Photochemical behavior of poly(organophosphazenes). IX. Internal photostabilization effects in (4-benzoylphenoxy) x (β-naphthoxy)2−x phosphazene copolymers

The synthesis and the photochemical behavior in solution and in films of a series of polyphosphazenes containing both benzophenone and naphthalene groups are described. The light energy absorbed by the benzophenone group is transferred to the naphthalene chromophore and wasted in photophysical processes which are not harmful to the polymer. This leads to a remarkable photostabilization of the benzophenone-containing phosphazene macromolecules, the extent of which is related to the amount of naphthalene substituents present in the copolymers. The naphthoxy groups directly bonded to the polyphosphazene backbone are more efficient photostabilizers than free naphthalene added to solutions or films of the benzophenone-substituted polyphosphazenes. This is the first example of photostabilization of a polyphosphazene achieved by an energy transfer process between the light-absorbing chromophore and an energy acceptor supported on the same inorganic \(\begin{array}{*{20}c} {} & | & {} \\ - & P & = \\ {} & | & {} \\ \end{array} N -\) skeleton.     

Synthesis and lithium ionic conductivity of Li3−2x(In1−xZrx)2(PO4)3 (0≦x≦0·20)

Lithium ion conductors, Li_3−2x(In_1−xZr_x)₂(PO₄)₃ (0≦x≦0·20), were synthesized by a solid state reaction. A superionic conductive phase of Li₃In₂(PO₄)₃ was stabilized down to room temperature, assisted by the substitution of Zr⁴⁺ for In³⁺ sites of Li₃In₂(PO₄)₃. TG-DTA analysis indicated no phase transition in the samples with x superior to 0·05. The substituted samples showed much higher ionic conductivity by a couple of magnitude than that of Li₃In₂(PO₄)₃. In particular, the highest conductivity at room temperature was 1·42×10⁻⁵ Scm⁻¹ for Li_2·8(In_0·9Zr_0·1)₂(PO₄)₃. Thin films with the composition of Li_2·8(In_0·9Zr_0·1)₂(PO₄)₃ was prepared by a sol–gel method. A coating solution was made from lithium isopropoxide, indium isopropoxide, zirconium isopropoxide and diphosphorus pentaoxide. Well crystallized films were obtained on silicon dioxide and quartz glass substrates by dropping the coating solution, followed by firing over 873 K. In the temperatures above 473 K the lithium ionic conductivity of the film was slightly higher than that of sintered samples prepared by the solid state reaction at 1373 K.     

A comparative raman study of the local structure in (Ge2S3) x (As2S3)1-x and (GeS2) x (As2S3)1−x glasses

The Raman spectra of glasses in the ternary (Ge₂S₃) _x (As₂S₃)_1−x and (GeS₂) _x (As₂S₃)_1−x systems are reported. It is shown that the degree of disorder in the (Ge₂S₃) _x (As₂S₃)_1−x glasses increases with an increase in the Ge content. The differences in the spectra of glasses with the same molar content of As₂S₃ are discussed in terms of the changes occurring in the local structure due to deviations from the stoichiometry. The observed changes in the intensity of the boson peak indicate changes in the medium-range order structure of the glasses under study.     

复合掺杂改性LiMn_(2-x)Cr_xO_(4-3x)F_(3x)正极材料的制备及性能

以CrF3为掺杂原料,采用高温固相法合成阴阳离子共掺杂LiMn2–xCrxO4–3xF3x锂离子电池正极材料。用X射线衍射、扫描电镜、充放电实验、循环伏安及交流阻抗等表征材料的结构、形貌和电化学性能,分析阴阳离子复合掺杂对材料结构和性能的影响。结果表明:掺杂材料LiMn2–xCrxO4–3xF3x具有完整的尖晶石结构。阴阳离子复合掺杂能改善尖晶石LiMn2O4的循环性能,当摩尔掺量x=0.10,电压为3.0～4.35V、充放电倍率为0.1C时,首次放电容量为120.1mA·h/g,室温、高温循环20次容量保持率分别为97.5%和94.1%。循环伏安实验发现:复合掺杂改性材料具有两对更完整、对称性更好的氧化还原峰。     

Microstructure–conductivity relationship of Na3Zr2(SiO4)2(PO4) ceramics

The ionic conductivity of solid electrolytes is dependent on synthesis and processing conditions, ie, powder properties, shaping parameters, sintering time (t_s), and sintering temperature (T_s). In this study, Na₃Zr₂(SiO₄)₂(PO₄) was sintered at 1200 and 1250°C for 0-10 hours and its microstructure and electrical performance were investigated by means of scanning electron microscopy and impedance spectroscopy. After sintering under all conditions, the sodium super-ionic conductor-type structure was formed along with ZrO₂ as a secondary phase. The microstructure investigation revealed a bimodal particle size distribution and grain growth at both T_s. The density of samples increased from 60% at 1200°C for 0 hours to 93% at 1250°C for 10 hours. The ionic conductivity of the samples increased with t_s due to densification and grain growth, ranging from 0.13 to 0.71 mS/cm, respectively. The corresponding equivalent circuit fitting for the impedance spectra revealed that grain boundary resistance is the prime factor contributing to the changing conductivity after sintering. The activation energy of the bulk conductivity (E_a,bulk) remained almost constant (0.26 eV) whereas the activation energy of the total conductivity (E_a) exhibited a decreasing trend from 0.37 to 0.30 eV for the samples with t_s = 0 and 10 hours, respectively—both sintered at 1250°C. In this study, the control of the grain boundaries improved the electrical conductivity by a factor of 6.     

Na_3Zr_(2-x)Mg_xSi_(2-2x)P_(1+2x)O_(12)系统的相关系和电性能

研究了Na_3Zr_(2-x)Mg_xSi_(2-2x)P_(1+2x)O_(12)系统的组成、结构和电性能。结果表明:Mg~(2+)能在一定的组成范围内取代Na_3Zr_2Si_2PO_(12)中的Zr~(4+)形成固溶体,单相固溶体区域延伸至x=0.5;当x=0.4时固溶体的结构由单斜转变为三方。固溶体的电导率随x的增加而降低。本文还从结晶化学的角度讨论了Na_3Zr_(2-x)Mg_xSi_(2-2x)P_(1+2x)O_(12)系统的组成、结构和电性能的关系。     

Low temperature Mössbauer spectroscopic study of CaO(Fe2O3)1−x(Al2O3)x system

Low temperature ⁵⁷Fe Mössbauer spectroscopic studies on CaO(Fe₂O₃)_1−x(Al₂O₃)_x, written as CF_1−xA_x, have been carried out. In view of the earlier findings based on room temperature data, the spectra have been analysed by assuming three Fe sites: two belonging to CF phase and the third site for the Fe atoms distributed in the CA phase. The Fe sites pertaining to the CF phase experience hyperfine field of about 49T and 47T, respectively, at 20K; whereas the third site is paramagnetic at this temperature.     

VOPO4⋅2H2O and Fe(H2O) x (VO)1-x PO4⋅2H2O Supported on TiO2 as Catalysts for Oxidative Dehydrogenation of Ethane

The effect of iron substitution on bulk and TiO₂-supported VOPO₄2H₂O on the catalytic performances in oxidative dehydrogenation of ethane has been studied in a fixed-bed reactor at 550 °C. The samples have been characterized by XRD, BET measurements, TPR and ammonia TPD experiments. A uniform dispersion of the active phase on the support has been obtained. Both iron substitution and dispersion on TiO₂ significantly modify redox and acid properties of vanadyl orthophosphate. A good correlation between the acid and redox properties of the catalysts and their catalytic performances has been observed.     

Microstructure and properties of (1 − x)La0.9Ca0.1CrO3/x ZrO2 (x = 0–30 wt-%) composites

The microstructure and properties of Ca doped lanthanum chromate [La_0.9Ca_0.1CrO₃ (LCCO)] and zirconia (ZrO₂) composites [abbreviated as (1???x)LCCO/xZrO₂, x?=?0–30?wt-%] prepared by solid state reaction method are investigated in this paper whose potential application in heat resistant ceramics are also discussed. The growth and fusion of the LCCO grains are hindered by the ZrO₂ grains, which make the matrix grains refined. In the stable system, it is discovered that the density of the composites decreases, the porosity increases and the decrease amplitude of the bend strength after thermal shock at 600°C reduces with the increasing ZrO₂ content, which results in diminishing the bend strength gradually and enhancing the thermal shock resistance. When x?=?10–15?wt-%, the samples show the best thermal shock resistance realising a maximum thermal cycle times of 8. The material with x?=?20?wt-% exhibits excellent slag resistance.     

Na_(5+x)YAI_xSi_(4-x)O_2快离子导体的导电机理

Na_(5+x)YAl_xSi_(4-x)O_(12)(NYAS)快离子导体中的铝、钇、硅、氧及部分钠离子堆积组成了独特的刚性结构,使之在其环与环之间、柱与柱之间形成了传导通道。另一部分钠离子很容易在通道中迂移传导,因而这类离子导体具有很高的离子电导率。本文从传导机理出发,计算了NYAS中的载流子浓度值,其结果与实验值接近,并从传导机理及简单跳跃模型出发,推出了NYAS中的离子电导率与组成X的变化趋势,获得了与实验结果完全吻合的结论。     

Structure,spectral analysis and microwave dielectric properties of novel x(NaBi)0.5MoO4-(1-x)Bi2/3MoO4 (x = 0.2 ∼ 0.8) ceramics with low sintering temperatures

Herein, the x(NaBi)_0.5MoO₄-(1-x)Bi_2/3MoO₄ (xNBM-(1-x)BMO, x = 0.2 ∼ 0.8) microwave dielectric ceramics with low sintering temperatures were prepared via the traditional solid-state method to adjust the τ_f value and dielectric constant. The crystal structure was determined using X-Ray diffraction and Raman spectroscopy, the microstructure was investigated using scanning electron micrograph and energy disperse spectroscopy, and the dielectric properties were studied using a network analyser and infrared spectroscopy. For the xNBM-(1-x)BMO composite ceramics, the (NaBi)_0.5MoO₄ tetragonal phase coexisted with the Bi_2/3MoO₄ monoclinic phase. With the rise of x value, the permittivity increased from 23.7–29.8, and the τ_f value shifited from -53.3 ppm/°C to -13.7 ppm/°C. The 0.8NBM-0.2BMO ceramic sintered at 680 °C possessed excellent microwave dielectric properties with a ε_r = 29.8 (6.7 GHz), a Qf = 11,800 GHz, and a τ_f = -13.7 ppm/°C. These results made the xNBM-(1-x)BMO composite ceramics great candidates in low temperature co-fired ceramics technology.     

Oxidative dehydrogenation of ethane and propane over magnesium–cobalt phosphates CoxMg3−x(PO4)2

The magnesium–cobalt phosphates Co_xMg_3–x(PO₄)₂ belonging to the olivine-type structure were synthesized by coprecipitation and then investigated in the oxidative dehydrogenation (ODH) of ethane and propane. The best yields, with the exception of Co_0.5Mg_2.5(PO₄)₂, were achieved with the compositions ranging between 1x2.5. Magnesium phosphate Mg₃(PO₄)₂ displayed no activity and pure cobalt phosphate Co₃(PO₄)₂ was found to be the less active component of the solid solution. Comparison of the catalysts performances showed that they all have similar activity in ethane and propane ODH, albeit, they are more selective in propylene than in ethylene production. The Co_xMg_3–x(PO₄)₂ solid solution was also studied, for characterization purposes, in butan-2-ol conversion. The samples presented acid–base properties due essentially to the (PO–H) groups but they do not bear conventional redox centers. All the catalysts were active at low temperatures in the alcohol dehydration. The dehydrogenation activity versus the phosphates composition displayed two maxima around x=1 and 2, respectively. Similar striking behavior was also observed in ethane and propane ODH. UV-visible investigations of Co_xMg_3–x(PO₄)₂ showed, in agreement with the XRD data, that the Co^{2 +} ions are distributed in the phosphate framework between six- and five-coordinated sites. The cobalt atoms in the five-coordinated sites Co(5) and their Co(5)–Co(5) interatomic distances were assumed to play the main role in the C–H bond activation and the appearance of maxima in the activity. Magnesium cations presumably intervene in acid–base properties of the samples and O₂ activation. Characterization of the samples showed that they do not undergo any noticeable transformation after the catalytic tests.     

白光LED用Ca_(8–x)Mg(SiO_4)_4Cl_2:xEu~(2+)荧光粉的制备及应用

采用高温固相法在强还原气氛下合成了Ca_(8–x)Mg(SiO_4)_4Cl_2:xEu~(2+)氯硅酸镁钙荧光粉。通过X射线衍射、荧光光谱和扫描电子显微镜对样品的晶体结构和发光特性进行了表征,探讨了Eu~(2+)掺杂量和助熔剂对发光性能的影响。结果表明:该荧光粉属于面心立方结构、Fd3空间群。样品的激发光谱和发射光谱均为宽带谱,位于451~463 nm范围的激发峰强度最大;在波长为458 nm蓝光激发下样品发射蓝绿光,发射峰在508~511 nm范围。当Eu~(2+)掺杂量为0.13时样品的发光强度最佳;分别加入摩尔分数为0.2%的Ca F_2、Ba F_2、Ba Cl_2助熔剂,能提高荧光粉的激发和发射光谱强度,且加入Ba Cl_2制备的荧光粉的发射光谱强度提高12%。考察了该材料在白光LED中的封装应用性能,结果显示蓝绿色荧光粉能够有效提升白光LED的显色性,显色指数达到95以上。     

Structure and microwave dielectric characteristics of Sr2[Ti1−x(Al0.5Nb0.5)x]O4 (x ≤ 0.50) ceramics

Sr₂[Ti_1−x(Al_0.5Nb_0.5)_x]O₄ (x = 0, 0.10, 0.25, 0.30, 0.5) ceramics were synthesized by a standard solid-state reaction process. Sr₂[Ti_1−x(Al_0.5Nb_0.5)_x]O₄ solid solutions with tetragonal Ruddlesdon-Popper (R-P) structure in space group I4/mmm were obtained within x ≤ 0.50, and only minor amount (1-2 wt%) of Sr₃Ti₂O₇ secondary phase was detected for the compositions x ≥ 0.25. The temperature coefficient of resonant frequency τ_f of Sr₂[Ti_1−x(Al_0.5Nb_0.5)_x]O₄ ceramics was significantly improved from 132 to 14 ppm/°C correlated with the increase in degree of covalency (%) with increasing x. The dielectric constant ɛ_r decreased linearly with increasing x, while high Qf value was maintained though it decreased firstly. The variation tendency of Qf value was dependent on the trend of packing fraction combined with the microstructure. Good combination of microwave dielectric properties was achieved for x = 0.50: ɛ_r = 25.1, Qf = 77 580 GHz, τ_f = 14 ppm/°C. The present ceramics could be expected as new candidates of ultra-high Q microwave dielectric materials without noble element such as Ta.     

Structural,magnetic and magnetocaloric properties of CoFe2−xMoxO4 (0.0≤x≤0.3) ferrites

We have investigated structural, magnetic and magnetocaloric properties of CoFe_2-xMo_xO₄ (0.0≤x≤0.3) ferrites. Polycrystalline samples were prepared by the sol gel method and characterized by the powder X-ray diffraction and scanning electron microscopy. X-ray diffraction patterns show that all samples have a cubic spinel structure and the lattice parameter, a, decreases monotonically with increase in Mo concentration. Scanning electron micrographs indicate that most of the particles are in the range of 400–850 nm size. Magnetic measurements, performed by using a cryogen free vibrating sample magnetometer, show that these samples are soft ferromagnets in the measured temperature range. The saturation magnetization, M_s, values of Mo-doped samples are larger than the parent compound with a maximum value of ~106 emu/g for x=0.2 sample. The magnetic entropy change (−ΔS) increases with increase in applied magnetic field and shows a peak in the vicinity of blocking temperature. A maximum value of 0.56 J kg⁻¹ K⁻¹ at 5 T field has been observed for x=0.2 sample.     

Reaction sintering of rhabdophane into monazite-cheralite Nd1-2xThxCaxPO4 (x = 0 – 0.1) ceramics

The direct sintering of Nd_1-2xCa_xTh_xPO₄·nH₂O rhabdophanes (x = 0 – 0.1) was achieved for the first time resulting in homogeneous high-density monazite-cheralite pellets. Thanks to their large specific surface area, rhabdophane precursors led to a lower shrinkage temperature compared to samples synthesized through solid-state reactions. The associated activation energy was found between 360 ± 90 and 530 ± 90 kJ.mol⁻¹, depending on the thorium incorporation. Meanwhile, sintering map was built up, showing that densification predominated for T ≤ 1200 °C. Conversely, the complete densification took place at 1400 °C concomitantly to grain growth and elimination of open porosity. Moreover, Th-Ca coupled substitution seemed to inhibit both densification and grain growth as the average grain size dropped down one order by one order of magnitude between x = 0.0 and x = 0.1. However, these differences did not affect microhardness, which reached 4.9 ± 0.8 GPa whatever the chemical composition tested.     

Role of competing phases in the structural,magnetic and dielectric relaxation for (1−x)CoFe2O4+(x)BaTiO3 composites

Magnetoelectric composites of (1−x)CoFe₂O₄+(x)BaTiO₃ (0.0≤x≤1.0) were prepared by ball milling method. X-ray diffraction analysis revealed the presence of cubic spinel (CoFe₂O₄) and tetragonal perovskite (BaTiO₃) phases in the prepared composites. Scanning electron micrographs confirmed the homogeneous phase distribution in the obtained composites. The magnitude of saturation magnetization and linear magnetostriction decreased with increasing BaTiO₃ content in the composite. Significant reduction in the magnetostrictive behavior is attributed to different elastic constants of the constituents which affect the mechanical coupling. In order to identify the different electro-active regions in the prepared composites, the experimental impedance spectroscopic data have been analyzed using different equivalent circuit models. The analysis of the impedance data is carried out by calculating the impedance of conductive (CoFe₂O₄) phase, resistive (BaTiO₃) phase and interconnectivity between the two constituent phases. With increasing BaTiO₃ content ‘x’ in the system, the dielectric permittivity decreased at low frequencies and increased at high frequencies. The observed behavior is mainly ascribed to the polarization in the CoFe₂O₄ and BaTiO₃ phases at low and high frequencies, respectively. Moreover, the AC conductivity analysis suggested the mixed polaron hopping type of conduction mechanism in the prepared composites.     

Electrochemical evaluation of LiZnxMn2−xO4 (x≤0.10) cathode material synthesized by solution combustion method

The spinel LiZn_xMn_2−xO₄ (x≤0.10) cathode materials have been synthesized by solution combustion method at 600 °C for 3 h. The structure and the morphology of LiZn_xMn_2−xO₄ were characterized by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM), respectively. All the obtained samples were identified as the spinel structure of LiMn₂O₄, the lattice parameters of samples decreased and the particle size increased as the Zn content increased. The effects of Zn-doping on the electrochemical characteristics of LiMn₂O₄ were investigated by galvanostatic charge–discharge experiments, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Among them, LiZn_0.05Mn_1.95O₄ particles presented outstanding cycling stability with a capacity retention of 82.9% at a discharge rate of 1 C (1 C=148 mA h g⁻¹) after 500 cycles. Spinel LiZn_0.05Mn_1.95O₄ had reversible cycling performance, revealing that doping LiMn₂O₄ with Zn improves its electrochemical performance.     

Electrical,structural and thermal properties of nanoceramic (Bi2O3)1−x−y(Ho2O3)x(Tm2O3)y ternary system

Ho₂O₃ and Tm₂O₃ doped Bi₂O₃ composite electrolyte type materials for solid oxide fuel cells (SOFCs) operating at intermediate-temperature were investigated. The bismuth-based ceramic powders were produced by using conventional solid-state synthesis techniques. The products were characterized by means of scanning electron microscopy (SEM), X-ray powder diffraction (XRD), differential thermal analysis/thermal gravimetry (DTA/TG), and the four-point probe technique (4PPT). XRD and DTA/TG measurements indicate that all of the samples have the stable fluorite type face centered cubic (fcc) δ-phase. 4PPT measurements were performed in the temperature range 150–1000 °C in air and these measurements showed that the electrical conductivity of the samples decrease with increasing amount of Tm₂O₃. This increase in the electrical conductivity of the samples could be attributed to the increase in the numbers of highly polarizable cations and oxide ion vacancies. The highest conductivity value was found as 5.31×10^?1 Ω cm^?1 for the (Bi₂O₃)_1?x?y(Ho₂O₃)_x(Tm₂O₃)_y ternary system (for x=20 and y=5 mol%) at 1000 °C. The activation energies of the samples were calculated from log σ graphics versus 1000/T. These calculated results showed that the translation motion of the charge carriers, oxygen vacancies, and space charge polarizations are responsible for the change in activation energy as a function of temperature.