Hexagonal Lattice Parameters Research Articles

Synthesis of titanium diboride by electric arc plasma in air

The paper reports data that demonstrate the feasibility of vacuum-free electric arc synthesis of titanium diboride. An optimal energy mode was found to synthesize submicron titanium diboride powder with the hexagonal lattice parameters a = 3.03 ± 0.04 Å, c = 3.23 ± 0.04 Å with no impurity crystal phases in its composition. A bulk ceramic sample with relative density of 99.1 % and hardness of 18 GPa was consolidated from the synthesized powder. The powder and bulk ceramic samples were analyzed by scanning electron microscopy and transmission electron microscopy. Structure of the synthesized material has a positive effect on the densification of the material. The sintered grains already formed in the process of synthesis under the influence of external pressure and heating from the current flow sinter each other, forming a single target structure with a minimum number of pores, of oxide impurities. Raman spectroscopy was employed to analyze the homogenized precursor mixture, synthesized powder, and TiB2-based bulk ceramic sample. The obtained Raman spectrum of sintering powder is characteristic of TiB2-based materials with a low concentration.

Wafer-scale development, characterization, and high temperature stabilization of epitaxial Cr2O3 films grown on Ru(0001).

This work outlines conditions suitable for the heteroepitaxial growth of Cr2O3(0001) films (1.5-20nm thick) on a Ru(0001)-terminated substrate. Optimized growth is achieved by sputter deposition of Cr within a 4mTorr Ar/O2 20% ambient at Ru temperatures ranging from 450 to 600 °C. The Cr2O3 film adopts a 30° rotated honeycomb configuration with respect to the underlying Ru(0001) substrate and exhibits a hexagonal lattice parameter consistent with that for bulk Cr2O3(0001). Heating to 700 °C within the same environment during film preparation leads to Ru oxidation. Exposure to temperatures at or above 400 °C in a vacuum, Ar, or Ar/H2 3% leads to chromia film degradation characterized by increased Ru 3d XPS intensity coupled with concomitant Cr 2p and O 1s peak attenuations when compared to data collected from unannealed films. An ill-defined but hexagonally well-ordered RuxCryOz surface structure is noted after heating the film in this manner. Heating within a wet Ar/H2 3% environment preserves the Cr2O3(0001)/Ru(0001) heterolayer structure to temperatures of at least 950 °C. Heating an Ru-Cr2O3-Ru heterostacked film to 950 °C within this environment is shown by cross-sectional scanning/transmission electron microscopy (S/TEM) to provide clear evidence of retained epitaxial bicrystalline oxide interlayer structure, interlayer immiscibility, and epitaxial registry between the top and bottom Ru layers. Subtle effects marked by O enrichment and O 1s and Cr 2p shifts to increased binding energies are noted by XPS in the near-Ru regions of Cr2O3(0001)/Ru(0001) and Ru(0001)/Cr2O3(0001)/Ru(0001) films after annealing to different temperatures in different sets of environmental conditions.

SYNTHESIS OF A SILICON CARBIDE FROM NATURAL RAW MATERIAL IN A SOLAR FURNACE

In this study, the processes involved in synthesis of silicon carbide (SiC) from a natural mineral raw material (diatomite mixed with coke) were investigated. The initial material mixture was placed in a graphite crucible installed on the focal zone of a large solar furnace. High-temperature heating was carried out using a stream of concentrated high-density solar radiation (200-300 W/cm<sup>2</sup>). After irradiating the material sample with the concentrated solar radiation, the crucible was cooled arbitrarily for 30 minutes. The synthesized material contained three phases: β-SiC with a cubic crystalline lattice and lattice parameter of 0.436 nm; α-SiC with a hexagonal crystalline lattice and lattice parameters of a = 0.307 nm and c = 1.511nm; and graphite with a hexagonal crystalline lattice. The SiC material obtained in the solar furnace in a freshly sintered state showed high refractoriness (up to 1650°C), while the material fired at 1550°C showed refractoriness up to 1580°C.

Entropy change reversibility in MnNi1−x Co x Ge0.97Al0.03 near the triple point

The nature of the phase transition has been studied in MnNi1−x Co x Ge0.97Al0.03 (x= 0.20–0.50) through magnetization, differential scanning calorimetry and x-ray diffraction measurements; and the associated reversibility in the magnetocaloric effect has been examined. A small amount of Al substitution for Ge can lower the structural phase transition temperature, resulting in a coupled first-order magnetostructural transition (MST) from a ferromagnetic orthorhombic to a paramagnetic hexagonal phase in MnNi1−x Co x Ge0.97Al0.03. Interestingly, a composition-dependent triple point (TP) has been detected in the studied system, where the first-order MST is split into an additional phase boundary at higher temperature with a second-order transition character. The critical-field-value of the field-induced MST decreases with increasing Co concentration and disappears at the TP (x= 0.37) resembling most field-sensitive MST among the studied compositions. An increase of the hexagonal lattice parameter a hex near the TP indicates a lattice softening associated with an enhancement of the vibrational amplitude in the Ni/Co site. The lattice softening leads to a larger field-induced structural entropy change (structural entropy change≫ magnetic entropy change, for this class of materials) with the application of a lower field, which results in a larger reversibility of the low-field entropy change (|ΔS rev| = 6.9 J kg−1 K for Δμ 0 H = 2 T) at the TP.

Growth, physico-chemical properties, opto-electrical characteristics, thermo-mechanical and DFT studies of 4-aminoantipyrine single crystals

The aim of this work was to grow organic single crystals of 4-Aminoantipyrine (4-AAP) under ambient conditions, using a solvent slow evaporation method, and then to investigate the crystal structure, optical band gap, optical transmittance behavior, second harmonic generation efficiency, thermal stability, material rigidity, and dielectric responses for opto-electrical based device applications. The powder X-ray diffraction (XRD) and single crystal XRD analyzes revealed the hexagonal crystal structure and lattice parameter values of the as-grown 4-AAP. The respective molecular vibration bands and functional groups of the as-grown 4-AAP were identified using the experimental and theoretical FT-IR analysis. The optical absorption and transmittance spectrum of the 4-AAP single crystals revealed good transparency throughout the visible region. The non-linear optical (NLO) characteristics of the 4-AAP crystals were tested using the Kurtz and Perry powder technique. Thermal gravimetric (TGA) and differential thermal analysis (DTA) were used on the as-grown crystals, to determine their weight loss and heat absorption/release process. The hardness vs load plot can be used to determine the hardness values and response of the hard as-grown 4AAP crystals under the influence of load. The electrical conductivity and dielectric behavior of the 4-AAP crystals changed as the applied frequency increased. Computational techniques were used to investigate the 4-AAP's optimized geometrical structure, theoretical optical band, molecular electrostatic potential, and Mulliken atomic charge population.

Enhancement of Exchange Bias and Perpendicular Magnetic Anisotropy in CoO/Co Multilayer Thin Films by Tuning the Alumina Template Nanohole Size.

The interest in magnetic nanostructures exhibiting perpendicular magnetic anisotropy and exchange bias (EB) effect has increased in recent years owing to their applications in a new generation of spintronic devices that combine several functionalities. We present a nanofabrication process used to induce a significant out-of-plane component of the magnetic easy axis and EB. In this study, 30 nm thick CoO/Co multilayers were deposited on nanostructured alumina templates with a broad range of pore diameters, 34 nm ≤ Dp ≤ 96 nm, maintaining the hexagonal lattice parameter at 107 nm. Increase of the exchange bias field (HEB) and the coercivity (HC) (12 times and 27 times, respectively) was observed in the nanostructured films compared to the non-patterned film. The marked dependence of HEB and HC with antidot hole diameters pinpoints an in-plane to out-of-plane changeover of the magnetic anisotropy at a nanohole diameter of ∼75 nm. Micromagnetic simulation shows the existence of antiferromagnetic layers that generate an exceptional magnetic configuration around the holes, named as antivortex-state. This configuration induces extra high-energy superdomain walls for edge-to-edge distance >27 nm and high-energy stripe magnetic domains below 27 nm, which could play an important role in the change of the magnetic easy axis towards the perpendicular direction.

Hierarchically porous and mechanically stable monoliths from ordered mesoporous silica and their water filtration potential.

Mechanically stable structures with interconnected hierarchical porosity combine the benefits of both small and large pores, such as high surface area, pore volume, and good mass transport capabilities. Hence, lightweight micro-/meso-/macroporous monoliths are prepared from ordered mesoporous silica COK-12 by means of spark plasma sintering (SPS, S-sintering) and compared to conventionally (C-) sintered monoliths. A multi-scale model is developed to fit the small angle X-ray scattering data and obtain information on the hexagonal lattice parameters, pore sizes from the macro to the micro range, as well as the dimensions of the silica population. For both sintering techniques, the overall mesoporosity, hexagonal pore ordering, and amorphous character are preserved. The monoliths' porosity (77–49%), mesopore size (6.2–5.2 nm), pore volume (0.50–0.22 g cm−3), and specific surface area (451–180 m2 g−1) decrease with increasing processing temperature and pressure. While the difference in porosity is enhanced, the structural parameters between the C-and S-sintered monoliths are largely converging at 900 °C, except for the mesopore size and lattice parameter, whose dimensions are more extensively preserved in the S-sintered monoliths, however, coming along with larger deviations from the theoretical lattice. Their higher mechanical properties (biaxial strength up to 49 MPa, 724 MPa HV 9.807 N) at comparable porosities and ability to withstand ultrasonic treatment and dead-end filtration up to 7 bar allow S-sintered monoliths to reach a high permeance (2634 L m−2 h−1 bar−1), permeability (1.25 × 10−14 m2), and ability to reduce the chemical oxygen demand by 90% during filtration of a surfactant-stabilized oil in water emulsion, while indicating reasonable resistance towards fouling.

The formation of strontium apatites through alkaline hydrolysis of strontium hydrogen phosphate and their crystallographic characterization

Pure and carbonate- or silicate-substituted strontium apatites (i.e., SrHAP, SrCAP and SrSiP) were synthesized via alkaline hydrolysis of strontium hydrogen phosphate using sodium hydroxide, carbonate, and metasilicate, respectively. Zinc substitution in SrSiP was performed by an ion exchange reaction to yield SrZnSiP. Characterization of these strontium apatites was carried out by powder XRD, Fourier-transform infrared (FTIR) spectroscopy, Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), SEM- Energy dispersive X-ray spectroscopy (EDS), FE-SEM and TEM- Selected Area Electron Diffraction (SAED). From elemental analyses, the Sr/P ratios of all samples were found to be around 1.5, suggesting that these are strontium-deficient apatites. From FTIR analysis, presence of both the structural OH group and the HPO4 group could not be confirmed. Crystal morphology strongly depends on the pH during sample preparation. At high pH, bundles of spindle-like nanocrystalline SrHAP, SrSiP and SrZnSiP were produced, whereas at lower pH, cubical crystallite of SrCAP with increased crystallinity was formed. Powder XRD analysis revealed the effects of these substituents on the hexagonal lattice parameters which agreed well with the known dependence for the corresponding substituted hydroxyapatite. The relationship between the lattice parameters a and c for calcium to barium hydroxyapatite groups collected from various studies together with our data, showed a universal linear relationship represented by the following equation, c = 1.1348a −3.8043 with a coefficient of determination (R2) of 0.9982. Dissolution behavior of SrZnSiP in pure water was investigated by the surface coating on β-TCP disc. For over 24 days, Sr, Si and Zn ions were released constantly within moderate concentration ranges.

Ga-, Y-, and Sc-substituted M-type ferrites for self-biasing circulators in LTCC microwave modules

The partial substitution of Fe3+ by diamagnetic Me3+ in BaMexFe12-xO19 with Me = Ga and Y (0 ≤ x ≤ 2) was studied. Samples were synthesized by the mixed-oxide route and their properties were compared to BaScxFe12-xO19 ferrites. It was shown by XRD that the hexagonal lattice parameters with x for Me = Ga and Sc vary continuously. For Me = Y no single-phase ferrites were obtained indicating that the solubility limit for Y in Ba ferrite is very limited. For Me = Ga and Sc, the saturation magnetization at room temperature is reduced with x. The coercivity as well as the ferromagnetic resonance frequency remain almost unchanged for Ga-substituted ferrites, whereas for Sc-substituted ferrites the coercivity and ferromagnetic resonance frequency decrease with x. Thick films of Sc-ferrite (x = 0.5) were screen-printed onto LTCC tape substrates and post-fired at 900°C. Application of a magnetic field during drying allows fabrication of textured ferrite layers. Alternatively, ferrite tapes and LTCC tapes were successfully co-fired at 900°C.

In situ synthesis of B4C–SiC, B4C–TiB2, and B4C–ZrB2 composites from organic–inorganic hybrid precursor via a simple bottom-up approach

Boron carbide (B4C) and its in situ composites were synthesized via a simple bottom-up process using low-cost boric acid and a sucrose-based precursor solution with silicon (Si), titanium (Ti), or zirconium (Zr) species. The precursor solution was first dried at 250 °C and then heat-treated at 1650 °C for 90 min under argon and hydrogen gas flow. Free boron oxide phases appeared in the boric acid-rich precursor compositions, whereas free carbon appeared in the sucrose-rich compositions. The B4C particles exhibited a coarser and elongated morphology with boron-rich stoichiometric compositions (B/C:4/1), whereas the particles had a finer equiaxed morphology in carbon-rich compositions (B/C:2/1). As the carbon concentration increased in the precursor solution, the hexagonal lattice parameters of B4C and its corresponding lattice volume decreased. On the other hand, the addition of Si, Ti, or Zr species into the precursor solution resulted in the formation of a silicon carbide (SiC), a titanium diboride (TiB2), or a zirconium diboride (ZrB2) phase along with the B4C phase and was associated with an overall reduction in the average particle size and a more uniform size distribution. Moreover, the addition of these species increased the B4C lattice parameter with a corresponding increase in the lattice volume; this was most likely due to an elemental substitution into the B4C lattice. In addition, the data provide evidence that the formation of an ideal B4C lattice is possible when synthesized from carbon-rich precursors using this method, despite the potential presence of free carbon.

Structural and Optical Properties of Indium Selenide (InSe) Thin Films Deposited on Glass and GaSe Single Crystal Substrates by SILAR Method

Structural, morphological and optical properties of undoped and boron doped Indium Selenide (InSe) thin films grown on glass and layered Gallium Selenide (GaSe) single crystal substrates with SILAR method have been investigated by XRD, AFM and UV-Vis spectrophotometer techniques. XRD measurements showed that the crystal structure of InSe thin films grown on glass substrates were hexagonal P61 γ-In2Se3 with lattice parameters a=7.1286 Å, c=19.382 Å and z=6 while the InSe thin films grew as hexagonal P63/mmc InSe with lattice parameters a=4.005 Å, c=16.640 Å and z=4 on GaSe single crystal substrates. The AFM images showed that average particle sizes of undoped and boron doped InSe thin films were found to be varying between 26.5-60.2 nm and 30.9-101.5 nm grown on glass and GaSe single crystal substrates, respectively. The optical absorption spectra of undoped and boron doped InSe thin films grown on both glass and GaSe single crystal substrates showed absorption maxima around the 2.00 and 2.24 eV, respectively. The calculated Urbach energies of the InSe thin films grown on glass substrates were found bigger than those of the InSe thin films grown on GaSe single crystal substrates.

Strengthening of columnar hexagonal phase of a room temperature discotic liquid crystalline material by using ferroelectric barium titanate nanoparticles

A discotic liquid crystalline (DLC) material possessing a wide room temperature columnar hexagonal phase has been used as a polymeric matrix to disperse ferroelectric barium titanate nanoparticles at the concentrations of 0.5 wt% and 1.0 wt% respectively. The influence of nanoparticles on the discotic liquid crystal has been studied with the help of Differential Scanning Calorimetry, impedance spectroscopy, polarizing optical microscopy and Ultraviolet-Visible spectroscopy. Small angle X-ray scattering (SAXS) measurements have also been performed. Thermal measurements reveal stabilization of the columnar hexagonal phase due to the addition of ferroelectric nanoparticles in the discotic system. Permittivity is decreasing due to the formation of anti-dipolar ordering in the presence of ferroelectric nanoparticles. A relaxation mode is visible in the high kHz to low MHz region. The relaxation frequency has been found to decrease with the incarceration of barium titanate nanoparticles in DLC. A shift in UV–Vis absorption/transmittance spectra indicates modification in the electronic structure and hence physical property of the nanocomposites. SAXS explains the variation of different hexagonal lattice parameters with respect to the temperature.

An average structure model of the intermediate phase between sodalite and cancrinite

Abstract Powder samples of the intermediate phase between sodalite and cancrinite (INT) have been synthesized hydrothermally. The formation of the INT phase was proved by both PXRD and TGA analysis and its stoichiometric composition was found to be |Na6.95(1)(CO3)0.48(2) (H2O)6.18(6)|[AlSiO4]6. The comparison of the intensity ratios of PXRD data with a SCXRD measurement indicates the formation of a comparable phase with the typical strong stacking disorder. The hexagonal lattice parameters with a=1266.3(2) pm and c=1586(1) pm and the unit cell setting were determined by Pawley fits. The average lattice and the stacking disorder along c axis could be confirmed by the reconstruction of three-dimensional ADT data. The average structure of INT was modeled considering only the combination of naturally existing (zeolitic) cages, restricted by the actual number of layers per unit cell. The possible combinations were further reduced by considering the amount of incorporated species. Through the comparison of simulated electron diffraction pattern to measured data the modeled framework could be confirmed. Using relative positions of the incorporated species in the natural cages as well as electron densities calculated by using only the framework of INT the positions of these species could be described.

Growth twins of R phase in the high Mo-containing nickel-base single crystal superalloy

The topological close packing phases in nickel-base single crystal superalloy aged at 1100 °C for 1000 h was investigated by the spherical aberration-corrected transmission electron microscope. There are R phases precipitated in the matrix, with the hexagonal lattice parameter as a = b = 11.154 Å, c = 17.782 Å. There are lamellar contrasts at the tip of the R phase, which were recognized to be {1-10-1} 〈01-1-1〉 type growth twins. The HRTEM results confirm that the formation of growth twins in R phase can release misfit stress to coordinate the distorted relationship between the R phase and the matrix.

Influence of Ti addition on the microwave absorbing behavior of Ba0.6Sr0.4Fe12-xTixO19 system at X-band frequencies

The synthesis and characterization of Ba0.6Sr0.4Fe12-xTixO19 system (x = 0, 1, 2, 3) have successfully performed by mechanical milling through solid state method. Stoichiometric quantities of BaCO3, SrCO3, Fe2O3, and TiO2 were mixed. The mixture were first milled for 48 h and sintered at 1000 °C for 5 hrs. The refinement of x-ray diffraction shows that a single phase material with a hexagonal structure and lattice parameters appears to increase with increasing Ti doping. The mechanical milling resulted in powders of all samples with mean size of 90 nm. Results of hysteresis curve shows that the samples are ferromagnetic and have low coercivity after Ti doping. Results of VNA evaluation show that the sample after Ti doping has absorption peaks with high reflection loss values at frequency ∼ 11 GHz. We concluded that this study has been successfully known effect of Ti addition on the microwave absorbing behavior of Ba0.6Sr0.4Fe12-xTixO19system at X-band frequencies.

Interaction of metals and alloys with gas media under spark discharges

The paper studies the penetration of nitrogen, oxygen, hydrogen, carbon, argon and krypton into copper, nickel, molybdenum, titanium, aluminum, iron and different steels under the action of spark discharges in various media based on radioactive indicators using step-by-step radiometric analysis, macro-, micro-, electron-microscopy and activation autoradiography, Mössbauer and Auger spectroscopy, secondary ion-ionic emission, X-ray diffraction and X-ray microanalysis. The study describes distribution features of penetrating atoms and their concentration profiles. Phase composition of near-surface layers is also determined. It is shown that supersaturated solid solutions of iron in copper and copper in iron are formed during simultaneous iron and oxygen penetration in copper and spinel (Fe6Cu3O4)4. Diffusion of iron and carbon results in supersaturated solid solutions of iron and carbon in copper, copper and carbon in iron, graphite and cementite. Inert gases and nitrogen form solid solutions with copper. Phase composition of near-surface layers in Fe is determined. Iron dioxide FeO, a carbon solid solution in iron with fcc lattice γ-Fe, tetragonal martensite and cementite, two iron (III) hydroxide FeOOH modifications, a supersaturated solid solution of nitrogen and nitride Fe4N, solid solutions of inert gases in iron are formed in the diffusion zone. Simultaneous interaction of molybdenum with iron (the anode material) and various gases results in the formation of substitutional solid solutions of iron in molybdenum and molybdenum in iron, a small amount of interstitial solid solutions of nitrogen and carbon in molybdenum and nitrogen in iron, interstitial phases: molybdenum nitrides and carbides and traces of nitrides of iron (Fe4N, Fe2N) and Fe1,9Mo (λ) phases in the form of needles. Treatment of nickel with a nickel anode in the nitrogen medium promotes formation of a solid solution of nitrogen and nitride Ni3N in the matrix with preserved hexagonal symmetry and lattice parameters that are characteristic of this phase under equilibrium conditions. Atoms of oxygen, nitrogen, carbon and argon are present in the interstitial solid solutions in treatment of nickel in ambient air; however, oxides are not found even on the surface (in the layer ~200 nm). Interaction of titanium with atmospheric gases leads to formation of a solid solution of nitrogen, oxygen, carbon, hydrogen and argon in titanium and titanium nitride Ti2N (ε). Simultaneous saturation of the titanium surface with nickel and nitrogen in the interaction zone causes formation of phases in the following order: nickel nitride; a solid solution of nitrogen and titanium in nickel and a solid solution of both alloying elements in titanium.

Interaction of metals and alloys with gas media under spark discharges

The paper studies the penetration of nitrogen, oxygen, hydrogen, carbon, argon and krypton into copper, nickel, molybdenum, titanium, aluminum, iron and different steels under the action of spark discharges in various media based on radioactive indicators using step-by-step radiometric analysis, macro-, micro-, electron-microscopy and activation autoradiography, Mössbauer and Auger spectroscopy, secondary ion-ionic emission, X-ray diffraction and X-ray microanalysis. The study describes distribution features of penetrating atoms and their concentration profiles. Phase composition of near-surface layers is also determined. It is shown that supersaturated solid solutions of iron in copper and copper in iron are formed during simultaneous iron and oxygen penetration in copper and spinel (Fe6Cu3O4)4. Diffusion of iron and carbon results in supersaturated solid solutions of iron and carbon in copper, copper and carbon in iron, graphite and cementite. Inert gases and nitrogen form solid solutions with copper. Phase composition of near-surface layers in Fe is determined. Iron dioxide FeO, a carbon solid solution in iron with fcc lattice γ-Fe, tetragonal martensite and cementite, two iron (III) hydroxide FeOOH modifications, a supersaturated solid solution of nitrogen and nitride Fe4N, solid solutions of inert gases in iron are formed in the diffusion zone. Simultaneous interaction of molybdenum with iron (the anode material) and various gases results in the formation of substitutional solid solutions of iron in molybdenum and molybdenum in iron, a small amount of interstitial solid solutions of nitrogen and carbon in molybdenum and nitrogen in iron, interstitial phases: molybdenum nitrides and carbides and traces of nitrides of iron (Fe4N, Fe2N) and Fe1,9Mo (λ) phases in the form of needles. Treatment of nickel with a nickel anode in the nitrogen medium promotes formation of a solid solution of nitrogen and nitride Ni3N in the matrix with preserved hexagonal symmetry and lattice parameters that are characteristic of this phase under equilibrium conditions. Atoms of oxygen, nitrogen, carbon and argon are present in the interstitial solid solutions in treatment of nickel in ambient air; however, oxides are not found even on the surface (in the layer ~200 nm). Interaction of titanium with atmospheric gases leads to formation of a solid solution of nitrogen, oxygen, carbon, hydrogen and argon in titanium and titanium nitride Ti2N (ε). Simultaneous saturation of the titanium surface with nickel and nitrogen in the interaction zone causes formation of phases in the following order: nickel nitride; a solid solution of nitrogen and titanium in nickel and a solid solution of both alloying elements in titanium.

Structural and Magnetic Properties of La-Substituted M-Type Hexagonal Sr–Ni Ferrites Synthesized by Ball-Milling-Assisted Ceramic Process

Sr0.5Ni0.5LaxFe12 − xO19 (x = 0, 0.08, 0.16, and 0.24) hexaferrites have been synthesized by ball-milling-assisted ceramic process. The calcined samples are characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectra (FTIR), and vibrating sample magnetometry (VSM). XRD reveals that all samples consist of the main M-type hexagonal Sr ferrite phase and a low amount of rhombohedral Fe2O3 as secondary phase, and a continuous increase of the hexagonal lattice parameters with substitution content (x). Magnetic characterization indicates that all Sr0.5Ni0.5LaxFe12 − xO19 samples have a hard magnetic property. Substitution of Fe3+ ions by La3+ ions can obviously improve the specific saturation magnetization, remanence, magnetic moment, and effective anisotropy constant. Specific saturation magnetization, remanence, and the magnetic moment reach a maximum at $x =$ 0.24 and calcination temperature of 1050 ∘C.

Experimental realisation of off-stoichiometric Fe-Mn-Si full Heusler alloy with hexagonal crystal structure by pulsed laser deposition

Full Heusler alloys are well known to either crystallize in a cubic structure (Cu2MnAl-type), or present tetragonal distortions. Both structure types present interesting properties, like room temperature magnetic memory shape effect and/or remarkable magnetocaloric effect, mainly ruled by strong magnetostructural coupling. Due to this interplay, our aim was to produce a new crystal phase for the Heusler alloys, different from those well-established cubic and tetragonal, responsible for those well-known physical properties. Thus, we have produced nanoparticles of full Heusler alloys using a pulsed laser deposition technique (from targets of Fe2MnSi) and obtained a core-shell pattern, presenting an amorphous shell and a crystalline core, with hexagonal symmetry. In accordance with these experimental findings, it was shown, by means of density functional calculation, the existence of a minimum of energy as a function of the hexagonal lattice parameters, with a true indication that the hexagonal phase is metastable. The magnetic properties differ considerably from those of bulk Fe2MnSi, including an increase of the Curie temperature from 220 K to 295 K, which is of potential interest for room-temperature applications. This work opens the door to research in a new family of materials, whose properties have only now begun to be explored.

Structural, spectral, thermal and dielectric properties of Nd-Ni co-doped Sr-Ba-Cu hexagonal ferrites synthesized via sol-gel auto-combustion route

Neodymium-nickel (Nd-Ni) substituted nanocrystalline ferrites of the following chemical formula SrBaCu2−xNixNdyFe12−yO22 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0, y = 0.0, 0.02, 0.04, 0.06, 0.08, 0.1) were synthesized by the sol-gel auto-combustion route. The synthesized samples were characterized by X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), fourier transform infrared spectroscopy (FTIR) and dielectric measurement techniques. The properties related to structure of the prepared samples were examined in detail in addition to thorough analysis of their dielectric properties. Microstructural studies exposed the formation of spherical, elongated grains and all the prepared samples showed single Y-type hexagonal phase and lattice parameters have been calculated. FTIR technique was employed to explore the local symmetry behavior in the synthesized crystalline materials and to probe the process of ordering in nano-crystalline ferrites. With increase in frequency and Nd-Ni contents, dielectric constant and dielectric loss of the samples was found to decrease. The complex impedance formalism confirms the role of grain-interior phenomenon to the dielectric properties. Resistive and capacitive characteristics of materials were exhibited by Cole-Cole plots having single semicircle, caused by contribution of grain boundaries in prepared Y-type nano materials.