Lanthanum-Magnesium and Lanthanum-Manganese Donor-Acceptor-Codoped Semiconducting Barium Titanate

BaTiO₃ powder doped with La donor and codoped with Mn or Mg acceptor was sintered at 1350°C/1 h in air. For Ladoped BaTiO₃, the room-temperature resistivity decreased to a minimum at [La³⁺] ∼ 0.15 mol%. For La-Mn-codoped BaTiO₃, the minimum resistivity occurred at [La³⁺] - 2[Mn²⁺] ∼ 0.15 mol%. When the ceramic was changed to a fine-grained insulator by high donor doping ([La³⁺] >0.15 mol%), its semiconductivity was restored, and the relatively homogeneous, coarse-grained microstructure recurred by codoping with either Mg or Mn acceptor, with the transition at [La³⁺] - 2[Mg²⁺] = 0.15 mol% or [La³⁺] - 2[Mn²⁺] = 0.15 mol%. The analogy of a compensation effect between La-Mn- and La-Mg-codoped BaTiO₃ suggested that Mn acceptor added to BaTiO₃ exists as Mn²⁺ ion in the bulk grain region; its influence on the positive temperature coefficient of resistivity behavior is then discussed.     

Valence state and ionic conduction in Mn‐doped MgO partially stabilized zirconia

The mechanism of the enhancement in the ionic conductivity resulting from cubic phase stabilization in MgO partially stabilized zirconia (MgPSZ) by Mn doping was studied by examining the local Zr‐O structure. Cubic phase (14 vol%) in MgPSZ was increased with the addition of MnO₂, and 10 mol% Mn‐doped MgPSZ exhibited the highest cubic phase fraction (98.72%), which was analyzed by Rietveld refinement. In addition, only the cubic phase, not the monoclinic and tetragonal phases, was observed in the TEM‐SAED pattern of 10 mol% Mn‐doped MgPSZ. Doped Mn exhibited a high Mn²⁺/Mn⁴⁺ ratio, which was identified by X‐ray photoelectron spectroscopy (XPS). In addition, it indicates that oxygen vacancy formation by substitution of Mn²⁺ in the Zr⁴⁺ site in MgPSZ increased cubic phase fraction. Ionic conductivity of MgPSZ was improved by the cubic phase increase attributed to Mn doping, and 10 mol% Mn‐doped MgPSZ exhibited higher ionic conductivity than MgPSZ. To investigate the mechanism of the ionic conductivity improvement, Zr‐O local structure in Mn‐doped MgPSZ was analyzed by Zr K‐edge EXAFS of MgPSZ, and the number of bonding of the Zr‐O first shell decreased with increased Mn substitution. Therefore, it was considered that the oxygen vacancy generation led to an increase in the cubic phase and the number of ionic conduction sites.     

Ferroelectric and Photostrictive Properties of Fine-Grained PLZT Ceramics Derived from Mechanical Alloying

Single-phase lead lanthanum zirconate titanate (PLZT) solid solution powder was synthesized from the constituent oxides at ambient temperature through a mechanical alloying (MA) process and was then densified to fine-grained ceramics by sintering and hot-pressing. The anomalous photovoltaic effect (APV) and photoinduced strain of the resultant PLZT ceramics were investigated and analyzed in association with the influence of grain size. It was found that a photoinduced voltage up to 6000 V·cm⁻¹ can be obtained as the grain size is reduced to 0.42 μm. This is extremely high and about three times that achievable in normal micrometer-grained PLZT ceramics. The maximum photoinduced strain of the PLZT ceramics with an average grain diameter of 0.54 μm reached 0.01%, which is equivalent to electric-field-induced strain of common piezoelectric materials.     

超声分散法制备含锰的二氧化钛光催化剂及其表征

以钛酸四丁酯为主要原料,硫酸锰溶液为掺杂剂,采用超声分散法制备了含锰的二氧化钛光催化剂。并用X射线衍射(XRD)和透射电镜(TEM)对粉体的结构、粒径大小、物相、形貌等进行了表征。经500℃焙烧2h后,锰掺杂的二氧化钛粉末为锐钛型结构,其平均粒径为13nm,由于在XRD图谱上未发现有新相的生成,因此,可知锰离子是经过焙烧渗入到了二氧化钛的晶格中,掺杂所引起的变化主要是由于锰离子渗入二氧化钛晶格引起的。     

钛柱撑蒙脱石对镍离子和锰离子的吸附机理

以钠基蒙脱石(Na-MMT)、钛酸四丁酯作基质材料,通过溶胶-凝胶法制备了钛柱撑蒙脱石(Ti-MMT)。利用XRD、FTIR及SEM对Ti-MMT进行了结构表征,考察了不同吸附条件对Ti-MMT吸附Ni~(2+)和Mn~(2+)的影响,并重点分析水溶液pH对Ti-MMT Zeta电位及吸附的影响,探究了Ti-MMT吸附Ni~(2+)和Mn~(2+)的机理。结果表明:Ti-MMT具有较大的晶面间距(d001=2.94 nm);pH对吸附Ni~(2+)与Mn~(2+)有较大影响,去除率随初始水溶液pH增加而提高。在pH=7,Ni~(2+)和Mn~(2+)初始质量浓度为50 mg/L,Ti-MMT投加量分别为5和9 g/L时,Ni~(2+)在318 K下吸附120 min,吸附量可达9.46 mg/g,去除率可达94.59%,Mn~(2+)在328 K下吸附180 min,吸附量可达4.82mg/g,去除率可达86.73%。此外,Ti-MMT对两种离子的吸附都更符合Temkin等温吸附模型及拟二级动力学模型,吸附过程受液膜扩散、颗粒内扩散等环节控制,且以离子交换的化学吸附为主。热力学分析表明,Ti-MMT对Ni~(2+)的吸附属于自发吸热熵增过程,而Mn~(2+)属于吸热熵增的非自发过程。     

Microstructural Evolution of Transparent PLZT Ceramics Sintered in Air and Oxygen Atmospheres

Transparent lanthanum-doped lead zirconate titanate (PLZT) ceramics were fabricated by air-pressure sintering. When the PLZT (9/65/35) specimens were sintered in air, the microstructure was not uniform throughout the body; the outer region near the surface was completely dense, while the inner region of the body was porous. The thickness of the outer dense layer increased parabolically with sintering time. When the specimen was sintered in air at 1200°C for 8 h, the thickness of the dense layer was ∼0.25 mm. Therefore, when the specimen had a thickness of <0.5 mm, it was dense and transparent. This difference in microstructure was attributed to the formation of lattice vacancies as a result of PbO evaporation from the surface. The sintering atmosphere also was important in determining the thickness of the dense layer. The thickness was strongly dependent on the oxygen partial pressure of the atmosphere. The oxygen-gas trapped in pores was deemed to migrate easily through the lattice vacancies. By sintering in an oxygen-gas atmosphere at 1200°C for 8 h, a transparent PLZT with thickness up to 2 mm was fabricated.     

Coprecipitation synthesis of Ca14Al10Zn6O35:Mn4+ deep-red phosphor and silica-modified waterproofing ability

Ca₁₄Al₁₀Zn₆O₃₅:Mn⁴⁺ (CAZ:Mn) phosphor material, which shows deep-red luminescence, was synthesized by the coprecipitation (COP) method using a Na₂CO₃/NaOH solution as the precipitant. COP–CAZ:Mn phosphor exhibited a 2.1 times higher luminescence intensity than the corresponding phosphor prepared using the conventional solid-state reaction (SSR) method. This substantial increase in luminescence was mainly ascribed to the existence of a greater proportion of tetravalent manganese in COP–CAZ:Mn phosphor. Furthermore, COP–CAZ:Mn phosphor was modified with SiO₂ via hydrolysis of tetraethoxysilane (TEOS) to waterproof the compound because it is easily decomposed through hydrolysis under humid conditions. The SiO₂-modified CAZ:Mn phosphor maintained its crystal structure and high photoluminescence intensity after the water-resistance test. Therefore, waterproof CAZ:Mn phosphor with a high luminescence intensity was successfully discovered by utilizing the coprecipitation method and SiO₂ modification.     

Formation mechanism and optimized luminescence of Mn4+‐doped unequal dual‐alkaline hexafluorosilicate Li0.5Na1.5SiF6

A novel red phosphor Li_0.5Na_1.5SiF₆:Mn⁴⁺ (LNSF:Mn) based on the unequal dual‐alkaline hexafluorosilicate with superior optical performances has been synthesized via ion‐exchange between [MnF₆]^2? and [SiF₆]^2? at room temperature. The composition and the crystal structure of the as‐obtained phosphor LNSF:Mn were determined by energy‐dispersive x‐ray spectroscopy (EDS) and x‐ray diffraction (XRD), respectively. The formation mechanism of the red phosphor LNSF:Mn has been discussed in detail. The phosphor LNSF:Mn exhibits good chromaticity properties and a quantum yield (QY) of 96.1%, which are better than the identified fluorosilicate phosphors Na₂SiF₆:Mn⁴⁺ (NSF:Mn) and K₂SiF₆:Mn⁴⁺ (KSF:Mn). A broad and intense absorption in the blue and a bright emission in red‐shifted wavelengths make the phosphor LNSF:Mn a desired candidate for applications in warm white light‐emitting diodes.     

Fabrication of Optically Transparent Lead Lanthanum Zirconate Titanate ((Pb,La)(Zr,Ti)O3) Ceramics by a Three-Stage-Atmosphere-Sintering Technique

An easy technique has been developed to fabricate optically transparent lanthanum-modified lead zirconate titanate (PLZT) ceramics. This technique consists of three stages: (1) sintering in an oxygen atmosphere, (2) elimination of pores in a carbon dioxide atmosphere, and (3) elimination of oxygen vacancies in an oxygen atmosphere. The carbon dioxide atmosphere enhances the diffusion of oxygen from the pores to outside the sintered body. The experimental results reveal that use of a carbon dioxide atmosphere effectively decreases residual pores and improves optical transmittance. From commercially available raw powders, an optical transmittance of 51% (wavelength of 550 nm) can be achieved for 0.7 mm thick polished PLZT9/65/35 ceramics using a carbon dioxide atmosphere, whereas the value is only 34% without a carbon dioxide atmosphere. The advantage of this technique is that PLZT ceramics having high optical quality can be obtained using conventional sintering tools.     

Defect Structure of PLZT Doped with Mn, Fe, and Al

Practically pore-free Mn-, Fe-, and Al-doped PLZT ceramics were prepared using isostatic hot-pressing. The incorporation of the dopants in the perovskite lattice of PLZT (Pb_0.9La_0.1 |Zr_0.5Ti_o.5O₃₊δ) ceramics was analyzed from measurements of the density, lattice constants, and weight loss during sintering. It was deduced that Mn, Fe, and Al are incorporated as trivalent ions at (Zr, Ti)⁴⁺ sites and that charge compensation is effected by elimination of cation vacancies present in the undoped PLZT.     

锂离子电池阴极材料LiCo_xMn_(2-x)O_4的研究

以甘氨酸为配合剂,用溶胶-凝胶法制备了掺钴的锂离子电池阴极材料LiCoxMn2-xO4,用XRD、SEM等方法研究了掺钴量、烧结温度等因素对LiCoxMn2-xO4的结构、表面形貌及电化学性能的影响,实验结果表明,烧结温度为750℃,x=0.12时,LiCoxMn2-xO4的电化学性能最佳。     

低温熔盐燃烧法合成LiNi_(0.5-x)Mg_xMn_(1.5)O_4(x=0,0.05)及其电性能

为了快速、高效地制备5V锂离子电池正极材料,采用低温熔盐燃烧法合成了LiNi0.5Mn1.5O4粉末。X射线衍射分析表明:使用该方法,将原料在600℃焙烧1h即可获得单相LiNi0.5Mn1.5O4材料,Mg的掺杂有利于产物结晶性的提高。扫描电子显微镜观察表明,LiNi0.45Mg0.05Mn1.5O4的粒径为亚微米级的,且粒径分布均匀。制成电极后电性能研究表明,在3.5～5.0V的电压范围,75mA/g的电流密度下,该材料进行50次充放电循环后,放电比容量没有明显衰减。微量的Mg掺杂,可以提高样品的放电比容量,改善材料的首次充放电效率并提高材料的放电平台。600℃下焙烧5h所制备的LiNi0.45Mg0.05Mn1.5O4首次放电比容量为134(mA·h)/g,在电流密度为75mA/g下进行50次循环后保持率达100%。     

层状锂离子电池正极材料LiNi0.8Co0.1Mn0.1O2的制备及性能

采用共沉淀法得到前驱体Ni0.8Co0.1Mn0.1(OH)2,利用前驱体与LiOH×H2O的高温固相反应得到高振实密度的锂离子电池层状正极材料LiNi0.8Co0.1Mn0.1O2 (2.3~2.5 g/cm3). 初步探讨了合成条件对材料电化学性能的影响. 通过X射线衍射(XRD)、扫描电镜(SEM)、热重-差热分析(TG/DTG)以及恒电流充放电测试对合成的样品进行了测试和表征. 结果表明,在750℃、氧气气氛下合成的材料具有较好的电化学性能. 通过XRD分析可知该材料为典型的六方晶系a-NaFeO2结构;SEM测试发现产物粒子是由500~800 nm的一次小晶粒堆积形成的二次类球形粒子. 电化学测试表明,其首次放电容量和库仑效率分别为168.6 mA×h/g和90.5%, 20次循环后容量为161.7 mA×h/g,保持率达到95.9%,是一种具有应用前景的新型锂离子电池正极材料.     

FE3 EPR investigation of PLZT 1/65/35 and 8/65/35

X-band EPR spectra of PLZT 1/65/35 and PLZT 8/65/35 doped with 1% FE³⁺ were recorded at temperature range -175°C to 200°C. Three types of paramagnetic centers were found. Two of them are in strong axial and rhombic crystal field due to neighboring oxygen and lead vacancies. The other center has symmetry determined by polarization and oxygen octahedra tilt. EPR spectra of PLZT 8/65/35 are in agreement with its glassy behavior.     

Fe/N改性TiO_2粉末的制备及其降解甲醛之初探

本文研究了Fe/N改性Ti02粉末降解甲醛的效果。以三乙胺为氮源,用TiCl4制备氮掺杂Ti02(N-Ti02)粉末,并用吸附法在N-Ti02粉末表面负载一定量铁离子,高温处理后形成铁、氮共掺杂Ti02(Fe/N-Ti02)粉末光催化剂。以光催化降解甲醛为模型反应,比较了掺铁量、光源和光强对甲醛降解效果的影响,结果表明,紫外光照下,当铁掺杂质量分数为0.5%时,粉末表现出最佳催化性能,光照2h后甲醛的降解率达到74.6%;Ti02的光催化活性随光照强度增大呈非线性增加。     

掺Mn的[YGdCa]3[FeVInMn]5O12复合石榴石

报道了含稀土量少的掺锰复合钇铁石榴石的制备。探讨了替代材料中铁位上锰的掺入对材料特性的影响。结果表明：锰掺入后的材料具有ＹＩＧ相同的结构，并具有良好的施磁性质。该材料适用于制备磁隔离器。     

Investigation of Lithium Diffusion in Octalithium Plumbate by Conductivity and NMR Measurements

Diffusion of lithium ion and tritium in octalithium plumbate (Li_sPbO₆) was studied. The electrical conductivity of the polycrystalline pellets measured by the two-terminal ac method in the temperature range of 300 to 973 K was one of the highest among oxide lithium ceramics. The temperature dependence of the conductivity is consistent with the nuclear magnetic resonance of lithium-7 powder samples, suggesting that the temperature dependence of the diffusion of lithium consists of three regions in this temperature range. Preliminary measurements of the diffusion coefficient of tritium in neutron-irradiated Li_sPbO₆ powder were also carried out. The results were compared with the diffusion of lithium ion, and the relationship between diffusion of lithium ion and tritium is discussed.     

Effect of Mo addition mode on the microstructure and mechanical properties of TiC–high Mn steel cermets

In TiC- and Ti(C,N)-based cermets, the wettability of the ceramic phase with the metallic binder is commonly increased through supplementation with Mo in the form of pure Mo powder or Mo₂C. Herein, TiC–high Mn steel cermets were fabricated by conventional powder metallurgy techniques using Fe–Mo pre-alloyed powders as binders to guarantee uniform Mo distribution, and the cermet preparation process was optimized and investigated in detail. The microstructures of the thus obtained cermets were observed by scanning electron microscopy and compared to those of a Mo-free cermet and a cermet prepared using pure Mo powder. The grain size of Fe–Mo powder cermets exceeded that of the Mo-free cermet but was much smaller and more homogeneous than that of the Mo powder cermet. For Fe–Mo powder cermets, angular and tetragonal TiC particles were observed at Mo contents of <1.2 wt%, while round shapes became dominant at higher Mo contents. The hardness of Fe–Mo powder cermets increased with increasing Mo content, as did transverse rupture strength, which was maximal (2264 MPa) at a Mo content of 2.4 wt%, while impact toughness was maximal (11.2 J/cm²) at a Mo content of 1.2 wt%. The above values exceeded those reported for similar conventional cermets, and the use of Fe–Mo pre-alloyed powder as a metallic binder was therefore concluded to be an attractive strategy of increasing the strength and toughness of TiC–high Mn steel cermets.     

A cyclic voltammetric study of the kinetics andmechanism of electrodeposition of manganese dioxide

The kinetics and mechanism of electrooxidation of Mn2+ ions to MnO2 (EMD) has been studied in electrolytes comprising MnSO4 and H2SO4 by cyclic voltammetry at 80°C. The voltammogram of a Pt electrode cycled between 0.6 and 1.6V vs SCE exhibits an anodic current peak at about 1.3V vs SCE resulting in the deposition of MnO2 on the electrode, while a cathodic peak appears at 0.8V vs SCE. It is shown that the pair of peaks do not correspond to a single reversible reaction but represent two separate irreversible electrode processes. The cyclic voltammetric peak current for the deposition of EMD is found to be proportional to the square root of Mn2+ ion concentration in the electrolyte and independent of acid concentration. Based on these results, a mechanism for the formation of EMD involving diffusion of Mn2+ ions to the electrode surface, oxidation of Mn2+surface to Mn3+ads, and H2O to OHads as the primary oxidation steps is invoked. Mn3+ads ions dissociate disproportionately into Mn2+ads and Mn4+ads ions at the electrode surface. The Mn2+ads and Mn4+ads ions, respectively, react with OHads and H2O resulting in the formation of EMD.     

Nonisothermal sintering of Mn doped ZnO

The sintering of pure ZnO and ZnO doped with Mn, obtained by addition of Mn(NO₃)₂. 4H₂O in the concentration from 0·1 to 1·2 mol%, was investigated by dilatometry at constant heating rates, from 1 to 15 °C min⁻¹. Mn shifts the onset of the sintering towards higher temperatures, but no significant effect of the Mn doping level on the shrinkage was observed. Accordingly, the calculated activation energy for the first stage, changed from ∼320 kJ mol⁻¹ for pure ZnO to ∼440 kJ mol⁻¹ for Mn doped ZnO. Using classical sintering models to analyse the initial stage sintering of all the compositions, two sintering mechanisms were found to control the initial stage sintering. The first region is identified with a grain boundary sliding mechanism, while volume diffusion is the controlling mechanism in the second region. With the increase of the Mn content, the grain boundary sliding rate remains constant, but the volume diffusion rate is reduced.