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Sci Adv. 2017 Jun 7;3(6):e1700270. doi: 10.1126/sciadv.1700270. eCollection 2017 Jun.

Novel phase diagram behavior and materials design in heterostructural semiconductor alloys.

Author information

1
National Renewable Energy Laboratory, Golden, CO 80401, USA.
2
Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309, USA.
3
Department of Metallurgical and Materials Engineering, Colorado School of Mines, Golden, CO 80401, USA.
4
Department of Physics, Oregon State University, Corvallis, OR 97331, USA.
5
Applied Energy Programs, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA.
6
Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA.
7
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA.

Abstract

Structure and composition control the behavior of materials. Isostructural alloying is historically an extremely successful approach for tuning materials properties, but it is often limited by binodal and spinodal decomposition, which correspond to the thermodynamic solubility limit and the stability against composition fluctuations, respectively. We show that heterostructural alloys can exhibit a markedly increased range of metastable alloy compositions between the binodal and spinodal lines, thereby opening up a vast phase space for novel homogeneous single-phase alloys. We distinguish two types of heterostructural alloys, that is, those between commensurate and incommensurate phases. Because of the structural transition around the critical composition, the properties change in a highly nonlinear or even discontinuous fashion, providing a mechanism for materials design that does not exist in conventional isostructural alloys. The novel phase diagram behavior follows from standard alloy models using mixing enthalpies from first-principles calculations. Thin-film deposition demonstrates the viability of the synthesis of these metastable single-phase domains and validates the computationally predicted phase separation mechanism above the upper temperature bound of the nonequilibrium single-phase region.

KEYWORDS:

alloy theory; computational materials science; materials design; metastable materials; non-equilibrium materials; phase diagrams; semiconductor alloys

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