Improvement of visible light-induced photocatalytic performance by Cr-doped SrTiO_3-carbon nitride intercalation compound (CNIC) composite

Novel organic-inorganic composite photocatalyst offers new opportunities in the practical applications of photocatalysis. Novel visible light-induced Cr-doped Sr Ti O3–carbon nitride intercalation compound(CNIC) composite photocatalysts were synthesized. The composite photocatalyst was characterized by X-ray diffraction(XRD), field-emission scanning electron microscopy(FESEM), high-resolution transmission electron microscopy(HRTEM), Fourier transform infrared(FT-IR) spectroscopy, UV-vis diffuse reflection spectroscopy, photoluminescence(PL) spectroscopy, and BET surface area analyzer. The photocatalytic oxidation ability of the novel composite photocatalyst was evaluated using methyl orange(MO) as a target pollutant. The photocatalysts exhibited a significantly enhanced photocatalytic performance in degrading MO. For maximizing the photodegradation activity of the composite photocatalysts, the optimal CNIC content was determined. The improved photocatalytic activity of the as-prepared Cr-doped Sr Ti O3–CNIC composite photocatalyst may be attributed to the enhancement of photo-generated electron–hole separations at the interface.

Visible Light-induced Cr-doped SrTiO_3-g-C_3N_4 Composite for Improved Photocatalytic Performance

Novel visible light-induced Cr-doped Sr Ti O3-g-C3N4 composite photocatalysts were synthesized by introducing polymeric g-C3N4. The composite photocatalyst was characterized by X-ray diffraction（XRD）, high-resolution transmission electron microscopy（HRTEM）, Fourier transform infrared（FT-IR） spectroscopy, UV-vis diffuse reflection spectroscopy, photoluminescence（PL） spectroscopy and BET surface area measurements. The photocatalytic oxidation ability of the novel composite photocatalyst was evaluated using methyl orange（MO） as a target pollutant. The photocatalysts exhibited a significantly enhanced photocatalytic performance in degrading MO. The optimal g-C3N4 content for the photodegradation activity of the composite photocatalysts was determined. The as-prepared composite photocatalyst exhibits an improved photocatalytic activity due to enhancement of photo-generated electron-hole separation at the interface.

Synthesis and Electrochemical Properties of Cr-doped Li_3V_2(PO_4)_3 Cathode Materials for Lithium-ion Batteries

Cr-doped Li3V2（PO4）3 cathode materials Li3V2-xCr（PO4）3 were prepared by a carbothermal reduction（CTR） process. The properties of the Cr-doped Li3V2（PO4）3 were investigated by X-ray diffraction （XRD）, scanning electron microscopic （SEM）, and electrochemical measurements Results show that the Cr-doped Li3V2（PO4）3 has the same monoclinic structure as the undoped Li3V2（PO4）3, and the particle size of Cr-doped Li3V2（PO4）3 is smaller than that of the undoped Li3V2（PO4）3 and the smallest particle size is only about 1 1μm. The Cr-doped Li3V2（PO4）3 samples were investigated on the Li extraction/insertion performances through charge/discharge, cyclic voltammogram （CV）, and electrochemical impedance spectra（EIS）. The optimal doping content of Cr was that x=0.04 in the Li3V2-xCrx（PO4）3 samples to achieve high discharge capacity and good cyclic stability. The electrode reaction reversibility was enhanced, and the charge transfer resistance was decreased through the Cr-doping. The improved electrochemical performances of the Cr-doped Li3V2（PO4）3 cathode materials are attributed to the addition of Cr^3＋ ion by stabilizing the monoclinic structure.

First-principles study on electronic structure, magnetic and dielectric properties of Cr-doped Fe_3C

The first-principles calculations were performed to investigate the electronic structure, magnetic and dielectric properties of Cr-doped Fe_3C, in comparison to those of pure Fe_3C and Cr_3C. The obtained results show that the thermodynamic stability of Crdoped Fe_3C becomes weaker in terms of the larger formation enthalpy, on the contrary, the metallicity and covalency are found to strengthen to some extent. The magnetic moments of Fe_3C, Fe_(11)CrC_4(g), and Fe_(11)CrC_4(s) are respectively 21.36 μB/cell, 16.92 μB/cell, and 17.62 μB/cell, and in Fe_(11)CrC4(g) and Fe_(11)CrC_4(s), the Fe of Wyckoff positions of 8d and 4c is substituted by Cr. The local magnetic moment of Cr at 8d site is larger than that at 4c site in the doped structure, which is opposite to that of Fe. In low frequency band, the permittivity follows the ranking of Fe_(11)Cr C_4(s)>Cr_3C>Fe_(11)Cr C_4(g)>Fe_3C. Once exceeding a certain frequency, the sequence will be broken. Besides the electron transition, the polarization of atoms also makes a contribution to the dielectric properties.

六方YMnO_3多铁性薄膜的制备与性质研究进展

六方YMnO3是一种集铁电性与反铁磁性于一体的新材料,具有丰富的物理内容和优良的应用前景。本文综述了近年来六方YMnO3薄膜在制备方法、电学、磁学等物理性质的研究进展。基于其电磁性质,阐述了该薄膜在自旋阀等器件方面的潜在应用。最后指出了六方YMnO3薄膜研究中存在的问题,提出解决的思路。

六方YMnO_3纳米棒的制备、微结构及磁性研究

采用水热法成功合成了YMnO3纳米棒,利用XRD、SEM、EDS、HRTEM和SAED对产物进行了表征。实验结果表明,产物为六方纯相YMnO3纳米棒,高分辨电镜图片显示晶面间距为0.298nm,对应(004)面间距,结合XRD及选区电子衍射结果,可以得出纳米棒沿[001]方向生长,并初步分析了纳米棒的形成机理。测试了YMnO3纳米棒的M-T曲线,观察到了由表面未补偿自旋引起的自旋玻璃态。

微波辅助溶胶-凝胶法合成YMnO_3纳米粉体

采用微波辅助溶胶-凝胶法制备了YMnO3纳米粉体,利用FTIR和TG-DSC对凝胶的组成及热分解过程进行分析,并通过XRD、FSEM、TEM和磁性能测试对制得的纳米粉体进行表征。结果表明:与传统的溶胶-凝胶法相比,该研究中采用的微波辅助溶胶-凝胶法可以在较短的制备时间内、较低的煅烧温度下得到单相的YMnO3粉体,且粉体颗粒细小,尺寸分布较均匀,平均粒径小于100nm。磁性能研究结果表明制得的YMnO3纳米粉体在室温下表现为顺磁性特征。

SiC/Si上六方YMnO_3薄膜的制备和铁电性能

采用化学溶液法在SiC/Si上制备了YMnO3薄膜。XRD结果显示所制备的薄膜为六方YMnO3,且具有部分择优取向生长。拉曼光谱和XPS的结果验证了样品为六方纯相YMnO3。以Pt为顶电极,测试了YMnO3薄膜的电滞回线,结果显示YMnO3薄膜具有良好的铁电性质。

Si(111)衬底上六方YMnO_3薄膜的制备与铁电性质

采用化学溶液法在Si(111)衬底上制备了YMnO3薄膜。XRD结果表明,所制备的薄膜为六方纯相YMnO3,且具有部分择优取向生长。以Pt为顶电极,测试了YMnO3薄膜的电滞回线,结果表明,所制备的YMnO3薄膜具有良好的铁电性质。

退火处理对YMnO3薄膜的结构和荧光性能的影响

室温下,采用脉冲激光沉积方法在Si(100)衬底上制备了YMnO3薄膜,并对其进行了不同温度的退火处理。采用X射线衍射和荧光光谱分析方法对薄膜的结构和荧光特性进行了研究。结果表明:通过退火处理,可以得到正交相和六方相共存的多晶态YMnO3薄膜,并且随着退火温度的升高,两相的比例发生变化,由正交相为主转变为六方相为主。YMnO3薄膜样品的荧光发射峰集中在波长430～620nm范围内,可能是由Mn3+离子从5T2到5E之间的能级跃迁所引起的。其荧光强度随着退火温度的升高逐渐增强,但峰位基本保持不变,说明薄膜结构的改变对Mn3+离子的能级跃迁几率有明显的影响,对能级位置的影响不大;而且荧光光谱还显示在同一薄膜中各个荧光峰的相对强度随着退火温度的变化不大。

微波辅助低温固相法制备YMnO_3纳米粉体

以金属无机盐为原料,柠檬酸为络合剂,采用微波辅助低温固相法制备前驱体,再经煅烧获得YMnO3纳米粉体,研究了煅烧温度和微波功率对合成产物的影响。结果表明:通过微波辅助低温固相法可得到钇和锰原子级混合的前驱体,前驱体经800℃煅烧3h后可合成六方YMnO3相;经900℃和1 000℃煅烧后,产物中出现较多的Y2O3和YMn2O5杂质相;当煅烧温度升高为1 100℃时,可合成高纯的六方YMnO3相,但粉体的团聚现象严重;与传统低温固相法相比,采用微波辅助低温固相法经800℃煅烧后制得的YMnO3粉体分散性和球形度较好。

离子部分取代YMnO_3多铁性材料研究现状

六方YMnO3是一种集铁电性与反铁磁性于一体的多功能材料,具有广阔的应用前景。论述了A位和B位部分取代对YMnO3微观结构和电、磁性能的影响,并对其研究前景做出了展望。

High pressure floating-zone growth and property characterization of Cr-doped hexagonal YMnO_3 crystals

Large crystal growth of Cr-doped h-YMnO3has been investigated by using a high pressure optical floatingzone method. The size of the grown crystals is typically 60–70 mm in length and 4–5 mm in diameter. The structure of the grown crystals is analyzed by powder X-ray diffraction and scanning electron microscopy.The defects in the as-grown crystals, including low-angle grain boundary and inclusions are studied. An off-stoichiometric phenomenon is found with a slight Cr deficiency in different parts. The relationship between defects and growth conditions during crystal growth is also discussed. The magnetic properties show spin-glass phase features with weak ferromagnetic behavior below 30 K.

Fabrication of Cr-doped SrTiO3/Ti-dopedα-Fe_(2)O_(3) photoanodes with enhanced photoelectrochemical properties

Cr-doped Sr TiO_(3)/Ti-dopedα-Fe_(2)O_(3) heterojunction has been constructed by an ingenious way,i.e.using segregation titanium oxide on the surface of the Ti-dopedα-Fe_(2)O_(3) electrode to in situ prepare Cr-doped SrTiO_(3).After construction of the heterojunction,the photocurrent onset potential for water oxidation on a Ti4+dopedα-Fe_(2)O_(3) cathodically shifts by about 100 mV.Moreover,the cathodic shift of the onset potential can be preserved well even after a long time running.The results indicate the effectiveness and credibility of the fabricated heterojunction.In order to make clear the reason for the onset potential shift,the asprepared Ti-dopedα-Fe_(2)O_(3) and Cr-doped SrTiO_(3)/Ti-dopedα-Fe_(2)O_(3) samples were investigated by X-ray photoelectron spectroscopy,electrochemical impedance spectroscopy,X-ray diffraction spectroscopy,etc.Based on the experimental evidences,it is proposed that cathodic shift of the onset potential is mainly due to the enhanced charge separation at the photoanode surface.This strategy can offer a reference to construct heterojunction on other films especially for those with surface segregation.

静电纺丝法制备超长YMnO_3单晶纳米纤维

采用改进的静电纺丝装置结合溶胶凝胶技术制备了超长的定向排列的YMnO_3/PVP复合纳米纤维,将其在900℃高温煅烧6 h得到了六方相YMnO_3(H YMnO_3)单晶纳米纤维。用SEM,XRD,TEM,SAED及VSM对样品的相纯度,表面形貌、晶体结构和磁性能进行了表征。结果表明:YMnO_3/PVP复合纳米纤维的长度可达数米,表面光滑,定向度高,形貌均一,平均直径为150-230 nm;H-YMnO_3纤维的直径为70-100 nm,表面光滑呈莲藕状;在室温下的磁测量结果表明,H-YMnO_3纳米纤维具有弱铁磁性。

YMnO_3薄膜的铁电行为及其纳米尺度铁电畴的研究

六方YMnO_3是一种特殊的多铁性材料,因其具有介电常数低、单一极化轴、无挥发性元素等特点,在磁电领域具有独特的优势,但目前关于YMnO_3薄膜的铁电性特别是畴结构的研究相对较少.本文采用溶胶-凝胶法在Si(100)基片上制备了多铁性YMnO_3薄膜,利用掠入射X-射线衍射、原子力显微镜对薄膜的结构及表面形貌进行了分析,用压力显微镜(PFM)技术研究了纳米尺度畴结构及微区电滞行为,并通过I-V,P-E曲线进一步研究了薄膜的漏电流和宏观电滞行为.结果表明,该薄膜为六方钙钛矿结构,YMnO_3晶粒大小均匀并且结晶性较好,薄膜表面粗糙度为7.209 nm.PFM图显示出清晰的电畴结构,结合典型的微区振幅蝴蝶曲线和相位电滞回线,证实该YMnO_3薄膜具有较好的铁电性.由于受内建电场的作用,振幅曲线和相位曲线都向正向偏移,表现出非对称特征.该薄膜的漏电流密度低于10^(-6)A·cm^(-2),因而其电滞回线基本能够达到饱和.

Ce、Fe共置换锰酸钇陶瓷的结构和磁性能研究

采用低温固相法制备Y_(0.85)Ce_(0.15)Mn_(0.8)Fe_(0.2)O_3粉体,经高温烧结制得陶瓷,研究了Ce、Fe共置换对锰酸钇陶瓷的微结构和磁学性能的影响。采用XRD对Y_(0.85)Ce_(0.15)Mn_(0.8)Fe_(0.2)O_3粉体和陶瓷进行物相分析,利用TEM和FESEM对样品进行显微形貌分析;同时研究了Y_(0.85)Ce_(0.15)Mn_(0.8)Fe_(0.2)O_3陶瓷的磁学性能,并利用XPS分析了其中磁性离子的价态分布。结果表明,前驱体经800℃煅烧后可制得单相Y_(0.85)Ce_(0.15)Mn_(0.8)Fe_(0.2)O_3纳米粉体;该粉体经1450℃烧结制得致密的Y_(0.85)Ce_(0.15)Mn_(0.8)Fe_(0.2)O_3陶瓷,其反铁磁转变温度为29 K,在低温下存在反铁磁有序;与YMn_(0.8)Fe_(0.2)O_3相比,Y_(0.85)Ce_(0.15)Mn_(0.8)Fe_(0.2)O_3中Fe2+含量降低,Mn离子的混价结构由Mn^(2+)/Mn^(3+)转变为Mn^(3+)/Mn^(4+),陶瓷的磁性转变温度降低。

Atomistic simulation of dynamical and defect properties of multiferroic hexagonal YMnO_3

Atomistic simulation has been performed to investigate the dynamical and defect properties of multiferroic hexagonal YMnO3 with newly developed interaction potentials. Dynamical calculation reveals that phonon vibrations of hexagonal YMnO3 are quite different from those of orthorhombic YMnO3. Defect calculation finds that O Frenkel is the most probable intrinsic disorder, and Mn antisite defect is favorable to exist, especially for Mn ions entering the Y2 sites. It is also found that holes prefer to localize at O2sites rather than at Mn3+ sites, while the electron can be localized at the Mn3+ site. The disproportionation of Mn3+ ions is unlikely to occur in hexagonal YMnO3.

锰酸钇薄膜中Mn^(3+)离子d—d跃迁的超快光谱学研究

本文利用时间分辨光谱技术,系统研究了飞秒激光诱导YMnO_3薄膜中Mn^(3+)离子3d轨道跃迁的载流子动力学过程.当抽运光子能量为1.7 eV,对应于Mn^(3+)离子的3d轨道跃迁,抽运-探测零延迟时间处的透射率变化随着温度的降低逐渐减小.这起源于低温下短程反铁磁有序诱导Mn^(3+)离子d—d能级发生'蓝移'.载流子弛豫过程由快、慢两个过程组成,分别对应于电子-声子相互作用和自旋-声子相互作用.实验发现,当温度低于80 K,电子-声子热化时间显著增加,表明低温下电子-声子的耦合强度受长程反铁磁有序的影响.