Negative-pressure polymorphs made by heterostructural alloying

Abstract

Mixing materials with different crystal structures leads to new phases that otherwise would require negative pressure to be made.

Accessing Metastability in Heterostructural Semiconductor Alloys

“…Here the different polymorph ordering in the endmember compounds A and B results in steeper slopes of the mixing enthalpies in the respective ground state structures α and β (see Figure B). This, in turn, can lead to a higher degree of stabilization for the high‐energy polymorph γ. Utilizing this design principle we recently reported on the stabilization of a new, high‐energy low‐density MnSe 1‐ x Te x wurtzite polymorph by alloying of the higher density MnSe‐RS and MnTe‐NC compounds . In this work we demonstrate that the WZ polymorph is stabilized at intermediate alloying concentration due to a local minimum in mixing enthalpy compared to the endmember structures.…”

“…In the same way that structural transitions are observed in heterostructural alloys (see Figure D), it is possible that entirely new phases emerge at intermediate alloying concentrations that are not observed in the endmember materials. If a material exhibits polymorphism, a polymorph which is unstable for the pure compound can become energetically favorable upon alloying with another material …”

“…The false color plots show the theoretical prediction and experimental validation from first‐principles calculations and XRD measurements, respectively. Adapted with permission . Copyright 2018, AAAS.…”

“…In addition, the phase screening of metastable heterostructural alloys using high‐throughput combinatorial experiments is discussed alongside recent examples of band gap tuning in such systems. Finally, it is described how differences in mixing enthalpies for different structures can be utilized to stabilize new alloy polymorphs with useful properties that cannot be found in either of the alloying endmembers . This conceptual approach can be applied to other materials, which motivates the future screening of high‐throughput computational databases, potentially revealing numerous materials systems where such novel metastable polymorphs can be discovered.…”

A combinatorial guide to phase formation and surface passivation of tungsten titanium oxide prepared by thermal oxidation

“…In an effort to accelerate the discovery and development of advanced materials computational data from first principles has been made available for many materials systems in online repositories, including W-Ti-O 19 . Recently, high-throughput combinatorial experiments have been used for an accelerated screening of synthesis-phase-diagrams in a variety of material systems [21][22][23][24][25] . This type of phase diagram screening is typically performed using non-equilibrium physical vapor deposition (PVD) techniques 25,26 , which often results in homogeneous alloy samples with high miscibility 27,28 .…”