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Center Highlights

The highlights here document the progress and impact of scientific research within the Center for Next Generation of Materials Design. Most of these highlights are associated with published journal articles by our principal investigators.
Pourbaix diagram with pH on x-axis and radius on y-axis. Eight different-shaped and different-colored regions are shown within the square plot, each labeled with the phase composition.

Non-Equilibrium Crystallization Pathways of Manganese Oxides in Aqueous Solution

Revealing the metastable energy landscape of Pourbaix diagrams helps to rationalize multistage crystallization pathways of transition-metal oxides from solution.

Map that shows grid of colors—various shades of blue, green, light red—in square cells within the grid.

A Map of the Inorganic Ternary Metal Nitrides

Constructed first comprehensive stability map of inorganic ternary metal nitrides to understand chemical origins of stability and to predict new nitrides, along with corresponding synthetic routes to realize them.

Schematic of crystal structure containing purple, green, and blue balls, and includes an identification key to the balls.

Discovery of a Metastable Photoactive Semiconductor Zn2SbN3

Zn2SbN3 was theoretically predicted and experimentally synthesized—the first Sb-based nitride and a photoactive semiconductor.

Plot showing vivid-colored regions—red along left edge, blue along bottom edge, and orange, yellow, and green filling the space in between.

Ternary Nitride Semiconductors in the Rocksalt Crystal Structure

Discovered new class of MgxTM1-xN (TM = Ti, Zr, Hf, Nb) nitrides that bridges properties and structures found in common nitride materials families.

AFM tomography image of domain formation on poling in MAPbI3 crystal.

The Existence and Impact of Persistent Ferroelectric Domains in MAPbI3

Methylammonium lead iodide (MAPbI3) exhibits exceptional photovoltaic performance. But a significant controversy remains over the existence and impact of ferroelectricity on the photovoltaic response. We confirm ferroelectricity in MAPbI3 single crystals and demonstrate mediation of the electronic response by ferroelectric domain engineering.

Quantitative predictive theory plot shows wurtzite single-phase structure at intermediate composition.

Negative-Pressure Polymorphs via Heterostructural Alloying

For some heterostructural alloys, a metastable low-density polymorph can be the preferred structure for non-phase-separated intermediate compositions. For the MnSe-MnTe system, where this effect was predicted theoretically, the low-density metastable wurtzite phase was successfully synthesized using non-equilibrium thin-film growth.

Plot of normalized probability versus change in Gibbs energy. Curve builds upward quickly in upper left and drops moderately to lower right. Several colored areas under the curve are shown, with colors keyed to an inset of four curves.

Physical Descriptor for the Gibbs Energy of Inorganic Crystalline Solids and Temperature-Dependent Materials Chemistry  December 2018

Developed a machine-learned descriptor enabling the chemically accurate high-throughput prediction of temperature-dependent thermodynamics (<40 meV/at MAE).

Plot of reaction time versus q, with sketch to right showing phase fraction from 0 to 100 % for three phases

Understanding Crystallization Pathways in MnO2 Polymorphs   June 2018

Demonstrated predictive synthesis of MnO2 polymorphs based on principle of remnant metastability—that synthesizable metastable phases nucleate under thermodynamic conditions where they were once the lowest free-energy phase, and then grow into conditions where they are metastable. Using in-situ X-ray diffraction measurements, we verify that this framework can predict which phases are more likely to form as well as the progression order of phases.

Plot of theoretically predicted stable wurtzite Zn3MoN4.

Materials Design Using Redox-Mediated Stabilization (May 2018)

New, stable and metastable Zn-Mo-N alloys with wurtzite-derived crystal structure were theoretically predicted and experimentally synthesized. A broad range of properties—from insulating and transparent Zn3MoN4 to conductive and absorptive ZnMoN2—is realized by tuning the composition.

Plot of relative intensity versus Raman shift, showing a black experimental brookite curve above a blue reference brookite curve, with highest peaks to the left side.

Amorphous Precursors: A Route to Polymorph Synthesis (January 2018)

Using theory-guided synthesis, we have synthesized TiO2 thin films with greater than 80% brookite fraction without substrate templating or the presence of helper ions via solid-phase crystallization of amorphous precursors.

Line illustration showing star that indicates formation energy of metastable nitrogen-rich nitride within convex hull

Thermodynamic Routes to Novel Metastable Nitrogen-Rich Nitrides  (December 2017)

We formulate how reactive nitrogen precursors can stabilize metastable nitrogen-rich nitrides during synthesis. With this synthesis strategy, we use DFT to predict 22 new nitrogen-rich binary nitrides stabilizable under ΔµN2 = +1 eV/N.

Plot of substrate temperature versus x in (Sn1-xTix)3N4, showing experimentally measured resistivities.

Design of Metastable Tin Titanium Nitride Semiconductor Alloys  (November 2017)

We predicted and synthesized new mixed-metal nitride alloys with improved optoelectronic properties. Specifically, we synthesized metastable (Sn,Ti)3N4 spinels using non-equilibrium synthesis. These (Sn,Ti)3N4 alloys have lower hole effectives masses and better transport than Sn3N4.

Temperature vs composition diagram showing several different-colored regions

Heterostructural Alloying — A Design Tool to Improve Functionality (October 2017)

Metastable (SnCa)Se with improved thermoelectric functionality was realized by combining theory-guided alloying with non-equilibrium growth.

Three crystal illustrations.

A Framework for Automating Point-Defect Calculations  (September 2017)

We completed and rigorously validated an open-source Python framework to automate first-principles point-defect calculations.

Plot of PROPhet gap versus GW gap, showing blue linear cloud of points from lower left to upper right, and two ammonia molecules (blue ball connected to three smaller silver balls), one in upper left with arrow pointing to lower end of cloud.

Framework for Coupling Machine Learning and Ab Initio Approaches (June 2017)

Developed computational framework for using neural networks to learn analytical potentials, non-linear density functionals, and structure-property relationships based on high-accuracy ab initio data. Demonstrated use of neural networks to create easily evaluated local DFT charge-density functionals for range of properties for model gas-phase system, NH3.

Phase diagram with pH on vertical axis and mu (Mg+) on horizontal axis. Six regions shown on plot: MnO2, MnOOH, Mn3O4, MgMnsO4, MgMnO2, and Mn2+.

Phase Selection in MnO2 Structures During Aqueous Growth  (May 2017)

We rationalized the synthesis of all common MnO2 polymorphs by forming off-stoichiometric intermediates during aqueous synthesis. We also derived general rules governing off-stoichiometric polymorph stabilization by alkali ions and hydration applicable to transition metal oxide chemistries.

Phase diagram with ORC region along left side, spinodal decomposition region in the lower half and upper left quadrant, metastable region in the upper right quadrant, and RS region in the right uppermost corner.

Novel Phase Diagram Behavior in Heterostructural Alloys  (April 2017)

We discovered wide metastable regions in the phase diagram of heterostructural alloys. The materials lie above the phase-separated free-energy minimum, but are stable against spinodal composition fluctuations.

Transmission electron micrograph of epitaxial Mg0.25Ca0.75O on indium aluminum nitride. Image is gray background with rows of light-colored dots, with blue-dashed box around a section of the image, including 'indium aluminum nitride' label..

ALD Oxides for Higher Performance Power Transistors (February 2017)

Successfully grew single-crystalline (Mg,Ca)O films epitaxially on InAlN transistors with unprecedentedly low density of defects and electron traps at the oxide/semiconductor interface.

Circular image with hexagonal orange pattern on dark background. Large orange dots at apices of hexagon and smaller orange/yellow ovals inside of hexagon. Vertical color scale from 2.0 to 4.5 to right of circle.

Structure Property Relationships in Wide-Gap Gallium Oxide Thin Films  (January 2017)

Successfully determined the synthesis space (substrate temperature, oxygen partial pressure, substrate selection) for the targeted growth of β-Ga2O3 thin films through theory-guided experiments. Grew high-quality, oriented β-Ga2O3 films.

Chart of Median Lattice Cohesive Energy vs Energy above Ground State, showing 11 horizontal bars of varying length and color (Groups V, VI, and VII)

The Thermodynamic Scale of Inorganic Crystalline Metastability  (Dec 2016)

Revealed the thermodynamic landscape of inorganic crystalline metastability. Proposed principle of Remnant Metastability: "Observable metastable phases are remnants of thermodynamic conditions where they were once the lowest free-energy phase."

Illustration of film/base layer/substrate stack with light wave incident on top of stack from the right and emitted electron going toward detector to the left.

Accelerated in-situ Photo-Electron Spectroscopy for Materials by Design  (Nov 2016)

Characterized the interfacial electronic band alignment using new high-throughput measurements by coupling spatially resolved photoelectron spectroscopy (PES) mapping with combinatorially deposited crossed-gradient thin-film samples.

Plot of intensity versus Q, showing two curves that generally slope downward from the upper left to the lower right, with one spike upwards in the middle of the slope.  One curve is for a 2-hertz sample and the other curve is for a 10-hertz sample.

Local Amorphous Structure Controls Polymorph Formation  (October 2016)

Used grazing incidence X-ray scattering measurements to identify local structural differences in amorphous thin-film precursors that subsequently determine the polymorph formed upon crystallization.

Block diagram with blue layer over red layer and labels indicating energy sources.

Epitaxial Polymorph Stabilization through a Computational Approach to Substrate Selection (May 2016)

Developed a computational framework combining calculations of formation energy, elastic strain energy, and topological lattice matching to guide substrate selection for epitaxial materials growth.

Graphic of energy on y axis and reaction coordinate on x axis. Chart, labeled Nitrides, shows two deep troughs in left and central and one higher shallow trough in right section of chart. Dotted red arrow goes from left deep trough to central deep trough.

Design of Nitride Semiconductors for Solar Energy Conversion (April 2016)

We provide a new perspective on the promising properties, unexplored chemistry, and metastable character of nitride semiconductors for solar energy conversion.

Crystal diagram of bismuth triiodide, with bismuth as smaller blue circles and iodine as larger purple circles. Each bismuth atom is surrounded by five iodine atoms.

MnO2 Polymorph Energetics — A Unique Theoretical Challenge (March 2016)

Through a collaboration with the Center for Computational Design of Functional Layered Materials EFRC, we have established that the new, non-empirical, SCAN (Strongly Constrained and Appropriately Normed Semilocal Density Functional) exchange-correlation functional for density functional theory provides a uniquely accurate first-principles model of polymorph energetics and properties.

Crystal diagram of bismuth triiodide, with bismuth as smaller blue circles and iodine as larger purple circles. Each bismuth atom is surrounded by five iodine atoms.

Bismuth Triiodide (BiI3) – A Candidate Photovoltaic Absorber  (December 2015)

We identified BiI3 as a candidate photovoltaic absorber using computational design criteria based on the methyl ammonium lead iodide perovskites. Initial experiments demonstrate room-temperature photoluminescence with application-relevant lifetimes.

Ball-and-stick figure for rutile, with several central green balls (titanium plus-3 charge complex) surrounded by smaller red (oxygen atom) and gray (titanium atom) balls.

Transition Metal Oxide Semiconductors  (Sept 2015)

Comprehensive assessment of semiconducting transition metal oxides using unbiased electronic structure calculations with integrated treatment of s, p, and d electrons.

Plot of potential energy surface with each polymorph (P0 through P5) having its own basin of attraction.

Predicting Polymorphism in Partially Ionic Solids (Aug 2015)

We developed a theoretical approach to search for new and realizable metastable polymorphs in ionic systems.

Triangular diagram of s-orbital versus p-orbital versus d-orbital fraction at valence band maximum.

Identifying Defect-Tolerant, High-Lifetime Semiconductors (May 2015)

The key role that band-edge orbital character has on defect tolerance (gained from MAPbX3 perovskites) underlies a new joint data-mining and theory approach to screen materials for long minority-carrier lifetimes, which is a critical photovoltaic absorber property.

Optical properties of Sn3N4, showing three curves (experiment, theory without excitons, and theory with excitons) on plot of absorption coefficient vs energy.

Semiconducting Metastable Sn3N4 and IV3N4 Polymorphs

Thin films of the metastable spinel γ-Sn3N4 were synthesized by sputtering and characterized for semiconducting properties, such as absorption spectra, electrical transport, ionization potential, and minority-carrier diffusion length.

Plot of enthalpy versus AX compounds.

The Center for Next Generation of Materials Design: Mission and Research Plan

The mission of the Center for Next Generation of Materials Design is to dramatically transform the discovery of functional energy materials through multiple-property search, incorporation of metastable materials into predictive design, and the development of theory to guide materials synthesis.

Polymorph Sampler will add not-yet-discovered polymorphs to Materials by Design.

Incorporating Metastable Polymorphs into Materials by Design

The Center for Next Generation of Materials Design is creating a high-throughput computational tool based on first-principles theory to predict the formation energy of polymorphs, including new unknown structures.

Plot of temperature (0 to 2000 K) versus MnZnO stoichiometry (x = 0 to 1). Five regions on plot.  Red,

Design of Semiconducting Tetrahedral Mn1-xZnxO Alloys

The Center for Next Generation of Materials Design is designing a novel semiconducting transition metal oxide alloy with absorption in the visible and with favorable electron and hole transport properties.