摘要
Ti02是一种新型的具有电容性和压敏性双功能的低压压敏陶瓷,具有广阔的应用前景。为获得较好的性能,一般需要对Ti02进行掺杂,掺杂离子的半径、含量及其价态、烧结温度和氧分压对Ti02压敏陶瓷的显微结构、化学组成、势垒结构和电学性能等有明显的影响。本文主要研究不掺杂Ti02、单施主Nb掺杂、单受主La掺杂、(La、Nb)共掺和(Ce、Nb)共掺Ti02的晶界偏析规律与机理、势垒结构的主要影响因素。
首先,采用传统电子陶瓷工艺制备在1300℃、1350℃、1400℃和1440℃烧结的不掺杂、单掺杂和共掺杂Ti02样品。采用SEM、EDS、XRD、XPS、AFM、TEM、SAED、HRTEM和电子探针等现代材料检测手段分析了样品的显微结构、化学组成、物相组成、离子价态、晶界热沟、晶界结构和元素偏析。测试了Ti02样品在不同温度和偏压的电学性能,采用热电子发射理论计算Ti02的势垒结构。势垒结构包括势垒高度ΦB和势垒宽度XD。
然后,基于点缺陷的热力学方法,研究了不掺杂、单掺杂和共掺杂Ti02陶瓷在不同温度的晶界静电势分布与空间电荷(缺陷)浓度分布,探讨晶界偏析的机理。
最后,建立了(310)晶界结构,组合使用第一原理和分子力场模拟计算了不掺杂、单施主、单受主和共掺杂Ti02(310)晶界的势垒高度,考查晶界势垒高度受掺杂离子、位置和含量的影响。
研究结果表明:
1、不掺杂Ti02压敏陶瓷在高温烧结后显微结构存在许多气孔,这些气孔是由于氧空位Vo的聚集、扩散和迁移逐渐形成的。从晶粒挥发出来的氧沿着晶界移动,在晶界和三叉晶界吸附,与Ca, Si等形成晶粒间相。不掺杂Ti02陶瓷在形成氧空位Vo的同时,四价钛会得到一个电子变成三价钛,TiTi'是补偿氧空位Vo的方式之一。三价钛和四价钛随氧空位的产生,形成间隙三价钛和四价钛,XPS证明了三价钛和四价钛的共存。
2、不掺杂Ti02在化学计量比和还原气氛下,其晶界静电势和缺陷浓度分布是不同的。保持化学计量比情况下,钛空位VTi""、氧空位Vo和钛间隙Tii是主要的点缺陷,它们不同的缺陷形成能gvn,gvo和gTii决定了静电势Φ(χ)的正负与大小。在还原气氛情况下,有氧空位和钛间隙两种补偿机制来满足电中性条件,静电势和缺陷浓度由氧分压和温度决定。
3、单施主Nb掺杂Ti02陶瓷Nb发生偏析,当Nb掺杂浓度较低时,XRD没有检测到第二相。Nb掺杂Ti02形成点缺陷NbTi,当钛空位与点缺陷NbTi满足电中性条件时,静电势由Nb的掺杂浓度、钛空位缺陷形成能和烧结温度所决定。随烧结温度增加势垒高度(静电势)降低,随掺杂含量增加势垒高度增加。
4、单受主La掺杂Ti02发生明显的La偏析现象,并生成第二相La4Ti9O24。晶界静电势和缺点浓度取决于La掺杂浓度,而La的偏析驱动力来自于La在晶界形成的弹性应变能。
5、(La、Nb)共掺杂Ti02中的静电势和缺陷浓度由Nb掺杂浓度、温度决定,而La的偏析由La在晶界所引起的弹性应变能来决定。(La, Nb)共掺杂Ti02压敏陶瓷中存在第二相,并且第二相随烧结温度转变。
6、(Ce4+、Nb)共掺杂Ti02中的静电势和缺陷浓度由Nb掺杂浓度、温度决定,而Ce4+的偏析由弹性应变能来决定。(Ce3+、Nb)共掺杂Ti02中的静电势和缺陷浓度由Ce3+、Nb掺杂浓度、温度决定,而Ce3+的偏析由静电势和弹性应变能来决定。
7、La单掺杂、(La, Nb)共掺杂和(Ce, Nb)共掺杂Ti02压敏陶瓷的晶界偏析驱动力为弹性应变能;而Nb单掺杂Ti02压敏陶瓷的晶界偏析驱动力为静电势。
8、掺杂Ti02压敏陶瓷中第二相来源于掺杂离子在能量较高的晶界面或晶粒表面偏析成核,然后是晶核在能量较高的晶界面晶粒表面逐渐生长成第二相。
9、Ti02压敏陶瓷的势垒结构接触界面模型为n型半导化晶粒和p型半导化晶界面的接触,即n-p-n型。第一原理计算表明:掺杂离子在晶界偏析和在晶粒固溶对势垒高度有明显的影响,这主要是施主固溶加强了Ti02晶粒的n型导电性,而金属离子在晶界的偏析则强化了晶界面的受主特征,因此增加了势垒高度。
10、影响势垒结构的主要因素包括:掺杂离子大小、掺杂量、烧结温度、降温工艺和纳米Ti02改性等,势垒结构对电学性能有直接影响。因此,通过改变组成和工艺调控晶界势垒结构,而得到电学性能较好的Ti02压敏电阻器。
TiO2 is a novel low-breakdown voltage varistor ceramic with double function of capacitance and varistor. Generally, doping is necessary for TiO2 ceramics to get better performances for a wider application fields. Radius, concentration and valence of doped ions, sintering temperature, oxygen partial pressure have obvious influence on microstructure, chemistry composition, barrier structure and electrical properties of TiO2 varistor ceramics. In this paper, space charge segregation at grain boundaries and grain boundaries barrier structure in (1)undoped, (2) single donor Nb, (3) single acceptor La, (4) (La,Nb) codoped and (5) (Ce,Nb) codoped Titanium dioxide ceramics were mainly investigated.
Firstly, Titanium dioxide samples were prepared by conventional electronic ceramic technology at 1300℃,1350℃,1400 and 1440℃. Microstructure, chemistry composition, crystal structure, ionic valence, thermal groove at grain boundary, grain boudanry structure and elemant segregation of TiO2 ceramics were tested via SEM, EDS, XRD,XPS and EPMA, respectively. The electrical prperties of TiO2 ceramics at different temperature and bias DC voltage were measured. Based on the thermoelectronic emissionat theory, grain boundaries barrier structures (GBBS) of TiO2 samples were calculated. GBBS mainly included barriers heightΦB and barriers width XD.
Secondly, under different temperature, distribution of electrostatic potential and defect concentration at TiO2 grain boundaries were studied by point defect thermodynamics method. Grain boundaries segregation driving force and mechanism of space charge in TiO2 ceramics were discussed.
Finally, the atomic structure of (310) grain boundary was built. Barrier heightΦB of (310) grain boundary in (1) undoped, (2) single doped and (3) codoped TiO2 ceramics was simulated by combination of first principle and molecular force field. Effects of doped ion, doping sites and concentration on barrier height were researched.
The studied results indicated that there exist much pores in undoped TiO2 ceramics sintered at high temperature. The formation of pores in undoped TiO2 is due to segregation, accumulation, diffusion and migration of oxygen vacancy Vo. Oxygen escaped from TiO2 grains transport along grain boundary, and is adsorbed in grain boundary or Triple junctions, and generate intergranular phase with Ca and Si element. Ti4+ gets an electron and is reduced into Ti3+ when oxygen vacancy formatted in undoped TiO2 ceramics. TiTi′is one of ways of compensations for Vo··. XPS showed that some Ti atom enter into interstitial sites and become interstitial titanium of Tii and Tii
For stoichiometric TiO2 and reduced TiO2, distribution of grain boundary electrostatic potential and defects concentration are different. For stoichiometric TiO2 case, titanium vacancy VTi″″, interstitial titanium Tii and oxygen vacancy Vo are primary point defects. The defect formation energy gVTi, gVo and gTi1 of point defect VTi″″, Vo and Tii dominate values of electrostatic potentialΦ(x). For reduced TiO2 case, there are two compensations mechanism of oxygen vacancy Vo and interstitial titanium Tii to satisfy electroneutrality. Grain boundary electrostatic potential and defects concentration are determined by oxygen partial pressure and temperature.
For single donor Nb doped TiO2, Niobium (Nb) segregated in TiO2 ceramics, but no secondary phase appears. Point defect NbTi formatted in Nb doped TiO2. When titanium vacancy VTi″″and donor defect NbTi satisfied electroneutrality conditions, electrostatic potentialΦ(x) was decided by Nb doping concentration, titanium vacancy defect formation energy gVTi and sintering temperature. With sintering temperature increasing, electrostatic potentialΦ(x) decreased. With Nb doping concentration increasing, electrostatic potentialΦ(x) increased.
For single acceptor La doped TiO2, Lanthanum (La) heavy segregated in TiO2 ceramics and produced secondary phase La4Ti9O24. Electrostatic potentialΦ(x) and point defects concentration was decided by La doping concentration. The driving force of La segregation was elastic strain energy formatted La segregated at grain boundary.
For (La,Nb) codoped TiO2 ceramics, Electrostatic potentialΦ(x) and point defects concentration was decided by Nb doping concentration and sintering temperature. La segregation was dominated by elastic strain energy. There exist second phases in (La,Nb) doped TiO2 varistors ceramics. With sintering temperature increasing, second phases will transit. For (Ce4+,Nb) codoped TiO2, Electrostatic potentialΦ(x) and point defects concentration was decided by Nb doping concentration and sintering temperature. Ce4+ segregation was dominated by elastic strain energy. For (Ce3+,Nb) codoped TiO2, ceramics, Electrostatic potentialΦ(x) and point defects concentration was decided by Ce3+, Nb doping concentration and sintering temperature. Ce3+ segregation was dominated by elastic strain energy.
The segregation driving force of single La. doped, (La,Nb) codoped and (Ce,Nb) codoped TiO2 ceramics is elastic strain energy while that of single Nb doped TiO2 ceramics is electrostatic potential. Secondary phase of codoped TiO2 ceramics is initiated from nucleation and segregation of doped ions in grain surface or grain boundary plane with higher energy, and then crystal nucleation grow gradually up to second phases in grain surface or grain boundary plane with higher energy.
Barrier structure model of codoped TiO2 ceramics is contact between n type semiconducting grain and p type semiconducting grain boundary plane, i.e. n-p-n type. Segregation of doping ions at grain boundary and solid solution in grains has effect on barrier height. Solid solution of donor in grains enhances n type conductivity of TiO2 grains. However segregation of doping ions at grain boundary enhances acceptor feature of grain boundary result in rising of barrier height.
The main factors of influencing barrier structure include doping ion radius, doping concentration, sintering temperature, cooling process and nano-TiO2 modification. Barrier structure has directly effect on electrical properties of TiO2 ceramics varistor. TiO2 varistor with better electrical properties can be obtained by controlling grain boundary barrier structure via varying composition and technology of TiO2 ceramics
引文
[1David R Clarke. Varistor ceramics[J]. J.Am.Ceram.Soc.1998,82(3):485-502.
[2]张丛春,周东祥,龚树萍.低压ZnO压敏电阻材料研究及发展概况[J].功能材料.2001,32(4):343-347.
[3]余尚银,秦效慈SrTiO3基多功能陶瓷的研究[J].压电与声光.1996,18(6):425-429.
[4]Yan M,Rhodes W. Preparation and properties of TiO2 varistors[J]. Appl. Phys.Lett. 1982,40(6):536-537.
[5]武明堂,李平,方湘怡.TiO2压敏陶瓷晶粒半导化[J].材料科学进展.993,7(3):244-247.
[6]张卫,武明堂,刘辅宜.Mn02添加剂对Ti02压敏陶瓷非线性的作用[J].压电与声光.1994,16(4):33-35.
[7]方湘怡,武明堂.Ti02环形电容压敏复合功能器件[J].电子元件.1994.2:18-19.
[8]张卫,武明堂,刘辅宜.Ti02低压压敏陶瓷材料研究[J].传感器技术.1995,2:13-16.
[9]罗建军,方湘怡,武明堂.La203掺杂的Ti02电容-压敏电阻器特性研究[J].西安交通大学学报.1997,31(9):62-66.
[10]Lingbing Kong, Liangying Zhang, Xi Yao.TiO2 Based Varistors derived from powders prepared by a sol-gel process[J]. Materials Letters.1997,32:5-8.
[11]罗建军,方湘怡,武明堂.热分解氧化反应对TiO2电容压敏电阻器性能的影响[J].无机材料学报.2000,15(1):93-96.
[12]Jianying Li, Shaohua Luo, Weihua Yao, Zilong Tang, Zhongtai Zhang, M.A. Alim. The effect of magnetized water on TiO2 based varistors[J]. Journalof the European Ceramic Society.2004, (24):2605-2611.
[13]李长鹏,王矜奉,陈洪存等.铌对(Y,Nb)掺杂的二氧化钛压敏-电容性能的影响[J].无机材料学报,2001,16(4):723-727.
[14]Changpeng Li, Jinfeng Wang, Xiaosu Wang, Hongcun Chen, Wenbin Su. Nonlinear electrical properties of Ta-doped titania capacitor-varistor ceramics[J]. Materials Chemistry and Physics 2002, (74):187-191.
[15]苏文斌,王矜奉,陈洪存等.钨掺杂对二氧化钛压敏电阻瓷电性能的影响[J].电子元件与材料.2002,21(5):1-3.
[16]C.P. Li, J.F. Wang, W.B. Su, et al. Effect of sinter temperature on the electrical properties of TiO2-based capacitor-varistors[J]. Materials Letters 2003, (57):1400-1405.
[17]季惠明,孙清池,王丹阳.Y系掺杂的TiO2压敏陶瓷性能研究[J].硅酸盐通报.2002,5:58-61.
[18]黎步银,周东祥,姜胜林等.Ti02高温电导及缺陷化学分析[J].压电与声光.2001,23(6):473-477.
[19]唐大海,庄严,李莉等.ZnO压敏陶瓷中的原子缺陷和界面电子态研究[J].华中科技大学学报(自然科学版).2002,30(11):46-49.
[20]陈志雄,林国漴,付刚等.深度热处理ZnO压敏陶瓷的晶界缺陷模型[J].中国科学(A辑).1997,27(9):851-857.
[21]周方桥,李莉,庄严等.SrO-Nb2O5-TiO2系压敏陶瓷中Nb5+和Sr2+的研究[J].无机材料学报,2002,17(6):1174-1180.
[22]周方桥,梁鸿东,庄严等.N型半导化Ti02压敏陶瓷的导电机制[J].哈尔滨理工大学学报,2002,7(6):29-31.
[23]朱道云,周方桥,丁志文等.Nb205掺杂及Ti02压敏陶瓷埋烧工艺的研究[J].华中科技大学学报(自然科学版).2004,32(2):54-57.
[24]许毓春,李慧峰,王士良等.Si02对Ti02系压敏陶瓷电性能的影响[J].压电与声光.1994,16(6):41-43.
[25]Yang S L, Wu J M. Varied atmosphere compensation exploring the roles of barium and bismuth in (Ba,Bi,Nb)-doped TiO2 varistors[J]. J.Am. Ceram. Soc.,1995,78 (8):2203-2208.
[26]Cheng J J, Wu J M. Effect of Mn on the electrical properties of (Ba,Bi,Nb)-added TiO2 ceramics prepared by the sol-precipitation method[J]. Materials Chemistry and Physics,1997 (48):129-135.
[27]W.Y. Wang, D.F. Zhang, T. Xu, et al. Nonlinear electrical behavior and dielectric properties of (Ca, Ta)-doped TiO2 ceramics[J]. Journal of Alloys and Compounds 2002, (335):210-215.
[28]Fanming Meng. Influence of sintering temperature on semi-conductivity and nonlinear electrical properties of TiO2-based varistor ceramics[J]. Materials Science and Engineering B,2005, (117): 77-80.
[29]陈朝霞,甘国友,严继康等.Sr掺杂对Ti02双功能压敏陶瓷介电性能的影响[J].昆明理工大学学报(理工版).2003,28(5):32-35.
[30]严继康,甘国友,杜景红.低压双功能Ti02压敏陶瓷的研究[J].昆明理工大学学报(理工版),2003,28(2):30-33.
[31]张小文,甘国友,严继康等.Ti02压敏电阻的现状与展望[J].材料导报.2003,17(8):41-43,50.
[32]张小文,甘国友,严继康.表面层对Ti02压敏陶瓷电学性能的影响[J].压电与声光.2005,27(3):260-262.
[33]T. Kuratomi, K. Yamaguchi and M. Yamawaki. Semiconducting properties of polycrystalline titanium dioxide[J]. Solid State Ionics 2002,(154-155):223-228.
[34]V.C. Sousa, E.R. Leite and J.A. Varela. The effect of Ta2O5 and Cr2O3 on the electrical properties of TiO2 varistors[J]. Journal of the European Ceramic Society 2002, (22):1277-1283.
[35]A.B. Gaikwad, S.C. Navale, V. Ravi, TiO2 ceramic varistor modified with tantalum and barium[J]. Materials Science and Engineering B 2005, (123):50-52.
[36]M. Okutana, Halil I. Bakanb, K. Korkmazc, Fahrettin Yakuphanoglu. Variable range hopping conduction and microstructure properties of semiconducting Co-doped TiO2[J]. Physica B 2005, (355):176-181.
[37]Qinglei Wang, Guoda Lian, Elizabeth C. Dickey. Grain boundary segregation in yttrium-doped polycrystalline TiO2[J]. Acta Materialia 2004, (52):809-820.
[38]Jeri Ann S. Ikeda and Yet-Ming Chiang.Space charge segregation at grain boundaries in titanium dioxide:Ⅰ, relationship between lattice defect chemistry and space charge potential[J].J.Am.Ceram.Soc.1993,76(10):2437-2446.
[39]Jeri Ann S. Ikeda and Yet-Ming Chiang.Space charge segregation at grain boundaries in titanium dioxide:Ⅱ, Model Experiments[J]. J. Am. Ceram. Soc.1993,76(10):2447-2459.
[40]Ying Pang, Noel T.Nuhfer and Paul Wynblatt. Segregation of Nb to TiO2 Grain Boundaries[J]. Microsc Microanal,2005,11(Suppl 2):1726-1727.
[41]李红耘,唐子龙,尧巍华等(Nb、Ce、Si、Ca)掺杂对Ti02压敏电阻陶瓷电性能的影响[J].功能材料.2002,33(6):635-637.
[42]Jianying Li, Shaohua Luo and Weihua Yao. Role of second phase in (Nb,Ce,Si,Ca)-doped TiO2 varistor ceramics[J]. Materials Letters 2003,(57):3748-3754.
[43]R. Parra,, M. S. Castro, J. A. Varela. Analysis of secondary phases segregated and precipitated in SnO2-based varistors[J]. Journal of the European Ceramic Society 2005, (25):401-406.
[44]Hsing-I Hsiang, Shi-Shu Wang. Cooling rate effects on the electrical properties of TiO2-based varistor[J]. Materials Science and Engineering B 2006, (128):25-29.
[45]严继康,甘国友,陈海芳等.(La、Nb)共掺杂Ti02压敏陶瓷中第二相的研究[J].压电与声光.2008.1:67-70.
[46]陈海芳,甘国友,严继康等.纳米Ti02添加剂对Ti02压敏陶瓷性能的作用[J].半导体技术.2006.2:102-104,118.
[47]S. Fabris, C. Elsasser. First-principles analysis of cation segregation at grain boundaries in α-Al2O3[J]. Acta Materialia 2003,(51):71-86.
[48]T.A.Arias, J.D.Joannopoulos. ab initio prediction of dopant segregation at elemental semiconductor grain boundaries without coordination defects[J].Physical Review Letters.1992,69(23):3330-3333.
[49]H.S. Domingos and P.D. Bristowe. Atomistic Simulation O F Grain Boundary Segregation In Zinc Oxide[J]. Scripta Materialia,1999,41(12):1347-1352.
[50]S. PICOZZI. A. PECCHIA, M. GHEORGHE AND A. DI CARLO. Schottky Barrier Height at Organic/Metal Junctions from First-Principles[J]. Journal of Computational Electronics 2003,(2): 407-411,
[51]李书平,王仁智,蔡淑惠.金属-半导体接触势垒高度的理论计算[J].固体电子学研究与进展.2003,23(4):412-416.
[52]LEI ZHENG,TINGDONG XU. Nonequilibrium Grain-Boundary Cosegregation of Nitrogen and Chromium in NiCrMoV Steel[J]. METALLURGICAL AND MATERIALS TRANSACTIONS A. 2005,36A:3311-3319.
[53]Christian Elsasser,Traude Elsasser.Codoping and Grain-Boundary Cosegregation of Substitutional Cations in a-Al2O3:A Density-Functional-Theory Study[J]. J.Am.Ceram.Soc.2005,88(1):1-14.
[54]T.K.Gupta.,W.G.Carlson.A grain boundary defect model for instability/stability of a ZnO varistor[J]. J.Mater.Sci.1985,20:3487-3500.
[55]R.Waser, R.HaGENBECK. Overview No.137 Crain boundaries in dielectric and mixed-conducting ceramics[J].Acta Mater.2000,48:797-825.
[56]Ying Pang,Paul Wynblatt. Correlation between Grain Boundary Segregation and Grain Boundary Plane Orientation in Nb-doped TiO2[J]. J.Am.Ceram.Soc.2005,88(8):2286-2291.
[57]P. Wynblatt, G.S. Rohrer, F. Papillon. Grain boundary segregation in oxide ceramics[J]. Journal of the European Ceramic Society 2003,(23):2841-2848.
[58]David M Saylor; Gregory S Rohrer.Measuring the influencing of grain-goundary misorientation on thermal groove geometry in ceramic polycrystals[J]. J.Am.Ceram.Soc.1999; 82(6):529-536
[59]P.Q.Mantas,J.L.Baptista.The Barrier Height Formation in ZnO Varistors[J].Jounal of the European Ceramic Sociaty.1995,15:605-615.
[60]王勇军,王矜丰,陈洪存等.Sn02压敏材料势垒电压的测量[J].压电与声光.2000,22(3):197-199.
[61]王评初,康颍,李峥等.低温烧结SrTiO3晶界势垒高度的研究[J].无机材料学报.1996,11(4):691-695.
[62]李盛涛,邹晨,刘辅宜.ZnO压敏陶瓷晶界势垒高度和宽度的研究[J].电瓷避雷器.2004,1:17-22.
[63]David N. Seidman. Subnanoscale Studies Of Segregation At Grain Boundaries:Simulations and Experiments[J]. Annual Review of Materials Research,2002,32:235-269.
[64]S.J. Pennycook,M.F. Chisholm,Y. Yan et al. A combined experimental and theoretical approach to grain boundary structure and segregation[J]. Physica B 1999, (273-274):453-457.
[65]Seok Hyun Yoon, Hwan Kim. Space charge segregation during the cooling process and its effect on the grain boundary impedance in Nb-doped BaTiO3[J]. Journal of the European Ceramic Society 2002, (22):689-696.
[66]Sung-Yoon Chung; Suk-Joong L Kang; Vinayak P Dravid. Effect of sintering atmosphere on grain boundary segregation and grain growth in niobium-doped SrTiO3[J].J.Am.Ceram.Soc. 2002,85(11):2805-2810.
[67]K.Ishida. Effect of grain size on grain boundary segregation[J]. Journal of Alloys and compounds. 1996,235:244-249.
[68]C. D. TERWILLIGERt,YET-MING CHIANG. Size-Dependent Solute Segregation And Total Solubility In Ultrafine Polycrystals:Ca In TiO2[J]. Acta metall, mater.1995,43(1):319328.
[69]Yan M,Rhodes W. Preparation and properties of TiO2 varistors[J]. Appl. Phys.Lett.1982, 40(6):536-537.
[70]Xiangyi Fang, J.T. Oh. Microstructure and electrical properties of Nb2O5 doped titanium dioxide.Materials Science and Engineering B 2007,(136):15-19.
[71]李春雷,肖景林.势垒的非对称性对隧穿几率的影响[J].内蒙古民族大学学报(自然科学版),2006,21(3):253-256.
[72]莫以豪,李标荣,周国良.半导体陶瓷及其敏感元件[M].上海:上海科学技术出版社,1983.10.
[73]徐廷献,沈继跃,薄占满,等编著.电子陶瓷材料[M].天津:天津大学出版社,1993,4.p336-337
[74]徐廷献,薄占满,曲远方等.复合扩散SrTiO3基半导体陶瓷的压敏特性[J].天津大学学报,1994,27(6):698-706.
[75]C. Berthod, N. Binggeli, A. Baldereschi. Schottky barrier heights at polar metal/semiconductor interfaces[J]. PHYSICAL REVIEW B 2003,(68):085323.
[76]Shinjiro Yagyu, Michiko Yoshitake. Measurement of bias voltage dependence of local barrier height at constant tip-sample separation[J]. Surface Science,2003,532-535:1136-1139.
[77]张卫,武明堂,刘辅宜.Ti02电容、压敏复合功能材料研究[J].功能材料,1994,25(2):137-141
[78]徐廷献,沈继跃,薄占满,等编著.电子陶瓷材料[M].天津:天津大学出版社,1993,4.p22-63.
[79]赵世玺,刘韩星.钛酸钡陶瓷晶界结构、偏析与性能[J].功能材料.2000,31(3):233-237.
[80]赵世玺.BaTiO3陶瓷的晶界结构及偏析研究[D].武汉工业大学硕士学位论文.2000.3.1
[81]K.L.Kliewer and J.S.Koehler. Space charge in Ionic Crystals.I.General Appeoach with Application to NaCl[J].Phys.Rev.1965,140[4A]:A1226.
[82]J. He, R.K. Behera, M.W. Finnis, X. Li, E.C. Dickey, S.R. Phillpot, S.B. Sinnott. Prediction of high-temperature point defect formation in TiO2 from combined ab initio and thermodynamic calculations[J]. Acta Materialia 2007, (55):4325-4337.
[83]J. B. Keith, Hao Wang, B. Fultz and J. P.Lewis. Ab initio free energy of vacancy formation and mass-action kinetics in vis-active TiO2[J]. J. Phys.:Condens. Matter 2008,20 (2):022202.
[84]刘恩科,朱秉升,罗晋生.半导体物理学(第6版)[M].京:电子工业出版社,2003.8.p29-231.
[85]张连俊.压敏电阻非欧姆特性的研究[J].山东工程学院学报,1997,11(3):44-45.
[86]T. Bak, J. Nowotny, M. Rekas, C.C. Sorrell. Defect chemistry and semiconducting properties of titanium dioxide:Ⅰ. Intrinsic electronic equilibrium[J]. Journal of Physics and Chemistry of Solids, 2003,64:1043-1056.
[87]Dongxiang Zhou, Congchun Zhang, Shuping Gong. Degradation phenomena due to dc bias in low-voltage ZnO varistors [J]. Materials Science and Engineering B 2003,(99):412-415.
[88]Y. Gao, S. Thevuthasan, D.E. McCready. MOCVD growth and structure of Nb-and V-doped TiO2 films on sapphire [J]. Journal of Crystal Growth 2000 (212):178-190.
[89]陈家才.TiO2压敏陶瓷晶界偏析的初步研究[D].昆明理工大学硕士学位论文,2006.7.
[90]I. Dawson, P.D. Bristowe, M.-H. Lee. Frist-principles study of a tilt grain boundary in rutile[J]. Physical Review B,1996,(54):13727-13733.
[91]R.S.Boughanour Roth, L.W. Phase-equilibrium relations in the systems titania-niobia and zriconia-niobia[J]. J, Res.Natl. Bur. Stand. (U.S.),1955;55(4):209-213.
[92]J.B. Braue MacChesney, H. A. System La2O3-TiO2 phase equilibriums and electrical properties[J]. J. Am. Ceram. Soc.,1962; 45(9):416-422.
[93]Vanderbilt, D. Soft self-consistent pseudopotentials in a generalized eigenvalue formalism[J].Phys. Rev. B,1990,41:7892-7895.
[94]Segall, M. D.Shah, R..Pickard. Population analysis of plane-wave electronic structure calculations of bulk materials[J].,Phys. Rev. B,1996,(54):16317-16320.
[95]Seidl. A.,Gorling. A,Vogl. P. Generalized Kohn-Sham schemes and the band-gap problem[J].Phys. Rev. B,1996,(53):3764-3774.
[96]冯少新,李宝会,金庆华.金红石结构Ti02晶体点缺陷形成能的经验途径计算[J].物理学报,2000,49(7):1307-1311.
[97]YANG Seng-lu, wu Jenn-ming. Effects of Nb2 O5 in (Ba, Bi, Nb)-added TiO2 ceramic raristors[J].J Mater Res,1995,10(2):345-352.
[98]T. Bak, J. Nowotny, M. Rekas, C.C. Sorrell. Defect chemistry and semiconducting properties of titanium dioxide:Ⅱ. Defect diagrams[J]. Journal of Physics and Chemistry of Solids.2003, (64):1057-1067.
[99]Victor V. Atuchin, Valery G. Kesler, Natalia V. Pervukhina, Zhaoming Zhang. Ti 2p and O 1s core levels and chemical bonding in titanium-bearing oxides [J]. Journal of Electron Spectroscopy and Related Phenomena.2006, (152):18-24.
[100]王建祺主编.电子能谱学引论[M].国防科技出版社.P556-557.
[101]Y.Tanaka, M.Nakai, T.Akahori. Characterization of air-formed surface oxide film on Ti-29Nb-13Ta-4.6Zr alloy surface using XPS and AES[J]. Corrosion Science xxx (2008) xxx-xxx.
[102]B.S. Bokstein, V.S. Gostomelskii, V.A. Ivanov. Kinetics of diffusion pores dissolving at intercrystalline boundary under coinfluence of compressive stresses and capillary forces[J]. Materials Letters 1999,(39):.77-79.
[103]M. G. Mynbaeva, D. A. Bauman, and K. D. Mynbaev. On the Role of Vacancies in Pore Formation in the Course of Anodizing of Silicon Carbide[J]. Physics of the Solid State,2005,47(9):1630-1636. Translated from Fizika Tverdogo Tela,2005,47(9):1571-1577.
[104]K. Darcovich, K. Shinagawa, F. Walkowiak. A three-dimensional dual-mechanism model of pore stability in a sintering alumina structure[J]. Materials Science and Engineering A 2004, (373):107-114.
[105]景晓宁,赵建华,何陵辉.固相烧结后期晶粒和气孔拓扑生长演化的二维相场模拟[J].材料科学与工程学报,2003,21(2):170-173.
[106]G. Tomandl, P. Varkoly. Three-dimensional computer modeling of grain growth and pore shrinkage during sintering. Materials Chemistry and Physics,2001, (67):12-16.
[107]H. H.Yu, Z. Suo. An axisymmetric model of pore-grain boundary separation, Journal of the Mechanics and Physics of Solids,1999, (47):1131-1155.
[108]施剑林.固相烧结-Ⅰ气孔显微结构模型及其热力学稳定性,致密化方程[J].硅酸盐学报,1997,25(2):499-513.
[109]施剑林.固相烧结—Ⅲ实验:超细氧化锆素坯烧结过程中的晶粒与气孔生长及致密化行为[J].硅酸盐学报,1998,26(1):1-13.
[110]林晓敏,宋文福,李莉萍等.Cel-xEuxO2-δ (x=0.05-0.50)固溶体的溶胶-凝胶法合成与性质研究[J].化学学报,2004,62(10):951-955.
[111]P. Verardi, F. Craciun, L. Mirenghi, M. Dinescu, V. Sandu. An XPS and XRD study of physical and chemical homogeneity of Pb_Zr,Ti/O thin films obtained by pulsed laser deposition[J]. Applied Surface Science,1999,(138-139):552-556.
[112]E.P. Bodina Savchenko, N.A.Celer E.K.Solid-phase reactions between pentoxides of niobium and tantalum and oxides of the rare-earth element[J].Pro. All-Union Conf,2na, Leningard, USSR,1965; Chem. High-Temp Mater.pp.108-113.
[113]V. I. Strakhov, O. V. Mel'nikova, and M. Dib, Izv. Akad. Nauk SSSR, Neorg. Mater.,27 [3] 593-597 (1991); Inorg. Mater. (Engl. Transl.),1991,27 [3]:495-498.
[114]丁铁柱,其其格,李健等.稀土氧化物LSCO/YSZ的XRD和XPS研究[J].中国稀土学报,2002,20(4):320-323.
[115]Zhaolin Liu, Bing Guo and Liang Hong. Preparation and characterization of Cerium oxide doped TiO2 nanoparticles[J]. Journal of Physics and Chemistry of Solids,2005, (66):161-167.
[116]吕卫星,方垄,郭卫华等.LB膜法制备Y203掺杂的Ce02超薄陶瓷膜的X光电子能谱(XPS)研究[J].光谱学与光谱分析,2002,22(1):16-19.
[117]谭莉萍.半导体陶瓷Schottky势垒型器件晶界势垒问题探讨[J].压电与声光,2004,26(3):237-239.
[118]钟吉品,王鸿,殷之文.晶界势垒对晶界层电容器电性能的影响[J].无机材料学报,1990,5(2):126-131.
[119]郑振华,陈羽BaTiO3半导体陶瓷从PTC特性向边界层电容效应过度问题探讨[J].物理学报,1996,45(9):1543-1550.
[120]W.R.L.Lambrecht, A.G.Petukhov and R.T.Hemmelman. Schottky barrier formation at ErAs-GaAs interfaces A case of Fermi level pinning by surface states[J]. Solid state communications,1998,108(6):361-365.
[121]P. R. Bueno, E. R. Leite and M. M. Oliveira.Role of oxygen at the grain boundary of metal oxide varistors:A potential barrier formation mechanism[J]. APPLIED PHYSICS LETTERS, 2001,79(1):49-50.
[122]刘恩科,朱秉升,罗晋生.半导体物理学(第6版)[M].北京:电子工业出版社,2003.8.p186.
[123]w.y. wang, d.f. zhang, t. xu et al. Nonlinear electrical characteristics and dielectric properti es of Ca, Ta-doped TiO2 varistors[J]. Appl. Phys. A,2003,76:71-75.
[124]陈后胜,陆士强,杨美玉等.受主含量和晶界势垒对PTRC性能影响的研究[J].电子器件,1996,19(3):165-170.
[125]陈亚杰,刘培生.烧结温度对PTC掺杂晶界势垒特性的影响[J].电子元与材料,1995,14(3):47-50.
[126]徐丹,殷景华.SBD势垒高度的影响因素[J].哈尔滨理工大学学报,2007,12(5):50-52.
[127]孙丹峰.应用纳米材料添加剂制备高压高能压敏电阻[J].电子元器件应用,2001,3(1-2):9-11.
[128]禹争光,杨邦朝,敬履伟.纳米氧化铋粉体的制备及对ZnO压敏电阻性能的影响[J].硅酸盐学报.2003,31(12):1184-1187.
[129]施建章,曹全喜,卫云鸽.复合纳米添加法制备ZnO压敏电阻器[J].压电与声光,2004,26(4):83-85.
[130]孙丹峰,季幼章,张立德等.纳米ZnO掺杂对高能压敏电阻的改性研究[J].功能材料,2001,32(10):606-608.
[131]严群,陈家钊,涂铭旌.纳米ZnO掺杂压敏电阻电位梯度与显微组织研究[J].压电与声光,2005,27(2):172-174.
[132]孙秀果,张建民,李更辰等.TiO2纳米粉体的烧结行为及其性能的研究[J].电子元件与材料.2006,25(2):15-17.
[1331崔国文主编,表面与界面[M],清华大学出版社,北京,1990.
[134]C. Leach. Crystallographic control of the barrier structure in zinc oxide varistors[J]. International Journal of Inorganic Materials,2001, (3):1117-1119.
[135]S.Chang, L.J.Brillson, Y.J.Kime. Orientation-dependent chemistry and Schottky-barrier formation at metal-GaAs interfaces[J]. Physical Review Letters,1990,64(21):2551-2554.
[136]赵双群.钛酸钡陶瓷离子缺位对晶界势垒的影响[J].电子元件与材料,2001,10(4):20-21.
[137]邹秦,孟中岩.涂覆扩散型SrTiO3基陶瓷晶界叠加势垒模型[J].硅酸盐学报.1996,24(2):185-190.
[138]徐保民,殷之文,王鸿.SrTiO3陶瓷晶界层电容器材料的离子偏析[J].中国科学院研究生院学报.1993,10(4):368-374.
[139]P. Prabhumirashi, V. P. Dravid and A. R. Lupini. Atomic-scale manipulation of potential barriers at SrTiO3 grain boundaries[J]. APPLIED PHYSICS LETTERS,2005,(87):121917.
[140]K. D. PATEL, R. SRIVASTAVA. Phase transition related barrier height in Ga-Si Schottky diode[J]. JOURNAL OF MATERIALS SCIENCE LETTERS,1997, (16):1509-1511.
[141]E.Olsson, G.L.Dunlop. Characterization of individual interfacial barrier in a ZnO varistor materials[J]. J.Appl.phys.66(8):3666-3675.
[142]M.B. Park, C.D. Kim, N.-H. Cho. Determination of diffusion coefficients and grain boundary potential barrier heights of semiconducting BaTiO3 ceramics[J]. Materials Science and Engineering, 2003 (B99):15-19.
[143]利明.陈宗璋.向蓝翔等.偏析对氧化锆晶界电导的影响及提高晶界电导的几种方法[J].硅酸盐通报,2004,(3):77-80,93.
[144]刘伟杰,张宝金.镁偏析对铝合金晶界性能影响的计算机模拟[J].中国有色金属学报.2000,10(4):476-480.
[145]Y. Ishimaru, Y. Wu, T. Suzuki, et al. Relation between barrier structure and electrical properties of interface-modified ramp-edge junctions[J]. Physica C,2003,(392-396):1373-1377.
[146]翟继卫,杨文.相界势垒对高B值高电导率NTC热敏材料电特性的影响[J].功能材料,1997,28(2):174-176.
[147]Fanming Meng. Influence of sintering temperature on semi-conductivity and nonlinear electrical properties of TiO2-based varistor ceramics[J].Materials Science and Engineering B, 2005,(117):77-80.