Interdiffusion of rare-earth cations in Ln1−x ′Ln x ″ Ba2Cu3O7 − δ (Ln′, Ln″ = Y, Dy, Ho) High-T c superconductors

The Y³⁺/Ho³⁺, Y³⁺/Dy³⁺, and Dy³⁺/Ho³⁺ interdiffusion coefficients in the YBa₂Cu₃O_{7 ? δ}-HoBa₂Cu₃O_{7 ? δ}, YBa₂Cu₃O_{7 ? δ}-DyBa₂Cu₃O_{7 ? δ}, and DyBa₂Cu₃O_{7 ? δ}-HoBa₂Cu₃O_{7 ? δ} systems have been determined in air at a temperature of 1233 K by the Boltzmann-Matano method from the yttrium/holmium, yttrium/dysprosium, and dysprosium/holmium concentration profiles across the diffusion zone between two pellets of the high-T _c superconductors. The composition dependences of the interdiffusion coefficients in the solid-solution systems are presented.     

Thermal Diffusivity of La1−x Sr x MnO3 (x < 0.3)

Perovskite manganites are interesting because of their colossal magnetoresistance. In this work high resolution thermal diffusivity measurements of La_1–x Sr _x MnO₃ (0 x 0.3) single crystals in the temperature range from 250 to 400 K are presented. A photopyroelectric device in the standard back configuration has been used. The thermal diffusivity through second-order magnetic phase transitions, as well as through first- and second-order structural phase transitions has been measured. The critical parameters of the sample with x = 0.3 at the ferromagnetic-to-paramagnetic transition have been obtained, and are close to the values predicted by the Ising model.     

Non-linearI–V characteristics of doped Sn1−x Ti x O2 (0.0 <x < 0.25) system

The solid solutions of Sn_1−x Ti _x O₂ (0.0 <x < 0.25) were prepared by the usual high temperature ceramic processing techniques with small amounts of dopants such as Nb, Co, Al. The electrical measurements (logI-logV) on the ohmically metal electroded sintered pellets showed the non-linear behaviour. The non-linear coefficient was found to decrease from 12 to 3 with increase inx. On the other hand, the breakdown voltage (E _b) showed the increase with the increase inx. This complex electrical behaviour is explained on the effects of the three dopants (as varistor former, performance enhancer and highlighter) on the microstructural features of the dense pellet.     

Microstructure and dielectric properties of Ba[Ti1 − x (Ln1/2Nb1/2) x ]O3 ceramics

We have studied the microstructure and dielectric properties of barium titanate-based ceramics containing niobium oxide and rare-earth (Nd, Sm, Gd, Dy, and Tm) oxide additions in a ratio needed for the formation of mixed perovskite solid solutions with the general formula Ba[Ti_{1 ? x} (Ln_1/2Nb_1/2) _x ]O₃. It was found that, after sintering at 1100–1120°C with the use of a zinc oxide-based sintering aid and manganese carbonate additions, the ceramics had a core-shell structure in which the core of the grains consisted of barium titanate and the shell consisted of a barium titanate-based solid solution. The average grain size of the major phase in the ceramics was within 0.7 μm. The ceramics contained additional phases in the form of inclusions which occasionally exceeded 5 μm in size. Their composition was determined. The Nd-, Sm-, and Gd-containing materials were shown to have the greatest potential as a base for the development of new engineering materials of stable groups with high dielectric permittivity for multilayer capacitors with electrodes containing 70% Ag and 30% Pd.     

Photoluminescence and dielectric properties of LnTiTaO<Subscript>6</Subscript> (Ln = Ce,Pr, Sm) polycrystals

Polycrystalline LnTiTaO₆ (Ln = Ce, Pr, Sm) compounds were prepared in the solid state ceramic route. The powders were calcined between 1250 °C and 1300 °C and sintered between 1480 °C and 1520 °C. The materials were characterized by XRD and SEM. The dielectric properties were measured in the frequency range 1 kHz–5 MHz. The absorption spectra and photoluminescence spectra of the samples were analysed. The materials are useful as gain media in micro lasers because of the optical absorption and photoluminescence.     

Controllable synthesis and luminescence of YPO<Subscript>4</Subscript>:Ln<Superscript>3+</Superscript> (Ln = Eu and Sm) nanotubes

YPO₄:Ln³⁺ (Ln = Eu and Sm) nanotubes were synthesized by a precipitation process in the presence of SDS. The XRD results showed that all samples have a xenotime type tetragonal structure, indicating that doped rare earth ions have no influence on the phase. The SEM and TEM images showed that all samples are nanotubes. On basis of the morphology of samples and the properties of SDS, the possible formation mechanism was speculated. YPO₄:Eu³⁺ and YPO₄:Sm³⁺ nanotubes showed characteristic emission bands of Eu³⁺ and Sm³⁺ ions, respectively. For YPO₄:Eu³⁺/Sm³⁺ nanotubes, the codoping Sm³⁺ ions can enhance the emission intensity of Eu³⁺ ions.     

Synthesis and luminescence spectra of (Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–YOF):Ln(III) composites

Sols were prepared by reacting yttrium, europium, and terbium trifluoroacetates with thioacetamide in ethyl acetate. The Eu³⁺ and Tb³⁺ concentrations in the sols were 0.10 to 10 wt % relative to yttrium, which corresponded to 0.061 (0.059) to 6.1 (5.9) at % Eu (Tb). The sols were converted into a gel-like state by slowly evaporating the solvent. After ripening, the gels were heat-treated at a temperature of 800°C. X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, and IR spectroscopy results showed that the resultant composites consisted predominantly of a mixture of Y₂O₃ and YOF. The Eu³⁺ and Tb³⁺ ions were shown to substitute for Y³⁺ ions in the crystal lattices of the yttrium oxide and yttrium oxyfluoride. The formation of the (Eu_0.6Y_0.4)₂O₃, Eu₂O₃, and EuOF phases was demonstrated. We determined the types and parameters of the crystal lattices of the synthesized materials in relation to activator concentrations. The luminescence of the composites is due to the ⁵ D ₀ → ⁷ F _j and ⁵ D ₄ → ⁷ F _j electronic transitions of the Eu³⁺ and Tb³⁺ ions and depends on the host and activator compositions, the excitation wavelength, and other factors.     

Study of structural and magnetoelectric properties of 1−x(Ba<Subscript>0.96</Subscript>Ca<Subscript>0.04</Subscript>TiO<Subscript>3</Subscript>)–x(ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript>) ceramic composites

Multiferroic ceramic composites of (1?x)Ba_0.96Ca_0.04TiO₃–(x)ZnFe₂O₄ (BCT-ZF) were prepared from ferroelectric (FE) barium calcium titanate (BCT) and ferromagnetic (FM) zinc ferrite (ZF) by using the solid state reaction method with different mol% fractions of x (x?=?0.1 and 0.2). The preliminary structural studies carried out by X-ray diffraction at room temperature reveals that the samples have a tetragonal structure along with the cubic spinel ferrite phase. Raman spectra of the composites also confirm the existence of BCT phase and ZF phase. The room temperature ferroelectric polarization measurements as a function of magnetic field show the existence strong magnetoelectric coupling of 10.85 (mV/(cm.Oe).     

Syntheses and Magnetic-Properties of Zn-Diluted Sr-Based Perovskite Cobalt Oxides, Sr1?x Zn x CoO3; 0.05≤x≤0.3

In order to check the solubility of Zn in the (Sr_1?x Zn _x )CoO₃ perovskite structure and their research findings, several polycrystalline samples have been prepared under wide extreme synthesis conditions at 6?GPa/1300?C1650?°C. While 0.05??x??0.3 compositions revealed single phased cubic structure materials, x>0.3 showed multi-phased materials for (Sr_1?x Zn _x )CoO₃ system. Like other substituted perovskite cobalt oxide systems (Ca, Y, Ho and Ce), the transport properties of the present materials show rather sizable changes with respect to ??x??, although there are insignificant variations in lattice parameter and in Curie temperature, T _c . All the present samples show soft ferromagnetism with T _c in the range of 272?C285?K for 0.05??x??0.3. The effective paramagnetic moment, P _eff determined from the paramagnetic region decreases upon the substitution of Zn for Sr-site. These P _eff (3.3?C2.8???_B/Co) values for 0.05??x??0.3 compositions seem to suggest that the Co⁴⁺ lie in intermediate spin (IS) state for the present (Sr_1?x Zn _x )CoO₃ series, although they are slightly smaller than those expected for IS-Co⁴⁺; P _eff=3.87???_B/Co. The electrical resistivity is found to increase with increase of ??x?? for the investigated samples. The temperature and field dependence of both positive and negative magnetoresistance (MR) are noted for the Zn substituted samples. About 5% of ?CMR is observed for x=0.05 sample around the transition temperature (280?K) under the field strength difference, ??H=90?kOe. The present research findings are compared with our previous results on different perovskite cobalt oxides.     

Low loss and temperature stable microwave dielectric ceramics in (1 − x)Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript>–xLi<Subscript>2</Subscript>Mg<Subscript>3</Subscript>TiO<Subscript>6</Subscript> (0.1 ≤ x ≤ 0.5) system

The (1???x)Li₂TiO₃–xLi₂Mg₃TiO₆ (x?=?0.1, 0.15, 0.2, 0.3, 0.4, 0.5) ceramics system was fabricated by solid-state synthesis. Test results of X-ray diffraction and electron diffraction spectrum show that all ceramic samples only contain Li₂TO₃ and Li₂Mg₃TiO₆ phase. Scanning electron microscope shows that pores were found in crystal grain due to Li volatilization in high temperature (>?1000 °C). With the rise proportion of Li₂Mg₃TiO₆ in ceramics, dielectric constant (?_r) decreases from 19.55 to 14.53, quality factor (Q×f) increases from 102,800 to 126,000 GHz and temperature coefficient (τ_f) decreases from +?15.9 to ??30.08 ppm/°C. High performance microwave dielectric properties of ?_r?=?18.5, Q×f?=?108,000 GHz, τ_f?=?4.2 ppm/°C were obtained at 1390 °C for 0.85Li₂TiO₃–0.15Li₂Mg₃TiO₆ ceramics. To suppress Li volatilization, LiF, a low temperature melting addition, was added to 0.85Li₂TiO₃–0.15Li₂Mg₃TiO₆ ceramics. LiF effective lowers sintering temperature from 1390 to 1175 °C due to LiF liquid-phase sintering and restricts Li evaporation, and a well-developed grain morphology and excellent dielectric properties (?_r?=?18.5, Q×f?=?87,000 GHz, τ_f?=???18 ppm/°C) was obtained which hold promise in 4G tele-communication applications.     

Synthesis,structural analysis and microwave dielectric properties of LnTiSb<Subscript>x</Subscript>Nb<Subscript>1−x</Subscript>O<Subscript>6</Subscript> (Ln = Ce,Pr) ceramics

LnTiSb_xNb_1−xO₆ (Ln = Ce, Pr) ceramics were prepared by the conventional solid state ceramic route for x = 0, 0.05, 0.1, 0.15, 0.2 and 0.25. The structure of the materials was analyzed using X-ray diffraction techniques. The cell parameters and the theoretical densities of the samples were calculated using least square methods. The samples are sintered to more than 90% of the theoretical density at 1,325–1,350 °C. The microwave dielectric properties were measured using the cavity resonator method. The surface morphology of the sintered sample was analyzed using Scanning Electron Microscopy. All the materials have good microwave dielectric properties and are suitable for dielectric resonator applications.     

Hydrothermal synthesis and multi-color photoluminescence of GdVO<Subscript>4</Subscript>: Ln<Superscript>3+</Superscript> (Ln = Sm,Dy, Er) sub-micrometer phosphors

GdVO₄: 5 mol% Ln³⁺ (Ln = Sm, Dy, Er) sub-micrometer phosphors have been synthesized by a facile hydrothermal technology and characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), and FT-IR spectroscopy. These phosphors present fusiform-like polyhedron microcrystals with tetragonal zircon structure and average particle size of about 300 nm. The luminescent properties of the three lanthanide ions activated GdVO₄ submicrometer phosphors are studied, which show the characteristic multicolor luminescence of Sm³⁺ (orange), Dy³⁺ (light yellow) and Er³⁺ (green) ions in visible region.     

Magnetic and electrical properties of ordered 112-type perovskite LnBaCoMnO<Subscript>5+δ</Subscript> (Ln = Nd,Eu)

Investigation of the oxygen-deficient 112-type ordered oxides of the type LnBaCoMnO_5+δ (Ln = Nd, Eu) evidences certain unusual magnetic behavior at low temperatures, compared to the LnBaCo₂O_5+δ cobaltites. The ordered NdBaCoMnO_5.9 depicts a clear paramagnetic to antiferromagnetic type transition around 220 K, whereas for EuBaCoMnO_5.7 one observes an unusual magnetic behavior below 177 K which consists of ferromagnetic regions embedded in an antiferromagnetic matrix. The existence of two sorts of crystallographic sites for Co/Mn and their mixed valence states favor the ferromagnetic interaction, whereas antiferromagnetism originates from the Co³⁺–O–Co³⁺ and Mn⁴⁺–O–Mn⁴⁺ interactions. Unlike the parent compounds, the present Mn-substituted phases do not exhibit prominent magnetoresistance effects in the temperature range 75–400 K.     

Synthesis and properties of Ca<Subscript>2.8</Subscript>Ln<Subscript>0.2</Subscript>Co<Subscript>4</Subscript>O<Subscript>9 + δ</Subscript> (Ln = La,Nd, Sm,Tb-Er) solid solutions

Ca_2.8Ln_0.2Co₄O_{9 + δ} (Ln = La, Nd, Sm, Tb-Er) solid solutions have been prepared via a citrate route and their structural parameters have been determined. Their thermal expansion, thermoelectric power, thermal conductivity, and electrical conductivity have been measured above room temperature. The results demonstrate that all of the materials obtained are p-type semiconductors. Their unit-cell parameters decrease with a decrease in the ionic radius of the Ln³⁺ cation substituted for Ca²⁺, and their thermoelectric power increases with an increase in the number of f electrons of the Ln³⁺ cation. We have determined the electron and phonon contributions to the thermal conductivity of the materials and evaluated the thermoelectric power factor and thermoelectric figure of merit of the oxide ceramics. The highest thermoelectric power factors are offered by the Ca_2.8Tb_0.2Co₄O_{9 + δ} and Ca_2.8Er_0.2Co₄O_{9 + δ} solid solutions: 0.27 and 0.29 mW/(m K²), respectively, at T = 1100 K.     

Tunable luminescence of Sr<Subscript>5(1−x)</Subscript>Ba<Subscript>5x</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>Cl:Eu<Superscript>2+</Superscript> (0 ≤ x ≤ 100%) phosphors from different Eu<Superscript>2+</Superscript> centers

In this paper, a series of Eu²⁺ activated Sr_5(1?x)Ba_5x(PO₄)₃Cl (0?≤?x?≤?100%) phosphors were prepared by solid-state reaction method, and their luminescence properties under near-ultraviolet excitation were investigated. For Eu²⁺-activated Sr₅(PO₄)₃Cl, a strong emission band located at 445 nm is observed upon 365 nm excitation, which could be attributed to the 4f ⁶5d ¹–4f ⁷ transition of different Eu²⁺ centers. When the Ba²⁺ is introduced into the Sr₅(PO₄)₃Cl:Eu²⁺, the emission band of Eu²⁺ is broadened largely. The fluorescence lifetimes for different Eu²⁺ centers were determined by the decay curves and time-resolved spectra. The excitation spectra of the as-prepared samples cover a wide wavelength range from 240 to 420 nm, which can well match the emission wavelength of the near ultraviolet LED chip. The investigation of the thermal luminescence stability reveals that the introduction of Ba²⁺ could improve the thermal quenching properties.     

Transport Properties of TlInSe2〈Ln〉 (Ln = Eu, Sm, Yb)

The electrical conductivity and Hall coefficient of TlInSe₂Ln (Ln = Eu, Yb, Sm) were measured between 300 and 900 K. The results were used to determine the band gap, ionization energy of impurities, conductivity type, and Hall mobility of charge carriers in TlInSe₂Ln. The temperature at which the Hall coefficient changes sign is shown to increase with doping level.     

Ln<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>:Mn<Superscript>4+</Superscript> (Ln = Y and Lu): non-rare-earth doped red phosphor for improving light properties of white light emitting diodes

We fabricated a series of Y₃Al₅O₁₂:Mn⁴⁺ and Y_1?yLu_yAl₅O₁₂:Mn⁴⁺ phosphors by a solid state reaction. The phase and the optical properties of the synthesized phosphors were investigated. Under the excitation at 465 nm, Y₃Al₅O₁₂:Mn⁴⁺ phosphors show emission bands locating at deep red regions, which is induced by the spin- and parity-forbidden ²E_g → ⁴A_1g transitions of Mn⁴⁺. The substitution of Y³⁺ by Lu³⁺ decreases the lattice parameter and thus strengthens the crystal field strength, which gives rise to the blue shift of emission band for Y_1?yLu_yAl₅O₁₂:Mn⁴⁺ phosphors. Due to the compensation of red light by Y₃Al₅O₁₂:Mn⁴⁺ or Y_1?yLu_yAl₅O₁₂:Mn⁴⁺ phosphor, the values of correlated-color-temperature for fabricated LEDs are decreased, which leads to the suitable application for them in indoor illumination.     

Behaviour of multiphase PVDF in (1−x)PVDF/(x)BaTiO<Subscript>3</Subscript> nanocomposite films: structural,optical, dielectric and ferroelectric properties

The present paper deals with the synthesis and characterization of (1?x)PVDF/(x)BaTiO₃ nanocomposite films with x?=?0.1, 0.2, 0.3, 0.4 and 0.5. The samples were synthesized by simple solution mixing method followed by tape casting process. FESEM images show the homogeneous dispersion of BaTiO₃ nanoparticles within the matrix of poly(vinylidene fluoride) (PVDF) with slight agglomeration. An improvement in the thermal stability of nanocomposite film is observed by TGA results. XRD as well as FTIR analysis indicate the α–β phase transition of PVDF in the nanocomposite films. The embedded BaTiO₃ forms an intermediate band among the PVDF structures and thus decreases the band gap of nanocomposite films by absorbing the wavelength of lower energies. The band gap of nanocomposite films for x?=?0.4 decreases to 2.4 eV as compared to 5.0 eV for pristine PVDF. The dielectric constant (?′) of pristine PVDF at 50 Hz is 8.9, which increases to 26.7 for (0.6)PVDF/(0.4)BaTiO₃ nanocomposite film. An increase in the charge storage ability is observed from PE loops, as (0.6)PVDF/(0.4)BaTiO₃ nanocomposite film has highest value of polarization (0.093 µC cm^?2) as compared to pristine PVDF (0.020 µC cm^?2). This shows an increase in the charge storage ability of (1?x)PVDF/(x)BaTiO₃ nanocomposite films as compared to pristine PVDF.     

CN<em>x/TiN多层复合涂层抗水蚀性能的研究

采用多弧-磁控溅射镀膜机在不锈钢2Cr13衬底上沉积CN_<em>x/TiN多层复合涂层。利用光电子能谱仪(XPS)和透射电子衍射(TED)对涂层的组成和结构进行分析。利用自行研制的高压水蚀试验装置对不锈钢、高铬铸铁、司太立合金以及CN_<em>x/TiN多层复合涂层的抗水蚀性能进行对比试验,最后对涂层的水蚀失效机理进行了探讨。试验结果表明:CN_<em>x/TiN多层复合涂层具有较高的硬度、附着力、抗热冲击性能以及优异的抗水蚀性能,是一种优良的汽轮机末级叶片抗水蚀用涂层。     

Pb1−x Bi x /Bi/Pb1−x Bi x Josephson junction

A superconductor/semimetal/superconductor (S/SM/S) Josephson junction has been developed. We have used an alloy of Pb_1–x Bi _x (0x 0.6) as the superconductor and Bi as the semimetal. By irradiating at X-band microwave of 10 GHz, Shapiro steps were observed for various bismuth barrier thicknesses inÅ and bismuth weight ratiosx. Finally, we obtained the empirical relationship for barrier thickness, below which microwaves could be detected for various bismuth weight ratiosx at the temperature of 4.2 K.