Capabilities of the HB-3A Instrument

The scientific communities that use the HB-3A instrument include condensed matter physics, chemistry, mineralogy, and materials science. Single-crystal, magnetic, and nuclear structural studies are more robust when using the 3D data collected with this instrument compared to powder diffraction methods. Typical applications of this instrument include studies of magnetic and nuclear structures, high-resolution crystallography, structural phase transitions, and short-range order (i.e., diffuse scattering).

Experiment durations depend on many factors: crystal size, crystal symmetry, unit cell volume, reflection intensities, what information is being sought (full nuclear structure refinement versus determining the magnetic structure), and the number of temperatures of interest. In the best cases, more than 1,000 reflection intensities can be measured in a day.

In the examples below, the number of days it took to complete the HB-3A portion of each experiment is given.

Magnetic structural studies

Order parameters, determining propagation vectors, fitting magnetic scattering data to determine spin arrangement and moments, effects of applied magnetic field, etc. With a dedicated closed-cycle refrigerator mounted on the diffractometer, magnetic structural studies can be undertaken over the temperature range of 4.5 to 450 K.

Examples:

Nuclear structural studies

H or light atom positions, phase transitions, ADP temperature dependence, nuclear density maps, thermal expansion mechanisms, etc. Positions and displacement parameters of light atoms can be particularly well determined compared to using x-ray diffraction. Intensity data are typically collected with omega scans in bisecting mode (omega ~ ½ 2-theta), and the horizontal angular divergence of the incident beam can be adjusted to maximize the scattered intensity.

Examples:

  • Sales, B. C., Chakoumakos, B. C., Lin, R., Thompson, J. R., and Mandrus, D.," Structural, magnetic, thermal, and transport properties of X8Ga16Ge30 (X = Eu, Sr, Ba) single crystals," Physical Review B 63, 245113-1–245113-8 (2001). 5 days
  • Groat, L. A., Chakoumakos, B. C., Hoffmann, C. M., Morell, H., Fyfe, C. A., and Schultz, A. J., "The amblygonite (LiAlPO4F) – montebrasite (LiAlPO4OH) solid solution: A single-crystal neutron diffraction and Li MAS-NMR spectroscopic study," American Mineralogist 88, 195-210 (2003). 7 days

High-resolution crystallography

Charge density studies, anharmonic ADP modeling, etc. Omega scanning can be done in a non-bisecting mode up to a scattering angle of 155º, which for our 1.00 Å, gives sin Q/l=0.98 Å-1 or Q = 12 Å-1. Data over a large Q-range provide the highest real-space resolution.

Example:

Macchi, P., Iversen, Bo B., Sironi, A., Chakoumakos, B. C., and Larsen, F. K., "Interanionic O-H...O interactions: the charge density point of view," Angewandte Chemie International Edition 39, 2719-2722 (2000). 5 days

Structural phase transformations

Symmetry changes, modulations, etc. The horizontal angular divergence of the incident neutron beam can be reduced by flattening the monochromator and thereby making the high resolution DQ/Q ~ 0.5%. This enables the resolution of small peak splittings due to symmetry changes.

Example:

Marty, K., Christianson, A. D., Wang, C. H., Matsuda, M., Cao, H., VanBebber, L. H., Zarestky, J. L., Singh, D. J., Sefat, A. S., and Lumsden, M. D., "Competing magnetic ground states in non-superconducting Ba(Fe1-xCrx)2As2," Physical Review B (Rapid Communications) 83, 064513 (2011). 2 days

Short-range order (i.e., diffuse scattering)

Detailed mapping of magnetic or nuclear scattering in 1-D, 2-D, or 3-D grids. Reciprocal space scanning can be done along lines or grids. We are testing a 2-D detector that will make this more efficient.

Example:

Frontzek, M., Ehlers, G., Podlesnyak, A., Cao, H., Matsuda, M., Zaharko, O., Aliouane, N., Barilo, S., and Shiryaev, S. V., "Magnetic structure of CuCrO2: a single crystal neutron diffraction study," Journal of Physics: Condensed Matter 24, 016004 (2012). 3 days