#################################################### # Prof. Waltraud M. Kriven # requesting 4 days, at minimum=3 days # beamline 33BM, Atomic pair distribution function study of transition-metal-ion doped 3:2 mullite structure # instrument 33BM-C fourc #################################################### # top:/home/www/beamtime-requests/req01041.txt # UNICAT Member Beam Time Request #1041 # created Fri Aug 25 16:56:56 CDT 2006 #################################################### apsrun: 2006-03 beamline: 33BM collaboration: Yes collaborator_Jenia: ON collaborator_Paul: ON contact: kriven@uiuc.edu days: 4 description: Mullite (Al(2)[Al(2+2x)Si(2-2x)]O(10-x)) is one of the most important mineral and material in crystallography and in ceramic science and technology. The 3:2 mullite (x = 0.25), Al(2)[Al(2.5)Si(1.5)]O(9.75), is considered to be the most stable one amongst others (2:1 mullite for x = 0.40; 3:1 mullite for x = 0.57). It is a strong candidate material for advanced structural applications at high temperature, because it has good chemical stability, creep resistance, high temperature strength and displays low thermal expansion. The 3:2 mullite has a highly stable open structure and it can accommodate a variety of transition metal ions into its structure as solid solution. Our earlier studies using in-situ high temperature X-ray diffraction (HTXRD) have shown that based on the type of the dopant ion and the amount of doping, the modified crystalline phase of mullite displays a range of thermal expansion characteristics. The thermal expansion behavior observed for all the transition-metal-ion doped mullites was found to be linear in the temperature range above ≈ 500ºC. The thermal expansion coefficient along the c-axis appeared to be less dependent on the type and the amount of the dopant transition-metal and varied from alpha-c = 5.9 x 10-6/ºC to 6.8 x 10-6/ºC. With increasing amount of the transition-metal concentration the coefficient of thermal expansion decreased along both the a- and the b-axes. However, a full structural analysis to explain the observed behavior is still incomplete. Various research efforts over the last decade used a variety of characterizing tools, both diffraction and spectroscopic, and were aimed at developing fundamental understanding of the metal-ion-doped mullite structure. Despite the multifaceted approach, these studies were limited in identifying the location of the doped ions in the structure, and lack consensus. We propose to undertake a comprehensive investigation of the metal ion doped 3:2 mullite system using (a) high resolution transmission electron microscopy (HRTEM); (b) X-ray photoelectron spectroscopy (XPS); (c) synchrotron X-ray diffraction (XRD), and d) pair distribution function (PDF) study. In this study the effect of both the type and the quantity of metal-ion doping on the structural modification of the 3:2 mullite, with the general formula Al(2)[Al(2.5-y)M(y)Si(1.5)]O(9.75), will be examined, where M is either Ti, Cr, or Ga. Preliminary work has already been completed. Powder samples of titanium-doped (y = 0.06, 0.12, and 0.18), chromium doped (y = 0.12, 0.24, 0.36, 0.48 and 0.60), and gallium doped (y = 0.12, 0.24, 0.36, 0.48 and 0.60) 3:2 mullite have been synthesized by either the sol-gel or steric entrapment methods. Synchrotron X-ray powder diffraction investigations have shown that while mullite was the only phase formed in the case of Ti-doped and Cr-doped mullites, alumina and silica were also observed for y ≥ 0.24 for Ga-doped mullites. Analysis of the diffraction data using Rietveld method is underway, and so is the sample preparation for HRTEM, and XPS studies. We seek beamtime to complete the PDF study on this material system. Comprehension of the atomic-scale structure is an important prerequisite to understand and predict the properties of materials. The structure of crystalline materials can be studied by traditional x-ray diffraction, however, for imperfect or structures modified by dopant ions, a statistical description of the structure can be adopted to understand their local structure. PDF analysis is one of the most suitable techniques for studying local structure in x-ray amorphous materials and in materials with internal atomic or nanometer scale disorder. It has been successfully applied to study amorphous (glassy) and disordered crystalline materials. This technique holds great potential in the analysis of transition-metal-ion doped mullite systems. The fundamental understanding acquired in the proposed studies is expected to play a critical role in the development of these materials for specific high-technology applications, such as tailorable thermal expansion, etc. For our proposed studies, the powder diffraction data suitable for PDF analysis, should meet the following requirements: (a) extended Q-space range (approx. 22) for probing the modification of structure; (b) good counting statistics to ensure quantitatively reliable structural information; and (c) good signal to background ratio. The above considerations make the use of synchrotron radiation mandatory for our proposed experiments. It is estimated that at least 3 days of beamtime on Beamline 33BM-C will be required to complete the work proposed in this proposal. Such an allocation of beamtime will provide the opportunity to obtain pair distribution functions of Ti, Cr and Ga-doped mullite to allow detailed analysis of transition-metal-ion ordering in 3:2 mullite system. equipment_required: Vortex Detector for Pair Distribution Function study experiment: Atomic pair distribution function study of transition-metal-ion doped 3:2 mullite structure foreign_nationals: Prof. Waltraud M. Kriven (citizen of Australia) Dr. Pankaj Sarin (citizen of India) Wonki Yoon (citizen of Republic of Korea) hazards: None. The samples are inert oxide (aluminosilicates) powders of mullite, and will be mounted in 0.3mm glass capillaries. instrument: 33BM-C fourc instrument_other: minimumdays: 3 name: Prof. Waltraud M. Kriven new_request: ON nonmembers: submit: Submit unacceptable_dates: 10/25/2006 – 10/29/2006; 11/18/2006 – 11/30/2006 z34ID_details: #REMOTE_HOST: mach-177.mse.uiuc.edu #REMOTE_ADDR: 128.174.228.177 #CONTENT_LENGTH: 6075 #HTTP_REFERER: http://www.uni.aps.anl.gov/admin/unireq.html #HTTP_USER_AGENT: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)