Neutrons User Facilities

TOPAZ | BL-12 | SNS

Single-Crystal Diffractometer

TOPAZ BL-12 SNS instrument

Mission Statement

TOPAZ is a high-resolution single-crystal diffractometer using wavelength-resolved Laue technique with an extensive array of neutron time-of-flight area detectors to address structural problems in diverse research areas: chemistry, earth sciences, materials science, engineering, and solid-state physics.

Instrument Description

Experiments can be conducted in ambient conditions or controlled sample environments for parametric study (temperature and electric field). A nitrogen cold stream offers temperature control in the range of 90 K to 450 K or a cryogenic goniometer equipped with a pulsed tube helium compressor offers temperature control in the range of 5 K to 300 K. Variable and static electric fields can be applied for the stroboscopic study of ferroelectric materials. The wide neutron wavelength band is well suited for efficient 3D Q space mapping of Bragg and diffuse scattering originating from magnetic and nuclear interactions simultaneously.

TOPAZ samples can be oriented with high precision for volumetric sampling of Bragg peaks in specific directions. Currently, TOPAZ has 25 of 48 detector ports populated with Anger camera modules covering a scattering angle between 20 and 160° in 2θ, matching 3.2 sr in solid angle coverage. A full dataset for structure analysis can be collected with 4 to 25 settings with an exposure time of about 0.5–5 hours each, depending on the crystal symmetry, sample scattering strength, and crystal size.

Applications

TOPAZ is well suited for determining atomic positions and displacement parameters of light elements (such as hydrogen) next to heavy metals. Moreover, the broad Q coverage makes TOPAZ ideal for studying magnetic structures, phase transitions, disorder, and local structure phenomena. Examples span a wide range of materials:

  • Functional inorganic materials for studying the interplay of nuclear and magnetic structures such as doping-driven structural distortion in iridates; Fe and Co site occupancies in a molecular precursor
  • Hydrogen bonding, guest-host interaction, and guest mobility in hydride perovskites; high-pressure synthesized mantle mineral and self-assembling tertiary amines
  • Catalytic and dihydrogen activation or exchange materials for the study of metal-hydrogen bonding in electrocatalyst and nano-sized copper clusters
  • Accurate atomic position and displacement parameters for charge density study of organic crystals containing a high percentage of hydrogen atoms

Specifications

ModeratorDecoupled poisoned supercritical hydrogen
Source to sample distance18 m
Sample to detector distance, evacuated39 – 46 cm
Detector coverage3.2 sr, 25 detectors
Detector size15 x 15 cm2 with 256 by 256 pixels
Detector angular range20 –160º 2θ; +/- 32° out-of-plane
Wavelength bandwidth3.1 Å
Frame 10.4 – 3.5 Å
Resolution> 0.4% Δd/d
Sample size> 0.05 mm3 in volume and  > 0.1 mm on an edge
d spacing range0.25 Å  – 14  Å
Q range0.45 – 25 Å-1
Neutron beam sizes2.0 – 5.0 mm diameter
Neutron beam divergence on sample15 mrad  – 25 mrad
Sample EnvironmentAmbient goniometer with c fixed at 135° ω: 0°–360° Φ: 0–360° Oxford Cryosystems Cobra 800 open-flow N2 gas stream: 90 – 450 K Cryogenic goniometer with precision motor controls for sample centering ω: 0°–360° Cryogen-free pulse-tube cryocooler with a helium compressor (Cryomech PT415-RM):  5 K – 300 K