to superstructure spots, diffuse scattering was observed along the <111> direction which is considered as a possible diffusion path of mobile Cu ions. In inelastic neutron scattering measurements with this single crystal sample strong inelastic scattering was observed along <111>. This shows that the diffuse scattering found in conventional diffraction experiment is mainly inelastic and most probably comes from low-energy phonons.     

Effect of annealing temperature on K-shell X-ray fluorescence parameters of zinc oxide thin films prepared by the sol-gel method

Zinc oxide thin films were grown on a glass substrate by a sol-gel process using a spin-coating technique. The obtained thin films were annealed between 350?°C and 550?°C in 50?°C steps and were then characterized using X-ray diffraction, scanning electron microscopy, and X-ray fluorescence techniques. The samples were stimulated by 59.5?keV gamma rays emitted from an Americium-241 annular radioisotope source. K X-rays emitted by samples were counted using an ultra-low energy germanium detector with a resolution of 150?eV at 5.96?keV. It was found that there was generally a decrease in both the Kβ/Kα X-ray intensity ratios and the K X-ray fluorescence cross sections for zinc oxide between 350?°C and 500?°C, but not at 550?°C. In addition, the X-ray diffraction patterns of the films showed that the transition phase from an amorphous to a polycrystalline hexagonal wurtzite structure was complete at an annealing temperature of 500?°C. The results show that variations in these parameters can be explained by the reorganization of atoms and the charge transfer process due to the effect of the annealing temperature on the elements forming the compounds.     

Superstructure and phase transitions in CsPbCl3

Superstructure of CsPbCl₃ is investigated by X-ray diffraction experiments. In the room temperature phase, three types of superlattice reflections are observed which correspond to the X, M and R points of the cubic Brillouin zone. On heating from room temperature, an integrated intensity of the X point reflection exhibits a discontinuous decrease at 37°C, while the R and M point reflections disappear at 42 and 47°C respectively. Explanations of these phase transitions in terms of condensation of soft-zone boundary phonon modes are presented.     

Low-temperature growth of epitaxial ZnO films on (001) sapphire by ultraviolet- assisted pulsed laser deposition

ZnO thin films have been grown on thin Si₃N₄ membranes and (001) sapphire substrates by an ultraviolet-assisted pulsed laser deposition (UVPLD) technique. The microstructure of the films grown on Si₃N₄ membranes, investigated by transmission electron microscopy, showed that crystalline and textured films can be grown by UVPLD at a substrate temperature of only 100 °C. For deposition temperatures higher than 400 °C, ZnO films grown on sapphire substrates were found to be epitaxial by Rutherford backscattering (RBS) and X-ray diffraction measurements. The minimum yield of channeling RBS spectra recorded from films deposited at 550 °C was around 2% and the FWHM of the rocking curve for the (002) diffraction peak was 0.17°; these values are similar to those recorded from ZnO layers grown by conventional PLD at 750 °C.