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High Resolution Powder Diffractometer - BT-1

The BT-1 high resolution powder diffractometer
Credit: Craig Brown

The BT-1 high resolution powder diffractometer

The BT-1 high-resolution neutron powder diffractometer is used to to obtain neutron powder diffraction data for crystallographic analysis by the Rietveld method or other characterization purposes. It is a 32 detector instrument that can be used with three different monochromators and two different incident Soller collimators, allowing the instrument response to be tailored to the needs of the experiment. The instrument can be used with furnaces, refrigerators and cryostats so that data may be collected at temperatures from 0.3 to 2000 K, and with magnet fields. For room-temperature data collection, a six-position sample changer is available.

The BT-1 instrument may be used for academic and proprietary measurements (Requests or Mail-in Proposals are made through your IMS account). While there is no fee associated with use of BT-1 for work that will be published in the open literature, Federal regulations require cost-recovery for proprietary work.

 

Specifications/Capabilities

Choice of Monochromator and Collimator

The choice of three focusing monochromators, Ge(311), Cu(311), and Ge(733), and either a 60', 15' or a 7' in-pile Soller collimator allows optimization of the instrument's resolution minimum versus relative diffraction intensities. All monochromators give data up to 165 degrees in 2 theta range.

  • The Ge(311) monochromator yields the highest neutron intensity and best resolution at low scattering angles. This monochromator has a takeoff angle of 75o and produces neutrons with wavelength 2.079 Å. Diffraction intensities are approximately three times that obtained with the Cu(311) monochromator. Typical data collection times range from 15 minutes to a few hours, depending on sample size and diffraction properties. The Ge(311) monochromator has been used for zeolite materials where high-angle diffraction measurements are not needed. It is also useful for studies of magnetic ordering and phase changes.
  • The Cu(311) monochromator is appropriate for the majority of samples, offering an optimal balance between intensity and resolution and a perfect gaussian line shape. This monochromator has a takeoff angle of 90o and produces neutrons with a wavelength 1.540 Å. Typical data collection times range from 1 to 12 h, averaging 3-4 h. The Cu(311) monochromator has been used with 15' collimation to collect data for Rietveld refinement of the structures of a wide variety of materials, including high Tc superconductors, fullerenes, ceramics, and intermetallics, as well as for determining phase fractions in multiphase powders.
  • The Ge(733) monochromator provides the best resolution at high scattering angles, but longer data collection times are needed, often from 4 to 24 h. This monochromator has a takeoff angle of 120o and produces neutrons with wavelength 1.197 Å. Diffraction intensities are approximately 25% of what is obtained with the Cu(311) monochromator. The Ge(733) monochromator is used for study of materials such as perovskites where a subtle lowering of the unit cell symmetry requires separation of reflections at high angles or where precise determination of oxygen vacancies is desired. With 7' collimation, gaussian line shapes with widths (FWHM) as small as 10' (delta d/d = 8 x 10-4) are observed but for most samples the intrinsic sample broadening exceeds the instrumental resolution. Thus, use of the Ge(733) monochromator is restricted to those applications where highest resolution is clearly needed and where samples are available in sufficient quality and quantity.

 

Scientific Opportunities/Applications

Beamtime Requests

For collaborative access to the diffractometer, please contact an instrument scientist or Craig Brown.

Mail-in Sample Service

The mail-in service is offered to everyone but is aimed at those with relatively 'basic' needs. By 'basic' we really mean we will collect data at room temperature, or within the temperature range of a closed-cycle fridge (5-300 K). The service began in April 2007 and, since then, has given good data to its many users. Each cycle, 25% of beamtime is allocated to mail-in service samples.

How it works

As a user you would make and package all samples in your laboratory and, when ready, send them to Craig Brown. A member of the crystallography team takes care of the samples and prepares them for neutron powder diffraction analysis.

All users must submit a proposal using the NIST IMS system and, once accepted, samples can be mailed to the address provided. Please be sure to choose the correct sample environment ('none' = 'room temp' data collection; 'CCR' will allow you to choose suitable temperatures in the 5K-300K range). Also, indicate that you are requesting the mail-in service when submitting a proposal.

If you see the need for more significant efforts on behalf of the Diffraction team, please consider that collaborations and beamtime requests are also available, and there is a possibility of obtaining very rapid access this way. E-mail Craig Brown to discuss options.

Once your beamtime has been allocated, you will be contacted to discuss your requirements for beamtime. With every sample the instrument scientists will do their best to give advice for the most appropriate conditions, use of the instrument and use of NCNR equipment as possible. At the end of discussions it is the user (you) who can make the final decision.

Advantages of using the mail-in service:

  • Users do not have to make their own trip to the NCNR to bring samples
  • Users do not have to sit at the instrument waiting and checking results
  • Users can view data online - view current BT-1 data
  • Within reason, users can use the expertise of the instrument scientist to design experiments.
  • All BT-1 data is examined by the instrument scientist
  • All correct data is converted to an appropriate format (standard is .gsas files for use with data refinement) and emailed to the user. Various other data file conversions are also available.
  • Samples can be stored at the NCNR with the appropriate instrument scientist until the user requests them for further experimental work OR users can request their return.
  • Users can requests samples to be returned at any point and the instrument scientist will take care to unload the samples under, and into, appropriate conditions for packaging and return. As always samples will need time after requesting their return to measure any activity within the sample for safety of transportation. This will take at least one week.

Disadvantage of using the mail-in service:

  • When running a sample the user will not be here at the instrument to make changes. While the instrument scientist will work to give the best results, if something unexpected occurs with the sample or the equipment during beamtime, the instrument scientist may not be able to make the correct decision on how the user would like to adjust the experiment. While the user will still get results at the end of running they may not perfectly be as wanted. So if, as a user, you feel you have very specific experiment details which may be awkward to plan and maintain, it may not be the service for you. Contact the instrument scientist with questions.

If you are interested in using this service you can submit a proposal directly by clicking here. It is very important that you indicate in the proposal that you are requesting the mail-in service.

If you have questions about the service please contact us

Proprietary Research using BT-1

The BT-1 diffractometer is available for proprietary research on a cost recovery basis. The cost depends on the amount of involvement needed from NIST personnel, but will generally be about $3000 per 24 hour period. There is no charge, however, for non-proprietary research performed by either industrial or academic users. For research to be considered non-proprietary, the participants must be willing to present their results in the literature in a timely fashion.

Proprietary Agreements

Contracts are prepared by the Industrial Partnerships Program in the Office of Technology Partnerships . For further information on establishing a proprietary research agreement, contact Craig Brown.

Scheduling Experiments

Organizations that have executed an appropriate proprietary research agreement may request time on the same expedited basis as other users via the Web-based NCNR proposal system.

Proprietary Information

When requests are made for proprietary research using BT-1, we need sufficient information to evaluate any safety hazards that may be related to the proposed experiment. However, do not include any proprietary information in the request. If NIST must be informed of proprietary information in order to evaluate the safety hazards of your experiment, contact Craig Brown by phone (301-975-5134) to discuss the nature of this information before communicating it to NIST.

Acknowledgements

It is expected that publications arising from guest researcher experiments, i.e., those publications that do not have an author at the NIST Center for Neutron Research, will include the following acknowledgement:  "We acknowledge the support of the National Institute of Standards and Technology, U. S. Department of Commerce, in providing the neutron research facilities used in this work."

 

It is very important that all publications containing experimental results from data collected at BT-1 be cited in the NIST Center for Neutron Research annual report. For publications that do not involve a coauthor at the NCNR, please be sure to send the citation information for your publication (reprints and preprints are appreciated) by e-mail (ncnraccess@nist.gov), fax (301-975-2351).

Created March 5, 2019, Updated September 6, 2019