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Mullite-type Bi2(FexGa1-x)4O9 (0 ≤ x ≤ 1) oxides, prepared by mecanochemical-thermal synthesis, were investigated by FTIR and Raman spectroscopies. Similarly to other mullite systems, IR (850–400 cm−1) and Raman bands (750–300 cm−1) are attributed to stretching and bending vibrations of tetrahedral and octahedral sites. A shift in the peak positions toward lower wavenumbers with the increase of iron content is observed. High-energy IR modes show only the presence of Ga-O-Ga and Ga-O-Fe/Fe-O-Ga stretching vibrations for x < 0.5. Raman bands between 500 cm−1 and 400 cm−1 revealed double band splitting for x < 0.5. [ABSTRACT FROM AUTHOR]

The present paper introduces a mathematical model for analysing dynamic grain growth. In particular, we show how the characteristic measurements grain volumes, centroids, and central second-order moments at discrete moments in time can be quickly turned into a continuous description of the grain growth process in terms of geometric diagrams (which largely generalize the well-known Voronoi and Laguerre tessellations). We give a theoretical analysis of common optimization-free heuristics in terms of discriminant analysis and evaluate the computational behaviour of our algorithm on real-world data. [ABSTRACT FROM AUTHOR]

Slip transmission between neighbouring grains is needed for the occurrence of plastic deformation in polycrystals. A geometric factor defined for a pair of grains with a certain orientation relationship is used to determine the slip transmission. Two slip transmission factors are calculated for randomly oriented grains. One is the slip transmission factor averaged for randomly oriented grains and the other is the minimum of the transmission factors among all possible orientation relationships. The possible number of slip systems in a grain varies for different metals and alloys. The effects of the number of slip systems on the transmission factors are discussed. [ABSTRACT FROM AUTHOR]

This paper focuses on the micromechanical modeling of pores and texture in 3D-printed polycrystals. A Gaussian-shape approximation is used to describe the orientation distribution function (ODF) and construct the initial homogenization model of the representative volume element (RVE). Spherical and ellipsoidal pores of varying sizes are added in stages to the RVE for homogenization, utilizing the modified Mori-Tanaka (MT) scheme in conjunction with the stepwise iterative method. Wherein, the mechanical interactions between pores and the spatial distribution of pore locations could be taken into account, when developing a cross-scale model from microstructure to macroelasticity. After obtaining the final elastic stiffness tensor, the Christoffel equation is combined with the Cardano's formula to derive a closed form solution for ultrasonic velocities depending on microstructure. According to the numerical results, this method can effectively capture the behavior characteristics of pores and texture on the elastic stiffness tensor, average velocity, and velocity distribution. [ABSTRACT FROM AUTHOR]

In this article, we report the observation of spin Seebeck effect (SSE) of hybrid structure in bulk sintering polycrystalline of yttrium iron oxide (Y3Fe5O12, YIG)/Pt. The bulk YIG polycrystalline is prepared by solid press mechanic and then coated with Pt 10 nm thickness. The voltage of inverse spin Hall effect (VISHE) in Pt/YIG polycrystalline is detected by in plane magnetization configuration (IM) and then filter out the anomalous Nernst effect (ANE) by perpendicular magnetization configuration (PM). The results show that the VISHEsignal can be observed in bulk YIG polycrystalline. In addition, the efficiency of spin injection from YIG to Pt is compared between Pt/YIG single crystal and bulk polycrystalline of hybrid structure. The VISHE signal of Pt/YIG single crystal and bulk polycrystalline are 197.61 nV/K and 23.22 nV/K, respectively. The VISHEvoltage of YIG single crystal is higher than bulk polycrystalline about 9 times. Whereas, the porous size in bulk YIG polycrystalline of solid press is determined around 214 ± 81 nm but it cannot detect in YIG single crystal. Thus, the porous size and surface roughness between YIG and Pt might be the major role of the spin current (Js) transfer. [ABSTRACT FROM AUTHOR]

Solid polycrystalline materials undergoing diffusion creep are usually described by Cauchy continuum models with a Newtonian viscous rheology dependent on the grain size. Such a continuum lacks the rotational degrees of freedom needed to describe grain rotation. Here we provide a more general continuum description of diffusion creep that includes grain rotation, and identifies the deformation of the material with that of a micropolar (Cosserat) fluid. We derive expressions for the micropolar constitutive tensors by a homogenisation of the physics describing a discrete collection of rigid grains, demanding an equivalent dissipation between the discrete and continuum descriptions. General constitutive laws are derived for both Coble (grain-boundary diffusion) and Nabarro-Herring (volume diffusion) creep. Detailed calculations are performed for a two-dimensional tiling of irregular hexagonal grains, which illustrates a potential coupling between the rotational and translational degrees of freedom. If only the plating out or removal of material at grain boundaries is considered, the constitutive laws are degenerate: modes of deformation that involve pure tangential motion at the grain boundaries are not resisted. This degeneracy can be removed by including the resistance to grain-boundary sliding, or by imposing additional constraints on the deformation. [ABSTRACT FROM AUTHOR]

Since the late 90s the use of zirconia in dentistry increases, it is used for example for all-ceramic restorations, brackets and implants. This article will deal with all-ceramic restorations. For the production of these restorations many manufacturing steps are necessary: Pre-sintering of the ceramic powder, soft machining (pre-sintered condition), sintering and a pre-processing of the 'finished' geometry like hard machining (fully sintered) or grit blasting (GB) in combination with a final staining or veneering step. Most of the steps (excluding soft machining in a pre-sintered condition and sintering) are still carried out manually. All these techniques are associated with the production of flaws in different scales, in conjunction with thermal and residual stresses and phase transformations. This study investigates how those surface and subsurface properties, which arise due to the manufacturing process, influence the bonding between a framework ceramic and a veneering ceramic. This will be investigated by means of a scratch test. [ABSTRACT FROM AUTHOR]

The choice of a proper interatomic potential is critical to obtaining accurate and realistic molecular dynamics results. However, previous studies that have tested the suitability of a potential to predict mechanical properties often do so using elastic constants from a triaxial stress state that ignores Poisson's effect. While this method is suitable it is not consistent with macroscale experimental methods and cannot provide the complete loading behaviour. Further, there is a lack of knowledge as to whether accuracy in predicting elastic constants from a fixed volume condition indicates accuracy for elastic moduli from uniaxial tensile simulations. Moreover, those studies that did account for Poisson's effect studied only one crystal orientation and thus assumed potential accuracy is independent of crystal orientation. Results from the current study demonstrated that accuracy of a potential is dependent on the crystal direction. Further, the most accurate potentials for elastic constants calculated using a fixed volume condition were not necessarily the most accurate at predicting elastic moduli from a physically realisable tension test. Finally, the Voigt Reuss Hill (VRH) method was shown to accurately predict polycrystalline mechanical properties from single crystal data as a function of temperature. [ABSTRACT FROM AUTHOR]

We present a computational approach for identifying the important descriptors of the ionic conductivities of lithium solid electrolytes. Our approach discriminates the factors of both bulk and grain boundary conductivities, which have been rarely reported. The effects of the interrelated structural (e.g. grain size, phase), material (e.g. Li ratio), chemical (e.g. electronegativity, polarizability) and experimental (e.g. sintering temperature, synthesis method) properties on the bulk and grain boundary conductivities are investigated via machine learning. The data are trained using the bulk and grain boundary conductivities of Li solid conductors at room temperature. The important descriptors are elucidated by their feature importance and predictive performances, as determined by a nonlinear XGBoost algorithm: (i) the experimental descriptors of sintering conditions are significant for both bulk and grain boundary, (ii) the material descriptors of Li site occupancy and Li ratio are the prior descriptors for bulk, (iii) the density and unit cell volume are the prior structural descriptors while the polarizability and electronegativity are the prior chemical descriptors for grain boundary, (iv) the grain size provides physical insights such as the thermodynamic condition and should be considered for determining grain boundary conductance in solid polycrystalline ionic conductors. [ABSTRACT FROM AUTHOR]

This work addresses the problem of the reconstruction of the local fields distribution occurring in heterogeneous linear elastic solids. The constitutive heterogeneities are crystals and cracks. Through comparisons with FFT computations, it is shown that self-consistent estimates together with an assumption of normal distribution at the phase scale provide an accurate description of the elastostatic field histograms in polycrystals without cracks. In the case of inter and transgranular cracks, full-field FFT simulations indicate that the field histograms present van Hove singularities. Their natures are determined analytically in the low-density regime, in the case of an homogeneous medium containing cracks. [ABSTRACT FROM AUTHOR]

Proposed is a methodology for an accurate description of triple junctions' network evolution in the course of severe plastic deformation (SPD). It is based on representations of polycrystalline solids with discrete combinatorial complexes, processes evolving different substructures (grains, grain boundaries, triple junctions) of these complexes, and methods for analyses of such substructures. It is demonstrated that the methodology can reproduce theoretical results available for the simplest case of quasi-homogeneous microstructure evolution, i.e. spatially random conversion of low to high angle grain boundaries during SPD. It is further shown that the proposed discrete approach can reproduce in a natural way results from recent experiments with copper alloys, where inhomogeneity development during SPD is strongly manifested. Finally, the evolution of different types of triple junctions and their connectivity is analysed to show that these substructure characteristics differentiate inhomogeneous from homogeneous evolution of the polycrystalline solid. It is suggested that such substructure characteristics can form the basis for characterisation of continuous dynamic recrystallisation process. [ABSTRACT FROM AUTHOR]

In the present study the Hu-Cocks micromechanical model [1,2] for dislocation-obstacle interactions, implemented in a crystal plasticity self-consistent model, is employed to simulate thermo-mechanical histories typical for AGR nuclear plants in order to assess the implications of creep-fatigue interactions in 316H stainless steel. Their physical model is enhanced by including the effect of dynamic recovery, which introduces a new material parameter - the annihilated segment length . The full model contains five independent material parameters; other parameters are prescribed by the fundamental physics of inelastic deformation processes. Having calibrated the model, we explore its ability to predict material response under complex loading histories to provide insight into the physical phenomena controlling cyclic-creep interactions. Introduction of strain dwells during cyclic loading results in an increase of the extent of relaxation with an increasing number of cycles, but histories with dwells at different strain levels indicate that relaxation is strongly dependent on initial stress and level of constant strain. Predictions of history-dependent relaxation demonstrate that the least stress relaxation results after creep into the secondary regime and the largest stress drop results during hold-dwells after monotonic elastic-plastic loading, with the cyclic-dwell history behaviour laying in between these two. Both prior cycling and the generated residual stress field are found to affect the primary creep regime under hold-stress dwells. These results are consistent with experimental observations; this demonstrates that deformation response is dependent on both the evolution of microstructural state and redistribution of stress between the grains of the polycrystalline aggregate. [ABSTRACT FROM AUTHOR]

The influence of a population of randomly oriented cracks on the macroscopic thermal and linear-elastic response of a hexagonal polycrystal is addressed using a self-consistent method. Coupling between micro-cracks and crystal anisotropy is taken into account through the effective medium where all inhomogeneities are embedded. In the absence of cracks, the proposed approach reduces to the self-consistent estimate of Berryman (2005). The accuracy of the present method is first assessed using numerical, Fourier-based computations. In the absence of crystal anisotropy, the estimates for the effective elastic properties are close to that obtained numerically for a homogeneous body containing disk-shaped cracks, with Boolean spatial dispersion. Various other analytical estimates and bounds, that are available for homogeneous cracked bodies, are also considered and compared to the present approach. Second, the combined role of crystal anisotropy and micro-cracks is investigated analytically, specifically when the in-plane shear modulus of the crystal becomes zero. The cracks-density percolation threshold is found to diminish abruptly in this limit. This 'advanced' percolation threshold is concomitant to the onset of large, weakly loaded regions surrounding cracks in strongly anisotropic crystals. [ABSTRACT FROM AUTHOR]

We report a quantitative comparison of measured intensities of neutron powder diffraction data collected in a single-crystal diamond anvil cell and in large-volume sintered diamond anvils. As expected from the difference in sample volumes, the latter provides 1-2 orders of magnitude higher intensities, depending on the anvil material. The remaining differences are due to effects of absorption and angular aperture. [ABSTRACT FROM AUTHOR]

Tungsten (W) has been regarded as one of the most promising plasma facing materials (PFMs) in fusion reactors. The formation of bubbles and blisters during hydrogen (H) irradiation will affect the properties of W. The dependence of implantation conditions, such as fluence and energy, is therefore of great interest. In this work, polycrystalline tungsten samples were separated into two groups for study. The thick samples were implanted by 18 keV H3+ ions to fluences of 1 × 1018, 1 × 1019 and 1 × 1020 H+/cm2, respectively. Another thick sample was also implanted by 80 keV H2+ ions to a fluence of 2 × 1017 H+/cm2 for comparison. Moreover, the thin samples were implanted by 18 keV H3+ ions to fluences of 9.38 × 1016, 1.88 × 1017 and 5.63 × 1017 H+/cm2, respectively. Focused ion beam (FIB) combined with scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used for micro-structure analysis, while time-of-flight ion mass spectrometry (ToF-SIMS) was used to characterize the H depth profile. It is indicated that bubbles and blisters could form successively with increasing H+ fluence. H bubbles are formed at a fluence of ∼5.63 × 1017 H+/cm2, and H blisters are formed at ∼1 × 1019 H+/cm2 for 18 keV H3+ implantation. On the other hand, 80 keV H2+ ions can create more trapping sites in a shallow projected range, and thus enhancing the blisters formation with a relatively lower fluence of 2 × 1017 H+/cm2. The crack-like microstructures beneath the blisters are also observed and prefer to form on the deep side of the implanted range. [ABSTRACT FROM AUTHOR]

In the present work the influence of milling process below 173 K (cryomilling) on the nanostructuration of BiFeO3 powders, synthesized by fast-firing thermal treatment allied to high-energy ball milling, is evaluated as function of milling time as well as balls size/mass ratio. The influence of the cryomilling process on the structural and magnetic properties of BiFeO3 powders is investigated and the key role of the crystallite size on the magnetic response is evidenced. The results show a strong nonlinear magnetic response, which is governed by the crystallite size while induced strain does not play an important role. [ABSTRACT FROM AUTHOR]

In this manuscript, microstructural, structural and magnetic properties of pure and La doped (0.6)BiFeO3-(0.4)PbTiO3 polycrystals were investigated. X-ray diffraction, transmission and scanning electron microscopy results reveal morphologically uniform particles of rhombohedral and rhombohedral/tetragonal symmetries for pure and La doped samples. An enhanced magnetization, characterized by slim loop hysteretic curves of null remnant magnetization and 2 emu/g saturation (15 kOe) magnetization, is observed at room temperature for samples with average particle size close to 5 nm. [ABSTRACT FROM AUTHOR]

Recently we have demonstrated that out-of-plane dielectric properties of polycrystalline SrTiO3 (ST) films depend on the strain/stress induced by the substrates due to thermal expansion misfit. Here, we present a complementary infra-red (IR) spectroscopy investigation of the role of Al2O3 and MgO substrates on the lattice dynamics and in-plane dielectric properties of ST thin films also prepared by sol-gel. We verify that ST films deposited on Al2O3 substrates, being under a tensile stress, present the soft mode behaviour similar to that of ST single crystals, deviating just below 150 K. In contrast, ST films deposited on MgO substrates, being under compressive stress, have higher soft mode frequency from 10 to 300 K. It is thus proved that for polycrystalline ST films the intrinsic in-plane relative permittivity may be tuned through an induced stress state. [ABSTRACT FROM AUTHOR]

Ab initio calculations were carried out to compare the mechanical properties of β-based non-canonical Al-Cu-Fe approximants of quasicrystals with cubic (β), monoclinic (η) and orthorhombic (ξ1, ξ2) structures, which all demonstrate high strengthening. The aim was to elucidate the competitive effects of the η- and ξ-ordering and iron content on deformation behaviour of these phases. We found that the Young’s modulus, polycrystalline shear modulus, mechanical stability and shear elastic modulus G(n,m) for different slip planes decrease for β-Al50Cu1-xFex with lowering iron content, but they grow from β-Al50Cu31.25Fe18.75 to the ordered η-Al50Cu45Fe5, and ξ2-Al45.5Cu50Fe4.5 that indicates a growing resistance to plastic deformation due to ordering and agrees well with our experimental finding. The preferable slip systems were predicted based on the calculated generalised stacking fault (GSF) energies in β-(Cu,Fe)Al and η-(Cu,Fe)Al with similar Fe concentration. The GSF energies confirmed also that the strengthening observed in η-phase is related to ordering rather than the Fe effect in consistence with a stronger covalent bonding in η-phase. [ABSTRACT FROM AUTHOR]

We report on observations of structural and chemical differences between samples of UBe13 that were synthesised using two different methods. Unexplained discrepancies in properties between samples with differing synthesis had previously been found in this heavy fermion superconductor. A polycrystalline UBe13 sample was made by arc-melting the constituents. Single crystals were grown using an aluminium flux and had a consistently slightly larger lattice parameter than the polycrystals, which merited further study. Neutron diffraction data were collected at the Lujan Center at LANSCE on the HIPPO diffractometer. Aluminium was detected by inductively coupled plasma mass spectrometry (ICP-MS) in the flux-grown single crystal (0.803 wt%), and small amounts (~0.2 wt%) of thorium were detected in the UBe13 polycrystalline sample. In order to probe the implications of the presence of Al, calculations by spin-polarised DFT-GGA+U show that the incorporation of Al onto the 96i site (the lowest symmetry site in the structure) is energetically more favourable than on other sites. In general, the trends calculated by DFT for bond lengths and lattice parameter increases are consistent with bond lengths experimentally observed by neutron diffraction, but specific percentage changes with aluminium incorporation may be obscured by the unexpected thorium in the polycrystalline sample. The aggregate of our initial observations suggests that incorporation of aluminium from the flux into single crystal UBe13 is significant. [ABSTRACT FROM AUTHOR]

We report on observations of structural and chemical differences between samples of UBe13 that were synthesised using two different methods. Unexplained discrepancies in properties between samples with differing synthesis had previously been found in this heavy fermion superconductor. A polycrystalline UBe13 sample was made by arc-melting the constituents. Single crystals were grown using an aluminium flux and had a consistently slightly larger lattice parameter than the polycrystals, which merited further study. Neutron diffraction data were collected at the Lujan Center at LANSCE on the HIPPO diffractometer. Aluminium was detected by inductively coupled plasma mass spectrometry (ICP-MS) in the flux-grown single crystal (0.803 wt%), and small amounts (~0.2 wt%) of thorium were detected in the UBe13 polycrystalline sample. In order to probe the implications of the presence of Al, calculations by spin-polarised DFT-GGA+U show that the incorporation of Al onto the 96i site (the lowest symmetry site in the structure) is energetically more favourable than on other sites. In general, the trends calculated by DFT for bond lengths and lattice parameter increases are consistent with bond lengths experimentally observed by neutron diffraction, but specific percentage changes with aluminium incorporation may be obscured by the unexpected thorium in the polycrystalline sample. The aggregate of our initial observations suggests that incorporation of aluminium from the flux into single crystal UBe13 is significant. [ABSTRACT FROM AUTHOR]

Properties of grain boundaries such as grain boundary energy, mobility and diffusion are reported to depend strongly on their crystallography. While studies on ceramic bicrystals with low Σ misorientations have shown highly ordered structures and low energies, studies on dense polycrystalline ceramics often show the significance of grain boundary planes. In the present study, grain boundary plane distributions were studied for yttria-stabilised cubic zirconia with varying grain sizes using Electron Back Scattered Diffraction technique combined with a stereological approach. Despite nearly isotropic grain boundary plane distributions, a highly anisotropic grain boundary character distribution is observed for specific misorientations. Certain low-energy symmetric tilts such as Σ3 and Σ11 are found to occur with high frequencies across the grain size range studied, leading to an inverse correlation between GB energy and frequency of occurrence, consistent with other ceramics studied in literature. [ABSTRACT FROM AUTHOR]

The polycrystalline samples of gadolinium-modified lead-zirconate-titanate (Pb1−xGdx (Zr0.52Ti0.48)1−x/4O3) (x = 0, 0.07, 0.10 and 0.12) (PGZT x/52/48) ceramics near morphotropic-phase boundary were prepared using conventional solid-state reaction route. XRD patterns show the formation of single-phase compounds in rhombohedral crystal system. SEM textures of the samples reveal uniform grain distribution. Frequency and temperature dependence of dielectric constant of the materials indicates non-relaxor behavior and indication of the diffuse phase transition at higher values of Gd concentration. The temperature dependence of P-E loops confirms ferroelectricity in the materials. The piezoelectric studies of the samples show enhancement in piezoelectric coefficients on substitution of Gd at the Pb site. [ABSTRACT FROM AUTHOR]

In the current paper, a macroscopic model is proposed to simulate the hysteretic dynamics of ferroelectric ceramics with creep phenomenon incorporated. The creep phenomenon in the hysteretic dynamics is attributed to the rate-dependent characteristic of the polarisation switching processes induced in the materials. A non-convex Helmholtz free energy based on Landau theory is proposed to model the switching dynamics. The governing equation of single-crystal model is formulated by applying the Euler-Lagrange equation. The polycrystalline model is obtained by combining the single crystal dynamics with a density function which is constructed to model the weighted contributions of different grains with different principle axis orientations. In addition, numerical simulations of hysteretic dynamics with creep phenomenon are presented. Comparison of the numerical results and their experimental counterparts is also presented. It is shown that the creep phenomenon is captured precisely, validating the capability of the proposed model in a range of its potential applications. [ABSTRACT FROM AUTHOR]

Measuring elastic strain with nanoscale resolution has historically been very difficult and required a marriage of simulations and experiments. Nano precession electron diffraction provides excellent strain and spatial resolution but has traditionally only been applied to single-crystalline semiconductors. The present study illustrates that the technique can also be applied to polycrystalline materials. The ±2σ strain resolution was determined to be 0.15% and 0.10% for polycrystalline copper and boron carbide, respectively. Local strain maps were obtained near grain boundaries in boron carbide and dislocations in magnesium and shown to correlate with expected values, thus demonstrating the efficacy of this technique. [ABSTRACT FROM AUTHOR]

In this paper, the two-stage process of the uniform distribution of n-layer graphenes in a mixture for sintering polycrystalline diamond at high pressures and temperatures is described. Due to the preliminary deposition of a nanopowder layer on the surface of diamond crystals, at the second stage of mixing the uniform application of a layer of the n-layer graphenes powder on the prepared surface and mixture uniform in the properties are achieved. This approach ultimately makes it possible to produce diamond polycrystals stable in properties. In particular, the current-conducting diamond polycrystals are obtained. [ABSTRACT FROM PUBLISHER]

The low-temperature polycrystalline silicon (LTPS) thin-film transistor (TFT) is the optimal device for the backplane of the organic light-emitting diode display. At the end thep-channel LTPS TFT fabrication, a charge-injection stress with a strong negative drain bias and a positive gate bias are applied to reduce the off-current by injecting electrons into the gate insulator near the drain. In this study, the charge density and the length of the charge-injection region in the gate insulator were estimated by comparing the measured TFT characteristics with the simulation models with various charge-injection lengths and charge densities. It was found that the effective length of the charge-injection region was 0.96 µm and the charge density was −3 × 1012/cm2for the 2-µm-channel-length device when VGSwas +20 V and VDSwas −10 V under the charge-injection stress condition. It was also found, based on the analysis of the electric field distribution under the bias stress condition, that the charge density and the length of the charge-injection region were invariant against the channel length variation. Therefore, the measured TFT characteristics also accorded closely with the simulation models for different channel lengths, such as 4 and 10 µm, when the same characteristic values of the charge-injection region were employed. [ABSTRACT FROM PUBLISHER]

This paper reports a comparative study of thermal stability between all-organic metal halide perovskite (MHP) CsPbBr3and organic–inorganic hybrid MHP (methylammonium lead bromide MAPbBr3). The film morphology, crystal structure, steady-state photoluminescence intensity, and photoluminescence lifetime of CsPbBr3and MAPbBr3polycrystalline films were measured after thermal annealing at temperatures from 70°C to 230°C. The CsPbBr3films exhibited little change in their structural and luminescent properties after being annealed even at 230°C, whereas the MAPbBr3films exhibited a significant change in such properties due to their decomposition into PbBr2when annealed at ≥180°C. This study increased the understanding of the difference in the thermal stability of MHP polycrystalline films with different A-site cations. [ABSTRACT FROM PUBLISHER]

We report results obtained from first principle calculations on APt3compounds with A=Mg, Sc, Y and Zr. Our results of the lattice parameteraare in good agreement with experimental data, with deviations less than 0.8%. Single crystal elastic constants are calculated, then polycrystalline elastic moduli (bulk, shear and Young moduli, Poisson ration, anisotropy factor) are presented. Based on Debye model, Debye temperatureϴDis calculated from the sound velocitiesVl,VtandVm. Band structure results show that the studied compounds are electrical conductors, the conduction mechanism is assured by Pt-d electrons. Different hybridisation states are observed between Pt-d and A-d orbitals. The study of the charge density distribution and the population analysis shows the coexistence of ionic, covalent and metallic bonds. [ABSTRACT FROM PUBLISHER]

The statistical characterisation and synthetic reproduction of a polycrystalline material's microstructure is assisted by mathematically representing its morphology by a tessellation model. The generalised balanced power diagram (GBPD) is a tessellation model that was shown in previous studies to accurately reproduce the microstructure morphology of various materials by closely matching micrographs obtained through electron microscopy. These studies employed costly optimisation procedures to determine the best-fit model parameters, limiting the scalability of the model. In this work, it is shown that setting the tessellation cell parameters to values such that the shape moments of the corresponding grains are matched results in a quality of fit that is commensurate with optimisation procedures. This fitting approach decouples the interaction among grains when fitting the tessellation parameters and, most notably, provides analytical, closed-form expressions for all the model parameters. The performance of this parameter fitting approach is demonstrated on multiple micrographs of various materials, and it compares similarly to the performance of optimisation procedures reported in recently published literature. As the fitted parameter values are obtained through trivial computations, this approach enables extensive scalability of the GBPD model such that it can be used to represent extremely large characterisation data sets. [ABSTRACT FROM AUTHOR]

Grain boundary extra free volume (GB EFV) can be considered as fundamental microstructural parameter for polycrystalline or nano-crystalline materials. Here, we present a systematic first principles study on a group of representative symmetric tilt grain boundaries of Al with various EFVs subjected to vacancy formation and Mg segregation. All grain boundaries were constructed using the coincident site lattice (CSL) and the structural unit (SU) models. It was found that the SU model is superior to the CSL in describing FCC-Al GBs, the same as we previously revealed for BCC-Fe. The predicted relation between GB misorientation angle and EFV, and the predicted EFV criteria for a stable GB, both agree with available experimental observations. Vacancy formation and Mg segregation show stronger preference to those GBs with high EFV values, due to the resultant high levels of atomic disorder. These findings not only provide a new, atomistic perspective on the significance of EFV, but also suggest a viable means of predicting GB properties based on direct experimental characterisation of GB EFVs. [ABSTRACT FROM PUBLISHER]

A series of polycrystalline La0.5Ca0.5Mn1−xNixO3(x = 0.00, 0.025, 0.050, 0.075, 0.100 and 0.125) was synthesised using solid state reaction. Measurements in a cooling and warming cycle between 300 and 80 K were carried out to study the Ni-doping effects on the electrical resistivity, thermopower and magnetisation of single-phase La0.5Ca0.5Mn1−xNixO3. Partial substitution of Ni for Mn leads to the suppression of charge ordering state, the evidence of which is shown by the dramatic decrease in electrical resistivity and thermal hysteresis width in electrical resistivity, thermopower and magnetisation. However, the magnitude of both electrical resistivity and thermopower increases with increasing Ni content. This can be attributed to an increase in the Mn4+concentration, which favours the antiferromagnetic state and leads to a gradual disappearance of ferromagnetic double exchange interaction. Besides, the metal–nonmetal transition temperature decreases with increasing Ni content untilx = 0.075, which might arise from increased electron–phonon coupling due to less ordered spins at temperatures above ferromagnetic transition. For samples withxgreater than 0.075, no metal–nonmetal transition is observed due to the suppression of double exchange mechanism. [ABSTRACT FROM PUBLISHER]

A new diamond cell with extreme apertures is described. It is tailored for a large variety of neutron scattering techniques such as inelastic neutron scattering and single-crystal diffraction both at the Spallation Neutron Source (SNS) and the High Flux Isotope Reactor at the Oak Ridge National Laboratory. Simple springs enable forces of over 10 metric tons to be clamped in for low-temperature measurements. At present, low-cost polycrystalline diamond (Versimax®) pressure anvils are used. We predict a routine pressure regime up to 20 GPa with sample volumes of ∼0.5 mm3. Future use of large CVD single-crystal diamond anvils will significantly expand this pressure range. We show examples for measurements at the SNAP, VISION and CORELLI beamlines of the SNS. [ABSTRACT FROM PUBLISHER]

We report a systematic first-principles density functional theory study on the pressure dependence of the structural parameters, elastic constants and related properties and thermodynamic properties of the complex transition metal hydrides Mg2OsH6, Ca2OsH6, Sr2OsH6and Ba2OsH6. The calculated structural parameters are in excellent agreement with the existing data in the scientific literature. The single-crystal elastic constants and related properties were predicted using the stress–strain method. The elastic moduli of the polycrystalline aggregates were evaluated via the Voigt–Reuss–Hill approach. The dependences of the lattice parameter, bulk modulus, volume thermal expansion coefficient, isobaric and isochoric heat capacity and Debye temperature on the pressure and temperature, ranging from 0 to 15 GPa and from 0 to 1000 K, respectively, were investigated using the quasi-harmonic Debye model in combination with first-principles calculations. [ABSTRACT FROM PUBLISHER]

The polycrystalline electro ceramic of composition Ba5CaTi2-xCuxNb8O30(x = 0.0, 0.02) is synthesized using high-temperature solid state reaction technique. The synthesized ceramics studied for their structural and ferroelectric properties. X-ray diffraction (XRD) analysis reveals the formation of single-phase compound structure at room temperature with tetragonal tungsten bronze structure. Scanning electron microscope (SEM) depicts that the compound has well defined grains. The average grain size of the compound is observed in range (∼5 to 8 μm). The ferroelectric nature has been confirmed by recording polarization–electric field hysteresis loop. Raman Spectra at room temperature used to study the internal lattice properties of the ceramics. [ABSTRACT FROM PUBLISHER]

Potassium sodium niobate (KNN) ceramics were prepared by solid state synthesis followed by liquid phase sintering using V2O5as a sintering aid. Sintering at 1120 ºC for 4 hours using V2O5caused significant improvement in relative density with maximum relative density reaching to more than 94%. Dense polycrystalline ceramics having grain size about 2 µm were obtained as a result of liquid phase sintering. Gradual improvement in dielectric constant was observed with increase in V2O5content coupled with increase in electrical conductivity. Maximum remnant polarization of 18 µC/cm2was recorded for ceramic sintered with 5 wt% V2O5. [ABSTRACT FROM PUBLISHER]

Electrical and optical studies have been carried out on aluminium-modified Ge2Sb2Te5 thin films to check its applicability as an active material in optical and electrical memory storage devices. Five polycrystalline bulk samples were prepared with compositions: Alx(Ge2Sb2Te5)1-x; x = 0, 0.08, 0.14, 0.21, 0.25. Amorphous thin films were deposited from the polycrystalline bulk by thermal evaporation. Temperature-dependent resistance shows the increase in crystallization temperature of Ge-Sb-Te films on aluminium addition. Activation energy for conduction, conductivity, optical band gap, coefficient of refraction and extinction coefficient are studied with respect to Al content in both amorphous and crystalline phases of Ge-Sb-Te alloy films. [ABSTRACT FROM AUTHOR]

Polycrystalline (1-x)BT-xBFN ceramics (x = 0, 0.02, 0.04, 0.06, 0.08) were synthesized in single perovskite phase by solid state reaction route. 1100°C/4 hours and 1250°C/4 hours were optimized as the calcination and sintering temperatures, respectively. XRD study revealed the absence of any secondary phase peaks with tetragonal structure in all the studied ceramics. Grain size initially decreased and then increased with the increase of BFN content. Maximum value of dielectric constant (3980) at room temperature with low temperature coefficient of capacitance (from RT to 70°C) was obtained in x = 0.06 ceramics. Polarization vs. electric field (P-E) study confirmed the ferroelectric nature of the studied ceramics. [ABSTRACT FROM AUTHOR]

Pure ZnO and Cu-doped ZnO thin films were prepared by successive ionic layer adsorption and reaction method with a Copper concentration of 0·05 and 0·1 mol%. The X-ray diffraction pattern confirmed that the films were polycrystalline in nature with a hexagonal wurtzite structure. The Scanning Electron Microscopy revealed a rod-like shaped grains and the compositional analysis confirmed the presence of Zn, O and Cu in the films. Atomic Force Microscopy and Ultra violet spectroscopy revealed that the surface roughness and band gap values of the films decreases with the increase of copper concentration. The presence of functional groups and chemical bonding was confirmed by infra spectra. Photo luminescence spectra showed that the intensity of the UV emission increases and green emission decreases with the increase of copper concentrations which confirmed the substitution of Cu into the ZnO lattice. [ABSTRACT FROM AUTHOR]

By applyingab initiocalculation within density functional theory (DFT), we study the structure parameters, electronic band structure, elastic coefficients, polycrystalline elastic properties, anisotropy factors and Debye temperature of ferroelectric and paraelectric phases of LiTaO3within the generalised gradient approximation at ambient pressure. The atomic structure in both phases is fully relaxed and the lattice constant, angle and atomic positions are well consistent with experimental values. The computed single-crystal elastic coefficients indicate that mechanical stability of LiTaO3in both phases is confirmed using the generalised Born criteria. The shear, bulk and Young’s modulus, Poisson’s ratio, and Vickers hardness were computed according to theoretical elastic constants by Voight–Reuss–Hill method. Several anisotropy factors and indexes are computed to illustrate mechanical anisotropy. Both phases are shown to be weakly anisotropic. The Debye temperature is estimated using the longitude and transverse elastic wave velocity of the ideal polycrystalline LiTaO3aggregates. We have found that LiTaO3in both phases has an indirect energy band gap. The differences in the electronic structure and density of states for both phases are quite small. Our results indicate that the mechanical and bonding properties of both phases are very similar. The obtained results were compared with the available experimental and theoretical values. [ABSTRACT FROM PUBLISHER]

We present the results of studies on the dielectric properties of polycrystalline Bi1-xCaxFeO3(x = 0.05, 0.10, 0.20) (BCFO) multiferroics. Rietveld refined XRD patterns confirm the single phasic nature of 5% & 10% Ca – doped samples crystallizing in superimposed R3c (Rhombohedral) + Pm 3m (Cubic) space group symmetry while 20% Ca – doped sample crystallize in Pm 3m symmetry. Frequency and temperature dependent dielectric constant (ϵ) studies show the contribution of grain and grain boundaries in the system. Complex impedance graph exhibits a single semicircular arc for all the samples, indicating the contribution of grain interior (bulk) property of the material. [ABSTRACT FROM AUTHOR]

The unique dielectric properties of CaCu3Ti4O12(CCTO) are a promising feature for capacitor applications. Polycrystalline Ca0.95Nd0.05Cu3Ti3.95Zr0.05O12ceramic was synthesized via conventional solid state method. XRD and Rietveld studies confirmed that crystal structure is cubic with space group Im3. Microstructural study by scanning electron microscopy (SEM) suggests that the compound has some abnormal grains embedded with small grains depict inhomogeneous microstructure. The dielectric properties were analyzed in frequency range from 100 Hz to 5 MHz at different temperatures. A giant dielectric constant (∼19,426) with minimal loss tangent (∼0.067 at 1 KHz) at room temperature is achieved in studied composition. [ABSTRACT FROM AUTHOR]

Polycrystalline yttrium iron manganites – YMn1-xFexO3(with x = 0.0, 0.1, 0.15, 0.20) were synthesized by ceramic method and sol-gel auto-combustion method. XRD confirmed the formation of hexagonal phase in all samples. The hexagonal a– and c- parameters for the samples prepared by the sol-gel method are found to be closer to the stoichiometric values. The room temperature frequency variation of electrical properties such as dielectric constant, dielectric loss and ac conductivity showed a dispersive behavior for all the samples. The values of dielectric constant and dielectric loss are found to be lower for the sol-gel prepared samples. [ABSTRACT FROM AUTHOR]

Effect of sintering temperature on the leakage current of polycrystalline multiferrioc DyFeO3material is reported. Samples were synthesized through Sol-Gel route. From the Rietveld refinement of X-Ray Diffraction (XRD) data it is observed that, samples were found to be of single phase. From the room temperature leakage current density study, it was observed that leakage current density decreases with increase of sintering temperature and Space charge limited conduction (SCLC) and Ohmic conduction mechanisms are dominant at lower and higher electric field values. The observations are corroborated in terms of microstructure changes with sintering temperature. [ABSTRACT FROM AUTHOR]

Lanthanide ions doped lithium niobate has many outstanding performances in upconversion (UC) emission. However, the low UC efficiency still constitutes the main limitation for practical applications. To improve the issue of low efficiency, whether visible green UC emission in holmium/ytterbium/lithium niobate can be improved through tridoping with 0, 2, 4, 6, 8, and 10 mol% potassium has been investigated. The results demonstrate that increasing the concentration of potassium ion enhances the fluorescence signal by 20 times of visible green UC emission and that the maximum fluorescence signal can be achieved at 8 mol%. Theoretical analysis, arising from the steady-state rate equations, proves that the enhancement of green UC fluorescence signal is due to the increased lifetime of the intermediate (5I6) state of the holmium ion and excited (5F5/2) state of the ytterbium ion. [ABSTRACT FROM PUBLISHER]

Yttria-tetragonal zirconia polycrystal (Y-TZP) ceramic with hydroxyapatite (HA) coating has been recognized as one of the most common biomaterials. However, its lower interfacial bonding strength has restricted its clinical application. In this study, CaCO3, Ca3(PO4)2(TCP), and Ag were added into the interface of the HA coating and Y-TZP substrate by a pressureless sintering process to increase interfacial bonding strength. The morphology and microstructure of the interlayers were analyzed by scanning electronic microscope. The results show that the comprehensive performances of HA/interlayer/ZrO2biomaterials were much better than that of the sample without interlayer, and the shear and tensile strengths of the HA/CaCO3/ZrO2biomaterial reached 15.19 and 16.88 MPa, respectively, which were higher than those of TCP and Ag. The CaZrO3and carbonated apatite, formed by decomposed products of CaCO3and HA reacting with ZrO2at the interface under sintering, increased the mechanical properties of the biomaterial. [ABSTRACT FROM AUTHOR]

This research work is to study the comparison between a response surface methodology (RSM) and artificial neural network (ANN) in the modelling and prediction of delamination factor during endmilling of glass fibre reinforced polymer (GFRP) composites. Aiming to achieve this goal, several milling experiments were performed with polycrystalline diamond inserts at different machining parameters namely feed rate, cutting speed, depth of cut and fibre orientation angle. Mathematical model is created using central composite face centred second-order in RSM and the adequacy of the model was verified using analysis of variance. ANN model is created using back propagation algorithm. With regard to the machining test, it was observed that feed rate is the dominant parameter that affects the delamination factor followed by the fibre orientation. The comparison results show that models provide accurate prediction of delamination factor in which ANN perform better than RSM. The data predicted from ANN is very nearer to experimental results compared to RSM, therefore we can use this ANN model to determine the delamination factor for various FRP composites and also for various machining parameters. [ABSTRACT FROM PUBLISHER]

Using first principles methods, we calculated the entire-surface of the first-order pyramidal planes in-titanium. Slip on these planes involving dislocations with-type Burgers vectors is one means by which-titanium polycrystals may supplement slip on prism planes with-type Burgers vectors to maintain ductility. We find one low energy and one high energy stacking fault with energies of 163 and 681 , respectively. Contrary to previous suggestions, we do not find a stable stable stacking fault at. [ABSTRACT FROM PUBLISHER]

The effect of thermomechanical processing on microstructure evolution and room temperature flow behaviour of polycrystalline magnesium in compression at strain rates of ~10−2and ~103s−1was investigated. Different initial microstructures were produced by optimising rolling and annealing cycles. Prior to annealing for 1 h at 350 °C, Mg samples were processed by two different treatments such as (i) hot rolling at 350 °C and (ii) hot rolling at 350 °C plus cold rolling at room temperature. Introduction of cold working step led to an increased fraction of hard oriented grains with a marginal grain size difference in post-annealed samples. A profound effect of thermomechanical processing on strain hardening rate as well as rate-sensitive flow behaviour of Mg was observed. The influence of prior processing history and strain rate on flow behaviour of Mg was clearly reflected in terms of texture strengthening/weakening phenomena and formation of microstructural deformation bands. [ABSTRACT FROM AUTHOR]

Polycrystalline bulk materials are ubiquitous in everyday life, including biological, geological, and engineered structural and functional materials. Their fundamental units are individual grains, which are characterized by their microstructure; i.e., the arrangement of lattice defects. The microstructure usually influences the materials properties critically. [ABSTRACT FROM AUTHOR]