氧化镓晶体氧空位及施主缺陷
Oxygen vacancies and donor impurities in β -Ga 2 O 3
J. B. Varley, J. R. Weber, A. Janotti, and C. G. Van de Walle
Citation: Applied Physics Letters 97, 142106 (2010); doi: 10.1063/1.3499306
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Oxygen vacancies and donor impurities in?-Ga2O3
J.B.Varley,1,a?J.R.Weber,1A.Janotti,2and C.G.Van de Walle2
1Department of Physics,University of California,Santa Barbara,California93106-9530,USA
2Department of Materials,University of California,Santa Barbara,California93106-5050,USA
?Received3September2010;accepted17September2010;published online6October2010?
Using hybrid functionals we have investigated the role of oxygen vacancies and various impurities in the electrical and optical properties of the transparent conducting oxide?-Ga2O3.We?nd that oxygen vacancies are deep donors,and thus cannot explain the unintentional n-type conductivity.
Instead,we attribute the conductivity to common background impurities such as silicon and hydrogen.Monatomic hydrogen has low formation energies and acts as a shallow donor in both interstitial and substitutional con?gurations.We also explore other dopants,where substitutional forms of Si,Ge,Sn,F,and Cl are shown to behave as shallow donors.?2010American Institute of Physics.?doi:10.1063/1.3499306?
Of all the wide-band-gap oxide semiconductors,?-Ga2O3is one of the few that remains transparent well into the ultraviolet?UV?,making it a promising deep-UV trans-parent conducting oxide?TCO?for applications in laser li-thography,solar cells,and UV optoelectronic devices.1,2Un-intentionally doped?-Ga2O3can have carrier concentrations up to1018cm?3.3Its band gap is4.9eV,2considerably larger than that of conventional TCOs such as In2O3,SnO2,and ZnO.?-Ga2O3in single-crystal form4has also been explored as an alternative substrate for epitaxial GaN growth,5despite having a crystal structure that differs from the GaN wurtzite https://www.wendangku.net/doc/574503005.html,e of?-Ga2O3is very appealing as it would com-bine the transparency of sapphire with the electrical conduc-tivity of SiC,the two primary substrates currently used for commercial GaN-based devices.
Currently,the lack of understanding and control of the unintentional n-type conductivity of?-Ga2O3still inhibits its applications.As with many other oxides,this conductivity has historically been attributed to the presence of oxygen vacancies?V O?,largely based on the correlation between conductivity and oxygen partial pressure in annealing environments.6Calculations have offered insight into the mi-gration mechanisms7and the relative energies of oxygen va-cancies in the inequivalent sites of the monoclinic structure7,8 but only minimal information about the charge states and ionization energies.
In this letter,we report formation energies and charge-state transition levels for oxygen vacancies and donor impu-rities based on density functional theory?DFT?using novel hybrid functionals that do not suffer from the band-gap prob-lem inherent in traditional DFT.We?rst discuss the band structure of?-Ga2O3,comparing with experiment and previ-ous calculations.We then describe the electronic structure and stability of the oxygen vacancy,showing that it does not contribute to the observed conductivity.Finally,we report results for donor impurities,and suggest that silicon and hy-drogen are the likely cause of the observed electrical conduc-tivity in unintentionally doped?-Ga2O3.
The calculations are based on generalized Kohn–Sham theory with the HSE06screened hybrid functional9and the projector augmented-wave method,as implemented in the V ASP code.10,11The Hartree–Fock mixing parameter is set to 35%,which reproduces the experimental band gap;2the re-sulting structural parameters are in good agreement with the experimental values?Table I?.
We use a120-atom supercell,a2?2?2mesh of Monkhorst–Pack k-points,and a plane-wave basis set with a cutoff of400eV.The semicore Ga d electrons were treated as core electrons;tests in which these d electrons were ex-plicitly included in the valence produced formation energies that differ by less than0.1eV.Corrections due to?nite-size effects resulting from the long-range Coulomb interaction of charged defects in a homogeneous neutralizing background were explicitly included following the scheme of Freysoldt et al.,15with a weighted spatial-averaged static dielectric constant of10.
Formation energies?E f?are key quantities from which we can derive impurity and defect concentrations,stability of different charge states,and the related electronic transition levels.16The formation energy of V O in Ga2O3is given by the following:
E f?V O q?=E tot?V O q??E tot?Ga2O3?+?O+q?F,
where E tot?V O q?and E tot?Ga2O3?represent the total energy of the supercell containing a vacancy in charge state q,and that
a?Electronic mail:jvarley@https://www.wendangku.net/doc/574503005.html,.
TABLE I.Calculated lattice parameters,formation enthalpy per formula
unit,direct and indirect band gaps,and electron effective masses for
?-Ga2O3,as compared to experiment and previous calculations.
Parameter HSE06B3LYP Experiment
a???12.2512.34a12.23?0.02b
b??? 3.05 3.035a 3.04?0.01b
c??? 5.84 5.799a 5.80?0.01b
??deg?103.9103.9a103.7?0.3b
?H?eV/f.u.??10.40ˉ?11.29c
E
g
d?eV? 4.87 4.69a 4.9d
E
g
i?eV? 4.83 4.66aˉ
m
c
?/m
e
0.281?0.0050.342a0.5–2.0e
a Reference12.
b Reference13.
c Reference14.
d Reference2.
e Reference1.
APPLIED PHYSICS LETTERS97,142106?2010?
0003-6951/2010/97?14?/142106/3/$30.00?2010American Institute of Physics
97,142106-1
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of a perfect crystal in the same supercell.The O removed from the crystal is placed in a reservoir which we reference to the energy of an O 2molecule.The chemical potential ?O can vary to represent experimental conditions during growth or annealing,i.e.,from O-rich ?Ga-poor ?to O-poor ?Ga-rich ?conditions.The electrons are exchanged with the Fermi level ?F ,which is conventionally referenced to the valence-band maximum ?VBM ?.The monoclinic crystal structure of ?-Ga 2O 3,space group C2/m ,is described by four lattice parameters ?Table I ?;the three lattice vectors and ?,the angle between the a and c axes.12It possesses three inequivalent O sites and two inequivalent Ga sites.O ?I ?and O ?II ?are threefold coordi-nated,while O ?III ?is fourfold coordinated.Ga ?I ?and Ga ?II ?are tetrahedrally and octahedrally coordinated,respectively.The calculated band structure of ?-Ga 2O 3is shown in Fig.1.We ?nd an indirect band gap of 4.83eV ,with the VBM
located just off of the M point,slightly smaller than the direct band gap of 4.87eV at ?.Analysis of the dipole ma-trix elements reveals that while the vertical transitions are
dipole-allowed at the ?point and at the VBM,they are
roughly an order of magnitude weaker at the VBM and rap-idly decrease to 0at the M -point.The weakness of the indi-rect transitions and the small energy difference between in-direct and direct gaps effectively make ?-Ga 2O 3a direct -gap
material,consistent with the experimentally observed sharp
absorption onset at ?4.9eV.2The electron effective mass is
small and almost isotropic,with a value of 0.281?0.005m e .
In contrast,the almost ?at valence band results in hole effec-tive masses ?m h ??that can be much larger,in agreement with previous calculations.12,17While the low dispersion along the ?-Z direction makes it dif?cult to extract an accurate value,
estimated around 40m e from our ?ts,we do ?nd a much
smaller m h ?along the ?-A direction ?0.40m e ?.
The calculated formation energies for V O in Ga 2O 3are
shown in Fig.2?a ?.The ??+2/0?transition levels,denoted by the kinks in the formation-energy plots,are more than 1eV
below the conduction-band minimum ?CBM ?.We thus con-clude that V O acts as a deep donor and cannot contribute to
n -type conductivity.As seen in Fig.2?a ?,V O is stable in the
neutral charge state for Fermi-level values in the upper part
of the band gap.The different oxygen sites lead to slightly different geometries,formation energies and transition lev-els:??2+/0?=3.31eV for O ?I ?,2.70eV for O ?II ?,and 3.57eV for O ?III ?.V O 0
has the lowest energy on the O ?II ?site,in
which two of the three O–Ga bonds are the longest among all
O–Ga bonds.Additionally,the E f
of the V O are high for most values of oxygen chemical potential,indicating a low con-centration of vacancies will be present.
The paramagnetic state V O +is not stable for any value of
the Fermi level but could be generated by photoexcitation.
By calculating V O +in the geometry of the V O 0con?guration,
we predict absorption energies of 2.71,3.37,and 2.52eV for O ?I ?,?II ?,and ?III ?sites,with corresponding emission ener-gies of 0.67,1.23,and 0.65eV .Since the reported electron paramagnetic resonance experiments do not mention inten-tional photoexcitation,the assignment of the reported EPR signal to oxygen vacancies 18should be re-examined.Addi-tional emission energies of 2.06,1.40,and 2.25eV can result from above-band-gap excitations,due to the recombination
of an electron localized on the V O 0
with a photogenerated hole
in the valence band.None of these emission energies match
the characteristic blue or green luminescence bands of
?-Ga 2O 3,19suggesting that these bands do not originate from
V O .Turning now to impurities,we ?rst investigated the role of hydrogen.We ?nd that H can occupy either interstitial ?H i ?or substitutional sites ?H O ?;20in both con?gurations,H acts as shallow donor.Due to the complex crystal structure of ?-Ga 2O 3,many con?gurations exist in which H i +forms a strong bond with an O atom and which are all close in en-ergy.In the lowest-energy con?guration ?included in Fig.2?b ??,H i +bonds to a lone pair of the threefold coordinated O ?I ?.The low formation energy of H i under both O-rich and O-poor conditions indicates it will be easily incorporated as an unintentional impurity whenever H is present in the growth or annealing environment.In the acceptor charge state,H i ?,the H atom preferentially sits near two Ga atoms,yielding a transition level ??+/??=4.90eV,just above the CBM.Interstitial hydrogen thus behaves exclusively as a shallow donor for any Fermi level within the band gap of ?-Ga 2O 3.21Substitutional hydrogen,H O ,has a low forma-tion energy only under O-poor conditions.22The energy barrier for the dissociation of the H O +
into H i +and V O 0
is only 1.33eV ,estimated as the sum of the binding energy ?0.99eV ?and the migration barrier of H i +?0.34eV ?.Such a low barrier indicates that both H i +and H O +are mobile at modest temperatures and may be readily removable by thermal annealing.1,3-6
-4-202468101214V Z ΓA M L
E n e r g y (e V )
FIG.1.?Color online ?Band structure for ?-Ga 2O 3calculated using the primitive unit cell of base-centered monoclinic ?-Ga 2O 3?see Ref.12?.The VBM,which occurs just off the M point and is only 0.03eV higher than at ?,is set to zero on the energy axis.
1
234–2–10
12345Fermi level (eV)
F o r m a t i o n e n e r g y (e V )
V O
O?poor
O?rich
(a)
V O
Fermi level (eV)
(I)
(II)(III)
(I)
(II)(III)
FIG.2.?Color online ?Formation energy vs Fermi level for the oxygen
vacancy ?a ?and H impurities ?b ?in ?-Ga 2O 3.Values for O-rich and O-poor conditions are shown.The labels ?I ?,?II ?,and ?III ?refer to the three in-equivalent O sites.
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In addition to hydrogen,we ?nd that other impurities may also contribute to the observed n -type behavior.In Fig.3,we show the formation energies of Si,Ge,and Sn substi-tuting on the Ga site,23as well as F and Cl on the O site,24all of which are shallow donors that may contribute to the n -type conductivity of Ga 2O 3.Si and Ge prefer the tetrahe-dral coordination of the Ga ?I ?site,while Sn prefers the oc-tahedral coordination of the Ga ?II ?site.F and Cl both prefer the threefold coordination of the O ?I ?site.The formation energies suggest that Si,Ge,Sn,F,and Cl are readily incor-porated.Indeed,it has been observed that Si is a dominant background impurity in both high-purity powders ?6N ?and single crystals,25with the increase in Si content of the single crystals possibly due to the presence of quartz in the various growth techniques.25,26When intentionally incorporated,both Si ?Ref.27?and Sn ?Ref.2?have been shown to notably enhance the conductivity.Our results suggest that F and po-tentially Cl will also be effective n -type dopants.
In summary,we have presented hybrid functional calcu-lations for oxygen vacancies and several candidate donor im-purities in ?-Ga 2O 3.We ?nd that oxygen vacancies cannot explain the observed unintentional n -type conductivity,since they are deep donors with an ionization energy of more than 1eV .Our results suggest that unintentionally incorporated impurities are likely to be responsible for the observed n -type conductivity.Hydrogen,Si,Ge,Sn,F,and Cl are all calculated to be shallow donors in ?-Ga 2O 3.
We gratefully acknowledge useful discussions with M.Y .Tsai,O.Bierwagen,T.Nagata,H.He,and R.Pandey.The work was supported by the NSF MRSEC Program ?Grant No.DMR05-20415?,the SRC ?Grant No.2009-VJ-1867?,
the UCSB SSLEC,and by Saint-Gobain Research.We ac-knowledge the use of computing facilities at CNSI ?Grant No.NSF CHE03-21368?,TeraGrid,and TACC ?Grant No.NSF DMR07-0072N ?.
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Fermi level (eV)
F o r m a t i o n e n e r g y (e V )
Fermi level (eV)
FIG.3.?Color online ?Formation energy vs Fermi level for several shallow donor impurities in ?-Ga 2O 3under ?a ?O-rich and ?b ?O-poor conditions.The labels ?I ?and ?II ?refer to the inequivalent Ga or O sites;only the results for the lowest-energy site are shown.
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第三章 晶体结构缺陷
第三章晶体结构缺陷 【例3-1】写出MgO形成肖特基缺陷得反应方程式。 【解】MgO形成肖特基缺陷时,表面得Mg2+与O2－离子迁到表面新位置上,在晶体内部留下空位,用方程式表示为: 该方程式中得表面位置与新表面位置无本质区别,故可以从方程两边消掉,以零O(naught)代表无缺陷 状态,则肖特基缺陷方程式可简化为: 【例3-2】写出AgBr形成弗伦克尔缺陷得反应方程式。 【解】AgBr中半径小得Ag+离子进入晶格间隙,在其格点上留下空位,方程式为: 【提示】一般规律:当晶体中剩余空隙比较小,如NaCl型结构,容易形成肖特基缺陷;当晶体中剩余空隙比较大时,如萤石CaF2型结构等,容易产生弗伦克尔缺陷。 【例3-3】写出NaF加入YF3中得缺陷反应方程式。 【解】首先以正离子为基准,Na+离子占据Y3+位置,该位置带有2个单位负电荷,同时,引入得1个F－离子位于基质晶体中F－离子得位置上。按照位置关系,基质YF3中正负离子格点数之比为1/3,现在只引入了1个F－离子,所以还有2个F－离子位置空着。反应方程式为:可以验证该方程式符合上述3个原则。 再以负离子为基准,假设引入3个F－离子位于基质中得F－离子位置上,与此同时,引入了3个Na+离子。根据基质晶体中得位置关系,只能有1个Na+离子占据Y3+离子位置,其余2个Na+位于晶格间隙,方程式为: 此方程亦满足上述3个原则。当然,也可以写出其她形式得缺陷反应方程式,但上述2个方程所代表得
缺陷就是最可能出现得。 【例3-4】写出CaCl2加入KCl中得缺陷反应方程式。 【解】以正离子为基准,缺陷反应方程式为: 以负离子为基准,则缺陷反应方程式为: 这也就是2个典型得缺陷反应方程式,与后边将要介绍得固溶体类型相对应。 【提示】通过上述2个实例,可以得出2条基本规律: (1)低价正离子占据高价正离子位置时,该位置带有负电荷。为了保持电中性,会产生负离子空位或间隙正离子。 (2)高价正离子占据低价正离子位置时,该位置带有正电荷。为了保持电中性,会产生正离子空位或间隙负离子。 【例3-5】TiO2在还原气氛下失去部分氧,生成非化学计量化合物TiO2-x,写出缺陷反应方程式。 【解】非化学计量缺陷得形成与浓度取决于气氛性质及其分压大小,即在一定气氛性质与压力下到达平衡。该过程得缺陷反应可用 或 方程式表示,晶体中得氧以电中性得氧分子得形式从TiO2中逸出,同时在晶体中产生带正电荷得氧空位与与其符号相反得带负电荷得来保持电中性,方程两边总有效电荷都等于零。可以瞧成就是Ti4+被还原为Ti3+,三价Ti占据了四价Ti得位置,因而带一个单位有效负电荷。而二个Ti3+替代了二个
Ti3+或者氧空位自掺杂二氧化钛化学缺陷的新视角
学年论文 题目：Ti3+或者氧空位自掺杂二氧化钛:化学缺陷的新视角学院：物理与电子工程学院 专业：物理学 学生姓名： 学号： 指导教师：
Ti3+或者氧空位自掺杂二氧化钛:化学缺陷的新视角 作者：Juan Su，Xiaoxin Zou和Jie-Sheng Chen翻译123 摘要：金属氧化物的化学缺陷是一个无机电晶体材料的重要研究方向。这是因为（i）相当一部分缺陷或瑕疵存在于金属氧化物材料中(ii）出现的缺陷有时甚至决定了材料的物理、化学特性；(iii）更重要的，缺陷不可避免的对材料的特性产生不利影响:正确地认识 " 缺陷工程学 " 使能改良为所需的特性，甚至是在自然材料中不是可得的一些新型有用的功能特性。基于这些观点，我们了解钛氧化物化学缺陷(例如Ti,TiO 2 ),并在研究多功能的金属氧化物方向努力进行研究,并 在这方面特意给予高度重视。经讨论，把部分精力放于合成氧空位/Ti3+自掺杂TiO 2材料和受欢迎的的缺陷对材料的特性及应用的影响。在这个评论中,把重心集中在 代表性的金属制的氧化物（也就是，TiO 2 ), 按预期提出一些新视角在金属氧化物的常见化学缺陷，并促进金属氧化物材料的“缺陷工程学”的发展。 1. 引言 钛（Ti）是地壳中的第九大元素（0.63%) ，它的含量仅次于大量存在的 O 、 Si 、Al 、Fe 、Ca 、Na 、K和Mg。[1]二氧化钛（TiO 2 )作为钛的最重要的氧化物，它主要以三种晶型（锐钛矿、金红石和板钛矿）存在, 是一种多功能的金属氧化 物材料2-8。二十的世纪初期以来，TiO 2 已经在商业中被当作白色染料,防晒添加剂等等。,这些传统的应用主要是基于它特殊的物理化学性质，例如:高的折射率,强的紫外线吸收的能力、优越的化学稳定性和丰富的含量。[2-8] 在1972 年， Fujishima 和Honda发现在紫外线的照射下TiO 2 电极上发生了水的电解。9这个开创性的工作立刻引起了化学研究员的兴趣,同时他们付出巨大 的努力致力于TiO 2材料的研究。[1-8]从而引起许多有前景的TiO 2 基础的应用，从太 阳能电池，光催化和自清洁技术到传感器和光电变色显示。[1-15] TiO 2 通常是这些 应用中的核心组件，并且TiO 2 的特性基本上决定了这些应用效率以及我们最终能使用的操作环境。因此，正确地调整TiO2的结构将它的特性/功能最佳化以及更进一步理解结构与特性/功能之间的相互关系已经成为相当活跃的追求。 TiO 2 的特性/功能与它主结构叁数有莫大的关系，典型的参数有:结晶相、结晶度、形状、大小、表面的结构和缺陷。[16-20]在许多方法中通过改变晶体的状态、 结晶度、形状、大小或者表面结构最优化TiO 2的特性/功能,TiO 2 的缺陷调整很难 弄懂,这样持续了很长一段时间。然而最近,在含大量缺陷（如Ti3+和氧空位）的TiO 2 材料的合成及应用上有了重的突破,尤其是这些缺陷对材料特性有利的效果已经引起广泛的关注。 在这些回顾中,在TiO 2 中产生特定命名为Ti3+离子和氧空缺的缺陷的方法称为 “自掺杂”。自掺杂方法的最重要的特征是通过有意在TiO 2 中引入缺陷来提高它 的属性。换句话说，通过有意的引入缺陷（如，除去或重排钛/氧原子）改变TiO 2的原子结构，TiO 2 的特性能得到很大程度提高。在此，我们概述了合成含Ti3离子 和/或氧空位的TiO 2 自掺杂材料以及这些缺陷对材料特性和应用的有利效果的近期发展。 2. 二氧化钛自掺杂合成方法 合成TiO 2 自掺杂的方法可粗略为“局部还原法”和“局部氧化法”两类。前者时
氧化镓晶体氧空位及施主缺陷
Oxygen vacancies and donor impurities in β -Ga 2 O 3 J. B. Varley, J. R. Weber, A. Janotti, and C. G. Van de Walle Citation: Applied Physics Letters 97, 142106 (2010); doi: 10.1063/1.3499306 View online: https://www.wendangku.net/doc/574503005.html,/10.1063/1.3499306 View Table of Contents: https://www.wendangku.net/doc/574503005.html,/content/aip/journal/apl/97/14?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Electron spin resonance parameters of cation vacancies in tin dioxide doped with fluorine and hydrogen J. Appl. Phys. 114, 143907 (2013); 10.1063/1.4824745 Defect engineering of the oxygen-vacancy clusters formation in electron irradiated silicon by isovalent doping: An infrared perspective J. Appl. Phys. 112, 123517 (2012); 10.1063/1.4770488 Hydrogen impurities and native defects in CdO J. Appl. Phys. 110, 063521 (2011); 10.1063/1.3641971 The role of threading dislocations and unintentionally incorporated impurities on the bulk electron conductivity of In-face InN Appl. Phys. Lett. 95, 022103 (2009); 10.1063/1.3173202 Radiation effects on the behavior of carbon and oxygen impurities and the role of Ge in Czochralski grown Si upon annealing J. Appl. Phys. 105, 123508 (2009); 10.1063/1.3148293 Reuse of AIP Publishing content is subject to the terms at: https://https://www.wendangku.net/doc/574503005.html,/authors/rights-and-permissions. Download to IP: 124.128.56.230 On: Tue, 12 Apr
”氧空位缺陷对绿色长余辉发光材料α-Zn3(PO4)2：Mn2+,Na+发光性能的改善作用”
https://www.wendangku.net/doc/574503005.html, DOI：10.14062/j.issn.0454-5648.2015.07.19 氧空位缺陷对绿色长余辉发光材料α-Zn3(PO4)2: Mn2+, Na+发光 性能的改善作用 谢婷，郭鸿旭，何裕能，陈垚，陈棽，林珩，陈国良，郑子山 (闽南师范大学化学与环境学院，福建漳州363000) 摘要：利用溶胶–凝胶结合高温煅烧法制备了绿色长余辉发光材料α-Zn3(PO4)2:Mn2+, Na+。通过X射线衍射对产物的相结构进行分析，通过荧光光谱和热释光谱研究其发光本质，并探究了Na+掺杂量对余辉性质的影响。结果表明：制备的样品的结构与α-Zn3(PO4)2相同。样品发射峰位于548nm处，为绿色发光材料，归属于Mn2+的4T1g–6A1g跃迁。当Na+掺杂量为4%时，样品的发光性能最佳。样品经过紫外光照射后，在暗室中目测其余辉时间达约2h。热释光谱分析表明，掺杂Na+可以增加晶体中Vo¨氧空位缺陷浓度。Vo¨氧空位缺陷浓度的提高有利于捕获更多的激发态电子，延缓激发态电子跃迁回基态，从而达到延长样品的余辉时间。 关键词：长余辉发光材料；掺杂；正磷酸锌；发光机理 中图分类号：TB 321 文献标志码：A 文章编号：0454–5648(2015)07–0969–06 网络出版时间：网络出版地址： Effect of Oxygen Vacancies on Luminescent Performance of Green Long-Lasting Phosphor Material of α-Zn3(PO4)2:Mn2+, Na+ XIE Ting, GUO Hongxu, HE Yuneng, CHEN Yao, CHEN Shen, LIN Heng, CHEN Guoliang, ZHENG Zishan (School of Chemistry & Environment, Minnan Normal University, Zhangzhou 363000, Fujian, China) Abstract:The long-lasting phosphor (LLP) of α-Zn3(PO4)2:Mn2+, Na+was prepared by a sol–gel method and subsequent conventional solid-state sintering. The phase composition of the sample was characterized by X-ray diffraction. The luminescent properties were investigated by using fluorescence spectra and thermoluminescence spectra, and the effect of Na+-doped content on the luminescence properties of the samples was analyzed. The results show that the structure of the samples prepared is the same as that of α-Zn3(PO4)2. The emission peak of green afterglow phosphor is located at 548 nm, assigned to the 4T1g–6A1g transition of Mn2+. The optimal luminescent property of the sample is obtained at the Na+ content of 4% in mole. The long-lasting phosphorescence appears for ~ 2 h in the absence of the irradiation light source. The thermoluminescence spectra indicate that the doping of Na+ ions results in the increase of V o¨oxygen vacancies. V o¨oxygen vacancies catch and store the excited electrons, and postpone their transition back to the ground levels, which can effectively extend the decay time of the samples. Key words: long-lasting phosphor; doping; zinc orthophosphate; luminescence mechanism 长余辉发光材料是一类吸收太阳能或人工能源，并在激发停止后仍可继续发出可见光的物质。它主要应用在装饰照明，交通标示，光学存储，仪表指示，军工等方面[1-2]。目前，长余辉材料体系虽然很多，但大多数存在着不足之处，如余辉时间短、稳定性差、亮度低、颜色单一等。因此，开发颜色 收稿日期：2014–12–07。修订日期：2015–01–29。 基金项目：福建省科技厅产学研重大项目(2010H6029和2012H6026)；福建省科技厅科技重点项目(2013H0053)；福建省高等学校学科 带头人培养计划；闽南师范大学研究生科研创新项目支持。第一作者：谢婷(1989—)，女，硕士研究生。 通信作者：郑子山(1963—)，男，博士，教授。Received date: 2014–12–07. Revised date: 2015–01–29. First author: XIE Ting (1989–), female, Master candidate. E-mail: xieting_nxu@https://www.wendangku.net/doc/574503005.html, Correspondent author: ZHENG Zishan (1963–), male, Ph.D., Professor. E-mail: Z.Zheng@https://www.wendangku.net/doc/574503005.html,
材料缺陷
第2节点缺陷(4) 缺陷化学反应式在描述材料的掺杂、固溶体的生成和非化学计量化合物的反应中都是很重要的，一定要正确掌握缺陷反应式的写法。在无机材料中，发生缺陷反应时以质点取代（置换）的情况为常见，不同取代的情况归纳为表5-2。如果读者能熟练掌握一定的规则，就可顺利导出结论，而不要死记硬背。下面将举例说明上述规则在缺陷反应中的应用。 例1.写出Ca Cl2溶解在K Cl中的缺陷反应式。 该缺陷反应存在3种可能性： ①C a2+取代K+，C l-进入Cl-晶格位置： （5-5） ②C a2+取代K+，C l-进入间隙位置： （5-6） ③C a2+进入间隙位置，Cl-占据晶格位置： （5-7）
例2. 写出M gO溶解到Al2O3晶格内形成有限型置换固溶体的缺陷反应式。 （5-8） （5-9） 上述两个例子中虽然写出了可能发生的几种缺陷反应式，但并不是每一种情况都必定会发生，这要根据缺陷反应条件以及基质晶体结构而定，正确严格判断它们的合理性需要根据固溶体的生成条件及固溶体研究方法，用实验来证实。但我们可以根据已经学过的晶体结构的基本知识，快速粗略地做出分析判断。第1个例子中，只有式（5-5）是合理的，第2个例子中，只有生成氧空位的反应式（5-8）是合理的，因后一反应Mg2+进入间隙位置，在刚玉型晶体中不易发生. 5.2.3 点缺陷的化学平衡 在晶体中，缺陷的产生与恢复是一个动平衡的过程。缺陷的产生过程可以看成是一种化学反应过程，因而可用化学反应平衡的质量作用定律来做定量处理。 1. 弗伦克尔缺陷?? 弗伦克尔缺陷可以看作是正常格点离子和间隙位置
反应生成间隙离子和空位的过程，即： 晶格离子+ 未被占据的间隙位置= 间隙离子+ 空位 如Ag Br晶体中弗伦克尔缺陷的生成式为 （5-10） 平衡时根据质量作用定律可得， （5-11） 式中，KF为弗伦克尔缺陷反应平衡常数。 当缺陷浓度很小时，[V i] ≈[Ag A g] ≈1，所以 （5-12） 又根据反应式，显见 （5-13） 平衡常数可以用阿累尼乌斯公式表示为 （5-14） 式中，ΔG f为弗伦克尔缺陷形成自由能，K0为常数，k为玻尔兹曼常数，T为开尔文温度。 所以 （5-15） 对于任何晶体中生成弗伦克尔缺陷，都可以用上式表示生成的缺陷浓度。 第3节 第4节
氧空位解析
氧空位(V O)作为金属氧化物中的一种本征缺陷，对金属氧化物的电子结构和物理性质有很大的影响。例如，缺陷萤石结构δ-Bi2O3中的氧空位(V O s)导致氧离子导电性；紫外光照射下TiO2表面产生的V O s能够使TiO2表面的润湿性从疏水性变成亲水性。氧空位还被认为是许多非磁性金属氧化物，如HfO2、ZnO、In2O3以及SnO2，纳米结构形成室温铁磁有序的原因。因此研究氧空位的稳定性以及它对晶体结构和电子结构的影响对于改善金属氧化物性能至关重要。但是氧空位(V O s)对传统的测量技术不敏感，目前对Vos进行直接的实验观察仍然具有挑战性。我们小组在氧空位的研究方面开展了如下两方面的工作： 1. 铁电材料广泛应用于当今快速数据存储器件诸如固态硬盘中。和磁性数据存储材料相比，铁电材料有着读写速率高、数据存储密度大、能耗低和存储数据稳定等优点。铁电畴结构是决定铁电材料性质的关键因素。畴的大小决定了数据的存储密度，其反转速率直接影响到数据读写速率，而其稳定性又直接对应到数据稳定性。因而对铁电畴结构的研究对提高存储器件的性能有着非常重要的意义。我们通过控制氧空位密度成功的调控了一种铁电材料YMnO3的铁电畴的结构和性质。利用压电力显微镜，我们发现铁电畴在电场作用下可以从三角形过渡到条状。究其原因，是因为氧空位在铁电体里的有序排列造成的。利用近场光学拉曼系统，我们发现4d–2p (Y3+-O2?)轨道杂化的程度受到氧空位的强烈影响并直接作用于YMnO3的铁电畴在外场中的动态过程。让复杂的三联铁电畴结构变为简单的条状畴结构。通过导电原子力显微镜的测量，我
们发现缺失氧的畴壁可以被调控出典型的半导体导电性质。这为今后铁电畴在多功能数据存储计算器件中的应用奠定了基础。如图1所示为在外加电场中，铁电畴从三联结构逐步变化为条状结构。这中结构的本征变化是由于氧缺陷有序化造成的。文章发表在PCCP上，并被选为封面文章。 2. 在γ-Bi2O3晶体结构的一个惯用晶胞中共存在40个阴离子位置，假如这40个阴离子位置完全被占据，那么我们将得到Bi26O40这样一个结构。但事实上形成化学计量比的γ-Bi2O3晶体结构，一个惯用晶胞中只需要39个氧离子(Bi26O39)，因此在化学计量比的γ-Bi2O3的一个惯用晶胞里总会留下一个未被占据的本征氧空位V O。我们利用第一原理计算了γ-Bi2O3各种氧空位V O s模型形成能的大小，确定V O s在γ-Bi2O3中优先占据四面体O3 (8c)位置。证明参考基体Bi26O40带隙中的那条能级是Bi 6s和O 2p态在对称环境下产生的一种结构效应，而不是由多余(中性)氧原子引起的局域态。当我们在四面体O3 (8c)位置引入V O s形成Bi26O39时，破坏了四面体结构单元的23对称性。失去对称环境后， Bi26O39中的Bi 6s-O 2p反键态无法再在带隙中的形成类似于参考基体
氧空位缺陷对光催化活性的影响及其机制
第33卷 第5期 2018年10月 天津科技大学学报 Journal of Tianjin University of Science & Technology V ol. 33 No. 5 Oct. 2018 收稿日期：2018–04–13；修回日期：2018–07–17 基金项目：国家自然科学基金青年基金资助项目(51404170) 作者简介：郝 亮（1980—），男，河北雄安人，副教授；通信作者：张慧娜，讲师，zhnzgx@https://www.wendangku.net/doc/574503005.html, 氧空位缺陷对光催化活性的影响及其机制 郝 亮1，张慧娜2，闫建成1，程丽君1，关苏军3，鲁 云4 (1. 天津市低碳绿色过程装备国际联合研究中心，天津市轻工与食品工程机械装备集成设计与 在线监控重点实验室，天津科技大学机械工程学院，天津 300222； 2. 天津大学仁爱学院，天津 301636； 3. 东京理科大学物理学院，东京 162-8601； 4. 千叶大学工学研究院机械系，千叶 263-8522) 摘 要：氧空位作为最常见且最重要的一类晶体缺陷，对半导体光催化剂的性能有着显著的影响．近年来，通过引入和调控氧空位的方法来改善光催化活性，尤其是可见光性能，成为光催化研究领域的热点之一．本文详细阐述了含氧化合物中存在的氧空位缺陷对光催化剂的电子结构、几何构造、吸光特性、表面吸附解离等的影响，并在此基础上讨论了氧空位对光生电荷分离、光催化选择性、紫外光及可见光催化活性的影响，以期为今后氧空位缺陷调控型高性能光催化材料的设计及开发提供科学依据． 关键词：氧空位；光催化；电荷分离；可见光；光催化活性 中图分类号：O643.36；O644.11 文献标志码：A 文章编号：1672-6510(2018)05-0001-13 Effect of Oxygen Vacancy on Photocatalytic Activity and Relevant Mechanism HAO Liang 1，ZHANG Huina 2，YAN Jiancheng 1，CHENG Lijun 1，GUAN Sujun 3，LU Yun 4 (1. International Joint Center of Low-Carbon Green Process Equipment ，Tianjin Key Lab of Integrated Design and On-line Monitoring for Light Industry & Food Machinery and Equipment ，College of Mechanical Engineering ，Tianjin University of Science & Technology ，Tianjin 300222，China ； 2. Renai College of Tianjin University ，Tianjin 301636，China ； 3. Department of Physics ，Tokyo University of Science ，Tokyo 162-8601，Japan ； 4. Graduate School of Science and Engineering ，Chiba University ，Chiba 263-8522，Japan) Abstract ：Oxygen vacancy ，as one of the most common and important crystal defects ，remarkably affects the photocatalytic activity of semiconductors. Improvement on the photocatalytic activity through the introduction and mediation of oxygen vacancies has attracted increasing attention in recent years. In this short review ，we discussed the influence of oxygen vacan-cies on the electronic and geometric structures ，and the optical absorption and dissociative adsorption properties of oxygen- ated chemicals. Based on the discussion ，the effect of oxygen vacancies on photogenerated charge separation ， photocatalytic selectivity ，UV light and visible light-responsive photocatalytic activity is also clarified. The review is expected to help the design and development of oxygen vacancy-mediated photocatalyst with high photocatalytic activity. Key words ：oxygen vacancy ；photocatalysis ；charge separation ；visible light ；photocatalytic activities 2000年，日本学者Nakamura 等[1]就针对TiO 2 中氧空位对其可见光催化降解去除NO 气体的影响 进行了研究，但该研究并没有引起足够的重视．直到 2011年，陈晓波等[2]利用在氢气气氛中高温煅烧纳米TiO 2粉末，在其表面引入氧空位及大量无序结构等，使其强烈地吸收可见光，进而极大地提高了可见光催 DOI:10.13364/j.issn.1672-6510.20180114