Types Of Structural Disorder Research Articles

Rethinking the existence of hexagonal sodium zirconate CO2 sorbent

Using a combination of characterisation techniques including 3D electron diffraction (3D ED) and powder X-ray diffraction, we reveal that the long-believed hexagonal Na2ZrO3, is, in fact, Na2ZrO3 with three different types of structural disorder.

Disorder effect on intersubband optical absorption of n-type δ-doped quantum well in GaAs

The inevitable structural disorder associated with the fluctuation of the applied external electric field, laser intensity, and bidimensional density in the low dimensional quantum system can affect noticeably optical absorption properties and the related phenomena. In this work, we study the effect of structural disorder on the optical absorption properties in delta-doped quantum wells (DDQWs). Starting from effective mass approximation and the Thomas-Fermi approach as well as using the matrix density, the electronic structure and the optical absorption coefficients of DDQWs are determined. It is found that the optical absorption properties depend on the strength and the type of structural disorder. Particularly, the bidimensional density disorder suppresses strongly the optical properties. Whilst, the disordered external applied electric field fluctuates moderately in the properties. In contrast, the disordered laser holds absorption properties unalterable. So, our results specify that to have and preserve good optical absorption properties in DDQWs, requires precise control of the bidimensional. Besides, the finding may improve the understanding of the impact of the disorder on the optoelectronic properties based on DDQWs.

Describing the Influence of Ball-milling on the Amorphization of Flubendazole Using the PDF and RMC Methods with X-ray Powder Diffraction Data

Flubendazole (FBZ) is a poorly water-soluble drug, and different methodologies have been proposed to improve its oral bioavailability. Obtaining the amorphous drug phase is an alternative to improve its water solubility. Several techniques for drug amorphization, such as spray drying, lyophilization, melt quenching, solvent-evaporation, and ball milling, can yield various types of structural disorder and possibly render variations in physicochemical properties. Herein, we focus on evaluating the influence of the ball-milling process on the amorphization of FBZ. The characterization of the average global and local structures before, during, and after the milling process is described by sequential Rietveld refinements, pair distribution function analysis, and the Reverse Monte Carlo method. We show that preserving the local structure (nearest molecules) can be responsible for avoiding the fast structure recrystallization commonly observed when using the solvent-evaporation process for the studied drug.

Influence of Structural Disorders on the Tribological Behavior of Phosphate-Intercalated Layered Double Hydroxide Additives in Polyalphaolefin.

In this work, several phosphate-intercalated Mg-Al layered double hydroxides (LDHs) were synthesized and evaluated as solid lubricant additives in polyalphaolefin (PAO-4) by means of tribotesting on coupled GCr15/cast iron contacts. The effects of test parameters such as normal loads, additive concentrations, and substrate surface roughness were investigated, while the LDH crystal structure received considerable attention. Several types of structural disorder after anion exchange were identified based on X-ray diffraction (XRD) analysis. The unstable structures promote feasible shearing during sliding to improve friction and wear. In addition, antiwear properties correlate well with the anion charge number or the quantity of anion in the interlayer region. Overall, the tribological performance increased in the order HPO42--LDH < PO43--LDH < P2O74--LDH < (PO3)66--LDH. (PO3)66--LDH demonstrated the best antiwear performance with a reduction of 69% of the ball volume loss compared to PAO-4 oil due to the synergy of the disordered stacking LDH sheets and flexible ring structure of the (PO3)66- anion. Furthermore, on polished surfaces, the coefficient of friction (COF) of the (PO3)66--LDH sample dropped significantly by 26%, while the wear loss reduction of more than 80% was also substantial compared to the base oil sample. A performance comparison between the best-performing LDH additive was also conducted against popular nanomaterials, such as hexagonal boron nitride (BN), graphene nanoplatelets (GNPs), and titanium oxide (TiO2). The performance of (PO3)66--LDH was close to that of GNPs.

Bound states in the continuum in periodic structures with structural disorder

Abstract We study the effect of structural disorder on the transition from the bound states in the continuum (BICs) to quasi-BICs by the example of the periodic photonic structure composed of two layers of parallel dielectric rods. We uncover the specificity in the robustness of the symmetry-protected and accidental BICs against various types of structural disorder. We analyze how the spatial mode localization induced by the structural disorder results in an effective reduction of the system length and limits the Q factor of quasi-BICs. Our results are essential for the practical implementation of BICs especially in natural and self-assembled photonic structures, where the structural disorder plays a crucial role.

Ferroelastic phase transition in the family of double fluoride crystals by Raman spectroscopy

In order to clarify ordering mechanisms of ferroic phase transitions in double fluoride salts (NH4)3SnF7, (NH4)3GeF7 and (NH4)3TiF7, their Raman scattering spectra have been studied in wide ranges of frequencies (20–3400 cm−1) and temperatures (8–410 K). Substitution of the central ion in the octahedron groups was found to change not only the phase transition types and sequences, but to modify the types of structural disorder as well, which is a special feature of these high-symmetry fluoride crystals.

Synthesis and structure of Sr14Zn1+xAs11 and Eu14Zn1+xAs11 (x ≤ 0.5). New members of the family of pnictides isotypic with Ca14AlSb11, exhibiting a new type of structural disorder

Systematic investigation of the ternary systems A–Zn–As (A = Sr, Eu) led to the discovery of two new ternary phases, Sr14Zn1+xAs11 and Eu14Zn1+xAs11 (x ≤ 0.5). Both title compounds were structurally characterized by single-crystal X-ray diffraction. The basic structure of these new arsenides is akin to that of the numerous other pnictides adopting the tetragonal Ca14AlSb11 structure type (space group I41/acd (No. 142); Z = 8). The main difference is the presence of an interstitial Zn atom, located in a nearly trigonal-planar coordination environment of three As atoms. Four such fragments share common edges with the regular ZnAs4 tetrahedron, to form an unusual new structural unit with the formula [Zn1+xSb8]. The small uptake of additional zinc is needed to augment the overall valence electron count, thereby driving the system to an electronically charge-balanced state. Upon partial substitution of the nominally divalent Sr with a trivalent La, the equivalent of electron doping, the structure rids itself of the interstitial zinc, as demonstrated on the example of Sr13.30(2)La0.70ZnAs11, which was also structurally characterized by single-crystal X-ray diffraction as part of this study. Electronic structure calculations for the idealized composition Sr14ZnAs11 confirm the speculated electron-deficient assignment, and suggest intrinsic semiconducting behavior for the one-electron richer Sr14Zn1+xAs11 (x = 0.5) and Sr13LaZnAs11, respectively.

Electronic structures and optical properties of partially and fully fluorinated graphene.

In this Letter, we study the electronic structures and optical properties of partially and fully fluorinated graphene by a combination of ab initio G0W0 calculations and large-scale multiorbital tight-binding simulations. We find that, for partially fluorinated graphene, the appearance of paired fluorine atoms is more favorable than unpaired atoms. We also show that different types of structural disorder, such as carbon vacancies, fluorine vacancies, fluorine vacancy clusters and fluorine armchair and zigzag clusters, will introduce different types of midgap states and extra excitations within the optical gap. Furthermore, we argue that the local formation of sp3 bonds upon fluorination can be distinguished from other disorder inducing mechanisms which do not destroy the sp2 hybrid orbitals by measuring the polarization rotation of passing polarized light.

ChemInform Abstract: Structural Disorder in Molecular Framework Materials

AbstractReview: 58 refs.

Dielectric and Relaxor Properties of Ba9MNb14O45Ceramics

The ceramics with two types of nominal compositions including (6:1:4.5) Ba6M2+Nb9O29.5 and (9:1:7) Ba9M2+Nb14O45 (M = Mg, Co, Zn) have been synthesized and studied with regard to their phase composition and dielectric properties. The materials with Ba6M2+Nb9O29.5 nominal compositions corresponded to the two-phase region containing 9:1:7 tetragonal tungsten bronze-type (TTB) phase and the 3:1:1 perovskite Ba(M2+1/3Nb2/3)O3. In contrast, 9:1:7 TTB ceramics were near single phase. All of the studied 9:1:7 TTB phases exhibited high values of dielectric permittivity (e = 800–1100) together with strong frequency dispersion. The observed dispersion of permittivity was accompanied by the monotonic rise of dielectric loss. The dielectric spectra of 9:1:7 TTBs demonstrated a typical relaxor behavior. At low temperatures (100–300 K), two relaxation modes have been found in the tan δ (T) dependencies, which can be associated with two different types of structural disorder in the TTB crystal lattice.

Theoretical studies on magnetic interactions between Cu(II) ions in salen nucleobases

The magnetic and other physical properties between Cu 2+ ions coordinated by salen–base pairs (Cu 2+–DNA) are examined by using DFT calculations. In order to consider effects of entanglement and dis-entanglement of the double helix chain, three types of structural disorders i.e. distance, rotation angle and discrepancy in XY-plane, are changed in the model dimer structure. All calculated results show that J ab values are weak anti-ferromagnetic couplings. It is also found that the J ab values strongly depend on the salen structure.

Theoretical studies on magnetic interactions between Cu(II) ions in hydroxypyridone nucleobases

The origin of a ferromagnetic interaction between Cu 2+ ions in the Cu 2+–DNA system which reported by Tanaka et al. is examined by using DFT calculations. In order to consider effects of an entanglement and a dis-entanglement of the double helix chain, three types of structural disorders i.e. distance, rotation angle and discrepancy in XY-plane, are considered in the model dimer structure. All calculated results show that J ab values are weak anti-ferromagnetic couplings. Boltzmann distribution simulation indicates that the high spin (HS) species exist 21% at 1.5 K by thermal excitation within the model structure.

The effect of structural disorder on guided resonances in photonic crystal slabs studied with terahertz time-domain spectroscopy

We measure the normal-incidence transmission coefficient of photonic crystal slabs with hexagonal arrays of air holes in silicon. The transmission spectra exhibit sharp resonant features with Fano line shapes. They are produced due to the coupling of the leaky photonic crystal modes, called guided resonances, to the continuum of free-space modes. We investigate the effects of several types of structural disorder on the spectra of these resonances. Our results indicate that guided resonances are very tolerant to disorder in the hole diameter and to interface roughness, but very sensitive to disorder in the lattice periodicity.

Line broadening in the PXRD patterns of layered hydroxides: The relative effects of crystallite size and structural disorder

Layered hydroxides crystallize in a hexagonal structure and incorporate a number of different types of structural disorders as an exigency of anisotropic bonding. Structural disorder contributes to the non-uniform broadening of lines in the powder X-ray diffraction pattern. Common among the disorders are stacking faults, which broaden theh0l/0kl reflections. Interstratification selectively broadens the 00l reflections and turbostratic disorder broadens the 0kl reflections. The line broadening caused by structural disorder has to be discounted before estimates of particle size are made by applying the Scherrer formula.

Neutron Powder Diffraction Study of Pb(HfxTi1-x)O3 Ceramics (0.10 ≤ x ≤ 0.50)

The crystal symmetries of lead hafnate titanate (Pb(HfxTi1-x)O3, PHT) powders with 0.10<or=x<or=0.50 were investigated by high-resolution neutron powder diffraction. Samples with x<or=0.40 were tetragonal (space group P4 mm), while the sample with x=0.50 contained both monoclinic Cm and rhombohedral (modeled using the R3c space group) phases. The role of the B cations (Hf and Ti) and the oxygen octahedra network, in addition to the displacement of Pb ions from their ideal sites, in promoting the phase transformation between the P4 mm and Cm phases was considered. Two types of structural disorder were identified. Diffuse scattering between Bragg reflection peaks was assigned to Pb ion displacement. A second type of structural disorder, revealed by the weak intensities of observed pseudo-cubic 00l reflections with l even and as 00l reflection peak widths significantly broader than the l00 reflection peaks, was observed. This behavior was attributed to disorder in the arrangement of the O-B-O rows parallel to the c axis. For small values of x, this shift was predominantly along the c axis, whereas shifts perpendicular to the c axis increased with increasing x. These features were modeled using an hkl-dependent line-broadening model. The origin of the hkl-dependent line broadening was assigned to the microstrain accompanying a spatial-composition variation. Structural models were tested by computing valence sums and spontaneous polarization values.

Model simulations of ground-state and finite-temperature properties of disordered magnetic nanostructures

The properties of two-dimensional ensembles of magnetic nanoparticles that interact by magnetic dipole coupling are investigated. The low-temperature magnetic arrangements, the average binding energy E dip due to dipolar interactions, and its scaling behavior with respect to the particle density C are calculated for different types of structural disorder and particle-size distributions. Many different metastable magnetic states are obtained, which exhibit strong noncollinearities and are reminiscent of a spin-glass behavior. For a given C, |E dip| increases with increasing disorder of the particle positions. For random distributions at low particle densities C≤0.2, E dip is dominated by the contributions of short interparticle distances. Thus, it scales as | E dip| ∝ C α with an unusually small exponent α = 0.85–1. The straightforward scaling of the dipole interaction, α≃3/2, is obtained only for C≥0.5 or for nearly periodic ensembles. The finite temperature behavior of these disordered interacting nanomagnets is explored. The specific heat and magnetic susceptibility are calculated by performing Monte Carlo simulations. The onset of long-range magnetic order is discussed. In addition we determine hysteresis loops at finite temperatures and compare the results for different degrees of disorder.

X-Ray Diffraction Studies on Structural Changes in Montmorillonite during Dehydration

Montmorillonite, a smectite group clay mineral having 2:1 type of layer structure, possesses different types of structural disorders which have been determined in the present investigation using the Fourier initial slope method and the variance analysis of the X-ray line profiles. The effect of structural changes during dehydration has been studied by heating the samples at several temperatures.

Chain length dependent polymorphism in even number n-alkanes: line profile analysis of synchrotron powder X-ray diffraction data

Normal alkanes form a basic building block unit in systems such as liquid crystals, oils, proteins, lipids and plastics and, as a result, short-chain alkanes, owing to their simplicity, are often used as simple representative models for probing the physical nature of the more complex hydrocarbon systems, nAlkanes crystallize to form thin plates with regular faces in which the chain direction is more or less perpendicular to the lamella surface. A combination of single-crystal and powder X-ray analysis has enabled some of these systems to be characterized; three solid-state structures have been identified [1, 2]: triclinic, 12 ~ 36 and n(odd). Prior to melting, n-alkanes are known to exhibit solid-solid phase transitions to crystalline rotator phases [3, 4]. In the low temperature phase (phase I) the chains adopt an overall trans configuration, after which the material may transform to a rotator phase (phase II) in which the chains undergo hindered rotation about the main carbon axis. Such a transformation can be accompanied by the introduction of gauche bonds [5, 6] into an otherwise all t rans structure: with each set of gauche bonds conferring different types of structural disorder (ukinks", chain twisting and chain folding). Such molecular disorder is innate to crystals of polyethylene [7] as well as being present in the longer chain linear hydrocarbons (n > 100) [8, 9]. In previous studies [10] we employed high resolution X-ray powder diffraction using the Daresbury synchrotron radiation source (SRS) to determine the unit cell parameters for a number of homologues taken from the series C13H28-C60H122. However, as well as being able to determine the unit cell parameters from the X-ray powder data, it is also possible to extract, by line profile analysis, other physical information such as crystallite size or lattice strain by observing the line broadening behaviour [11-14]. In this study we present a strain analysis of the [00I] plane for a series of even n-alkanes (C18H38-C60H122) in order to attain further under-

Polarized Raman spectra of Cs5H3(SO4)4· H2O single crystals

The Raman spectra of the superprotonic conductor Cs5H3(SO4)4·H2O have been investigated in the 300-500 K range. An assignment of bands due to internal and external vibrations in term of approximate type of motions is proposed. The spectroscopic results are used for discussing crystal structures of different phases, the type of structural disorder and phase transitions.

The magnetic properties of planar ferromagnets with different types of structural disorder

The magnetic properties of planar ferromagnets are investigated in the frame of the integral operator technique. The various kinds of structural disorder described by solid dilution and amorphisation are examined. For the calculation of the phase diagrams, a simple comparative method is proposed. This method can be applied to such disordered systems where, for the unperturbed lattice, exact solutions exist.