Structural Characterization of Nanocrystalline Titania

I- Purpose/Objective:


The goals of this laboratory are to:

  • Study the collection and analysis of x-ray diffraction patterns to determine crystal structure and other properties of powder samples
  • Learn and practice techniques for powder diffraction analysis
  • Investigate the phase transformation and grain growth of nanocrystalline TiO2 using x-ray powder diffraction and scanning electron microscopy

II - Experimental Procedure:

A. Week I:

  1. An x-ray diffraction training session for all students will be presented first.
  2. Heat treatment of nanocrystalline titania powder. Students will heat treat powder samples at 600, 800 and 1000oC. All samples will be treated for one hour.
  3. Disks consisting of 0.5g of as-received TiO2 powder will be compacted with a pressure of 180 MPa for later sintering studies. One set of compacted samples will be sintered at 800oC for two hours and the second set will be sintered at 1000oC for two hours. (Arrangements may need to be made to perform the sintering after hours).
  4. A powder diffraction analysis of as received material will be performed.


B. Week II:

  1. X-ray diffraction patterns of as as-received powders will be analyzed using the Hannawalt Powder Diffraction Files.
  2. X-ray diffraction of thermally treated powders from Week I.
  3. Volume measurement of sintered compacts to determine extent of sintering as a function of sintering temperature.


C. Week III:

  1. Scanning electron microscopy of TiO2 compacts, and measuring the density of sintered compacts
  2. Completion of diffraction analyses.


D. Suggested Line of Reasoning

  1. From your diffraction pattern
    1. Measure all peak 2θvalues
    2. Estimate σ2θ, or estimate a minimum and maximum value plausible for 2θ to get an idea of the accuracy of the measurement.
    3. Measure the full width at half maximum (FWHM) for the rutile 110 reflection and the anatase 101 reflection.
    4. Measure the intensities of all peaks. (Don’t forget to subtract background intensities.)
  2. For each peak, calculate d spacing, σd (or minimum and maximum plausible d spacing) and relative intensity (Ipeak/Imax). You may use the equation below for σd.  Sort the information from Step 2 in order of decreasing intensity.
    Nanotitania Equation 1

  3. Identify peaks that belong to the rutile and anatase phases, respectively.
  4. Compare the relative intensities measured with the values found in JCPDS cards.
  5. Determine the impurity peaks if any exist.
  6. Determine the weight fraction of the rutile phase in each powder sample using the following equation, where IR and IA are the intensities of the rutile (110) reflection and the anatase (101) reflection, respectively.  Determine the average grain size of as-received powder and heat-treated powders
    Nanotitania Equation 2
    Nanotitania Equation 3
  7. Compare the average grain size of as-received powder with the value calculated from the SSA.

III - Theory/Background Information:

X-ray diffraction can be used to identify the chemical composition of an unknown or the specific crystal structure of a known material. In the powder diffraction technique, monochromatic radiation strikes a sample with a large number of randomly oriented grains. The generated diffraction pattern shows the d-spacings of the planes of the crystal. The d-spacings and relative intensities of the peaks usually allow the determination of the chemical identity and the volume fraction of mixed phases. The width of the peaks depends on the dimension of crystallites and thus can be used to determine the mean grain size of powder samples.


Three titania (TiO2) crystalline phases are found in nature: anatase (tetragonal), brookite (orthorhombic), and rutile (tetragonal). Of these phases, rutile is stable at all temperatures, while anatase and brookite are metastable and are usually formed at low temperatures. The formation of the anatase phase is more kinetically and thermodynamically favored than brookite formation. Therefore, the crystalline titania powder synthesized by low temperature processing techniques is usually a mixture of anatase (majority) and rutile phases (small fraction). The anatase phase will transform into the stable rutile phase over the entire temperature range between 400 and 1000oC, depending on factors such as powder preparation methods, atmosphere, and impurity levels. Since rutile is the only stable phase, the anatase to rutile phase transformation is irreversible.


Nanocrystalline titania powder used in this lab was synthesized by flame spray pyrolysis of a titanatrane complex, which is a mixture of anatase and rutile phases. The crystal density is 3.84 g/cm3 for anatase and 4.26 g/cm3 for brookite. The specific surface area (SSA) of this powder is 35 ± 5 m2/g. In this lab, we will use x-ray diffraction to determine the weight fraction of the rutile phase in the as-received powder and to study the anatase to rutile phase transformation using powders heated to different temperatures. The average grain size will be determined using the Debye-Scherrer method. The grain growth of nanocrystalline compacts will be studied using SEM.


IV - Theory/Background References:

Copies of these will be available in the Van Vlack Lab  or on the website:

  1. Cullity, B. D. , Elements of X-ray Diffraction, Addison-Wesley Publishing Co., Inc., Reading, MA, 1978.
  2. C. R. Bickmore, et al., "Ultrafine Titania by Flame Spray Pyrolysis of a Titanatrane Complex," J. Eur. Ceram. Soc. 18, 287-297 (1998).
  3. W. D. Kingery, et al., Chapter 10 in "Introduction to Ceramics," John Wiley & Sons, New York, 1976.
  4. Presentation to Class by Jose Azurdia.

V- Activity Schedule:

  • Week I:
    An x-ray diffraction training session for all students will be presented first.

    1. Heat treatment of nanocrystalline titania powder. Students will heat treat powder samples at 600, 800 and 1000°C.  All samples will be treated for one hour.

    2. Disks consisting of 0.5g of as-received TiO2 powder will be compacted with a pressure of 180 MPa for later sintering studies.  One set of compacted samples will be sintered at 800 °C for two hours and the second set will be sintered at 1000 °C for two hours. (Arrangements may need to be made to perform the sintering after hours).

    3. A powder diffraction analysis of as received material will be performed.

  • Week II:

    1. X-ray diffraction patterns of as as-received powders will be analyzed using the Hannawalt Powder Diffraction Files.

    2. X-ray diffraction of thermally treated powders from Week I.

    3. Volume measurement of sintered compacts to determine extent of sintering as a function of sintering temperature.

  • Week III:

    1. Scanning electron microscopy of TiO2 compacts, and measuring the density of sintered compacts.

    2. Completion of diffraction analyses.


VI -Format and Important Questions for Lab Report:

The written lab report will follow the standard format and grading scheme.

  1. What is the structure and composition of the as-received nanocrystalline TiO2 powder?

  2. What is the weight fraction of the rutile phase in each powder sample?

  3. What is the average crystallite size of each powder sample (determined by x-ray diffraction)?

  4. Compare the average crystallite size of the as-received nano-powder determined by x-ray diffraction with the value calculated from the SSA. Explain similarities or differences that you discover.

  5. What is the density of each sintered compact?

  6. What is the volume shrinkage during sintering (at 800 and 1000oC)? Explain the change in volume and its temperature dependence. What is the grain size of sintered compacts (at 800 and 1000oC)? Explain why grain size might vary with sintering temperature.