Effect of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> doping on the structure,magnetic properties and electrical properties of La<Subscript>0.7</Subscript>Ca<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript>

The (La_0.7Ca_0.3MnO₃)_1x /(NiFe₂O₄) _x (x = 0 to 0.09) composites were prepared using a conventional solid state reaction method. The structural, magnetic properties, and electrical properties of LCMO/NFO composites were investigated using X-ray diffraction, scanning electron microscopy, field cooled DC magnetization, and magnetoresistance (MR) measurements. The resistivity measured as a function temperature demonstrates that the pure LCMO and x = 0.01 samples display metal to semiconductor transitions. However, the composites of x > 0.03 samples clearly present the electrical behavior as an insulator/semiconductor type behavior. It was observed that the resistivity of the samples increased systemically with an increase of the NFO content. From the MR measurements, it was found that the MR effect is enhanced for x = 0.01 with a NFO composition. In all, the spin-polarized tunneling and the spin-dependent scattering may be beneficial for an improved low-field magnetoresistance effect. These phenomena can be explained by the segregation of a new phase related to NFO at the grain boundaries or surfaces of the LCMO grains.     

New ternary compound La<Subscript>8</Subscript>Al<Subscript>13</Subscript>Sn<Subscript>3</Subscript>

A new ternary compound La₈Al₁₃Sn₃ was synthesized and studied by means of X-ray powder diffraction technique. The compound La₈Al₁₃Sn₃ crystallizes in a hexagonal AlB₂-type structure with space group P6/mmm (No. 191) and the lattice parameters a = 0.44919(1) nm and c = 0.43835(1) nm. The Smith and Snyder figure of merit for index, F _N , is F ₃₀ = 197.3(30). The Rietveld refinement for the crystal structure of the compound was carried out successfully. The liability R-factors of Rietveld refinement are R _p = 0.114 and R _wp = 0.148. The compound La₈Al₁₃Sn₃ decomposes into LaAl₂ with cubic structure and space group Fd $ \bar 3 $ \bar 3 m (227), LaAl₃ with hexagonal structure and space group P6₃/mmc (194), and Sn at 720°C.     

Up-Date of a Thermodynamic Database of the ZrO<Subscript>2</Subscript>-Gd<Subscript>2</Subscript>O<Subscript>3</Subscript>-Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> System for TBC Applications

The thermodynamic database of the ZrO₂-Gd₂O₃-Y₂O₃-Al₂O₃ system is up-dated taking into account new data on lattice stabilities of ZrO₂, Gd₂O₃ and Y₂O₃ and heat capacity measurements for the monoclinic phase Gd₄Al₂O₉ and phase with garnet structure Gd₃Al₅O₁₂. New data for the heat capacities of Gd₂Zr₂O₇ (pyrochlore) and GdAlO₃ (perovskite) as well as on the enthalpy of formation of fluorite solid solutions (Zr_1−x Gd _x )O_2−x/2 were found to be in good agreement with calculated results. In comparison with the previous assessment, taking into account new experimental data resulted in a change of the melting character of the Gd₄Al₂O₉ phase from a peritectic one to a congruent one in the Gd₂O₃-Al₂O₃ system. Correspondently, in the ternary system ZrO₂-Gd₂O₃-Al₂O₃, the melting character of the three-phase assemblage Gd₂O₃ (B), Gd₄Al₂O₉ and GdAlO₃ changed from eutectic to transition type U. The T ₀-lines for T/M and F/T diffusionless transformations and driving force of partitioning to equilibrium assemblage T + F were calculated in the ZrO₂-Gd₂O₃-Y₂O₃ system.     

Enhancement of room-temperature magnetoresistance in La<Subscript>0.6</Subscript>Dy<Subscript>0.1</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript>/Ag<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

The samples of La0.6Dy0.1Sr0.3MnO3/(Ag2O)x/2(x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10, 0.20, 0.25, and 0.30) were prepared by using the solid-state reaction method.Their magnetic property, transport behavior, transport mechanism and magnetoresistance effect were studied through the measurements of magnetization-temperature(M-T) curves, ρ-T curves and the fitting of ρ-T curves.The results indicated that Ag could take part in the reaction when the doping amount is small.However, when the doping amount is compar...     

Effect of yttrium doping on the resistivity and magnetoresistance of La<Subscript>0.80</Subscript>Sr<Subscript>0.20</Subscript>MnO<Subscript>3</Subscript>

The temperature and magnetic field dependence of resistivity of crystals of nominal compositions of La_0.75Y_0.05Sr_0.20MnO₃ grown by floating zone method at different growth rates are studied. The yttrium doping is found to result in the decrease of Curie temperature, suppression of the Pnma-R $ \bar 3 $ \bar 3 c structural transition, increase of resistivity and magnetoresistance. It is shown that the physical properties of the manganites studied are determined by not only the nominal composition but also the growth rate.     

Magnetoresistance of the La<Subscript>0.7</Subscript>Ca<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> single crystal

The dependence of the resistance ρ of the La_0.7Ca_0.3MnO₃ single crystal on the temperature (in a range of 77 < T < 410 K) and magnetic field H is studied. The dependence of the magnetoresistance Δρ/ρ of the ferromagnetic phase on the field is shown to be determined by the competition of two mechanisms. In low magnetic fields, the magnetoresistance is positive Δρ/ρ > 0 and is determined by changes in the resistance with changing magnetization orientation with respect to the crystallographic axes; in high magnetic fields, the magnetoresistance is negative Δρ/ρ < 0, since it is the suppression of spin fluctuations in the magnetic field that plays the principal role. The phase transition from the ferromagnetic to paramagnetic state is a first-order transition close to the second-order one. In the transition range, the magnetoresistance is determined by the resistivity in the zero field ρ(T) and by the shift of the transition temperature T _C(H) in the magnetic field. In the paramagnetic state, the resistivity ρ(T) has an activation character; similarly to the magnetoresistance of other lanthanum manganites, the magnetoresistance of this single crystal is controlled by a change in the activation energy in the magnetic field.     

Phase Relations in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-V<Subscript>2</Subscript>O<Subscript>5</Subscript>-MoO<Subscript>3</Subscript> System in the Solid State. The Crystal Structure of AlVO<Subscript>4</Subscript>

Phase relations in the ternary oxide system Al₂O₃-V₂O₅-MoO₃ in the solid state in air have been investigated by using the x-ray diffraction (XRD) and differential thermal analysis/thermogravimetric (DTA/TG) methods. It was confirmed that in the subsolidus area of the Al₂O₃-V₂O₅-MoO₃ system, there exist seven phases, that is Al₂O₃, V₂O_5(s.s.), MoO₃, AlVO₄, Al₂(MoO₄)₃, AlVMoO₇, and V₉Mo₆O₄₀. Seven fields, in which particular phases coexist at equilibrium, were isolated. The crystal structure of AlVO₄ has been refined from x-ray powder diffraction data. Its space group is triclinic, , Z = 6, with a = 0.65323(1) nm, b = 0.77498(2) nm, c = 0.91233(3) nm, α = 96.175(2)°, β = 107.234(3)°, γ = 101.404(3)°, V = 0.42555 nm³. The crystal structure of the compound is isotypic with FeVO₄. Infrared (IR) spectra of AlVO₄ and FeVO₄ are compared.     

Dilatometric analysis of the process of the nanocrystallization of Fe<Subscript>72.5</Subscript>Cu<Subscript>1</Subscript>Nb<Subscript>2</Subscript>Mo<Subscript>1.5</Subscript>Si<Subscript>14</Subscript>B<Subscript>9</Subscript> soft magnetic alloy

The process of the nanocrystallization of magnetically soft Fe_72.5Cu₁Nb₂Mo_1.5Si₁₄B₉ alloy has been studied using dilatometry and thermomagnetic analysis, together with structural investigations. It has been shown that the amount of nanocrystalline phase precipitated upon heating of the amorphous precursor is in good agreement with a shortening of the ribbon length in the course of crystallization. Thermal expansion at the different stages of heating and cooling depends on the structural and phase states, as well as on the magnetic state of the alloy. The numerical value of the coefficient of linear thermal expansion decreases with an increase in the fraction of the ferromagnetic crystalline phase.     

The effect of boron oxide on the crystallization behavior of MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> spinel phase during the cooling of the CaO-SiO<Subscript>2</Subscript>-10 mass.% MgO-30 mass.%Al<Subscript>2</Subscript>O<Subscript>3</Subscript> systems

The microstructural characteristics of the CaO-SiO₂-B₂O₃-10 mass.% MgO-30 mass.% Al₂O₃ systems solidified during slow cooling from 1600 °C were investigated using SEM-EDS and a thermochemical computation package. The effect of boron oxide on the crystallization behavior of the spinel in the aluminosilicate system was observed because boron oxide is believed to become a potential flux to reduce the melting point of the liquid oxides. The primary crystalline phase was spinel, mainly MgAl₂O₄, irrespective of the boron content. The liquidus temperature T _L continuously decreased as the boron oxide content increased, indicating that the boron oxide decreased the activity of the MgAl₂O₄ spinel phase in liquid melts at high temperatures. The size of the spinel crystals increased as the temperature range for the solid + liquid coexisting region, viz. the mushy zone, increased. In the present systems, because the T _L continuously decreased with the increase in the boron oxide content, the viscosity of the liquid oxide may have affected the crystallization behavior of the spinel during cooling. Based on these results, an injection of a small amount of B₂O₃ flux into molten steel containing liquid aluminosilicate inclusions is not recommended because large spinel crystals can originate from the changes in the thermophysical properties of the liquid inclusions due to the incorporation of boron oxide into the aluminosilicate networks.     

Effect of Dy doping on magnetism of La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>CoO<Subscript>3</Subscript> system

The effect of Dy doping on magnetism of La0. 7Sr0. 3CoO3 system was studied through the measurements of M-T curves and M-H curves. The results show that with Dy content increasing, Tc decreases, M weakens, the coercive force strengthens, and the samples exhibit the abnormal phenomenon that M increases continuously with T decreasing in low temperature range. Research indicates that the variation of magnetism in the system comes from the changes of lattice parameters and magnetic environment caused by Dy doping and from the spin-state transition of Co ions induced by Dy ions.     

Orientation dependence of superelasticity in ferromagnetic single crystals Co<Subscript>49</Subscript>Ni<Subscript>21</Subscript>Ga<Subscript>30</Subscript>

Dependence of the amount of reversible deformation on the orientation of the crystal axis and testing temperature has been studied using [001] and [$ \bar 1 $ \bar 1 24] single crystals of the Co₄₉Ni₂₁Ga₃₀ (at %) alloy upon compression. It has been shown that in the [001] crystals with T ≤ M _s (M _s is the temperature of the onset of the forward martensitic transformation upon cooling) the reversible deformation is equal to 5.5–6.5% and consists of the deformation connected with the shape-memory effect (SME) equal to 4–4.2%, and of “ferroelastic” deformation equal to 1.5–2.2%, which is reversible upon unloading. The total reversible deformation exceeds the lattice deformation ɛ₀ observed upon the B2-L1₀ martensitic transformation, which is equal to 4.5%. At T > A _f (A _f is the finish temperature of the reverse martensitic transformation upon heating), the reversible deformation in [001] crystals is equal to 6.5%. It has been shown electron-microscopically that the reversible deformation equal to 1.5–2.2% in the temperatures range of T = 77−300 K is connected with the development of mechanical twinning in the L1₀ martensite on (110) _L10 planes, which proves to be reversible in the [001] crystals and can be partly irreversible in the [$ \bar 1 $ \bar 1 24] crystals. Upon heating, the (110) _L10 twins of the stabilized L1₀ martensite pass into the ($ \bar 1 $ \bar 1 12) _B2 twins of the B2 phase.     

Microstructures of Ti<Subscript>50</Subscript>Al<Subscript>45</Subscript>Mo<Subscript>5</Subscript> alloy powders produced by plasma rotating electrode process

Microstructures of Ti₅₀Al₄₅Mo₅ (at.%) alloy powders produced by the plasma rotating electrode process (PREP) were investigated. The powders have inhomogeneous structures, which consist of dendrites and rounded grains. The dendrites, which show a “rosettelike” morphology, are formed on the powder surface and around the rounded grains. The rosettelike dendrites are of hexagonal α ₂ (D0₁₉) phase even though the dendrites have an equiaxial morphology, and a small amount of β ₂ (B2) phase is also contained inside. It is suggested that the solidification to α (hcp-A3) phase occurred by the peritectic reaction between the primary β (bcc-A2) dendrites and the liquid: L+β→L+β+α. The rounded grains, on the other hand, are of β ₂ phase in which acicular α or α ₂ laths are precipitated with the Burgers orientation relationship. Antiphase domain boundaries in the β ₂ matrix are intersected by α(α ₂) laths. It is interpreted that the α(α ₂) laths were formed by the solid-state transformations: β ₂→β ₂+α→β ₂+α ₂. The formation of the two different microstructures in the powder particles is rationalized in terms of the changes in local composition of the liquid phase during the rapid solidification process.     

Tunneling magnetoresistance in sintered Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> samples diluted with Fe and α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

Electric transport and magnetoresistance characteristics were investigated for Fe₃O₄-x Fe(x=0, 10, 20 wt.%) samples and Fe₃O₄-α-Fe₂O₃ samples sintered at 500°C. For composition dependence of Fe₃O₄-x Fe samples, the largest room temperature MR, 3.3% at 10 kOe, was obtained from a Fe₃O₄-10 Fe sample. For the surface heat treatment dependence of Fe₃O₄ powders, the largest room temperature MR, 4% at 10 kOe, was obtained from a Fe₃O₄-α-Fe₂O₃ sample sintered with Fe₃O₄ powders heated at 200°C in air. It was found that these enhanced MR ratios always appear together with the appropriate excess resistance which is regarded as the tunneling barrier. These enhanced MR ratios of Fe₃O₄-10 Fe and Fe₃O₄-α-Fe₂O₃ samples can be explained by the increased interparticle contact sites and the appropriate thickness of α-Fe₂O₃, respectively.     

Luminescence properties of red-emitting Ca<Subscript>2</Subscript>Al<Subscript>2</Subscript>SiO<Subscript>7</Subscript>:Eu<Superscript>3+</Superscript> nanoparticles prepared by sol-gel method

A series of red-emitting Ca2-xAl2SiO7:xEu3+(x = 1 mol.%-10 mol.%) phosphors were synthesized by the sol-gel method.The effects of annealing temperature and doping concentration on the crystal structure and luminescence properties of Ca2Al2SiO7:Eu3+ phosphors were investigated.X-ray diffraction(XRD) profiles showed that all peaks could be attributed to the tetragonal Ca2Al2SiO7 phase when the sample was annealed at 1000℃.Scanning electron microscopy(SEM) micrographs indicate that the phosphors have an irregularly rounded morphology with particles of about 200 nm.Excitation spectra showed that the strong broad band at around 258 nm and weak sharp lines in 350-490 nm were attributed to the charge transfer band of Eu3+-O2-and f-f transitions within the 4f6 configuration of Eu3+ ions,respectively.Emission spectra implied that the red luminescence could be attributed to the transitions from the 5D0 excited level to the 7FJ(J = 0,1,2,3,4) levels of Eu3+ ions with the main electric dipole transition 5D0→7F2(618 and 620 nm),and Eu3+ ions prefer to occupy a lower symmetry site in the crystal lattice.Moreover,the photoluminescence(PL) intensity was strongly dependent on both the sintering temperature and doping concentration,and the highest PL intensity was observed at an Eu3+ concentration x = 7 mol.% after annealing at 1100℃.The obtained Ca2Al2SiO7:Eu3+ phosphor may have potential application for the red lamp phosphor.     

Fabrication and Properties of Plasma-Sprayed Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/ZrO<Subscript>2</Subscript> Composite Coatings

Al₂O₃ /xZrO₂ (where x = 0, 3, 13, and 20 wt.%) composite coatings were deposited onto mild steel substrates by atmospheric plasma spraying of mixed α-Al₂O₃ and nano-sized monoclinic-ZrO₂ powders. Microstructural investigation showed that the coatings comprised well-separated Al₂O₃ and ZrO₂ lamellae, pores, and partially molten particles. The coating comprised mainly of metastable γ-Al₂O₃ and tetragonal-ZrO₂ with trace of original α-Al₂O₃ and monoclinic-ZrO₂ phases. The effect of ZrO₂ addition on the properties of coatings were investigated in terms of microhardness, fracture toughness, and wear behavior. It was found that ZrO₂ improved the fracture toughness, reduced friction coefficient, and wear rate of the coatings.     

Synthesis and Characterization of New Bismuth Lead Vanadate Pb<Subscript>2</Subscript>BiV<Subscript>3</Subscript>O<Subscript>11</Subscript>

It has been shown that BiVO₄ and Pb₂V₂O₇ react with each other, forming a new compound of the formula Pb₂BiV₃O₁₁ at molar ratio equal to 1:1. This compound has also been obtained from PbO, Bi₂O₃, and V₂O₅, mixed at a molar ratio of 4:1:3. It melts congruently at a temperature of 725 ± 5 °C and crystallizes in the triclinic system with unit-cell parameters: a = 0.710076 nm, b = 1.41975 nm, c = 1.42972 nm, α = 134.552°, β = 97.2875°, γ = 89.6083°, and Z = 4.     

Sol-gel preparation and characterization of Li1.3Al0.3Ti1.7（PO4）3 sintered with flux of LiBO2

Li_1.3Al_0.3Ti_1.7(PO₄)₃ pellets sintered with different mole fractions of LiBO₂ were prepared by sol-gel method. The structural identification, surface morphology, ionic conductivity, and activation energy of the pellets were studied by X-ray diffraction, scanning electron microscopy, and electrochemical impedance spectroscopy. The results show that all the Li_1.3Al_0.3Ti_1.7(PO₄)₃ pellets sintered with different mole fractions of LiBO₂ have similar X-ray diffraction patterns. The sintered pellet becomes denser and the boundary and corner of the particles become illegible with the increase of LiBO₂. Among the Li_1.3Al_0.3Ti_1.7(PO₃)₄ pellets sintered with different mole fractions of LiBO₂, the one sintered with 1 mol% LiBO₂ shows the highest ionic conductivity of 3.95×10⁻⁴ S.cm⁻¹ and the lowest activation energy of 0.2469 eV.     

Symmetry analysis of magnetic structures with a wave vector k<Subscript>6</Subscript> = μb<Subscript>3</Subscript> possible in the intermetallic compound Ce<Subscript>2</Subscript>Fe<Subscript>17</Subscript>

To estimate the reliability of literature data on the magnetic structure of Ce₂Fe₁₇, we performed a symmetry analysis of the possible magnetic structures characterized by the wave vector k ₆ = μb ₃ = 2π(0, 0, π/c). The previously developed procedure for calculating the basis functions of the irreducible representations of the space group D_3d ⁵ (R[`3]m)(R\bar 3m), which enter into the magnetic representation with the above wave vector, is described briefly and is employed for an analysis. The results of the calculations of these basis functions for Fe atoms located in 6c, 9d, 18f, and 18h positions are given and discussed. A conclusion is made that in this intermetallic compound there can exist magnetic structures of the type of longitudinal or transverse spin waves or of the type of a complicated spiral with the magnetic moment which varies according to a harmonic law as the coordinate z of the site occupied by the Fe atom changes.     

Dependency of fracture toughness of plasma sprayed Al<Subscript>2</Subscript>O<Subscript>3</Subscript> coatings on lamellar structure

The fracture toughness of plasma-sprayed Al₂O₃ coatings in terms of critical strain energy release rate G _Ic was investigated using a tapered double cantilever beam (TDCB) approach. This approach makes the fracture toughness be measured only using the critical fracture load disregarding crack length during test. The Al₂O₃ coatings were deposited under different spray distances and plasma powers to clarify the effect of spray parameters on the G _Ic of the coatings. The fracture surfaces were examined using scanning electron microscope. On the basis of an idealized layer microstructure model for thermal sprayed coatings, the theoretical relationship between the cohesive fracture toughness and microstructure is proposed. The correlation between the calculated fracture toughness and observed value is examined. It was found that the fracture toughness of plasma sprayed Al₂O₃ coatings is not significantly influenced by spray distance up to 110 mm, and further increase in spray distance to 130 mm resulted in large decrease in the fracture toughness of the coatings. The G _Ic value predicted based on the proposed model using lamellar interface mean bonding ratio and the effective surface energy of bulk ceramics agreed well with the observed G _Ic data. Such agreement evidently shows that the fracture toughness of thermally sprayed ceramic coatings at the direction along coating surface is determined by lamellar interface bonding.     

Electrochemical properties of carbon-coated LiFePO<Subscript>4</Subscript> and LiFe<Subscript>0.98</Subscript>Mn<Subscript>0.02</Subscript>PO<Subscript>4</Subscript> cathode materials synthesized by solid-state reaction

Olivine structured LiFePO4/C (lithium iron phosphate) and Mn2+-doped LiFe0. 98Mn0. 024/C powders were synthesized by the solid-state reaction. The effects of manganese partial substitution and different carbon content coating on the surface of LiFePO4 were considered. The structures and electrochemical properties of the samples were measured by X-ray diffraction (XRD), cyclic voltammetry (CV), charge/discharge tests at different current densities, and electrochemical impedance spectroscopy (EIS). The electrochemical properties of LiFePO4 cathodes with x wt. ％ carbon coating (x=3, 7, 11, 15) at γ=0. 2C, 2C (1C=170 mAh·g-1) between 2. 5 and 4. 3 V were investigated. The measured results mean that the LiFePO4 with 7 wt. ％ carbon coating shows the best rate performance. The discharge capacity of LiFe0. 98Mn0. 02PO4/C composite is found to be 165 mAh·g 1 at a discharge rate, γ=0. 2C, and 105 mAh·g-1 at γ=2C, respectively. After 10cycles, the discharge capacity has rarely fallen, while that of the pristine LiFePO4/C cathode is 150 mAh·g-1 and 98 mAh·g-1 at γ=0. 2 and 2C, respectively. Compared to the discharge capacities of both electrodes above, the evident improvement of the electrochemical performance is observed, which is ascribed to the enhancement of the electronic conductivity and diffusion kinetics by carbon coating and Mn2+-substitution.