The ternary chalcopyrite semiconductor CuInSe 2 has emerged as a leading material for the preparation of photo- voltaic devices. 1,2 In fact, CuInSe 2 -based solar cells, even in polycrystalline form, have achieved 18% power conversion efficiency. 1,2 The ordered defect compounds ? ODCs ? belong- ing to the Cu–In–Se system have also attracted considerable interest recently. 3– 6 This is because it is believed that these ODCs could play an important role in the optimization of CuInSe 2 -based solar cells. 3 Four In-rich phases of this compound, namely, CuIn 5 Se 8 , CuIn 3 Se 5 , Cu 2 In 4 Se 7 , and Cu 3 In 5 Se 9 , are reported 4 to form on the tie-line of the (Cu 2 Se) x – (In 2 Se 3 ) 1 ? x pseudobinary system. In studying the defect physics of CuInSe 2 , Zhang et al. 4 have suggested that the presence of the donor–acceptor defect pair (In Cu 2 ? ? 2V Cu 1 ? ) could be used to explain the existence of CuIn 5 Se 8 , CuIn 3 Se 5 , Cu 2 In 4 Se 7 , and Cu 3 In 5 Se 9 ODCs as due to the repeat of a single unit of this defect pair for each n ? 4, 5, 7, and 9 units, respectively, of CuInSe 2 . Several authors have reported that, with the exception only of CuIn 5 Se 8 and perhaps Cu 3 In 5 Se 9 which exhibit hex- agonal and orthorhombic structures, 6 –9 respectively, these ODCs crystallize in a chalcopyrite-related structure. 10–12 This is because, except for the presence of a few unidentified lines of weak intensities, x-ray diffraction ? XRD ? patterns of these In-rich phases are found to be very similar to that of CuInSe 2 . The information about the nature of the fundamental absorption edge of CuIn 5 Se 8 and CuIn 3 Se 5 , and its temperature dependence has been published. It is found that both these ODCs have a direct allowed band gap. 5,12–14 However, experimental data about the physical properties of Cu 3 In 5 Se 9 is very scarce 9 and only a limited number of papers on the optical absorption, 15 photoluminescence ? PL ? , 16 electro- reflectance, 16 and Raman 17 spectra of Cu In Se have ap-
peared in the literature. The temperature dependence of the optical absorption coefficient of bulk crystal of Cu 2 In 4 Se 7 was reported by Djega-Mariadassou et al. 15 From the analysis of the data, the optical band gap E G of this semiconductor was found to vary between about 1.11 and 1.05 eV in the temperature range from 10 to 300 K. However, probably due to the presence of a band tail, the nature of the band–to– band transition was not established in Ref. 15. Furthermore, the interpretation based on the analysis of the limited amount of optical data near the band edge reported in the literature on Cu 2 In 4 Se 7 are contradictory. For example, photocurrent spectra of the pseudobinary (Cu 2 Se) x – (In 2 Se 3 ) 1 ? x system shows 7 that most of the phases with compositions in the range 0.15 р x р 0.31, which are very close to Cu 2 In 4 Se 7 ( x ? 0.33), have an indirect lowest-band gap at 0.85–0.87 eV and also highest-direct gap between 1.00 and 1.15 eV. On the other hand, two distinct broad bands with peaks at about 0.90 and 1.12 eV were observed 16 in the PL spectra of Cu 2 In 4 Se 7 . These were assigned as due to donor–acceptor pair ? DAP ? emission, and to the band–to–band transition, respectively. From these results it can be concluded that a detailed com- parative study of the optical properties of Cu 2 In 4 Se 7 near the fundamental absorption edge is required to establish the nature of the band gap and the origin of the two bands observed from optical absorption and PL measurements. For this rea- son, in the present work we report on the study of the temperature dependence of the optical absorption coefficient spectra of Cu 2 In 4 Se 7 bulk crystals near the band gap. From the analysis of the data, an allowed direct gap is found in the high-energy region ( h ? у 1.0 eV). In addition, from a combined analysis of the PL and optical absorption spectra, the band observed in the energy range from 0.90 to 0.99 eV is identified as due to band tails–to–band transitions caused by high concentrations of native defects. The temperature dependence of the direct energy gap is also discussed in terms of the current theoretical models reported in the literature for the shift of E . Ingots of Cu 2 In 4 Se 7 were prepared by the vertical Bridgman–Stockbarger technique. Circular shaped void and crack free samples for the characterization and optical studies were obtained by slicing the ingot perpendicularly to the growth direction. They were prepared by heating the sto- ichiometric mixture of Cu, In, and Se that where sealed in an evacuated quartz ampoule. The ampoule was placed in a multiple zone vertical furnace. Initially they were heated from room temperature to 1200 °C at a rate of 10 °C/h with a dwell time of 18 h at 300 °C. The molten mixture was kept at this temperature for 36 h. To assure a homogeneous mixing, the ampoule was agitated periodically. It was later cooled down at a rate of 10 °C/h up to 900 °C, then at 1 °C/h to 700 °C. The cooling rate from 700 to 530 °C was 5 °C/h. The ingots were annealed at this temperature for 120 h. The furnace was then turned off and the ingot cooled down to room temperature at 40 °C/h. Chemical composition of the ingots was determined at several points by energy dispersive x-ray ? EDX ? analysis using a Kevex Model Delta-3 system con- nected to a Hitachi Model S-2500 scanning electron micro- scope. The XRD patterns were registered with a Rigaku D/Max-IIIB diffractometer using a Cu-target. Rigaku ana- lytical software was used for the structural analysis. The optical transmittance spectra were measured with an automated CARY 17I Spectrophotometer using a 170 W tungsten lamp as a light source. The transmitted radiation was detected by a cooled PbS detector. For the measurements of transmittance spectra at various temperatures, the sample was placed in a He 2 cryostat operating in the temperature range from 10 to 300 K. The absorption coefficient _ was obtained from the measured transmittance through the relation _ ? (1/ t )ln( I 0 / I ) ? _ R , where t is the thickness of the sample, I o and l the incident and transmitted radiation, respectively, and _ R a nearly constant residual absorption observed in the low energy region of the spectra. Chemical analysis performed by EDX spectroscopy on samples of Cu 2 In 4 Se 7 , taken from the central part of the ingots, gave representative composition of Cu:In:Se close to the ideal 2:4:7 value. The analysis of the registered peak positions of the XRD patterns of Cu 2 In 4 Se 7 produced as a unique solution a tetrag- onal unit cell corresponding to a chalcopyrite-like structure. The refined unit cell parameters a and c thus obtained are given in Table I. Values of these parameters for CuInSe 2 and CuIn 3 Se 5 reported earlier are also given in this table for comparison. It can be observed that a and c decrease in the sequence CuInSe 2 → Cu 2 In 4 Se 7 → CuIn 3 Se 5 . This is consis- tent with the fact that in these compounds the fraction m of (2V Cu ? 1 ? In Cu ? 2 ) defect pair for each unit of CuInSe 2 increases in the sequence of 0, 1/7, and 1/5 for the 1:1:2, 2:4:7, and 1:3:5 phases, respectively. It is also found that the unit cell parameters of Cu In Se are smaller by about 0.5% and larger by 0.1% than those of the corresponding CuInSe 2 and CuIn 3 Se 5 phases, respectively. These differences lie outside the limit of error in the x-ray measurements in the present case which is 5 ? 10 ? 4 % and 2 ? 10 ? 3 % for a and c , respectively. In Fig. 1, the unit cell constants given in Table I, are plotted as a function of m that represents the fraction of defect pair for each unit of CuInSe 2 . As observed, a and c tend to decrease linearly with increasing m . These results indicate that a homogeneous 247 phase in the Cu–In–Se system, stable at room temperature, is effec- tively formed. The absorption coefficient spectra of Cu 2 In 4 Se 7 at several temperatures between 10 and 300 K are shown in Fig. 2. Two distinct bands in the high- and low-energy sides of the spectra are observed. As shown in Fig. 3, where ( _ h ? ) 2 is plotted against the photon energy h ? , it is found that in the high-energy region these spectra follow a linear relation of the form ( _ h ? ) 2 ? ( h ? ? E G ) indicating an allowed direct band gap. The broad absorption band in the low-energy region initially can be associated with the indirect band–to– band transition reported in Ref. 7. In this case, the absorption spectra is expected to follow a dependence of the form 18 _ h ? ? ( h ? ? E G ) 2 . To verify this possibility, we plot in Fig. 4 the absorption coefficient data in the form of ( _ h ? ) 1/2 versus h ? for low values of _ . As observed at all temperatures, these spectra follow a linear relation apparently indicating that the lowest energy gap in Cu 2 In 4 Se 7 corresponds to band extrema that are at different points in the Brillouin zone. However, other possible absorption mechanisms should also be considered before this interpretation can be accepted. It is a well-known fact that in heavily doped direct gap semiconductors, in addition to states given by the usual square-root dependence of absorption coefficient, a tail of states that extends to lower energies below the band edge is also to be expected. Experimentally, it is observed, in general, that this band tail tends to be exponential. 20,21 In the case of parabolic bands, the spectral dependence of the absorption coefficient for band tail–to–band transitions _ BT near the band edge is given by 21 _ B ? C BT E 3/2 0 exp ? h ? / E 0 ? , ? 1 ? where C BT is a constant and E 0 is a characteristic energy that depends mainly on the ionized impurity concentration. Equation ? 1 ? was fitted to the absorption coefficient spectra for _ ? 5 ? 10 2 cm ? 1 using C BT and E 0 as adjustable parameters. An excellent fit to the data, very similar to that obtained by fitting the expression _ ? (1/ h ? )( h ? ? E G ) 2 , was achieved with Eq. ? 1 ? . This is shown in Fig. 5 where four representative spectra of _ in the low-absorption region at 10, 200, 250, and 300 K, together with the curves obtained from the fit are plotted. This indicates that this band can also be associated with transitions from band tails–to–band, caused by a high concentration of defect states. It is worth- while mentioning that the value of E 0 obtained from the fit at different temperatures is very nearly constant around 30 meV. This is in very good agreement with that obtained in binary compounds which, depending on impurity concentration, varies from 5 to 30 meV ? Ref. 21 ? . These results thus indicate that analysis of the optical absorption data alone is not enough and other complementary optical measurements are required to establish the nature of the absorption band observed in the low-energy region. The distinction between the two mechanisms, that is indirect band gap or transitions from band tails–to–conduction band, is possible from a combined analysis of the PL and optical absorption spectra. This is because in the PL of Cu 2 In 4 Se 7 , reported by Shirakata et al. 16 two distinct broad PL bands at 8 K with peaks at about 0.90 and 1.12 eV are observed. Based on the excitation intensity dependence of the PL, the first band is assigned to donor–acceptor pair DAP emission and the latter to the band–to–band transition. According to these authors, the broadening of the PL peaks ? full width at half maximum of about 0.13 eV ? indicates that the band edge is highly perturbed due to a high concentration of native defects. From this analysis, it is then suggested that the broad absorption band below h ? ? 1.0 eV is due to band tail–to– band transitions originated by a high concentration of native defects. Therefore, the existence of an indirect gap in Cu 2 In 4 Se 7 can be discarded. It is then concluded that the band gap in this compound is allowed direct as in the case of CuInSe , CuIn Se , and CuIn Se . 14 The value of the direct energy gap E G at each temperature can be estimated, after subtracting the absorption coefficient due to band tails, by extrapolating the linear part of the plot of ( _ h ? ) 2 versus h ? to ( _ h ? ) 2 ? 0. This procedure, not shown here, gives an energy gap around 0.996 and 0.964 eV at 10 and 300 K, respectively. However, a more precise value of E G can be obtained by the analysis of the absorption coefficient spectra at each temperature using an expression obtained from the Elliot model 23 after convoluting the total absorption coefficient with a Lorentzian function ? ? ? 1 ? ( h ? ) 2 ? ? 2 ? . According to this approach, _ can be expressed as 5Join ResearchGate to access over 30 million figures and 100+ million publications – all in one place.Copy referenceCopy captionEmbed figurePublished in
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Article & Jul 2003
& Journal of Applied Physics
ABSTRACT: A comparative study of the unit cell parameters and volume of the chalcopyrite-related ordered defect compounds and other In-rich phases of the Cu–In–Se ternary system is made. These compounds fall on the tie-line of (Cu2Se)1 - x(In2Se3)x. It is found that the unit cell parameters and volume of the compounds that can be derived from the formula Cun - 3Inn + 1Se2n, where n = 4,5,6,7,8 and 9, decrease with an increase in the fraction of cation vacancies to the total number of cation positions, m, or interacting donor–acceptor defect pairs
per unit l in the chemical formula. The reduction in the unit cell dimensions is explained as due to the decrease in the effective cation radius caused by the increase in m or l. This behaviour is consistent with Vegard's law. However, the unit cell parameters of other In-rich phases such as CuIn4Se6 and CuIn4Se7 reported in the literature do not follow this trend. It must be noted that with indium having a 3+ oxidation state, the formation of these materials can only be explained if the valence of Cu atoms is 0 and 2+, respectively, different from the 1+ expected for the members of the Cu2Se–In2Se3 system.
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Article & Feb 2004
& Journal of Physics D Applied Physics
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ABSTRACT: A comparative study of the effect of donor acceptor defect pairs [(In,Ga)Cu+2,2VCu-1] on the unit cell parameters a, c and V of the ordered defect compounds that are intermediate phases of the pseudo-binary [Cu2(Se,Te)]1-X[(In2,Ga2)(Se3,Te3)]X system has been carried out. It is found that a, c and V decrease linearly with the increase in the fraction of cation vacancies to the total number of cation positions, m, or the fraction of the interacting donor acceptor defect l per unit, respectively, in the chemical formula. The reduction in the unit cell dimensions is explained as due to the decrease in the effective cation radius reff caused by the increase in m or l or decrease in n. The linear dependence of reff on a, c, and V has important consequences. This behavior can be used to predict the unit cell parameters of other ODCs that may have chalcopyrite-related structure and have not been reported so far.
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Article & Nov 2005
& Journal of Physics and Chemistry of Solids
0Comments 7Citations
ABSTRACT: Room temperature pseudodielectric function spectra ε(ω) = ε1 (ω) + iε2(ω) of the ordered defects compounds Cu2In4Se7, CuGa3Se5 and CuGa5Se8 have been measured by spectroscopic ellipsometry. The values of refractive index n and extinction coefficient k are given. The structures observed in ε(ω) spectra have been analysed using different methods, including fitting the numerically differentiated experimental spectrum (second derivative) to analytical line shapes. As a result, the energies corresponding to the fundamental gap (E0) and higher critical points have been determined. A linear correlation of the fundamental gap values with Ga/Cu atomic ratio contents in CuGaxSey samples is deduced.
Article & Jan 2007
& Journal of Physics D Applied Physics
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A study of absorption coefficient spectra in a-SiH films near the transition from amorphous to crystalline phase measured by resonant photothermal bending spectroscopy
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A study of absorption coefficient spectra in a-SiH films near the transition from amorphous to crystalline phase measured by resonant photothermal bending spectroscopy
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3秒自动关闭窗口非金属阳离子掺杂锐钛矿相TiO2的第一性原理研究；赵宗彦,柳清菊,朱忠其,张瑾,刘强；(云南大学云南省高校纳米材料与技术重点实验室,云；摘要:采用基于第一性原理的平面波超软赝势方法；研究了非金属阳离子掺杂锐钛矿相TiO2的晶体结构；原理;光催化性能；中图分类号:O472;O77文献标识码:A文章编；1引言；自从1972年Fujishima等[1]发现受紫；目
非金属阳离子掺杂锐钛矿相TiO2的第一性原理研究
赵宗彦,柳清菊,朱忠其,张　瑾,刘　强
(云南大学云南省高校纳米材料与技术重点实验室,云南昆明650091)
摘　要:　采用基于第一性原理的平面波超软赝势方法
研究了非金属阳离子掺杂锐钛矿相TiO2的晶体结构、杂质形成能、电子结构及光学性质。计算结果表明掺杂后发生的晶格畸变、原子间的键长及原子的电荷量的变化,导致了晶体中的八面体偶极矩增大,使光生电子2空穴对能有效分离;掺杂离子的p态电子与O2p态杂化形成杂质能级、价带宽化,TiO2宽度变窄、2在可见关键词:　2;非金属阳离子掺杂;第一性
原理;光催化性能
中图分类号:　O472;O77文献标识码:A文章编号:08)
自从1972年Fujishima等[1]发现受紫外光照的TiO2具有光催化效应以来,以TiO2为代表的光催化材料得到了广泛的研究。TiO2本身具有良好的化学稳定性、抗磨损性、低成本和无毒等特性,因而广泛被应用于太阳能电池、污水及空气净化、自清洁涂层、抗菌、光解水制氢等领域[2～4]。但是由于锐钛矿相TiO2是一种宽禁带半导体,其禁带宽度为3.23eV,只有在紫外光(λ&383.8nm)的激发下才能显示出催化活性,而太阳光中紫外光能量仅占5%(可见光能量占45%),这严重限制了TiO2应用的范围和规模。因此,如何有效地利用可见光是决定TiO2光催化材料能否得到大规模应用的关键。近年来,对TiO2进行改性以实现可见响应,从而充分发挥其光催化性能的研究十分活跃。
目前研究得比较多的实现TiO2可见光响应的改性方法有:过渡金属元素和非金属元素掺杂、半导体氧化物复合、有机染料敏化等。其中非金属掺杂是较为有效的方法之一,如N[5]、C[6]、I[7]、S[8]等。非金属元素的掺杂一般是用非金属元素取代TiO2中的部分氧,形成TiO2-xAx(A代表非金属元素)晶体,由于O的2p轨道和非金属中能级与其能量接近的p轨道杂化后使价带宽化,禁带宽度会相应减小,从而拓宽了TiO2
的光响应范围КTiO2的光[5]。,、实验条件和TiO2光催化性能的因素,同时由于缺少杂质元素对TiO2电子结构,从而导致对掺杂改性的机理说法不一。与实验研究相比,利用计算机模拟计算可以克服实验研究中各种不利因素的影响、突出主要矛盾,更有利于分析掺杂元素对体系电子结构和光学性质的影响,近年来一些研究者已开始了这方面的研究工作[9,10]。
为了进一步系统地研究非金属阳离子掺杂锐钛矿相TiO2的微观机理,澄清不同非金属阳离子在掺杂改性中的作用与对TiO2光催化性能影响的差别,本文采用基于密度泛函理论的超软赝势方法,计算了锐钛矿相TiO2中一个Ti原子被非金属阳离子(C4+、N5+、P5+、S4+、I5+)取代的2×1×1的超晶胞模型的晶格常数,然后在结构优化的基础上计算杂质形成能、电子结构和光学性质。基于这些结果,比较并解释了不同非金属阳离子掺杂对锐钛矿相TiO2在可见光下光催化活性改变的差别及原因。
2　计算模型与方法
本文中所考虑的锐钛矿相TiO2的正格矢晶胞及
(b)所示。锐钛矿相掺杂的超晶胞模型如图1(a)、
TiO2属四方晶系(I41/amd,D194h),一个晶胞中含有两个Ti原子和4个O原子,掺杂的2×1×1超晶胞模型中一个Ti原子被非金属阳离子所取代掺杂的原子数分数大约为4.17%。
应用Accelrys公司开发的MaterialsStudio3.2中的CASTEP模块进行计算[11]。价电子平面波函数的截断能设置为380eV。交换关联能应用局域密度近似中的CA2PZ函数[12,13]。所有的计算均在倒易空间中进行,这样可以同时提高计算的效率和精度。对不可约布里渊区的积分计算采用3×7×3的Monkorst2park特殊k点进行取样求和,快速付里叶变换的网格设置为45×24×54,迭代过程中的收敛标准设置为:
基金项目:教育部新世纪优秀人才支持计划资助项目(NCET);教育部科学技术研究重点资助项目(205147);云南省
自然科学基金资助项目(M)
收到初稿日期:收到修改稿日期:通讯作者:柳清菊
()()作者简介:赵宗彦　1975-,男白族,云南鹤庆人,在读硕士,师承柳清菊教授,主要从事光催化材料的理论计算与性能研
原子位移不大于5×10-4nm,原子间作用力不大于
0.01eV/nm,原子间的内应力不大于0.02GPa,体系总能量的变化不大于5×10-6eV/atom。为了得到稳定精确的计算结果,先根据能量最小化原理得到合适的晶格常数,并优化其内坐标,然后在此基础上进行电子结构和光学性质的计算。在光学性质的计算中采用非极化多晶模型,并使“剪刀算符”对结果进行修正,以便于与实验数据进行比较
3　结果与讨论
3.1　晶体结构
纯锐钛矿相TiO2经过结构优化后,得到的晶格常数为:a=b=0.37436nm,c=0.94779nm,dap=
θ=155.917°0.19695nm,deq=0.19138nm,2。这与实
验测量的结果[14]:a=b=0.,c=0.95124nm,
θ=156.230°dap=0.19799nm,deq=0.非常
Ef的定义采用如下[](1)Ef=ETiO2:D-ETiO2-ED+ETi　　其中ETiO2:D是掺杂后的体系总能量,ETiO2是与掺
杂体系相同大小的纯TiO2的超晶胞体系总能量,ED、ETi分别是单质元素的能量,得到结果如表1所示。从表1中可以看出,非金属阳离子掺杂的杂质形成能都很大,这就意味着在实验制备中需要较高的能量才使非金属阳离子掺入TiO2的晶格中。
图1　2示意图
Fig1PrimitiveunitcellofTiO2intheanatasestruc2
tureandsupercellmodelconsideredinthepres2entwork表1　掺杂体系结构优化后得到的杂质形成能、平均键长、晶格畸变、平均净电荷和八面体的平均偶极矩Table1Formationenergies,latticedistortions,averagebondlengths,averagenetchargesandaveragedipole
momentsofnonmetal2dopedTiO2bygeometryoptimizing
平均键长(nm)
Ti―O0...1943D―O
1.91.299净电荷
O-----0.60...941.40偶矩(Debye)
TiO60..DO60..(eV)
pureTiO2C2dopedN2dopedP2dopedS2doped9..　0..　-7.407×10-3-0.393×10-3-8.585×10-3-1.255×10-3-2
　　光催化反应是一个非常复杂的现象,包括光的吸
收、载流子的激发和迁移、表面的氧化还原反应等过程。其中关键因素是对太阳光的吸收能力和光生载流子的量子产生效率。半导体的光学性质主要决定于其电子结构,因此研究掺杂体系的电子结构与光学性质的关系可以发现其对TiO2光吸收能力的影响。光生载流子产生后,在从内部向表面的迁移过程中,将会发生电子2空穴对的复合,复合几率的大小一方面与杂质能级有关,另一方面与晶体结构密切相关:Sato等[16]曾报道,由偶极矩产生的局域内电场有利于光生电子空穴对的分离,从而可提高光催化剂的光催化活性。表1中同时列出了掺杂体系结构优化后的晶格畸变、平均键长、由Mulliken布居分析得到的平均净电荷以及八面体的平均偶极矩。从表中可以看出,除碘离子掺杂外,由于掺杂后Ti―O键变小,而D―O键明显小于Ti―O键,使晶格体积大幅减小。由于掺杂后晶格发生了畸变、原子间的键长及原子的电荷量都发生了变化,这就意味着掺杂后八面体中负电荷的中心不再与Ti4+离子重合,从而产生内部偶极矩。从表1中可以看到掺杂后体系中TiO6八面体和以非金属阳离子为中心的DO6八面体的偶极矩发生明显的变化,由于掺杂后体系偶极矩的变化,使TiO2的光生电子2空穴对分离更有效,降低了其复合几率,导致非金属阳离子掺杂锐钛矿相TiO2的光催化性能有了明显的提高。3.2　电子结构的计算结果
计算得到的纯锐钛矿相TiO2的禁带宽度为2.68eV,小于实验测量值3.23eV,这是由密度泛函理论本身的缺陷的造成的,即没有考虑交换2关联势的不连续性,从而使半导体和绝缘体的带隙的理论计算值一般要小于实验值[17]。在图2中,给出了各体系经平滑处理的态密度、分波态密度和禁带宽度的变化情况。从图2中可以看出各体系的导带与价带主要由O2p态与Ti3d态组成,而杂质的p态电子与O2p态、Ti3d态杂化形成杂质能级,掺杂后导带位置下移而且价带的宽度增大,这些原因使掺杂体系的禁带宽度有一定的减小。在图中有两个较为明显的特征:(1)是非金属阳离
子掺杂后在价带下方形成了孤立杂质能级;(2)是与纯锐钛矿相TiO2的态密度图相比,掺杂体系中价带与导带中的峰形明显平滑变宽而形成一个连续体,这说明由于晶体对称性的降低而导致掺杂后电子的非局域性更明显,从而使光生电子空穴对的迁移更加容易。C4+、I5+掺杂使TiO2的禁带宽度减小最为明显。除C4+掺杂外,在禁带中都有杂质能级,由于这些能级与价带顶或导带底的距离较小,从而形成浅受主能级或施主能级,这种形式的杂质能级可以成为电子或空穴的捕获中心,对光生电子2空穴对的分离是非常有利的。同时禁带中的杂质能级可以作为中间能级使价带中的电子先跃迁到杂质能级中,子便可再次跃迁到导带,光子,使TiO2矿相TiO2大时,2,因此在实验中应当控制掺杂浓度以避免形成复合中心
3.3　光学性质的计算结果
为了与文献报道的实验结果进行对比,图3给出了经过“剪刀算符”修正和高斯宽化处理的光吸收系数图谱。从图3中可以看出纯TiO2的光吸收曲线与文献报道的实验值相当吻合,其起始吸收带边位于390nm附近。这说明对光学性质的计算结果进行修正是完全必要和合理的。定的红移,使TiO2在400～+,这与禁带宽度,而I+,掺杂应的。但由于在计算中只考虑了电子从占据态到未占据态之间的直接跃迁过程,并且采用了电偶极子近似,没有考虑电子的二次激发、间接跃迁、电四极子、磁偶极子、声子、激子等的影响,使计算结果与实验结果有一定的差别
图3　计算得到非金属阳离子掺杂锐钛矿相TiO2的
光吸收系数的谱图
Fig3Thecalculatedabsorptioncoefficientspectraof
nonmetal2dopedTiO2
采用第一性原理的平面波超软赝势方法计算了不同非金属阳离子掺杂锐钛矿相TiO2的晶体结构、电子结构、杂质形成能和光学性质,分析了掺杂对锐钛矿相TiO2的晶体结构、电子结构和光学性质的影响,在此基础上,研究了掺杂对锐钛矿相TiO2在可见光下的光催化性能的影响。掺杂后晶格发生畸变、原子间的键长及原子的电荷量也发生了变化,导致体系中的八面体偶极矩增大,从而有利于光生电子2空穴对的分离,提高了TiO2在可见光区的光催化活性;综合分析比较计算结果,可以认为当C4+、N5+、S4+掺杂将更有利于锐钛矿相TiO2在可见光照射下光催化性能的提高。
图2　计算得到的掺杂体系的态密度图及禁带宽度的
Fig2Thecalculateddensityofstatesandthechanges
ofbandgapsofnonmetal2dopedTiO2
致谢:感谢云南大学高性能计算中心在模拟计算方面提供的技术支持与帮助。
[1]　FujishimaA,HondaK.[J].Nature,38.[2]　DhananjaySB,VishwasGP,AnthonyAB.[J].J
[11]　SegallMD,PhilipJDL,etal.[J].JPhys:Dondens
Matter,722743.
[12]　CeperleyDM,AlderBJ.[J].PhysRevLett,1980,
45:5662569.
[13]　PerdewJP,ZungerA.[J].PhyRevB,1981,23:
[14]　BurdettJK,HughbanksT.[J].JAmChemSoc,
[15]　CuiXY,MedvedevaJE,B,etal.[J].Phys
Rev2005,:[16]SatoJ,K,JPhysChemB,
,79702]P,RevLett,42
ChemTechBiot,2116.[3]　JingLQ,SunXJ,ShangJ,etal.[J].SolarEnergyMa2
terialsandSolarCells,2151.[4]　JuanZ,XuDY.[J].BuildingandEnvironment,2003,
38:6452654.
[5]　AsahiR,MorikawaT,OhwaklT.[J].Science,2001,
293:2692271.
[6]　IrieH,WatanabeY,HashimotoK.[J].ChemLett,
[7]　HongXT,WangZP,CaiWM.[J].ChemMater,
[8]　UmebayashiT,YamakiT,TanakaS.[J].ChemLett,
.[9]　杜　娟,季振国.[J].]　赵宗彦,柳清菊,张　瑾,等.[J].物理学报,2007,:
First2principlesdopinganataseTiO2
ZHAOZong22,Zhong2qi,ZHANGJin,LIUQiang
(YunnanKeyLaboratoryNanotechnology,YunnanUniversity,Kunming650091,China)Abstract:Thestformationenergy,electronicstructureandopticalpropertiesofanataseTiO2dopingwerestudiedbytheplane2waveultrasoftpseudopotentialmethodbasedonthefirst2paper.Thecalculationsshownthatthedipolemomentsofoctahedralincrystalwereincreaseduetothechangesoflatticeparameters,bondlengthandchargesonatoms,whichwasveryeffectivefortheseparationofphotogeneratedelectron2thebandgapnarrowedandthecurvesoflightabsorp2tionred2shiftedtovisible2lightregionduetothewidthofvalencebandbroadeningfromhybridizingdopants’e2lectronsinpstatewithO2pstatesandTi3dstates.Alloftheseresultscouldexplainthehigherphotocatalyticpropertiesofnonmetalliccation2dopedanataseTiO2invisible2lightregion.
Keywords:anataseTiO2;nonfirst2photocatalyticproperties(上接第952页)
[10]　YuQ,SteenWA,JerrageKM,etal.[J].JElectro2
chemSoc,):E1952203.
[11]　SteenWA,SchwartzDT.[J].ChemMater,2003,
[12]　HaoX,YuQ,JiangS,etal.[J].TransNonferrous
MetSocChina,):8972902.
[13]　HaoX,SchwartzDT.[J].ChemMater,2005,17
[14]　HaoX,GuoJ,ZhangZ,etal.[J].TransNonferrous
MetSocChina,):5562561.
[15]　郝晓刚,郭金霞,张忠林,等.[J].化工学报,2005,56
[16]　张　玫,郝晓刚,马旭莉,等.[J].稀有金属材料与工
程,2006,35(增2):2492253.
[17]　SalimiA,AbdiK.[J].Talanta,2483.[18]　ZamponiS,BerrettoniM,KuleszaPJ,etal.[J].Elec2
trochimActa,124269.
[19]　ReyesGJ,MedinaJA,JeerageKM,etal.[J].J
ElectrochemSoc,):D87292.
[20]　LinY,CuiXJ.[J].MaterChem,2592.
Preparationandcharacterizationofcarbonfiber/graphitesubstrate
NiHCFcompositeelectrodesforelectrochemicallycontrolledionseparation
LIYong2guo,HAOXiao2gang,MAXu2li,ZHANGZhong2lin,LIUShi2bin,SUNYan2ping
(DepartmentofChemicalEngineering,TaiyuanUniversityofTechnology,Taiyuan030024,China)
Abstract:Inthispaper,electrodesofcarbonfiber/graphitesubstrateweremadeandnickelhexacyanoferrate(NiHCF)thinfilmsweresynthesizedwithintheelectrodesbycapillarychemicaldeposition.In1mol/LKNO3solution,thecyclicvoltammetry(CV)wasusedtoinvestigatetheseparationcapacity,cyclelifeandregenera2bilityofNiHCFfilmelectrodes.Thepreparationconditionsforhighseparationabilityareobtained:thediame2
μm,4mlethanoland0.05gPTFEareneededinagramgraphite,theconcentrationterofgraphiteparticleis100
ofK3Fe(CN)6andNiSO4is0.1mol/L.Themorphology,compositionandapplicationofthefilmwerecharac2terizedbyscanningelectronmicroscopy(SEM),X2rayphotoelectronspectroscopy(XPS).ExperimentalresultsshowthattheelectrodeshaNiHCFthinfilmelectrodeswithcarbonfiber/graphitesub2stratehavehigherseparationcapacity,goodstabilityandregenerability.Thefilm2electrodesystemsaresuitableforelectrochemicallycontrolledionseparation(ECIS)process.
Keywords:electrochemicallyconcapillanickelhexacyanoferratethin
fiber/graphitesubstrate
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