Dielectric properties of NaF-B2O3 glasses doped with certain transition metal ions

Dielectric constant ε, loss tan δ, a.c. conductivity Σ and dielectric breakdown strength of NaF-B₂O₃ glasses doped with certain transition metal ions (viz. Cu²⁺, VO²⁺, Ti⁴⁺ and Mn⁴⁺) are studied in the frequency range 10²-10⁷ Hz and in the temperature range 30–250°C. The values of ε, tan δ, Σ_a.c. are found to be the highest for Cu²⁺ doped glasses and the lowest for Mn⁴⁺ doped glasses. Activation energy for a.c. conduction and the value of dielectric breakdown strength are found to be the lowest for Cu²⁺ doped glasses and the highest for Mn⁴⁺ doped glasses. With the help of infrared spectra, increase in the values of ε and tan δ of these glasses with frequency and temperature are identified with space charge polarization. An attempt has been made to explain a.c. conduction phenomenon on the basis of quantum mechanical tunneling model (QMT)/carrier barrier hopping model.     

Acoustic investigations on PbO-Al2O3-B2O3 glasses doped with certain rare earth ions

Elastic moduli (Y, η), Poisson’s ratio (σ), microhardness (H) and some thermodynamical parameters such as Debye temperature (θ_D), diffusion constant (D _i),latent heat of melting (ΔH _m) etc of PbO-Al₂O₃-B₂O₃ glasses doped with rare earth ions viz. Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺ and Yb³⁺, are studied as functions of temperatures (in the temperature range 30–200°C) by ultrasonic techniques. All these parameters are found to increase with increasing atomic numberZ of the rare earth ions and found to decrease with increasing temperature of measurement. From these results (together with IR spectra of these glasses), an attempt is made to throw some light on the mechanical strength of these glasses.     

掺稀土离子玻璃的光放大效应

光放大材料是光纤放大器的主要组成部分,它决定光纤放大器的光放大功率。本文介绍了掺稀土离子如Er^3 、Nd^3 、Pr^3 及Dy^3 等玻璃的光放大原理以及影响光放大的各种因素。稀土离子本身存在的多种发射跃迁、无辐射跃迁,稀土离子间相互作用以及玻璃基质都影响稀土离子的光放大跃迁效率。上述分析对掺稀土离子玻璃的光放大材料性能的改进和新材料的设计可提供有益的指导。     

Elastic properties of ZnF2-PbO-TeO2 glasses doped with certain rare earth ions

The elastic moduli (Y, η, σ andH) and some thermodynamical parameters, such as Debye temperatureθ _D, diffusion constantD _i and latent heat of melting ΔH _m, of ZnF₂-PbO-TeO₂ glasses doped with some rare earth (Pr³⁺, Nd³⁺, Eu³⁺ and Tb³⁺) ions are determined as functions of temperature using piezo electric composite oscillator technique. All the parameters are found to decrease with increase in the atomic number Z of the rare earth ions and with increase in the temperature of measurement. The results are explained on the basis of the density of localized bonding defect states within the band gap of the material.     

稀土元素与N共掺杂TiO2光催化剂的研究进展

TiO2作为一种重要的光催化剂,对其进行掺杂改性可有效扩展其光谱响应范围,提高其光催化活性。介绍了稀土元素与N对TiO2进行共掺杂改性的机理及研究现状,分析了共掺杂对TiO2晶体结构、电子结构以及光学性能、氧化还原性能的影响,总结了稀土元素与N共掺杂改性TiO2存在的问题以及今后的研究前景。     

Some thermodynamic aspects of the high-temperature transition in doped V2O3

Measurements of the entropy change are reported for the high-temperature metal-insulator (MI) transitions in the (V_1–xCr_x)₂O₃ and (V_1–xAl_x)₂O₃ systems. It is emphasized that the entropy of the I phase exceeds that of the M phase. Evidence is presented to show that the M and I phases coexist over a narrow temperature range. The transformation is attended by enormous hysteresis effects; these indicate that the lattice plays an important role in the transition. The probable role of Cr³⁺ and Al³⁺ as a dopant in the V₂O₃ lattice is briefly discussed. A phase diagram for the dilute V₂O₃-Al₂O₃ alloy system is presented.     

Optical properties of zirconia doped with yttria and some rare earth oxides

Nanometric powders of cubic zirconia stabilized with yttria and rare element oxides (Sm, Nd, Gd) were prepared by crystallization under hydrothermal conditions. The powders were uniaxially compacted, repressed isostatically, pressure-less sintered in oxygen atmosphere and hot isostatically pressed under 300 MPa Ar atmosphere. Fully dense samples were polished from both sides. The optical properties were analyzed based on the spectral dependence of the transmittance (T) and reflectance (R). Spectroscopic measurements have shown that all materials fabricated in the present work are highly transparent, with total transmission above 90% towards the long-wavelength end of the near-IR range of the spectrum. Discussion of these results will be given.     

稀土气相掺杂BaTiO3基PTC陶瓷的制备与电性能

采用稀土气相掺杂的方法制备了La,Pr,Gd改性的BaTiO3 基PTC陶瓷,通过室温电阻率和温-阻效应的测试及SEM分析,对其PTC特性进行了研究.结果表明:BaTiO3基PTC陶瓷经稀土气相掺杂后,室温电阻率明显下降,在不同粉料配方基础上制备的4组BaTiO3基PTC陶瓷,经La,Pr,Gd气相掺杂后,其室温电阻率分别下降为2.5×105、70.0、220.0、40.0、3.5×104、50.0、9.6、5.0 Ω·m以及1.3×104、98.5、2.3×104、32.4 Ω·m.而稀土液相掺杂的BaTiO3 基PTC陶瓷的室温电阻率均在104Ω·m以上.稀土气相掺杂BaTiO3 基PTC陶瓷的温-阻效应与稀土液相掺杂结果截然不同,产生了明显的NTCR效应.     

Microwave properties of vanadium borate glasses

A.c. conductivity, dielectric constant and loss, and variation with temperature (302–373 K) for four different compositions of V₂O₅-B₂O₃ glasses were reported at 9.586 GHz microwave frequency. The quality factor (Q) and attenuation factor (α being the important parameters in the microwave range of applications were also studied. The change in the dielectric constant and loss was observed with composition of V₂O₅. The maximum loss was found to be at 15V₂O₅ mol‰ The peak was observed in loss with temperature.     

FTIR spectroscopic study of some bismuth germanate glasses containing gadolinium ions

Since infrared spectroscopy and density are advantageous tools for the investigations of glasses, we have used them to obtain information concerning the local structure of xGd₂O₃·(100 − x)[4Bi₂O₃·GeO₂] glass system, with 0 ≤ x ≤ 30 mol%. Gd₂O₃ play the network modifier role in the studied glasses and determines, by progressive addition, the increase of structural volume difference between the hypothetical crystalline compounds and the quenched samples. FTIR spectroscopy data show that the glass structure consists on the BiO₆, GeO₄ and GeO₆ structural units, and the conversion among these units mainly depends on the Gd₂O₃ content.     

氧化铟-稀土氧化物共掺CeO2基导电电解质材料的制备与表征

设计了以氧化铟与稀土氧化物（La2O3或Nd2O3）为共同掺杂元素的新型掺杂技术，并利用以聚乙烯醇为聚合剂的化学合成方法制备了CeO2基氧离子导电电解质材料。X射线衍射分析表明，本实验采用的湿化学合成方法容易获得具有纳米结构的高纯氟化钙型结构的CeO2基导电材料．材料导电性的交流阻抗测试分析说明，适当比例的氧化铟与稀土氧化物共掺能有效提高CeO2的导电性；其导电性比相同合成方法制备的Sm2O3掺杂CeO2的导电性更好。利用有效离子半径和相关结合焓理论分析了不同掺杂氧化物对CeO2基材料离子导电性影响。     

Mechanical properties and microstructure of Al2O3/TiAl in situ composites doped with Cr2O3

Al₂O₃/TiAl composites were successfully fabricated from powder mixtures of Ti, Al, TiO₂ and Cr₂O₃ by a hot-press-assisted exothermic dispersion method. The effect of the Cr₂O₃ addition on the microstructures and mechanical properties of Al₂O₃/TiAl composites was characterized, and the results showed that the Rockwell hardness, flexural strength and fracture toughness of the composites increased as the Cr₂O₃ content increased. When the Cr₂O₃ content was 2.5 wt%, the flexural strength and the fracture toughness attained peak values of 925 MPa and 8.55 MPa m^1/2, respectively. This improvement of mechanical properties was due to the more homogeneous and finer microstructure developed from the addition of Cr₂O₃ and an increase in the ratio of α₂-Ti₃Al to γ-TiAl matrix phases.     

Structural and optical properties of spray pyrolytically prepared Fe2O3 thin films

Fe₂O₃ thin film was prepared using aqueous solution of FeCl₃ by spray pyrolysis. The substrate temperature was 450°C. The lattice parametersa andc for different concentrations were calculated from X-ray diffraction study. Hexagonal structure of the Fe₂O₃ thin film was confirmed. Band gap values of Fe₂O₃ prepared from different concentrations were determined from optical transmission data.     

Dielectric properties of sol-gel derived Ta2O5 thin films

The dielectric constant and the dielectric loss of tantalum pentoxide (Ta₂O₅) thin films, produced by sol-gel spin-coated process on Corning glass substrates, have been investigated in the frequency range of 20-10⁵ Hz and the temperature range of 183-403 K, using ohmic Al electrodes. The frequency and temperature dependence of relaxation time has also been determined. The capacitance and loss factor were found to decrease with increasing frequency and increase with increasing temperature. The activation energy values were evaluated and a good agreement between the activation energy values obtained from capacitance and dielectric loss factor measurements were observed.     

稀土掺杂碲铌锌系统玻璃的非线性光学性能

碲铌锌系统玻璃是一种性能优良的三阶非线性光学玻璃材料,综合品质优于其它非线性光学玻璃材料。在碲铌锌系统玻璃中引入稀土离子,利用其4f电子的跃迁提高谐波光子激发的可能性,从而提高玻璃的三阶光学非线性。研究表明,随着稀土离子的加入,532nm附近玻璃的光吸收明显增加,使由相同波长激光激发的光学非线性呈线性增长。掺入Ce3+、Ho3+、Y3+的玻璃三阶非线性极化率最高可达2.3×10-12esu。     

Synthesis and characterization of β type solid solution in the binary system of Bi2O3-Eu2O3

We have investigated Bi₂O₃-Eu₂O₃ binary system by doping with Eu₂O₃ in the composition range from 1 to 10 mole% via solid state reactions and succeeded to stabilize β-Bi₂O₃ phase which is metastable when pure. Stability of β-Bi₂O₃ polymorph was influenced by heat treatment temperature. Tetragonal type solid solution was obtained in 3–6 mole% addition range when annealed at 750°C and the range was 2–7 mole% when annealed at 800°C. We have also carried out investigations on lattice parameters, microstructural properties and elemental compositions of this β type solid solution for each doping ratio. Lattice parameters increased with amount of Eu₂O₃ addition. Our experimental observations strongly suggested that oxygen deficiency type non-stoichiometry is present in doped β type solid solutions.     

Transmittance enhancement of micro-grating structure sapphire with high-refractive index Y2O3 layer

The theoretical analysis of micro-grating structure sapphire (sapphire MGS) with Y₂O₃ layer using the finite-difference time-domain method is presented. The results show that the total transmittance and reflectance of Y₂O₃/sapphire MGS have a close relationship with the thickness of Y₂O₃ layer, where about 300 nm is the ideal thickness. According to the simulant results, 300 and 600 nm of thicknesses of Y₂O₃ layer deposited onto sapphire MGS substrate by reactive magnetron sputtering method are studied experimentally. The experimental results agree well with the calculated data and further have better optical properties because of the rough surface of Y₂O₃ layer. It illustrates that the 300-nm Y₂O₃/sapphire MGS exhibits the best increase in the total transmittance and diffuse transmittance due to the greater graded refractive index profile than sapphire MGS. The results of this paper have potential applications in solar cells and diffraction grating.     

Relaxation studies on V2O5-TeO2 glasses using heterogeneous conductor model

The dielectric modulus spectra of glasses in the system V₂O₅-TeO₂ have been studied as a function of frequency in the temperature range 230 to 330K. A heterogeneous conductor model developed recently with the assumption of a sinusoidally varying local conductivity in the conducting phase has been successfully applied to analyse the data in this glass system. The Kohlrausch-Williams-Watts (KWW) stretched exponential function has also been used to fit the measured modulus spectra. The exponentβ is found to be correlated to the conductivity fluctuation in the conducting phase as assumed in the heterogeneous model.     

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。     

Microstructure and electrical properties of Al2O3-ZrO2 composite films for gate dielectric applications

Al₂O₃-ZrO₂ composite films were fabricated on Si by ultrahigh vacuum electron-beam coevaporation. The crystallization temperature, surface morphology, structural characteristics and electrical properties of the annealed films are investigated. Our results indicate that the amorphous and mixed structure is maintained up to an annealing temperature of 900 °C, which is much higher than that of pure ZrO₂ film, and the interfacial oxide layer thickness does not increase after annealing at 900 °C. However, a portion of the Al₂O₃-ZrO₂ film becomes polycrystalline after 1000 °C annealing and interfacial broadening is observed. Possible explanations are given to explain our observations. A dielectric constant of 20.1 is calculated from the 900 °C-annealed ZrO₂-Al₂O₃ film based on high-frequency capacitance-voltage measurements. This dielectric characteristic shows an equivalent oxide thickness (EOT) as low as 1.94 nm. An extremely low leakage current density of ∼2×10⁻⁷ A/cm² at a gate voltage of 1 V and low interface state density are also observed in the dielectric film.