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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on BaF2 by Materials Project

BaF2 is Cotunnite structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Ba2+ is bonded in a 9-coordinate geometry to nine F1- atoms. There are a spread of Ba–F bond distances ranging from 2.64–3.10 Å. There are two inequivalent F1- sites. In the first F1- site, F1- is bonded in a 5-coordinate geometry to five equivalent Ba2+ atoms. In the second F1- site, F1- is bonded to four equivalent Ba2+ atoms to form a mixture of edge and corner-sharing FBa4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BaF2 by Materials Project

BaF2 crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Ba2+ is bonded in a 3-coordinate geometry to eleven F1- atoms. There are a spread of Ba–F bond distances ranging from 2.57–3.11 Å. There are two inequivalent F1- sites. In the first F1- site, F1- is bonded to six equivalent Ba2+ atoms to form FBa6 octahedra that share corners with twelve equivalent FBa6 octahedra, corners with twelve equivalent FBa5 trigonal bipyramids, edges with six equivalent FBa6 octahedra, faces with two equivalent FBa6 octahedra, and faces with six equivalent FBa5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 51°. In the second F1- site, F1- is bonded to five equivalent Ba2+ atoms to form distorted FBa5 trigonal bipyramids that share corners with twelve equivalent FBa6 octahedra, corners with eight equivalent FBa5 trigonal bipyramids, edges with six equivalent FBa5 trigonal bipyramids, and faces with six equivalent FBa6 octahedra. The corner-sharing octahedra tilt angles range from 31–59°.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Hadron-Induced Radiation Damage in Fast Heavy Inorganic Scintillators

Fast and heavy inorganic scintillators with suitable radiation tolerance are required to face the challenges presented at future hadron colliders of high energy and intensity. Up to 5 GGy and 5 × 1018 neq/cm2 of one-MeV-equivalent neutron fluence is expected by the forward calorimeter at the Future Hadron Circular Collider. This paper reports the results of an investigation of proton- and neutron-induced radiation damage in various fast and heavy inorganic scintillators, such as LYSO:Ce crystals, LuAG:Ce ceramics, and BaF2 crystals. The experiments were carried out at the Blue Room with 800 MeV proton fluence up to 3.0 × 1015 p/cm2 and at the East Port with one MeV equivalent neutron fluence up to 9.2 × 1015 neq/cm2, respectively, at the Los Alamos Neutron Science Center. Experiments were also carried out at the CERN PS-IRRAD proton facility with 24 GeV proton fluence up to 8.2 × 1015 p/cm2. Research and development will continue to develop LuAG:Ce ceramics and BaF2:Y crystals with improved optical quality, F/T ratio, and radiation hardness.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

Pulsed laser deposition and structural evolution of BaF 2 nanolayers in Eu-doped BaF 2 /Al 2 O 3 layered optical nanocomposite thin films

Here, we have developed a pulsed laser deposition (PLD) geometry for the growth of uniform BaF 2 nanoscale thin films, through control of the deposition conditions. Our goal is to use the BaF 2 layers with controllable structure as component layers in layered optical nanocomposites. The structure of the BaF 2 nanolayer evolves as a function of the layer thickness: BaF 2 grows via a layer-by-layer growth mode on Al 2 O 3 ; the layers are amorphous for a thickness < 3 nm, and then become nanocrystalline as the layer thickness increases. The BaF 2 nanocrystals have an FCC crystal structure with a weak < 111 > texture that becomes stronger for thicker films. We then demonstrate that our BaF2 films can be introduced into layered Al 2 O 3 /BaF 2 /EuO x nanocomposite films, which allows for control of the relative position of the Eu ions and the BaF 2 layer. Cross-section samples of the multilayered films show interfacial intermixing between the layers, which is related to implantation during the PLD process. This intermixing enables the incorporation of Eu ions into BaF 2 layers and form a thin Eu-doped BaF 2 nanolayer at the interface. The layered nanocomposite films show photoluminescence (PL) emission from Eu 3+ ions, and the PL intensity changes can be correlated with the crystallinity and crystal size changes in the BaF 2 layer. Our results provide guidance for achieving thin film nanocomposite materials with controllable structure and photoluminescence behavior for light emitting diodes, photovoltaics and other optical applications.

36 MATERIALS SCIENCE↗