Semiconducting properties of barium vanadate glasses doped with barium chloride

Semiconducting barium vanadate glasses doped with BaCl₂ from 0 to 15 mol% were studied. Electrical d.c. conductivity measurements and an electron spin resonance investigation in the X-band were made. The concentration dependence of d.c. conductivity exhibits a minimum at 7 mol% BaCl₂. The activation energy increases with increasing BaCl₂ content up to 7% and decreases at higher concentrations of BaCl₂. The temperature dependence of the d.c. conductivity shows the effect of BaCl₂ as an oxidizing agent which controls the electrical conductivity, as a result of modification of the reduced vanadium valence ratio and a change in concentration of the paramagnetic ions. The plots of log versus 1 000/T are linear for all the BaCl₂-doped glasses. The data of the d.c. investigations were analyzed in terms of small polaron theory, and this confirms the applicability of the polaronic hopping model of electrical transport. The influence of BaCl₂ content on density indicates that in this ternary system the additivity role is not obeyed. The minimum occurs at the same concentration of 7 mol% BaCl₂ as noted for the electrical conductivity.     

Electrical properties of niobium doped barium bismuth-titanate ceramics

BaBi₄Ti_4–5/4xNb_xO₁₅ (BBNTx, x = 0, 0.05, 0.15, 0.30) ceramics have been prepared by solid state method. XRD data indicate the formation of single-phase-layered perovskites for all compositions. SEM micrographs suggest that the grain size decreases with Nb doping. The effect of niobium doping on the dielectric and relaxor behavior of BaBi₄Ti₄O₁₅ ceramics was investigated in a wide range of temperatures (20–777 °C) and frequencies (1.21 kHz to 1 MHz). Nb doping influences T_c decrease as well as the decrease of dielectric permittivity at Curie temperature. At room temperature, undoped BaBi₄Ti₄O₁₅ exhibits dielectric constant of ～204 at 100 kHz, that slightly increases with Nb doping. The conductivity of BBNT5 ceramics is found to be lower than that of other investigated compositions. The value of activation energy of σ_DC was found to be 0.89 eV, 1.01 eV, 0.93 eV and 0.71 eV for BBT, BBNT5, BBNT15 and BBNT30, respectively.     

Thermoelectric properties of niobium doped hexagonal barium titanate

The ceramic samples of Nb doped hexagonal barium titanate (h-Ba₁Nb_xTi_1−xO₃) were prepared by the usual solid state reaction using stoichiometric amounts of BaCO₃, TiO₂, and Nb₂O₅ powders for different concentrations of Nb. These samples were characterized by X-ray diffraction (XRD), electric and magnetic measurements. The XRD patterns of all these samples showed an average hexagonal structure refined in space group P6₃/mmc. The electrical resistivity showed a semiconducting like behavior from 400 K down to the lowest possible measured temperature. The magnetic susceptibility measured up to 400 K in an applied field of 1 T changes from diamagnetic to paramagnetic one, reaches a certain maximum at x=0.02 and then decreases with increased dopant concentration. The density of states (DOS) deduced from the paramagnetic susceptibility showed a peak at x=0.02 nominal concentration of Nb. We attribute this phenomenon as an increase in the effective mass of carriers with dopant concentration. The thermoelectric power measured from 77–300 K for all these samples is negative showing that conduction carriers are electrons in this system and its magnitude is directly proportional to the temperature. We suggest that conduction in this system occurs through variable range hopping between localized states within an impurity band at low temperature.     

Dielectric properties of polycrystalline CaTiO3 doped with yttrium oxide

Y³⁺ was substituted for Ca²⁺ in polycrystalline CaTiO₃ in amounts up to 15 at %. Sintering conditions (1450° C, 15 h) were such that grain sizes were > 25 m. Stoichiometry was adjusted on the assumption that the excess charge of the dopant was compensated by the creation of calcium vacancies. This assumption was supported by measurements of the Ca/Ti ratio in the grains by electron-probe microanalysis. Unlike yttrium-doped SrTiO₃, material sintered in air was light-coloured with no evidence of semiconductivity. On the other hand, when sintering was done in nitrogen, dielectric relaxation characteristic of boundary layers was observed for dopant levels > 1 mol %. The experimental data support the view that dielectric relaxation in SrTiO₃ and CaTiO₃ results from semiconducting grains with resistive surface layers and that the semiconductivity arises because oxygen loss from the grains during sintering is increased by donor doping.     

Structural and luminescent properties of cerium-ion doped barium borophosphates

The effects of synthesis conditions on the luminescence characteristics of Ce³⁺ in barium borophosphate phosphors are investigated in the present study. Synthesis of cerium-ion doped BaBPO₅ in the oxidizing atmosphere results in partial reduction of Ce⁴⁺ to Ce³⁺. The dominant emission at 320 nm arises due to Ce³⁺ located at Ba²⁺ sites without local charge compensation; while, the relatively weak emission at 380 nm is ascribed to Ce³⁺ substituting at Ba²⁺ sites in association with charge compensatory vacancy. The complete reduction of Ce⁴⁺ to Ce³⁺ occurs for the samples heated in the reducing atmosphere. The increased luminescence of BaBPO₅ codoped with cerium and sodium ions is attributed to the reduction in non-radiative energy transfer.     

Effect of sintering temperature on the microstructure and electrical properties of zirconium doped barium titanate ceramics

Lead-free Ba(Zr_0.15Ti_0.85)O₃ (BZT15) ceramics were synthesized by adopting the solid-state synthesis method. The effect of increasing sintering temperature (T_s) in the range of 1,350–1,450 °C on the microstructure, dielectric, polarization, and electric field induced strain of the ceramics was studied. Fine grained (~260 nm) BZT15 ceramics displayed single phase perovskite structure with relative densities >94 % of the theoretical density. Both grain size and shape were influenced by the sintering parameters. With increase in T_s, not only the maximum dielectric constant decreased from 11,412 to 8,734 along with an increase in the degree of diffuseness, but also interestingly the Curie temperatures were found to vary within an interval of 61–73 °C. Optimum sintering temperature has been found resulting in high remnant polarisation and strain in these ceramics. The properties observed are attributed to a contribution from all polar vectors present in coexistent phases.     

掺杂稀土元素镧的钡铁氧体超微粉末的微波吸收特性研究

采用溶胶-凝胶法制备了掺杂稀土元素镧的钡铁氧体超微粉末,就镧元素的掺杂含量对钡铁氧体吸波性能的影响进行了对比研究.实验表明,用聚乙二醇凝胶法制备的BaLaxFe12-xO19超微粉末,当x为0.03时,对微波吸收效果最佳.在涂层厚度1.0mm,测试频段为7.5～11.9GHz内,吸收量均在25dB以上,在11.6GHz处,吸收峰值达41.4dB.     

Structural characteristics and dielectric properties of neodymium doped barium titanate

Neodymium (Nd) doped barium titanate powder (Ba_(1−x)Nd _x TiO₃) with x value varying from 0, 0.01, 0.03, 0.05, 0.07, 0.10 and 0.13 was prepared using the sol gel method. The powder samples were calcined at 700 °C and tetragonal phase appeared in the powders before they were sintered at 1250 °C for 3 h. The undoped samples have a polycrystalline tetragonal structure, but Nd doping into the BaTiO₃ caused phase transformation from tetragonal to cubic. The smaller grains (0.35 μm) produced with the addition of Nd is associated to the inhibition of grain growth of samples. The powders for each composition were pressed into pellets and tested as dielectric resonator antenna (DRA). It was found that on the actual antenna circuit, each sample showed a resonance frequency at X-band application and a dielectric constant value in the range of 51.25–56.89 and tangent loss was 0.039–0.045, depending on the concentration of the Nd at room temperature.     

Chemical bonding and optoelectrical properties of ruthenium doped yttrium oxide thin films

Highly infrared transparent conductive ruthenium doped yttrium oxide (RYO) films were deposited on zinc sulfide and glass substrates by reactive magnetron sputtering. The structural, optical, and electrical properties of the films as a function of growth temperature were studied. It is shown that the sputtered RYO thin films are amorphous and smooth surface is obtained. The infrared transmittance of the films increases with increasing the growth temperature. RYO films maintain greater than ∼65% transmittance over a wide wavelength range from 2.5 μm to 12 μm and the highest transmittance value reaches 73.3% at ∼10 μm. With increasing growth temperature, the resistivity changed in a wide range and lowest resistivity of about 3.36 × 10⁻³ Ω cm is obtained at room temperature. The RYO thin films with high conductivity and transparency in IR spectral range would be suitable for infrared optical and electromagnetic shielding devices.     

Physical properties of natively textured yttrium doped zinc oxide films by sol-gel

Sol-gel derived yttrium doped ZnO films of various thicknesses have been deposited by the dip coating technique. The investigations of microstructural, electrical and optical properties of post heat-treated films in air as a function of thickness have been made. It is found that high quality films are obtained at an annealing temperature of 550 ^∘C. The (002) preferential growth of both the doped and undoped ZnO films changes to (101) as the thickness of the films were increased. The full width at half maximum of (002) X-ray peak decreases with annealing temperature and the lattice constant is found to approach the value of bulk ZnO. Natively textured films have been obtained for film having thickness greater than 0.8 μm. The thinner films are found to be non-textured with high resistivity. The formation of the textured surface of the film is linked to the suppression of c-axis (002) orientation and the columnar growth in the thick film.     

Ferroelectric properties of barium calcium titanate ceramics doped with bismuth oxide

Ferroelectric properties of Bi doped (Ba_1 − xCa_x)_0.925Bi_0.05TiO₃ (Bi-BCT, 0.10 < x < 0.30) ceramic prepared by the solid-state technique have been studied. An interesting double-like hysteresis (P-E) loop at room temperature (300 K) with the remarkable linear dielectric response was observed over a certain electric field range. Room temperature P-E loops before and after de-aging, as well as those at different values of field cycling, could exclude the possibility that the double P-E loops might result from the antiferroelectric components and the electric field induced paraelectric-ferroelectric (PE-FE) transition near Curie temperature (T_c) in Bi-BCT, and verify that there exists a diffusional aging effect in Bi-BCT. A symmetry-conforming short-range ordering (SC-SRO) of point defects is suggested to be responsible for the observations of the interesting double-like P-E loop in Bi-BCT.     

Study on luminescent properties of Eu3+ doped new type yttrium tungsten oxide nanophosphors

In this paper, a novel nanophosphor, Y10W2O21:Eu, was synthesized through co-precipitation which is a simple and low-costing method. The structure and morphology of the nanocrystal samples were characterized by using XRD and FE-SEM. The emission spectra, excitation spectra and fluorescence decay curves were measured. J-O parameters, quantum efficiencies of Eu3+ 5D0 energy level, color coordinates and Huang-Rhys factor of Y10W2O21:Eu nanophosphors were calculated. The results indicate that EU3+ 5D0-7F2 red luminescence at 610 nm can be effectively excited by 394 nm near-UV light and 464 nm blue light in Y10W2O21 host, which is similar to the familiar Eu3+ doped tungstate phosphors (e.g., Gd2(WO4)3:Eu, CaWO4:Eu). Besides, compared with the other types of tungstate phosphors, a less expensive tungsten was used, which can effectively reduce cost. Therefore, the Y10W2O21:Eu red nanophosphors may have a potential application for white LED.     

不同稀土元素掺杂M型钡铁氧体超微粉末的磁性研究

利用溶胶－凝胶自蔓延高温合成法制备了4种稀土元素（La、Nd、Sm、Gd）掺杂钡铁氧体超微粉末。就烯土元素的种类、稀土掺杂量、合成工艺条件对钡铁氧体磁学性能的影响进行了较系统的研究。采用振动样品磁强计对粉末的磁学性能进行了检测。     

Dielectric properties of vanadium doped barium titanate synthesized via high-energy ball milling

The study shows the advisability of using a mechanochemical synthesis method, based on a high-energy planetary ball milling, to a modification of barium titanate by a vanadium doping. This method improves useful properties of BaTi_0:95V_0:05O₃ as a capacitor material. It has a high value of electric permittivity ?′ in the wide range of temperature and low dielectric losses ?″ as well as a low electrical conductivity.     

真空烧结Nd:YAG透明陶瓷的研究

以高纯Al2O3、Y2O3和Nd2O3粉体为原料,少量MgO和SiO2为添加剂,采用真空烧结方法制备了不同掺杂浓度的NdYAG(Y3Al5O12)透明陶瓷,并且对烧成的NdYAG陶瓷的显微结构和光学性能进行了研究.结果发现,真空烧结有利于气孔的排出,从而达到几乎完全致密化;适量烧结助剂的添加,有利于提高陶瓷的烧结活性和透光性;NdYAG陶瓷能够实现高浓度掺杂,但是透过率随着Nd掺杂量的增加有所降低,光吸收随着掺杂量的增加而增加;掺杂浓度升高,发射谱峰出现展宽,并且出现红移现象,当Nd3+的掺杂浓度大于3.0%(原子分数)时,发射强度急剧降低.     

The low magnetic field properties of superconducting bulk yttrium barium copper oxide-sintered versus partially melted material

A comparison of the low magnetic field properties of sintered (990°C) and partially melted samples (1050°C) has been performed. Changes in the microstructure produced by recrystallization from the melt result in a significant increase in flux pinning at 77 K. Low-frequency (10–100 Hz), low-a.c. magnetic field (0.01–9.0 Oe) a.c. susceptibility data show that gross changes in the a.c. loss component accompanies the observed changes in microstructure. The effects of applied d.c. magnetic fields (10–220 Oe) on the a.c. responses of these microstructures have also been probed. Data are analyzed and critically discussed in terms of current models appropriate for granular superconductors and in terms of older models appropriate for metallic alloys and compounds. Particular attention is given to published interpretations of the in-phase or loss component of the a.c. magnetic susceptibility and to the possible roles which minority phases and sample inhomogeneities may play in determining the detailed a.c. responses of these high-T _coxides.     

Effect of the composition of starting yttrium aluminum hydroxide sols on the properties of yttrium aluminum garnet powders

A technique has been developed for the synthesis of yttrium aluminum garnet sols aggregationstable in water as a dispersion medium. Depending on the type of precursor used, the temperature of yttrium aluminum garnet formation varies from 900°C to 1100°C. We have obtained yttrium aluminum garnet nanopowders with an average particle size from 40 to 300 nm, depending on the aluminum yttrium hydroxide hydrosol synthesis procedure and annealing temperature.