1. X-ray diffraction spectra during in situ annealing of FCZ glass
Relating Optical Properties to Nanostructure Jacqueline A. Johnson, University of Tennessee Space Institute, DMR
Aim of the Project: The aim of the project is to understand the structure property relationship in fluorochlorozirconate (FCZ) glasses in order to increase photoluminescence and photo-stimulated luminescence for applications in mammography, homeland security and solar up- and down-conversion. Research Results: The Advance Photon Source at Argonne National Laboratory was used to conduct in situ x-ray diffraction (XRD) experiments to follow the nucleation, growth and phase transformations of fluorochlorozirconate (FCZ) glass. These FCZ glasses are a class of material based on ZBLAN glasses, which are being developed for uses in advance mammography systems. The FCZs of interest have been doped with Eu (II) for use as either a scintillator or a storage phosphor material, but need to be partially crystalline to function with the desired optical property. The optical properties depends on the crystal structure of the nucleated BaCl2 nanocrystals. By following different heat treatments in situ with XRD it was found that the hexagonal BaCl2 nanocrystals nucleated at ~220°C, which was previously thought to occur at ~260°C. The BaCl2 nanocrystals continue to grow until undergoing a phase transformation from hexagonal to orthorhombic at 280°C. This phase transformation results in a change of optical function from scintillation to storage phosphor. Additionally, the time required for the phase transition and nucleation of the nanocrystals was highly dependent on the heat treatment. Significance of the Results: Identifying the nucleation and phase transformation temperatures prompts new heat treatments to control the nanocrystalline size and phase. The different heat treatments can help determine whether the nucleation and phase transformation are diffusion or interface controlled processes. Furthermore, compositional changes could show significant variation in the nucleation and phase transformation indicating the dominate elements for the process. Additional electron microscopy to view the nanocrystals during the different stages of nucleation and growth will help indicate the constraints for phase transformation between the hexagonal and orthorhombic BaCl2 phase. Acronyms and symbols: XRD = X-ray Diffraction FCZ = fluorochlorozirconate
The Advanced Photon Source at Argonne National Laboratory was used to study the annealing process in fluorochlorozirconate (FCZ) glass-ceramics. In situ x-ray diffraction experiments showed that nucleation of hexagonal BaCl2 nanocrystals occurs at 220C, a process previously thought to occur at 260C. The nanocrystals continue to grow until undergoing a phase transformation from hexagonal to orthorhombic at 280C, resulting in a change in optical properties from scintillation to x-ray storage.
Schematic showing nucleation and growth of the nanocrystals; (a) nucleation and (b) growth of hexagonal BaCl2; (c) phase transformation to orthorhombic; (d) growth of orthorhombic BaCl2. Color corresponds to photoluminescence from 365 nm excitation.
X-ray diffraction spectra during in situ annealing of FCZ glass
2θ [deg] 10 12 16 18 14

2. Chemical Correlation to Structure Jacqueline A
Chemical Correlation to Structure Jacqueline A. Johnson, University of Tennessee Space Institute, DMR
Aim of the Project:
The aim of the project is to understand the structure property relationship in fluorochlorozirconate (FCZ) glasses in order to increase photoluminescence and photstimulated luminescence for applications in mammography, homeland security and solar up- and down-conversion.
Research Results:
Transmission electron microscopy (TEM) investigations of Fluorochlorozirconate (FCZ) glass have led to the discovery of previously unreported BaF2 in the face-centered-cubic (FCC) and orthorhombic phases. These FCZ glasses are a class of materials based on ZBLAN glasses, which are being developed for use in advanced mammography systems. The FCZs of interest have been doped with Eu (II) for use as either a scintillator or a storage phosphor material but need to be partially crystalline to show good optical properties. The nanobeam diffraction (NBD) analysis on individual nanocrystals indicates that both the BaF2 and BaCl2 nanocrystals are present in the glass. Additionally, the nanocrystals were identified using energy-filtered TEM (EFTEM) maps, which identified the presence of Ba and Cl. The maps showed that not all areas with concentrations of Ba had a Cl signal, meaning they were BaF2 nanocrystals. The nanocrystals nucleate and grow through-out the glass matrix when annealing FCZ glasses, therein producing a nanocomposite glass-ceramic system. The traditional BaCl2 orthogonal phase in addition to the unreported FCC and orthogonal BaF2 phase have been found in multiple ZBLAN compositions in which the content of Cl and F has been varied. This indicates that annealing FCZ glasses produces polymorphic crystals of both BaCl2 and BaF2, which vary in size from 10 nm to 100 nm.
Significance of the Results:
The new crystalline phases found in the FCZ glass leads to questions about their influence on the optical properties as a scintillator and storage phosphor, and specifically as to their influence on the location of the dopant Eu within the material, which has been thought to reside within and around the BaCl2 crystals. Beyond their macroscopic optical influences, understanding the effect that the formation of these different phases has on the nucleation, growth and phase transformation of the primary BaCl2 crystals is required. Additional in-situ heating experiments at high resolution to view the nucleation and growth process could help describe the conditions needed for phase transformation between the hexagonal and orthorhombic BaCl2 phase.
Related Publication:
Alvarez, Liu, Leonard, Johnson and Petford-Long J. American Ceramic Soc. 1 5 (2013). DOI: /jace.12540
Acronyms and symbols:
FCZ = Fluorochlorozirconate TEM = Transmission electron microscopy NBD = Nanobeam diffraction EFTEM = Energy-filtered transmission electron microscopy
Transmission electron microscopy (TEM) including nanobeam diffraction (NBD) were used to identify nanocrystals in partially crystallized fluorochlorozirconate (FCZ) glass (which shows novel optical behavior). The nanocrystals form as randomly-oriented spheroids up to 150 nm in size. NBD patterns show both orthorhombic BaCl2 and face-centered cubic BaF2 nanocrystals.
Energy-filtered TEM (EFTEM) maps were used to confirm the nanocrystal composition. BaCl2 nanocrystals in the bright field TEM image can be identified from the Ba and Cl maps. Some of the nanocrystals do not show a Cl signal, which shows that they are BaF2.
The optically active dopant, Eu, has been associated with both the BaF2 and BaCl2 nanocrystals, suggesting that both influence the optical behavior. a b a c c b
Dark field TEM image of nanocrystals in FCZ. The circles indicate locations of corresponding NBD patterns
Bright field TEM image of FCZ annealed at 305°C for 5 min, EFTEM map of Ba M peak (orange), and EFTEM map of Cl M peak (green).
Alvarez, Liu, Leonard, Johnson and Petford-Long, J. American Ceramic Soc. 1 5 (2013)

3. Summer Intern Program Jacqueline A
Summer Intern Program Jacqueline A. Johnson, University of Tennessee Space Institute, DMR
For the last three years UTSI has run a summer intern program. The program is multifaceted in that it aims to provide a real research experience to prospective graduate students, promote diversity, educate and market graduate school. Over the years we have averaged 50% females and minority students. The students range in educational level from high school to seniors in college. The interns undergo a lecture course, laboratory instruction and training in literature searches before being assigned to a research project. During the course of the summer the students help write a journal article, prepare a proposal, give a presentation, obtain career advice, as well as participate in social activities. a b a c c b