Effect of structural anisotropy on the dislocation nucleation and evolution in 6HSiC under nanoindentation

Single crystalline 6HSiC possesses complex microstructure and its deformation is strongly anisotropic. With the aid of molecular dynamics analysis, this paper investigated the dislocation nucleation and evolution in 6HSiC under nanoindentation on three major planes, i.e., $\left(0001\right)$, $\left(01\overline{1}0\right)$ and $\left(2\overline{1}\overline{1}0\right)$. It was found that the half loops of prismatic dislocations could form during the nanoindentation on the $\left(0001\right)$plane, while the prismatic dislocation loops emerged on the $\left(01\overline{1}0\right)$ and $\left(2\overline{1}\overline{1}0\right)$planes. Further analysis revealed that the half loops were generated via the interaction of the nucleated dislocations in the basal plane and the first prismatic planes $\left\{01\overline{1}0\right\}$; while the formation of the prismatic loops can be attributed to either the “lasso”-like mechanism or the combination of dislocation interaction and “lasso”-like mechanism. Such strong effect of structural anisotropy was clarified through the generalised stacking fault (GSF) energy surface and stress distribution.     

Transport properties in spinel ferrite/graphene oxide nanocomposites for electromagnetic shielding

Herein, $\left({\text{Co}}_{0.5}{\text{Ni}}_{0.5}\right){\text{Cr}}_{0.3}{\text{Fe}}_{1.7}{\text{O}}_4$/graphene oxide nanocomposites were fabricated by ultrasonication technique, using pure spinel ferrite and graphene oxide synthesized by sol-gel method and modified Hummers' method, respectively. The effect of graphene incorporation with ferrite nanoparticles was studied by X-ray diffraction (XRD), electrical and dielectric measurements. XRD analysis revealed the spinel phase for the ferrite sample and confirmed the formation of graphene oxide. The crystallite size was found in the range of $37-43\text{ nm}$ and the porosity increased with the increase in the concentration of graphene oxide in the composites. The DC electrical resistivity of spinel ferrite was found equal to $3.83\times {10}^9\text{ Ω}.\text{cm}$ and it substantially decreased with the increase in the percentage of graphene oxide at room temperature. The real and imaginary part of relative permittivity followed the Maxwell-Wagner type of interfacial polarization. AC conductivity confirmed the conduction by hopping mechanism and increased on increasing the GO content. The coupling of magnetic ferrite with graphene oxide tunes the magneto-electrical properties for potential applications at high frequencies.     

Proton mobility in Ruddlesden–Popper phase H2La2Ti3O10 studied by 1H NMR

To study protons localization in H_1.83K_0.17La₂Ti₃O₁₀·0.17H₂O and their motional characteristics, complementary Nuclear Magnetic Resonance (NMR) techniques have been applied. ¹H Magic Angle Spinning NMR evidences the presence of different proton containing species. By analyzing the temperature dependence of the ¹H MAS NMR spectrum we attribute the observed lines to interlayer H⁺ in regular sites (isolated and in water rich environment), water protons and protons from various defects. The temperature behaviors of the spectral lines intensities and widths point out that intercalated water molecules are involved in translational motion that is confirmed by spin lattice relaxation rate ($R_1$) and spin-lattice relaxation rate in rotating frame ($R_{1\rho }$) measurements. It has been shown that for a correct determination of the proton motional parameters the Kohlrausch-Williams-Watts correlation function must be used. Its application results in the following parameters of proton motion in the interlayer space of H_1.83K_0.17La₂Ti₃O₁₀·0.17H₂O: $E_{\mathrm{a}}$?=?0.194(2) eV, $\mathrm{\beta }$?=?0.28(1), ${\tau }_0=6.2(1)\times {10}^{?10}$?s.     

Investigation on the structural,multiferroic and magnetoelectric properties of BaTi1-xNixO3 ceramics

In this paper, we report the influence of Ni doping on the structural, electrical, magnetic and magnetoelectric properties of BaTiO₃ (BTO) ceramics. X-ray diffraction (XRD) analysis indicates a phase transition from tetragonal to hexagonal at x?=?2.5?mol%. Further, XRD data has been refined using Rietveld method to extract the phase formation, lattice parameters, and the phase fraction of BaTi_1-xNi_xO₃ $\left(\mathrm{BTNO}\right)(0\le x\le 10\mathrm{mol}\%)$ ceramics. The ferroelectric polarization decreases with Ni doping concentration. The relative permittivity of BTNO compositions decreases while the corresponding dielectric loss increases with Ni doping concentration. Room temperature magnetic hysteresis (M-H) loop of all BTNO samples exhibit ferromagnetic nature with a saturated loop except for x?=?2.5?mol% Ni doping concentration. At x?=?2.5?mol% Ni doping concentration, a small amount of diamagnetism is observed at higher fields along with ferromagnetism. The origin of ferromagnetism is due to the F- center exchange interaction via oxygen vacancies. The highest remnant magnetization (M_r) is 11.76 memu/g for x?=?10?mol%. The Magnetodielectric coefficient (MD) and magnetoelectric coefficient (ME) gradually increases with increasing Ni doping concentration, and are 1.72% and 4.51 $\mathrm{mV}{\mathrm{cm}}^{?1}{\mathrm{Oe}}^{?1}$ respectively for x?=?10?mol%.     

Molecular dynamics study of a macromolecular model of hydrous sodium aluminosilicate geopolymer with charge balancing by extra-structural aluminum for prediction of its properties

Geopolymer is a material with unique properties and has various uses. This substance is mainly amorphous, and its qualitative characteristics are related to its binder phase that is called the hydrous sodium aluminosilicate geopolymer. The molecular structural model of this geopolymer includes ${\text{Q}}^4\left(4\text{Al}\right),{\text{Q}}^4\left(3\text{Al}\right),{\text{Q}}^4\left(2\text{Al}\right)$, and ${\text{Q}}^4\left(1\text{Al}\right)\text{Si}$ units, which have been balanced in terms of electric charge by extra-framework $\text{Al}$ and ${\text{Na}}^{+}$ ions. In this study, we calculated the density, Young's modulus, and RDF curve of the geopolymer from the molecular dynamics simulation. The results of the simulation were in good agreement with the results of the laboratory obtained from several studies.     

Microstructure development in (Co,Ta)-doped SnO2-based ceramics with promising varistor and dielectric properties

Following the $\mathit{3}Sn{\mathit{(}IV\mathit{)}}_{Sn\mathit{(}IV\mathit{)}}^{\times }\leftrightharpoons Co{\mathit{(}II\mathit{)}}_{Sn\mathit{(}IV\mathit{)}}^{\mathrm{″}}+2Ta{\mathit{\left(}V\mathit{\right)}}_{Sn\mathit{(}IV\mathit{)}}^{\cdot }$ charge compensation mechanism we optimized densification and electrical properties of Ta₂O₅-doped SnO₂–CoO ceramics. We show that incorporation of acceptor dopant Co²⁺ in SnO₂ is promoted after the addition of donor dopant like Ta⁵⁺, whereas any surplus of Co would form secondary Co₂SnO₄ phase. A balanced addition of both dopants is needed to promote densification, and any surplus of donor dopants that remain present at the grain boundaries retard the grain growth and deteriorate electrical properties. Varistor and dielectric properties are then strongly influenced by donor doping. Optimum varistor properties (α = 40, U_T = 272 V/mm, I_L = 1.2 μA) were measured for the sample with 1 mol% Ta₂O₅ and the best dielectric properties (ε = 6525; tan(δ) = 0.057@1kHz) were measured for the sample with 0.10 mol% Ta₂O₅ with the largest SnO₂ grain sizes.     

Comparison of theoretical and experimental microhardness of tetrahedral binary Zn1-xErxO semiconductor polycrystalline nanoparticles

${\mathrm{Zn}}_{1?\mathrm{x}}{\mathrm{Er}}_{\mathrm{x}}\mathrm{O}$ polycrystalline nanoparticles with various compositions $(x=0.01,0.02,0.03,0.04,0.05,$ and $0.10)$were prepared using sol–gel techniques, for which zinc acetate dihydrate and erbium 2–4 pentanedionate are used as precursors. Nanoparticles were pressed under a pressure of $4$?tons for $5$?min into disk-shaped compacts with 2?mm thicknesses and 10?mm diameters. The pressed samples were annealed at 400?°C for $30$?min. X-ray diffraction (XRD), scanning electron microscopy (SEM), and Vickers microhardness analyses of the produced Er-doped $\mathrm{ZnO}$ bulk nanomaterials were performed. Specifically, in this study we focused on the analysis of their mechanical properties. Undoped and Er-doped bulk samples were investigated according to Meyer's law; the proportional sample resistance (PSR), elastic/plastic deformation (EPD), and indentation-induced cracking (IIC) models; and the Hays–Kendal (HK) approach. As a result, the IIC model was more suitable to determine the micromechanical properties and the reverse indentation size effect ($\mathrm{R}\mathrm{ISE}$) behavior of Er-doped $\mathrm{ZnO}$ semiconductors.     

Enhancing pyroelectric properties in (Pb1–1.5xLax)(Zr0.86Ti0.14)O3 ceramics through composition modulated phase transition

Currently, there is an urgent need of extraordinary comprehensive pyroelectric materials for the wide application in detectors and energy harvesters. In this study, the (Pb_1–1.5xLa_x)(Zr_0.86Ti_0.14)O₃ (abbreviated as PLZT, x?=?0.02, 0.03, 0.04 and 0.05) ceramics located in ferroelectric-antiferroelectric (FE-AFE) phase boundary were designed and synthesized by using conventional solid-state reaction method. The microstructures, phase structures, dielectric, ferroelectric, thermal depolarization and pyroelectric properties of the PLZT ceramics with different La content were investigated thoroughly. The XRD results show that the PLZT ceramics change from FE phase to AFE phase with increasing La content. The significant improvement of pyroelectric coefficient $p$ and figures of merit (FOMs) are achieved in the PLZT ceramics with the increase in La content because of the increased metastable ferroelectric phase under the application of electric field. The (Pb_0.955La_0.03)(Zr_0.86Ti_0.14)O₃ (x?=?0.03) ceramic exhibits not only high $p$ of $5.2\times {10}^{?8}\mathrm{C}/{\mathrm{cm}}^2\mathrm{K}$ and high depolarization temperature (T_d) of 179?℃ but also excellent FOMs with $F_i=2.2\times {10}^{?10}\mathrm{m}/\mathrm{V}$, $F_v=5.0\times {10}^{?2}{\mathrm{m}}^2/\mathrm{C}$, and $F_d=3.47\times {10}^{?5}{\mathit{Pa}}^{?1/2}$. In addition, the highest $p$ of $6.8\times {10}^{?8}\mathrm{C}/{\mathrm{cm}}^2\mathrm{K}$ is achieved in (Pb_0.94La_0.04)(Zr_0.86Ti_0.14)O₃ (x?=?0.04) ceramic. These results demonstrate that the PLZT ceramics of x?=?0.03 and 0.04 are promising candidates for pyroelectric applications.