Machinable and mechanical properties of sintered Al2O3-Ti3SiC2 composites

Two-phase composites consisting of (1 – x) Al₂O₃ and xTi₃SiC₂ (x = 0–1) were prepared by spark plasma sintering (SPS). Sintered densities larger than 98% of theoretical density were achieved when the specimens were sintered at 1300°C for 5 min (in vacuum, at pressure 30 MPa). When content of Ti₃SiC₂ increased up to 30 wt%, composites were found to be machinable—they could be drilled easily using conventional Fe-Mo-W drills or gravers. The mechanical properties of the (1 – x) Al₂O₃–xTi₃SiC₂ composites were evaluated. The bending strength, Vickers hardness of the specimens had the following ranges: 428 ± 10.2 (x = 0) to 673 ± 15.4 Mpa (x = 1) (bending strength at room temperature); 19.9 (x = 0) to 4.0 GPa (x = 1) (Vickers hardness).     

Doping effects on protonic conduction in SrCeO3- and BaCeO3-based perovskites

Electrical conductivity of SrCe_1-x M _x O₃ and BaCe_1-x M _x O₃ (M = rare earth) protonic conductors with the perovskite structure was examined as a function of doping level. The anomalous properties of BaCe_1-x Fr _x O₃ ceramics in the two-phase region (0.2 <x < 0.4) were interpreted in terms of percolating clusters.     

Effect of Nonstoichiometry on the Structure and Dielectric Properties of PbMg1/3Nb2/3O3–PbTiO3 Ceramics

(1 – x)PbMg_1/3Nb_2/3O₃–xPbTiO₃ ceramics with x = 0.20–0.36 were prepared and characterized by x-ray diffraction, microstructural analysis, and dielectric measurements at different temperatures and frequencies. The phase composition, structural parameters, and ferroelectric transition temperatures of the ceramics were determined. The unit-cell volume and transition temperature were shown to decrease with increasing Pb vacancy concentration.     

Emission (Gd3+ and Sm3+) and ESR (Gd3+) studies of La1−xLnxB3O6 (Ln = Gd,Sm; 0 ≤ x ≤ 0.2 for Gd; 0 ≤ x ≤ 0.1 for Sm) phosphors

Polycrystalline powders of rare-earth doped La_1?xGd_xB₃O₆ (0?≤?x?≤?0.2) and La_1?xSm_xB₃O₆ (0.0?≤?x?≤?0.1) phosphors were successfully prepared by a B₂O₃ flux method. All the phosphor samples are well characterized by powder X-ray diffraction (XRD), infrared (IR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) methods and fluorescence lifetime of Sm³⁺ ion. The XRD patterns show that La_1?xM_xB₃O₆ (M?=?Gd and Sm) adopt monoclinic with the I2/a space group. The SEM–EDS results confirmed the doping of Gd and Sm into LaB₃O₆ lattice. The IR and Raman spectra of these solid solutions gave distinctive bands corresponding to planar BO₃ and tetrahedral BO₄ groups. The photoluminescence (PL) spectra of La_1?xGd_xB₃O₆ gave a strong emission band, ⁶P_J?→?⁸S_7/2, at 310 nm. The PL spectra of La_1?xSm_xB₃O₆ phosphor showed orange-red emission at 598 nm when excited using light of wavelength of 402 nm. The results were obtained by the transition ⁴G_5/2?→?⁶H_7/2 of Sm³⁺ ions. The influence of dopant concentration on the emission profiles was studied. The ESR spectra of La_1?xGd_xB₃O₆ (x?=?0.02) gave a typical U-spectrum and spin-Hamiltonian parameters are deduced.

     

High dielectric constant ceramics in the PbSc0.5Ta0.5O3-PbZrO3 and PbSc0.5Ta0.5O3-PbTiO3 systems

The properties of (1-x) PbSc_0.5Ta_0.5O₃-(x) PbZrO₃ ceramics (0.075 <x < 0.2), have been investigated using three different mixed oxide preparation routes. These were (i) a single-stage calcination (at 900°C) between lead, scandium, tantalum and zirconium oxides, (ii) the reaction between single phase PbSc_0.5Ta_0.5O₃ and PbZrO₃ powders (also at 900°C), and (iii) the formation of zirconium-modified scandium tantalate (via a high-temperature prereaction stage) prior to calcination with lead oxide. It was found that this third preparation route results in transparent, 100% dense, single-phase perovskite ceramics which exhibit particularly sharp first-order ferroelectric to paraelectric phase transitions. Material with a maximum relative permittivity of 36 × 103 at 64°C, and a dielectric loss of 7.5 × 10^–4, was obtained for anx value of 0.125. Results are compared with those for ceramics in a similar range of compositions in the (1-x) PbSc_0.5Ta_0.5O₃-(x)PbTiO₃ system; these were prepared using only one of the above routes, and involved calcining PbSc_0.5Ta_0.5O₃ with PbTiO₃ powder.     

Crystallization and properties of CaO-P2O2-B2O3 glasses

Glasses were prepared with compositions (50–0.5 x) CaO.(50–0.5 x) P₂O₅ · x B₂O₃ with B₂O₃ contents (x) from 0 to 45 mol%. The glass transformation temperature (T _g), dilatational softening temperature (T _D) and Vickers hardness (H _V) initially increased with x, but showed maxima at about x=20 for T _g and T _D and at about x=35 for H _V. The thermal expansion coefficient decreased with x, levelling off at about 35 mol% B₂O₃. The maximum tendency to crystallize occurred at around 25 mol% B₂O₃. Volume nucleation (and hence glass-ceramic formation) and surface nucleation were obtained for x between 15 and 25 mol%. The first phase to appear was BPO₄, which was probably homogeneously nucleated. Subsequently the 4CaO · P₂O₅ phase was heterogeneously nucleated on the BPO₄. For 10 x 35 only surface nucleation was observed. The kinetics of nucleation were investigated in the 20 mol% B₂O₃ glass. The changes in properties and crystallisation behaviour with B₂O₃ content were related to short-range structural information. Infrared spectra and literature data indicated a threedimensional network of B-O-B and B-O-P linkages in the glasses.     

Electrochemical Al2O3–Cr2O3 alloy coatings on non-oxide ceramic substrates

Aqueous solutions of xAl(NO₃)₃ + (1−x)Cr(NO₃)₃ were used for electrodeposition of ceramic Al₂O₃–Cr₂O₃ alloy coatings on TiC, TiB₂ and SiC substrates. Cell voltage and deposit weight were studied as function of deposition duration, current density and electrolyte composition. It was shown that the electrochemical parameters permit simple control of the deposition process. Optimal current densities and deposition durations were determined to obtain maximal deposit weights for different solutions and substrates. Deposits with thicknesses up to 10 μm were formed. The green deposits revealed a crystalline nature for compositions of x < 0.3, and an amorphous nature for x ≥ 0.3, independent of the substrate material. Voltage–electrolyte composition dependencies exhibited an ubiquitous minimum at x ≈ 0.3 to 0.4 independent of substrate type and deposition duration. These minima were attributed to the change in the electrical resistance of the deposit with composition and degree of crystallinity. This revised version was published online in November 2006 with corrections to the Cover Date.     

Dielectric properties of low-fitting Pb(Mg1/3Nb2/3)1−xTixO3-Bi2O3/Li2O ceramics

Dielectric properties of low-firing Pb(Mg_1/3Nb_2/3)_1–x Ti _x O₃-Bi₂O₃/Li₂O ceramics are studied in this work. With the addition of Bi₂O₃/Li₂O eutectic composition, the sintering temperature of PMN_1–x PT _x could be lowered to 900° C. Relaxor behaviour of PMN_1–x PT _x is enhanced by the incorporation of Bi₂O₃/Li₂O due to the substitution of Bi⁺³/Li⁺ into the PMN_1–x PT _x framework. Bi₂O₃/Li₂O eutectic composition is used as a fluxing agent, Curie shifter and depressor. Evaporation of Bi₂O₃/Li₂O and PbO during firing is checked and examined via energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) is used to clarify the Curie shifting and depressing effect of Bi₂O₃/Li₂O.     

Superconducting Studies of Nd<Superscript>3+</Superscript>- and Dy<Superscript>3+</Superscript>-substituted GdBaSrCu<Subscript>3</Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> System

The compounds Gd_1−x Nd _x BaSrCu₃O_7−δ (where x=0, 0.1 and 0.2) and Gd_1−x Dy _x BaSrCu₃O _y (where x=0, 0.1 and 0.3) were synthesized using the solid state reaction technique. The tetragonal crystallization of the compounds was identified by powder X-ray diffraction. The microrange crystallite formation and the substitution elements present in the compounds were observed by SEM and EDX analyses. The suppression of superconducting transition temperature and the variation of magnetization parameters for the substitution of rare-earth magnetic elements Nd and Dy ions were observed by low-temperature electrical resistance and magnetization measurements.     

Optical properties of CH3NH3PbX3 (X = halogen) and their mixed-halide crystals

Thin films of microcrystalline CH₃NH₃PbX₃ (X = halogen) as well as their mixed-halide crystals were fabricated by the spin-coating technique, and their optical properties were investigated. X-ray diffraction investigation revealed that CH₃NH₃PbBr_{3 – x} Cl _x (x = 0–3) were successfully formed on glass substrate self-assembly and oriented with the a-axis. Owing to due to their large exciton binding energy, these materials showed clear exciton absorption and free-exciton emission in the visible region at room temperature. Replacing Br with CI made it possible to control the band structure of these materials. As a result, the peak position of the exciton band shifted continuously towards blue region with increasing the CI content in the films.     

Preparation and properties of Bi2−x As x S3 thin films by solution-gas interface technique

The solution gas interface technique by which thin films of Bi_2−x As _x S₃ were deposited is described in this paper. The semiconducting properties of the interface grown Bi_2−x As _x S₃ thin films are studied. The optical absorption, dark resistivity and thermoelectric power of the films were studied and results are reported.     

Dielectric characterization of BaTiO3-BaM1/3N2/3 O3 systems (with M=Co,Mg and N=Nb or Ta)

The dielectric behaviour of (1–x)BaTiO₃–x BaM_1/3N_2/3O₃ systems, in which M=Co, Mg and N=Nb, Ta is described whenx varies from 0 to 0.1. The evolution of the Curie temperature and of the dielectric constant, either in the ferroelectric state or in the paraelectric state are correlated to the structure and the ceramic microstructure. An observed diffuse phase transition is discussed.     

Synthesis of perovskite-type (La1−x Ca x )CoO3 at low temperature using ethylene glycol and citric acid

To synthesize perovskite-type (La_1−x Ca _x )CoO₃ with good crystallinity (regularity of ions), a gel was prepared by adding ethylene glycol and citric acid to an aqueous solution of La(NO₃)₃ · 6H₂O, CaCO₃, and Co(CH₃COO)₂ · 4H₂O. Perovskite-type (La_1−x Ca _x )CoO₃ (0.0 ≤ x ≤ 0.3) was obtained by firing the gel above 600 °C in air for 3 h. Samples were examined for oxygen content, crystallite size, specific surface area, and the catalytic activity of CH₄ oxidation. The samples were also investigated by transmission electron microscopy (TEM). Based on the variation in crystallite size and in the average particle size, the (La_1−x Ca _x )CoO₃ particle became finer as x increased. In all samples, CH₄ oxidation occurred above 300°C. The catalytic activity of (La_1−x Ca _x )CoO₃ fired at 700 °C monotonously increased as x increased.     

Magnetic susceptibility, spin transition, and electrical conductivity of LaCo1 + xO3 and NdCo1 + xO3

The magnetic susceptibility of Nd₂O₃, NdCo_{1 + x} O₃, and LaCo_{1 + x} O₃ (x = 0, 0.05, 0.1, 0.15) has been measured at temperatures from 80 to 950 K, and the electrical conductivity of the neodymium and lanthanum cobaltites (enriched in cobalt relative to neodymium or lanthanum) with the general formulas Nd(La)Co_{1 + x} O_{3 + 1.5x} , or Nd_{1/(1 + x)}(La)_{1/(1 + x)}CoO_{(3 + 1.5x)/(1 + x)}, has been measured between 300 and 1050 K. The effective magnetic moments of paramagnetic ions have been determined in the temperature ranges of CurieWeiss behavior and have been used to evaluate the fractions of low-, intermediate-, and high-spin Co³⁺ ions. Raising the temperature from 320 to 660 K (non-Curie—Weiss behavior) increases the fraction of high-spin Co³⁺ ions in LaCo_{1 + x} O_{3 + 1.5x} (La_{1/(1 + x)}CoO_{(3 + 1.5x)/(1 + x)} from 27–43 to 56–61%. Moreover, in this temperature range the conductivity of the lanthanum cobaltites rises most steeply. In the range 660–950 K, no spin transition occurs in LaCo_{1 + x} O_{3 + 1.5x} , the slope of the conductivity versus temperature curves gradually decreases, and the conductivity gradually saturates. The conductivity of NdCo_{1 + x} O_{3 + 1.5x} (Nd_{1/(1 + x)}CoO_{(3 + 1.5x)/(1 + x)}) varies considerably in the range 550–950 K, and the spin transition in these cobaltites takes place between 260 and 760 K. Above 760 K, the NdCo_{1 + x} O_{3 + 1.5x} cobaltites with x = 0.05 and 0.10 contain, respectively, 72 and 83% high-spin Co³⁺ ions and 28 and 17% high-spin Co⁴⁺ ions, whereas neodymium cobaltite with x = 0.15 contains 83% high-spin and 17% intermediate-spin Co³⁺ ions. Original Russian Text ? S.V. Shevchenko, L.A. Bashkirov, G.S. Petrov, S.S. Dorofeichik, N.N. Lubinskii, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 1, pp. 88–94.     

Synthesis and structural characterization of (Bi2O3)1?x (Y2O3)x and (Bi2O3)1?x (Gd2O3)x solid solutions

Solid solution series, (Bi₂O₃)_1−x (Y₂O₃)_x and (Bi₂O₃)_1−x (Gd₂O₃)_x, forx = 0.10, 0.20, 0.30 and 0.40 were synthesized by standard ceramic technique. The structural phase characterization was carried out using X-ray powder diffraction technique. It was found that the solid solution containing 20–40 mole% of Y₂O₃ had face-centred cubic structure. All samples of the solid solution series, (Bi₂O₃)_1−x (Gd₂O₃)_x, had rhombohedral single phase in the concentration range 0.10 ≤x ≤ 0.40. Lattice parameters offcc phase of Y₂O₃ doped samples were calculated from the X-ray diffraction data. The lattice constant ‘a’ gradually decreases with increasing content of dopant concentration (x) for the Y₂O₃ doped system and obeys Vegard’s rule. The unit cell parameters for the (Bi₂O₃)_1−x (Gd₂O₃)_x doped samples showing rhombohedral phase were obtained on hexagonal setting.     

Dielectric and Nonlinear Optical Properties of SrTeO3-Based Solid Solutions

Sr_1–x Pb _x TeO₃ (0 < x < 0.2) and Sr_{1 – x} La_2x Te_{1 + 2x} O_{3 + 6x} (0 < x< 0.15) solid solutions are synthesized (the latter, for the first time), and their properties are studied. The results demonstrate that partial substitutions of Pb and La for Sr extend the temperature stability range of ferroelectric SrTeO₃.     

Microstructure and dielectric properties of BaZr x Ti1−x O3 ceramics

The crystalline structure and dielectric properties of BaZr _x Ti_1−x O₃ ceramics with x = 0.05, 0.10, 0.15, and 0.20 were investigated. As zirconium increased, the a-axis lattice constant gradually increased, however, the c-axis lattice constant and c/a ratio gradually decreased. When x = 0.20, the crystal structures of the BZT ceramics are very close to cubic, different from the tetragonal structure when x < 0.20. The temperature dependence of the dielectric constant was studied and an enhanced diffuse phase transition behavior is found to be caused by the increased Zr content. The decreases of coercive electric field and remanent polarization were the result of increase of Zr/Ti ratio in BaZr _x Ti_1−x O₃.     

Composition and temperature-induced structure evolution in Bi0.5Na0.5TiO3-based solid solutions

In this study, the temperature and composition dependence of the dielectric, ferroelectric properties, and polarization current characteristics of the (0.935 − x)Bi_0.5Na_0.5TiO₃–0.065BaTiO₃–xSrTiO₃ (BNBSTx) with x ranging from 0.02 to 0.22 were systematically investigated. At elevated temperature the BNBSTx solid solution with x < 0.18 underwent a transition from ferroelectric to short-range displacement order and then to non-polar phases. The corresponding transition temperature decreased with Sr content x increasing and the critical composition x was determined to be around 0.18–0.22. In addition, the maximum-permittivity temperature T _m, which exhibited broad peaks with nearly frequency-independent behavior, almost disappeared for x > 0.18, which may be related with the formation of certain sublattices in the complex solid solution.     

Dielectric and piezoelectric properties of (1 ? 2x)BiScO3 · xPbTiO3 · xPbMg1/3Nb2/3O3 (0.30 ≤ x ≤0.46) solid solutions

We have synthesized ceramic samples of (1 − 2x)BiScO₃ · xPbTiO₃ · xPbMg_1/3Nb_2/3O₃ perovskite solid solutions with 0.30 ≤ x ≤ 0.46 and studied their structural, dielectric, and piezoelectric properties. At x = 0.40, the system has a morphotropic phase boundary between tetragonal (x > 0.40) and rhombohedral (x < 0.40) solid solutions. The dielectric permittivity and loss tangent of the solid solutions have been measured at temperatures from 100 to 800 K and frequencies from 0.1 to 200 kHz. The maximum in the permittivity of the solid solutions lies in the range 390–440 K. With increasing BiScO₃ content, features characteristic of fer-roelectric relaxors emerge and become more pronounced. Near the morphotropic phase boundary, the piezoelectric charge coefficients d ₃₃ and d ₃₁ of the solid solutions reach 410 and 150 pC/N, respectively, and their radial-mode mechanical Q drops to 22, which makes these materials potential candidates for a number of applications.     

Preparation and Properties of Al2O3-doping LiNi1/3Co1/3Mn1/3O2 Cathode Materials

LiNi_1/3Co_1/3-xMn_1/3O₂ doped with Al₂O₃ (x = 0%, 2.5%, 5%, 10%) was synthesized by co-precipitation of Ni, Co, and Mn acetates. The influence of Al₂O₃ doping on structure and electrochemical performances of LiNi_1/3Co_1/3Mn_1/3O₂ was studied using X-ray diffraction (XRD) analysis, scanning electron microscopy, charge/discharge tester, and electrochemical workstation. It was found that the materials achieved the best electrochemical properties when x was 5%. The first discharge capacity was 156.3 mAh · g^?1(0.1 C, 2.0–4.8 V), which was close to the un-doped sample (156.8 mAh · g^?1). After 20 cycles, the capacity retention ratios at the C-ratios of 0.1C, 0.2C, and 0.5 C were 96.1%, 94.9%, and 89.4%, respectively, while the capacity retention ratios of the un-doped samples were only 92.6% (0.1 C), 91.8% (0.2 C), and 88.7% (0.5C). The alternating current impedance shows that the charge transfer in the electrode interface was the easiest when x was 5%.