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MASC534term paper-Huijian Tian

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MASC534term paper-Huijian Tian

  1. 1. MASC 534 term paper Use XRD to identify the molecular structure of NiO films annealed for different durations or in different temperature Huijian Tian USC ID:2386525387 Fall 2014
 MASC 534 HUIJIAN TIAN !1
  2. 2. MASC 534 term paper Use XRD to identify the molecular structure of NiO films annealed for different durations or in different temperature Abstract In this paper, the nickel oxide (NiO) thin films were prepared by sol–gel dip coating process on indium tin oxide glass which is known as ITO. In this situation, the nickel oxide samples were prepared in the same atmosphere while annealed for different durations in the same temperature, or annealed in different temperature for the same time. XRD was used to analyze the structure of the film and the composition of the film. Through x-ray diffraction pattern, structures of these sample films were showed, and the particle size could be calculated by Scherrer formula. After different annealed durations, nickel oxide films structure showed to be different. While annealed duration is long as 60 mins, its structure become a crystalline nature. While annealed durations were shorter than 45 mins, x-ray diffraction patterns showed to be amorphous in nature. In different temperatures situations, all films showed a crystalline structure. While annealing temperatures increase, crystalline size of nickel thin film increase too. Keywords: X-ray diffraction, nickel oxide films, annealing temperature, annealing durations MASC 534 HUIJIAN TIAN !2
  3. 3. 1. Introduction X-ray particle can be derived by atomic transitions in the energy gap difference between the two energy levels generated. It is a kind of electromagnetic radiation and its wavelength is between ultraviolet and γ-rays. Its wavelength is very short and is between about 0.01 to 100 angstroms. In 1895, a genius German physicist WK Roentgen discovered it, so it is called X-rays. “X- ray crystallography is a tool used for identifying the atomic and molecular structure of a crystal, in which the crystalline atoms cause a beam of incident X- rays to diffract into many specific directions.”[‑ ] This paper introduce the principle1 of XRD, and its applications in studying properties and structure of materials. Electrochromic material is a kind of material whose optical property (reflectivity, transmissivity, absorptivity) occurs a stable, a reversible color change under the applied electric field, and it shows a reversible change in color and transparency in appearance. Material has electrochromic properties is called electrochromic material. What’s more, electricity electrochromic material made devices are called electrochromic devices. “Microporous and mesoporous transition metal oxide films find use in a number of potential applications like sensors, batteries, electrochromic (EC) devices, and photonic and electrocatalytic materials”[‑ ]. Oxides of Nb, Mo, W, Ta and Ti exhibit cathodic2 electrochromism. However oxides of Ir, Rb, Ce, Fe, Co, Mn, and Ni exhibit anodic electrochromism. Except for both cathodic oxides and anodic oxides, V2O5 is MASC 534 HUIJIAN TIAN !3
  4. 4. something special and it exhibits both types of electrochromism. “This strongly indicates that electrochromism has a strong relation with the electronic structure oft he materials”.[‑ ] Nickel oxide films are this kind of metal oxide, and they have3 many essential advantages. “NiO adopts the NaCl structure, with octahedral Ni(II) and O2− sites.”[‑ ] “Nickel oxide is a very popular and new electrochromic4 materials, with many advantages such as high electrochromic efficiency, cyclic reversibility, durability, and grey coloration”.[‑ ] Usually people make5 electrochromic multilayer with nickel oxide and tungsten oxide, but their optical performance are still not high as much as people expect. With different annealing durations and different annealing temperatures, NiO films have different microstructures which show different electrochromic properties. There are four main techniques to prepare nickel oxide films such as spraying[‑ ], pulsed laser deposition[‑ ], vacuum deposition[‑ ], sol–gel process[‑ ].6 7 8 9 In this paper, several theory of electrochromism and some application of electrochromism will be mentioned, and sol–gel dip coating process on indium tin oxide glass which is known as ITO will be discussed to prepare nickel oxides thin film. After that we will discuss the principle of x-ray diffraction and state that how to use XRD method to identify the molecular structure of NiO film, and then we state the impact of different annealing durations and temperatures on the electrochromic properties of NiO film. MASC 534 HUIJIAN TIAN !4
  5. 5. 2. Theory of electrochromism Inorganic electrochromic material’s electron shell structure is generally unstable and prone to accept or release the electrons, then the valence turn to difference, along with color’s change occurred. There are two types of electrochromic metal oxides. One of them is called cathodic, and another is called anodic. “Figure 1 shows which metals are capable of forming oxides of these two varieties and also indicates that oxides based on vanadium can be viewed as a hybrid”[‑ ]. From this figure, nickel oxide is defined by anodic oxide.10 Actually a standard electrochromic device combines two types of electrochromic films, and it is easy to derive that to combine one “cathodic’’ oxide and one “anodic’’ oxide is better than just one kind of oxide. When electrons transfer from one side to another, both oxides color. 2.1 Electrochromic chemical reaction and optical properties In this paper, we just discuss about the anodic oxide: nickel oxide. When anodic coloring materials in its reduced state, it is in achromatic state, losing electrons to become high valence(oxidation state) and it is in the colored state, the electrochromic reaction is: MASC 534 HUIJIAN TIAN !5 (1)
  6. 6. In this formula, MOy is the electrochromic metal oxides. A is a positive ion, and e is the electrons. If this metal oxide is nickel oxide, discoloration of NiO film was mainly due to the proton and the electron’s injecting and extracting from the film [‑ ], so that11 some Ni(OH)2 convert to NiOOH. The formula has this form: NiO + OH- == Ni(OOH) + e- It means that the injection of OH ion makes NiO transfer to NiOOH, and color shows. Although the mechanism of nickel oxides’ electrochromism still has a lot of controversy, researchers have done a lot of research under different experimental conditions, made a lot of different theories, but no matter what views, during the reaction of NiO film’s electrochromic, the view that nickel ions’ MASC 534 HUIJIAN TIAN !6 Figure 1: Periodic system of the elements (apart from the lanthanides and actinides). The differently shaded boxes indicate transition metals whose oxides display clear ‘‘cathodic’’ and ‘‘anodic’’ electrochromism. From Ref. [10]
  7. 7. transferring from the divalent to trivalent caused coloration is accepted by everyone. Table 1[‑ ] shows some electrochromic materials’ coloration, and we know12 that NiO is black brown in oxidation state. 2.2 Structure and energy band Why do these electrochromic oxides show electrochromic properties? It is fair to argue that crystalline structure play a big role in it. “All of these structures can be treated with in a frame work of “ubiquitous’’ MeO6 octahedra (with Me denoting metal) connected by sharing common corners and/or by sharing common edges”[‑ ]. NiO belongs to the close-packed face-centered cubic13 sodium chloride structure with lattice constants a = 0.418 nm[‑ ]. It is arranged14 by NiO6 octahedral with highly regulated, and the gap between the octahedron can be used as a channel for H, Li and other small ions’ migration or injection. Table 1 Classfication Materials oxidation state reduction state Cathodic oxides WO3 None Blue MnO3 None Blue Nb2O5 None light Blue TiO2 None light Blue NiO Black brown None Anodic oxides Ir2O3 Black blue None MnO2 Blur purple None MASC 534 HUIJIAN TIAN !7
  8. 8. Figure 2 is the lattice structure of NiO; from this pattern, the big shade circle stands for oxide atom, and the small transparent circle stands for nickel atoms. The existence of octahedral coordination is very important for the electronic properties of the EC oxides[‑ ]. As we know, every atom has lots of energy band,15 such as 1s, 2s, 2p, 3s, 3p, 3d, and electrons stay in these energy state following some certain principles. Outer electrons of nickel atoms are arranged 3d84s2. D band will split into eg and t2g band. The oxygen 2p band is separated from d band. Figure 3 illustrates the band levels of Tungsten oxides and nickel oxides[‑ ]: the left hand panel is for tungsten oxide, while the right hand panel is16 for nickel oxide. It is enough for us to just discuss nickel oxides. In Nickel oxides, MASC 534 HUIJIAN TIAN !8 Figure 2
  9. 9. when nickel is trivalent, which means NiOOH, it has an unfilled oxygen band. Some photons are absorbed by electron transition if , so this material is colored. While nickel is divalent, which means NiO, t2g state is filled. If only the band gap is large enough, electrons cannot jump to eg state by absorbing photons, so this material becomes transparent. 3. X-ray diffraction and its application on electrochromism X-ray diffraction techniques get more and more attentions in materials, chemical, physical, minerals, geology and other disciplines. In addition to study the microscopic structure of the crystal, it has developed into a practical application of laser science. X-ray is an analysis of non-destructive testing methods, and it uses few samples, with good accuracy, no damage to the sample. But this approach also has its shortcomings. Its equipment is relatively MASC 534 HUIJIAN TIAN !9 Figure 3
  10. 10. complex and expensive, and it requires people to maintain a certain expertise, what’s more it also belong to indirect tests. In actual work, X-ray analysis is usually used in conjunction with other methods[‑ ].17 3.1 X-ray’s production The traditional way to produce x-rays is that a high voltage is applied on two electrodes, in several tens of kV, then electrons will be emitted in high speed with enough kinetic energy, from the cathode to anode. When electron hits the metal target, they slow down and all its kinetic energy turn into photons, which are x-ray. Since there are different kinds of slow down to electrons, the produced x-rays will have different wavelength. 3.2 X-ray diffraction theoretical basis X-ray diffraction analysis method is based on the crystalline samples diffracted x-ray’s characteristic, then people calculate crystalline structure and lattice parameters. The basic principle of x-ray diffraction can be illustrated by Bragg’s law: That is, to a certain wavelength beam, if the angle between the incident direction and a group of the crystal plane and the interplanar spacing of crystalline plane both satisfy the equation, the diffraction spots show in a certain direction. One thing should be pointed is that the interplanar spacing d can be derived by plane’s miller indices. For example, to cubic system: MASC 534 HUIJIAN TIAN !10
  11. 11. If we have an x-ray diffraction pattern, we can trial that which miller indices satisfy this equation, which means that we can get the structure of crystalline sample. Figure 4[‑ ] is an example of standard x-ray diffraction pattern. In this pattern, six18 peaks represent different crystal plane. MASC 534 HUIJIAN TIAN !11 Figure 4
  12. 12. While in actual samples, a particle of a real crystalline grain sample generally consists of many very small units called “crystallites”. This fine unit can be considered as a single crystal[‑ ]. Figure 5 [‑ ] shows this situation. Although19 20 in some situations the grain size is the same as crystallites’s size, they are totally different physical principles because it is the crystallite to make a diffraction peak in x-ray diffraction, not the whole grain. It is necessary for us to us x-ray diffraction to identify a sample material’s crystallite size. The following equation is called Scherrer’s equation[‑ ]:21 MASC 534 HUIJIAN TIAN !12 Figure 5
  13. 13. In this equation, Ɵ is Bragg angel. B is the full width at half its maximum intensity for the corresponding peak, and ƛ is x-ray wavelength. The value of t stands for the diameter of crystallites, which is related to the corresponding peak. The wider the corresponding peak is, it means the smaller the crystallite’s size is. “The dislocation density (ð) is defined as the length of dislocation lines per unit volume of the crystal”[‑ ]. It is derived by the following equation[‑ ]:22 23 3.3 Use x-ray diffraction to identify the structure of NiO film annealed for different durations In this work, nickel oxide films were made by using sol-get process, “3.7329 g of Ni(Ac)2 4H2O was dissolved in 100 ml of 2-methoxyethanol and 2 drops of concentrated HCl was added to the solution. The solution was stirred at 60 centigrade for an hour and then aged for 24 h at room temperature. The NiO films were coated on FTO(fluorine doped tin oxide) coated glass substrate at a withdrawal speed of 15cm/min. After each coating, the films were dried in air for 5 min and oxidized at300 1C for 5 min. Totally 8 layers have been coated(optimized number of layers is 8 and optimized temperatures 300 centigrade).”[‑ ] In the end of this work, what is the most important, the sample24 films were annealed at 300 centigrade for 4 kinds of durations, 15, 30,45 and 60 mins. Then the work is to get x-ray diffraction from prepared nickel oxide films, MASC 534 HUIJIAN TIAN !13
  14. 14. and x-ray diffractometer use CuK radiation, which wavelength is 1.54 angstrom[‑ ]. Figure 6 [‑ ] following is the x-ray diffraction pattern annealed for25 26 different durations: Figure 6 shows the x-ray diffraction pattern. It is obvious that when it comes to the films annealed for 15 mins, 30 mins, or 45 mins, the structure of films seems to be amorphous in nature. However, when duration extends to 60 mins, there are diffraction corresponding peaks, which means the structure shows some crystalline nature. MASC 534 HUIJIAN TIAN !14 Figure 6: x-ray diffraction pattern annealed for different durations in 300 centigrade. (a) curve is 15 mins, (b) is 30 mins, (c) is 45 mins, (d) is 60 mins
  15. 15. XRD results show that NiO film annealed for 60 mins shows the cubic phase structure, and characteristic diffraction peaks corresponding to (111), (200) crystal plane were formed when the values of 2Ɵ were 37.290, 43.270. Here we use Scherrer’s equation to calculate the crystallite’s size corresponding to the crystal plane (200), where wavelength is 0.154 nm. From this pattern, we take the value of B for 0.0243 and Bragg angel for 43.056, then we get the value of crystallite’s size t is about 6.15 nm. It presents a characteristic of crystalline particles, and XRD analysis with the sol-gel films showed that with the annealed duration increases, NiO crystallization degree and the grain size has been greatly enhanced, resulting a deterioration of uniformity in the film’s surface, which is bad for its electrochromic properties. 3.4 Use x-ray diffraction to identify the structure of NiO film annealed in different temperature In this work, nickel oxide films were made by using sol-get process. “0.5 M nickel acetate tetrahydrate [Ni(CH3COO)2 4H2O (99%)] was dissolved in absolute ethylalcohol. The solution was stirred in a closed vessel at 313K until a very clear transparent solution (green color) was obtained. The sol was left to cool firstly in the ordinary atmosphere, after that, the sol was kept into the refrigerator for 24 h to allow the gelation process. “[‑ ] Finally, what is the most important, these27 sample films were prepared and annealing in different temperatures for 15 mins, MASC 534 HUIJIAN TIAN !15
  16. 16. and these temperatures are 673, 693, 713 and 733 K. After getting sample films, the work is to get x-ray diffraction pattern and analysis the structure of NiO films, including calculating the grain size. The X-ray diffractometer use CuK radiation, which wavelength is 1.54 angstrom[‑ ]. Following figure 7 is x-ray diffraction28 pattern of NiO films at different annealing pattern: From this pattern, it is obvious that all four kinds of NiO films show a crystal nature, and there are three main characteristic diffraction peaks, which corresponding to (111), (200), and (220) crystalline plane. The corresponding MASC 534 HUIJIAN TIAN !16 Figure 7: NiO films prepared at different annealing temperature. (a) 673 K; (b) 693 K; (c) 713 K and (d) 733 K
  17. 17. crystalline plane can be derived by Bragg’s law. To a cubic system, the planar spacing d is given by the following equation: Then we get the formation of Bragg’s law: The right side of this equation is always a constant to any X-ray diffraction pattern. In this pattern, the Bragg angels corresponding to three peaks are 37.1, 43.1, 62.9, so the ratio of square sine Bragg angel value is 0.364:0.467:0.792. If we turn this ratio to integer, the ratio is approximate 3:4:8. There are only three possibilities in cubic systems except for diamond lattice, and the following figure 8 shows Miller indices, and we know that NiO films are simple cubic structure. As the annealing temperature increasing, the intensity of diffraction peaks increases, indicating the degree of crystallization of NiO increase. Use Scherrer’s equation to calculate the crystallite’s size corresponding to (200) crystalline plane, where the wavelength of X-ray is 0.154 nm. Along with the increasing of B1/2 (the full width at half its maximum intensity), the crystallite’s size t will decrease, and dislocation density is inversely proportional to the value of t. The result is that with the annealing temperature’s increase, the dislocation MASC 534 HUIJIAN TIAN !17
  18. 18. density decreases, which means a better quality of NiO films formed in a higher annealing temperature. Conclusion: In this paper, electrochromism’s theory basis has been discussed and the anodic electrochromic material NiO has been analyzed particularly. X-ray diffraction is introduced to analysis the structure of NiO films. When it comes to sol-gel process to prepare NiO films, different annealing temperature and different annealing durations have an impact on NiO films’ structure, and X-ray diffraction patterns show that with the annealed duration increases, NiO MASC 534 HUIJIAN TIAN !18 Figure 8
  19. 19. crystallization degree and the grain size has been greatly enhanced; and with the annealing temperature’s increase, the dislocation density decreases, which means a better quality of crystal structure.
 MASC 534 HUIJIAN TIAN !19
  20. 20. References "X-ray Crystallography." Wikipedia. October 18, 2014. Accessed October 23, 2014.1 Solarska R, Alexander BD, Augustynsci J. C R Chim 2006;9:301–6.2 Granqvist CG. Handbook of inorganic electrochromic materials. Amsterdam: Elsevier; 1995 reprinted3 2002. "Nickel(II) Oxide." Wikipedia. October 19, 2014. Accessed October 23, 2014.4 Ferreira, F. "Electrochromic Nickel Oxide Thin Films Deposited under Different Sputtering5 Conditions." Solid State Ionics: 971-76. Kamal H, Elmagharby EK, Ali SA, Abdel-Hady K. J Cryst Growth 2004;262:424–34.6 Bouessay I, Rougier A, Moscovici J, Michalowicz A, Tarascon JM. Electrochim Acta 2005;50:3737–45.7 Sasi B, Gopchandran KG, Manoj PK, Koshy P, Prabhakara Rao P, Vaidyan VK. Vacuum 2003;68:149–8 54. He Z, Ji Z, Zhao S, Wang C, Liu K, Ye Z. Sol Energy 2006;80:226–30.9 C.G. Granqvist, Handbook of Inorganic Electrochromic Materials, Elsevier, Amsterdam, The10 Netherlands, 1995. Jiang S. R., Yan P. X., Feng B. X., et al. The response of a NiOx thin film to a step potential and its11 electrochromic mechanism. Materials Chemistry and physics, 2002, 77(02): 384~389. 殷顺湖, 徐健. 灵巧窗电致变⾊色复合薄膜﹑器件及应⽤用. 材料导报, 1995, 6: 70~75.12 Granqvist, Claes G. "Oxide Electrochromics: An Introduction to Devices and Materials." Solar Energy13 Materials and Solar Cells: 1-13. Joint Committee of Powder Diffraction Standard, Powder Diffraction File, International Center for14 Diffraction Data, Swarthmore, PA,1954, Card 4-0838. Granqvist, Claes G. "Oxide Electrochromics: An Introduction to Devices and Materials." Solar Energy15 Materials and Solar Cells: 1-13. Granqvist, Claes G. "Oxide Electrochromics: An Introduction to Devices and Materials." Solar Energy16 Materials and Solar Cells: 1-13. 胡恒亮,穆祥祺.X射线衍射技术.北京:纺织⼯工业出版社,1990.17 Waseda, Yoshio, and Eiichiro Matsubara. X-Ray Diffraction Crystallography Introduction, Examples18 and Solved Problems. Berlin: Springer, 2011. 114 Waseda, Yoshio, and Eiichiro Matsubara. X-Ray Diffraction Crystallography Introduction, Examples19 and Solved Problems. Berlin: Springer, 2011. 123 MASC 534 HUIJIAN TIAN !20
  21. 21. Waseda, Yoshio, and Eiichiro Matsubara. X-Ray Diffraction Crystallography Introduction, Examples20 and Solved Problems. Berlin: Springer, 2011. 123. Waseda, Yoshio, and Eiichiro Matsubara. X-Ray Diffraction Crystallography Introduction, Examples21 and Solved Problems. Berlin: Springer, 2011. 125. Sawaby, A., M.s. Selim, S.y. Marzouk, M.a. Mostafa, and A. Hosny. "Structure, Optical and22 Electrochromic Properties of NiO Thin Films." Physica B: Condensed Matter: 3412-420. G.B. Williamson, R.C. Smallman, Philos. Mag. 1 (1956) 34.23 Purushothaman, K.k., and G. Muralidharan. "Enhanced Electrochromic Performance of Nanoporous24 NiO Films." Materials Science in Semiconductor Processing: 78-83. Purushothaman, K.k., and G. Muralidharan. "Enhanced Electrochromic Performance of Nanoporous25 NiO Films." Materials Science in Semiconductor Processing: 78-83. Purushothaman, K.k., and G. Muralidharan. "Enhanced Electrochromic Performance of Nanoporous26 NiO Films." Materials Science in Semiconductor Processing: 78-83. Sawaby, A., M.s. Selim, S.y. Marzouk, M.a. Mostafa, and A. Hosny. "Structure, Optical and27 Electrochromic Properties of NiO Thin Films." Physica B: Condensed Matter: 3412-420. Sawaby, A., M.s. Selim, S.y. Marzouk, M.a. Mostafa, and A. Hosny. "Structure, Optical and28 Electrochromic Properties of NiO Thin Films." Physica B: Condensed Matter: 3412-420. MASC 534 HUIJIAN TIAN !21

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