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Branton Campbell in the lab

Branton J. Campbell

Professor

Department of Physics & Astronomy

Brigham Young University

Provo, UT 84602, USA

Tel: 801-422-5758, Fax: 801-422-0553

Email: branton_campbell[at]byu.edu

//physics.byu.edu/faculty/campbell/

Research Interests

I apply state-of-the-art x-ray and neutron scattering techniques to study local and long-range structures in a variety of complex solids, including fast-ion conductors, ferroelectric relaxors, high-temperature superconductors, and colossal magnetoresistive manganites, where nanoscale structural features influence macroscopic physical properties. This includes the development of symmetry-mode analysis as a tool for the determination, refinement and interpretation of distorted structures involving lattice strains, atomic displacements, magnetic moments and occupational orderings at both commensurate and incommensurate wavevectors.

(3+d)-Dimensional Superspace Groups

Wave-like modulations with non-lattice periodicities accompany a variety of important physical phenomena (e.g. magnetism and superconductivity). Though such a material is not properly crystalline in three dimensions, it does have a regular crystal lattice in a higher dimensional superspace. The superspace symmetry groups in (3+1), (3+2) and (3+3) dimensions have now been exhaustively tabulated, which will make it easier to solve modulated structure and understand their properties.

NMR study of ammonium magnesium langbeinite

Branton J. Campbell, Harold T. Stokes, and Juliana Boerio-Goates

Recent studies have shown that ammonium langbeinites have low-temperature phase transitions uncharacteristic of the rest of the langbeinite family. In this study, proton NMR spin-lattice relaxation times T1 and spin-spin relaxation times T2 for powder samples of (NH4)2Mg2(SO4)3 are reported in the temperature range from 77 to 373 K. The ammonium ions occupy two different kinds of sites in the crystal. The measured barrier to thermally activated ammonium reorientations is found to be 2.0 and 3.3 kcal/mol for the two sites, respectively. Additionally, there is no observable discontinuity in T1 at the reported phase transition at 161 K, in agreement with heat-capacity studies, suggesting that the transition mechanism may be different from those of most langbeinites.

Goldhelox: A Soft X-Ray Solar Telescope

D. S. Durfee, J. W. Moody, K. D. Brady, C. Brown, B. Campbell, M. K. Durfee, D. Early, E. Hansen, D. W. Madsen, D. B. Morey, P. W. A. Roming, M. B. Savage, P. F. Eastman, and V. Jensen

The Goldhelox Project is the construction and use of a near-normal incidence soft x-ray robotic solar telescope by undergraduate students at Brigham Young University. Once it is completed and tested, it will be deployed from a Get-Away-Special (GAS) canister in the bay of a space shuttle. It will image the sun at a wavelength of 171-181Å with a time resolution of 1 sec and a spatial resolution of 2.5 arcsec. The observational bandpass was chosen to image x-rays from highly ionized coronal Fe lines. The data will be an aid in better understanding the beginning phases of solar flares and how flaring relates to the physics of the corona-chromosphere transition region. Goldhelox is tentatively scheduled to fly on a space shuttle sometime in 1995 or 1996. This paper outlines the project goals, basic instrument design, and the unique aspects of making this an undergraduate endeavor.

Exploitation of pseudo-symmetry in the Cambridge Structural Database for molecular ferroelectric discovery

Harold T. Stokes and Branton J. Campbell (et al.)

The search for new useful molecular ferroelectrics is a non-trivial problem. We present the application of an automated symmetry-searching method (FERROSCOPE) to the Cambridge Structural Database (CSD) in order to identify polar structures with a closely-related non-polar phase. Such structures have the possibility of undergoing a polarization-switching phase transition thus forming a ferroelectric-paraelectric pair. FERROSCOPE successfully identifies this relationship in 84% of a curated list of 156 known molecular ferroelectrics from the literature and identifies an additional 17 000 potentially ferroelectric compounds in the CSD. Our analysis shows that the method identifies CSD structures which have potentially been described in incorrect space groups, extending previous analyses. We describe experimental case studies which reveal phase transitions in two polar systems predicted to have related non-polar phases.

Small-angle rigid-unit modes requiring linear strain compensation

Bryce T. Eggers, Harold T. Stokes, and Branton J. Campbell

Group-theoretical and linear-algebraic methods and tools have recently been developed that aim to exhaustively identify the small-angle rotational rigid-unit modes (RUMs) of a given framework material. But in their current form, they fail to detect RUMs that require a compensating lattice strain which grows linearly with the amplitude of the rigid-unit rotations. Here, we present a systematic approach to including linear strain compensation within the linear-algebraic RUM-search method, so that any geometrically possible small-angle RUM can be detected.

A recapitulation of magnetic space groups and their UNI symbols

B. J. Campbell and H. T. Stokes (et al.)

The mathematical structure, description and classification of magnetic space groups is briefly reviewed, with special emphasis on the recently proposed notation, the so-called UNI symbols [Campbell et al. (2022). Acta Cryst. A78, 99–106]. As illustrative examples, very simple magnetic space groups from each of the four possible types are described in detail.