双钙钛矿Sr2-xLaxCrReO6的电子结构和磁性

采用密度泛函理论(DFT)在广义梯度近似(GGA)下的平面波超软赝势法, 研究了Sr2-xLaxCrReO6(x=0, 0.25, 0.5, 1)的晶体结构、电子结构和磁性. 通过几何结构优化, 得到了材料的晶格常数、电子和自旋分布以及磁矩的大小. 分析了La电子掺杂对Sr2CrReO6材料结构的影响, 发现当La掺杂浓度较小(x<1)时, Sr2-xLaxCrReO6仍保持半金属特性, 但刚好在费米面以下自旋向上的电子密度逐渐增大, 自旋向下能带的带隙增加, 总磁矩减小; 当掺杂浓度较大(x=1)时, Sr2-xLaxCrReO6从具有亚铁磁半金属性转化为铁磁金属性.     

双钙钛矿型Ba2SmSbO6的水热合成和结构表征

在温和水热条件下合成了双钙钛矿型Ba2SmSbO6,通过XRD,IR,ICP,XPS,VSM和121SbMöss-bauer谱对产物的物相、结构、锑离子价态和磁化率等进行了表征.Ba2SmSbO6具有立方钙钛矿结构,Fm3m空间群,晶胞参数a=0.85097(20)nm,V=0.61623(20)nm,Sm和Sb离子呈岩盐型有序排列,锑为+5价.     

双钙钛矿氧化物REEuCr2O6的^151Eu Mossbauer谱研究

利用高温固相反应合成了双钙钛矿氧化物ＲＥＥｕＣｒ２Ｏ６（ＲＥ＝Ｌａ，Ｐｒ，Ｎｄ，Ｓｍ，Ｅｕ，Ｇｄ，Ｔｂ，Ｄｙ，Ｈｏ，Ｅｒ，Ｔｍ）。对样品进行了ＸＲＤ、ＩＲ及＾１５１Ｅｕ的Ｍｏｓｓｂａｕｅｒ谱测试，结果表明所有化合物为正交结构；随着ＲＥ原子序数的增加，晶胞体积减小，同质异能移位与样品的晶胞体积呈线性关系；四极裂矩为负值，且随ＲＥ原子序数的增加其绝对值增大。     

双钙钛矿Pr2NiMnO6的X射线光电子能谱研究

利用固相反应法合成了双钙钛矿Pr2NiMnO6.通过X射线衍射确定了样品物相的单一性.利用X射线光电子能谱和磁性测量系统分别对Ni、Mn的价态以及样品的低温磁性质进行分析.结果表明,在Pr2NiMnO6中,Ni、Mn主要以2价、4价的形式存在,低温下的铁磁行为来源于Ni2+-O-Mn4+铁磁超交换作用.该研究为探索同系双钙钛矿La2 NiMnO6的磁性起源提供了重要参考.     

过渡金属掺杂的双钙钛矿Ba2InNbO6的光催化分解水性能研究

双钙钛矿材料由于其丰富的化学组成及晶体结构被认为是一类优良的光催化材料,但大多数双钙钛矿氧化物仅表现出紫外光催化活性。因此,本文通过过渡金属离子Fe、Cr、Ni等掺杂调控双钙钛矿化合物Ba2InNbO6的能带结构,期望实现高效的可见光催化活性,并研究掺杂元素对晶体结构、微观形貌、表面状态等物化性质的影响。结果表明,过渡金属能够成功地引入到双钙钛矿的Ba2InNbO6的In位点,并能拓宽材料的可见光吸收范围。此外,过渡金属引入晶胞发生收缩,颗粒尺寸增大,表面亲水性也得到了极大的改善。与Ba2InNbO6相比,过渡金属掺杂的样品光催化析氢活性得到了极大的改善。其中,Ba2In0.9Fe0.1NbO6在全范围照射(λ≥250 nm)下的析氢量最高,达到了15.8μmol,并且在可见光(λ≥420 nm)照射下的析氢速率为2.71μmol/h,其对应的表观量子效率为0.016%。     

双钙钛矿La2CoNiO6无机纳米纤维的制备及超级电容器性能

以聚乙烯吡咯烷酮/硝酸镧-乙酸钴-乙酸镍(PVP/LCN)为前驱体, 采用静电纺丝法, 经预氧化、碳化, 制得双钙钛矿La₂CoNiO₆无机纳米纤维超级电容器电极材料. 利用X射线衍射(XRD)、扫描电镜(SEM)和透射电镜(TEM)对其形貌和结构进行表征. 结果表明, 纤维由菱形结构的La₂CoNiO₆纳米颗粒相互连接而成, 呈链状空间网状结构. 循环伏安(CV)、恒流充放电(CP)和循环寿命测试表明, La₂CoNiO₆纳米纤维电极材料在三电极体系中, 电流密度为0.25 A·g^-1时, 比电容值达335.0 F·g^-1; 在对称型双电极体系中, 电流密度为0.25 A·g^-1时, 比电容值可达到129.1 F·g^-1,表现出良好的电容性能.     

掺杂型稀土双钙钛矿光催化剂La2FeTiO6葡萄糖络合法制备与表征

采用葡萄糖络合法制备了双钙钛矿型催化剂La2FeTiO6,进行不同量Sr掺杂改性。利用X射线粉末衍射(XRD)、H2-程序升温还原(H2-TPR)、比表面(BET)、扫描电镜(SEM)、磁性与电性测试等手段对其进行表征,以可见光催化降解对氯苯酚为探针讨论了Sr掺杂对La2FeTiO6催化剂的物理化学性质及可见光催化活性的影响。结果表明:催化剂La2FeTiO6在掺杂Sr后,催化剂的可见光催化活性均有所提高,其中Sr掺杂量为0.08时,催化剂的光催化活性提高最大,光照1 h时对氯苯酚的降解率就已经达到了90%,5 h后降解率达到99.2%。La2FeTiO6通过Sr掺杂改性后光照5 h降解率提高了37.1%。比表面测试和程序升温还原试验结果表明,碱土金属Sr的掺杂提高了催化剂的比表面,促进了双钙钛矿La2FeTiO6中Fe的还原,使其还原峰面积增大,还原温度也有所降低。电性和磁性测量结果说明,碱土金属Sr的掺杂明显影响其催化剂的电磁性能。     

甲脒基铅卤钙钛矿结构及光电特性的第一性原理研究

甲脒基铅卤钙钛矿作为光电转换材料,引起了人们的广泛关注. 采用第一性原理对甲脒基铅卤钙钛矿FAPbI_xCl_3-x（FA=NH₂CH=NH₂⁺,x=0～3）的结构及光电特性进行了理论研究. 计算结果表明,FA在三方晶系的FAPbX₃（X=Cl,Br,I）中沿[001]方向排布,而在混合FAPbI_xCl_3-x中,八面体PbX₆（X=Cl,I）的扭转导致FA朝向发生了微小的偏移. FA对于平衡晶体结构起着重要的作用,并作为电荷供体为PbI₃骨架贡献约0.76 e的电荷. FAPbI_xCl_3-x属于直接带隙半导体,其价带顶（VBM）主要由I 5p（Cl 3p）和少量Pb 6s轨道杂化的反键轨道组成,而导带底主要由Pb 6p轨道组成. 随着I/Cl比例的增大,FAPbI_xCl_3-x的晶格常数和体积逐渐增大,禁带宽度逐渐减小,吸收光谱发生红移. FAPbI₃的禁带宽度为1.53 eV,表现出最佳的吸收光谱特性,是一类极具潜力的光电转换材料.     

Eu3+掺杂双钙钛矿Sr2CaMoO6橙红色荧光粉的结构特征及其发光性能

采用EDTA-柠檬酸联合配位法制备一系列组成的(Sr1-xEux)2CaMoO6橙红色荧光粉。通过X射线衍射、拉曼光谱、扫描电镜及荧光光谱研究不同Eu3+离子掺杂浓度下Sr2CaMoO6∶Eu3+荧光粉的晶体结构、掺杂位置、形貌及其光致发光性能。Rietveld全谱拟合结果表明:掺杂后样品为(Ca/Mo)O6八面体少量倾斜的空间群为P21/n的正交双钙钛矿结构,随着Eu3+离子共掺杂浓度的增加,样品的晶胞体积减小;Eu3+离子取代八面体间隙的Sr2+位置致使双钙钛矿的T2g(1)拉曼振动模发生蓝移;在近紫外区宽而强电荷迁移带和蓝光激发下,该荧光粉分别发射以Eu3+离子5D0-7F1磁偶极跃迁为主的橙光和以5D0-7F2电偶极跃迁为主的红光,组成为(Sr0.98Eu0.02)2CaMoO6的荧光粉具有最强的橙红光发射强度,是一种潜在的适用于近紫外LED芯片的光转换红光材料。     

Ba2SbInO6双钙钛矿的水热合成和表征

利用水热晶化法制备了Ba₂SbInO₆纯相，并通过XRD、SEM、IR、XPS和ICP等方法，对产物的物相、形貌、结构和组成进行了表征。初步结构表征结果表明，产物可能为B位离子无序排列的立方钙钛矿结构，空间群为Pm3m，晶胞参数为a=0.4132 mm。产物粉末呈现立方晶型，粒度约为0.5～2 μm。     

Crystal Structure of the Ordered Double Perovskite,Sr2NiTeO6

The crystal structure of the ordered double perovskite Sr₂MnTeO₆ has been refined at ambient temperature from high resolution neutron and X‐ray powder diffraction data in the monoclinic space group I 1 2/m 1 with a = 5.6166(1) Å, b = 5.5807(1) Å, c = 7.8797(1) Å and β = 90.048(2)°. The structure is the result of out‐of‐phase (–) rotations of virtually undistorted NiO₆ and TeO₆ octahedra in the (0 – –) sense about two of the axes of the ideal cubic perovskite. Electron diffraction measurements have been used to confirm the proposed space group and structure.     

双钙钛矿Sr_2FeMn_(1-x)Co_xO_6催化剂的制备及其催化性能

通过溶胶凝胶法制备了一系列双钙钛矿催化剂Sr_2FeMn_(1-x)Co_xO_6(x=0.1,0.3,0.5,0.7,0.9),其结构经XRD,BET,H_2-TPR和SEM表征。以催化甲烷燃烧为模板反应,考察掺杂不同量Co~(2+)对Sr_2FeMn_(1-x)Co_xO_6催化性能的影响。结果表明:催化剂经800℃焙烧后可形成完整的双钙钛矿晶型,且Co离子掺杂量不同其催化活性不同,当Co离子掺杂量为0.3时,催化剂Sr_2FeMn_(0.7)Co_(0.3)O_6具有较高的催化活性,样品比表面积为9m~2·g~(-1),起燃温度T_(10%)为442℃,T_(90%)为654℃,Fe~(3+)、Mn~(2+)、Co~(2+)之间有一定协同作用。     

Hexagonal Double Perovskite Cs2AgCrCl6

The quaternary halide Cs₂AgCrCl₆ was prepared in the form of dark purple crystals by reaction of CsCl, AgCl, and CrCl₃, at 700 °C. It crystallizes in the trigonal Ba₂NiTeO₆‐type structure [space group R3 m, Z = 6, a = 7.2692(4) Å, c = 36.443(2) Å] belonging to the family of perovskite polytypes containing sequences of hexagonal close‐packed layers. Groups of three face‐sharing octahedra, which are occupied in the sequence Ag–Cr–Ag, are connected through corner‐sharing by Cr‐centered octahedra. The UV/Vis/NIR diffuse reflectance spectrum shows absorptions arising from d–d transitions typical of octahedral Cr³⁺ complexes, as confirmed by electronic structure calculations. The compound melts at 506 °C. Magnetic measurements revealed simple paramagnetic behavior consistent with the presence of isolated Cr³⁺ ions.     

Sr2MgOsO6: A Frustrated Os6+ (5d2) Double Perovskite with Strong Antiferromagnetic Interactions

The Os⁶⁺ (t_2g²) double perovskite Sr₂MgOsO₆ was prepared as polycrystalline material from the respective binary metal oxides. Sr₂MgOsO₆ crystallizes with the tetragonal space group I4/m. Magnetization and specific heat measurements show a broad anomaly near 100 K, but no well‐defined cusp. The magnetism is governed by strong antiferromagnetic interactions. Sr₂MgOsO₆ constitutes a new example for the peculiar, poorly understood magnetism of 5d² ions on a frustrated fcc lattice, where spin‐orbit coupling and orbital physics are expected to play an important role.     

ChemInform Abstract: Pressure‐Induced Structural and Electronic Transition in Sr2ZnWO6 Double Perovskite.

Polycrystalline Sr₂ZnWO₆ is prepared by staged calcination of stoichiometric amounts of SrCO₃, ZnO, and WO₃ in air (Al₂O₃ crucible, 1.     

Variable Temperature Behaviour of the Hybrid Double Perovskite MA2KBiCl6

Perovskite-related materials show very promising properties in many fields. Pb-free perovskites are particularly interesting, because of the toxicity of Pb. In this study, hybrid double perovskite MA₂KBiCl₆ (MA = methylammonium cation) was found to have interesting variable temperature behaviours. Both variable temperature single crystal X-ray diffraction, synchrotron powder diffraction, and Raman spectroscopy were conducted to reveal a rhombohedral to cubic phase transition at around 330 K and an order to disorder transition for inorganic cage below 210 K.     

Hydrothermal Synthesis and Dielectric Characterization of a Double Perovskite Ba2FeSbO6

A double perovskite oxide Ba₂FeSbO₆ was hydrothermally synthesized and structurally characterized by X-ray diffraction. This solid compound shows a single phase and has a trigonal structure with space group R m and cell parameters of a=0.57261 nm and c=1.40244 nm. The dielectric constant and loss tangent of the solid measured in a frequency range from 100 Hz to 1 MHz at temperatures from 313 K to 513 K reveal a relaxation process of frequency dependence of the real part(ε') of dielectric constant and dielectric loss tand. The frequency dependence of electrical property led to the framework of conductivity and electric modulus formalisms. The scaling behavior of imaginary part of electric modulus suggests that the relaxation describes the single mechanism at various temperatures. The variation tendency of the alternating current impedance indicates the thermally activated conduction process follows Jonsche’s power law.     

Lead-Free Halide Double Perovskite Cs2AgBiBr6 with Decreased Band Gap

Environmentally friendly halide double perovskites with improved stability are regarded as a promising alternative to lead halide perovskites. The benchmark double perovskite, Cs₂AgBiBr₆, shows attractive optical and electronic features, making it promising for high-efficiency optoelectronic devices. However, the large band gap limits its further applications, especially for photovoltaics. Herein, we develop a novel crystal-engineering strategy to significantly decrease the band gap by approximately 0.26 eV, reaching the smallest reported band gap of 1.72 eV for Cs₂AgBiBr₆ under ambient conditions. The band-gap narrowing is confirmed by both absorption and photoluminescence measurements. Our first-principles calculations indicate that enhanced Ag–Bi disorder has a large impact on the band structure and decreases the band gap, providing a possible explanation of the observed band-gap narrowing effect. This work provides new insights for achieving lead-free double perovskites with suitable band gaps for optoelectronic applications.