类球形正交LiMnO2的制备、微结构和电化学性能

以共沉淀法得到的类球形MnCO₃为前驱物，制备了类球形正交LiMnO₂(So-LiMnO₂)，采用XRD、SEM和N₂吸附技术对样品进行表征；与非球形正交LiMnO₂(No-LiMnO₂)进行了对比研究。结果表明：o-LiMnO₂的堆垛层错度、结晶状况、颗粒形貌和大小与前驱物的微结构密切相关；在80次电化学循环测试过程中，So-LiMnO₂经15次循环可达最大的放电容量152 mAh·g^-1，其容量衰减平均每次循环0.58 mAh·g^-1；而No-LiMnO₂要经过38次循环才能达到最大放电容量128 mAh·g^-1，容量衰减平均每次循环高达1.24 mAh·g^-1。TEM和EDS分析证明：由一次粒子团聚的类球形So-LiMnO₂能有效地抑制电解液对材料的腐蚀、减少Mn的溶解，从而提高了电化学循环能力。     

层状LiMnO2的固相合成及电化学性能

以Mn₂O₃和氢氧化锂为原料，通过焙烧合成出o-LiMnO₂。用X射线衍射和扫描电镜对不同温度下合成的粉末样品进行了表征，并研究了材料的电化学性能。通过对不同温度条件下烧结样品的晶胞参数、布拉格(110)晶面峰半高宽及电化学性能研究发现：600 ℃下合成样品的半高宽最大，堆垛层错率高，同时电化学性能也最好，首次放电容量达到156 mAh·g^-1，20次循环后仍保持在140 mAh·g^-1以上。中高温固相合成的o-LiMnO₂材料，在晶粒范围大小相近时，材料电化学性能与材料堆垛层错率相关。     

正交层状LiMnO2在电化学循环过程中的相变和活化特性

用高精度非原位XRD结合Rietveld结构精修对固相法制备的正交层状LiMnO₂(简写为o-LiMnO₂)在电化学循环过程中的相变进行了研究。结果表明：首次循环就出现相变,循环5次后o-LiMnO₂相变完全;产物中除了有类尖晶石型锰酸锂(Li_0.86Mn_0.14)(Mn_0.92Li_0.08)₂O₄(Fd3m)外,还证实了文献的理论计算和晶体学推测出的岩盐型锰酸锂(Li,Mn)O₂(Fd3m)的存在;并定量计算了两物相的相含量。证实两物相均参与了电化学循环,其中类尖晶石型锰酸锂对电化学容量的变化起主要作用;岩盐型锰酸锂在电化学循环过程中逐渐向类尖晶石型锰酸锂转变,使电极的放电容量不断增加,这种转变停止时,放电容量达到最大,活化过程结束。     

Electronic Structure and Optical Properties of K2Ti6O13 Doped with Transition Metal Fe or Ag

Based on the experimental study of the optical properties of K₂Ti₆O₁₃ doped with Fe or Ag, their electronic structures and optical properties are studied by the first-principles method based on the density functional theory (DFT). The calculated optical properties are consistent with the experiment results. K₂Ti₆O₁₃ doped with substitutional Fe or Ag has isolated impurity bands mainly stemming from the hybridization by the Fe 3d states or Ag 4d states with Ti 3d states and O 2p states and the band gap becomes narrower, the absorption edge of K₂Ti₆O₁₃ thus has a clear red shift and the absorption of visible light can be realized after doping. For Fe-doped K₂Ti₆O₁₃, the impurity bands are in the middle of the band gap, suggesting that they can be used as a bridge for valence band electrons transition to the conduction band. For Ag-doped K₂Ti₆O₁₃, the impurity bands form a shallow acceptor above the valence band and can reduce the recombination rate of photoexcited carriers. The experimental and calculated results are significant for the development of K₂Ti₆O₁₃ materials that have absorption under visible light.     

Band structure calculations on the monoclinic bulk and nano-SrAl2O4 crystals

The electronic structure of SrAl₂O₄ is calculated by density functional method and exchange and correlation have been treated by the generalized gradient approximation within the scheme due to Perdew-Burke-Ernzerhof. The bond length and bond covalency are also calculated by chemical bond method. Compared with the SrAl₂O₄ bulk crystal, the bond covalency of nanocrystal has an increasing trend; its band gap also is wider; the bond lengths of SrAl₂O₄ nanocrystal become shorter, which is responsible for the change of the covalency and band gap.     

正交结构LixMnO2正极材料的合成及其电化学性能研究

0引言随着社会的进步,人们对化学电源提出了高能量、长寿命、低成本、低环境污染的要求。1990年由日本Sony能源公司率先研制成功的锂离子电池可以部分满足上述要求,一经问世,便迅速在便携式电子设备、电动汽车等众多领域展示了广阔的应用前景,掀起了锂离子二次电池的研究热潮。     

A first principles study of NO2 chemisorption on silicon carbide nanotubes

Using methods based on first principles, we find that an NO₂ molecules can be chemisorbed on silicon carbide nanotubes (SiCNTs) with an appreciable binding energy (∼−1.0 eV), and that this is not the case for either carbon nanotubes (CNTs) or boron nitride nanotubes (BNNTs). A detailed analysis of the energetics, geometry, and electronic structure of various isomers of the complexes was performed. The SiCNT–NO₂ complex can be metallic or nonmetallic depending on the type of adsorption site and the chirality of the tube. However, our analysis of the electronic structure predicts that a strong p-type effect of the adsorption turns semiconducting systems into metallic ones at room temperature, irrespective of the chirality of the tube.     

CeO2改性Ag-V2O5/TiO2催化剂的甲基吡啶氧化脱甲基性能

以锐钛矿TiO_2为载体,考察了CeO_2改性对Ag-CeO_2-V_2O_5/TiO_2催化3-甲基吡啶氧化脱甲基性能的影响,并优化了催化剂组成与制备条件.结果表明:Ce掺杂改性不仅能够与V物种作用形成Ce VO_4,而且促进V_2O_5分散,改善活性组分的氧化还原性能,从而提高3-甲基吡啶脱甲基转化率与选择性,改善Ag-V_2O_5/TiO_2催化性能.适宜的催化剂组成为V_2O_5负载量15%,Ce/V的摩尔比0.33,Ag质量分数1.0%.过高的焙烧温度将导致TiO_2载体向金红石型转变,Ag-CeO_2-V_2O_5/TiO_2适宜制备条件为450℃焙烧4 h.     

Preparation of ZrO2-TiO2-CeO2 and Its Application in the Selective Catalytic Reduction of NO with NH3

TiO₂,ZrO₂-TiO₂,andZrO₂-TiO₂-CeO₂ were prepared by co-precipitation method and characterized by X-ray diffraction (XRD), specific surface area measurements (BET), temperature programmed desorption (NH₃-TPD), oxygen storage capacity (OSC), and temperature programmed reduction (H₂-TPR). The results showed that ZrO₂-TiO₂-CeO₂ exhibited large number of surface strong acid, possessed some oxygen storage capacity, and strong redox property. The three materials were used as supports and the monolith catalysts were prepared with 1% (w) V₂O₅ and 9% (w)WO₃ for selective catalytic reduction (SCR) of NO with ammonia in the presence of excessive O₂, and the results of catalytic activity showed that the catalyst used ZrO₂-TiO₂-CeO₂ as support yielded nearly 100% NO conversion at 275 °C at a gas hourly space velocity (GHSV) of 10000 h⁻¹, and it had the best catalytic activity and showed great potential for practical application.     

Synthesis and properties of the double perovskites La2NiVO6, La2CoVO6, and La2CoTiO6

The double perovskites La₂CoVO₆, La₂CoTiO₆, and La₂NiVO₆, are described. Rietveld fitting of neutron and powder X-ray diffraction data show La₂NiVO₆ and La₂CoVO₆ to have a disordered arrangement of B-cations whereas La₂CoTiO₆ shows ordering of the B-cations (with ∼5% Co/Ti inversion). Curie-Weiss fits to the linear region of the 1/χ plots reveal Weiss temperatures of −107, −34.8, and 16.3 K for La₂CoVO₆, La₂CoTiO₆, and La₂NiVO₆, respectively, and magnetic transitions are observed. La₂CoTiO₆ prepared by our method differs from material prepared by lower-temperature routes. A simple antiferromagnetic spin model is consistent with the data for La₂CoTiO₆. These compounds are semiconductors with bandgaps of 0.41 (La₂CoVO₆), 1.02 (La₂CoTiO₆) and 0.45 eV (La₂NiVO₆).