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Nanocrystals with rationally tailored morphologies and properties are a thriving research field. The phase-change material (PCM) germanium telluride (GeTe) has recently been synthesized in a plethora of nanocrystalline forms and morphologies, but a mechanistic understanding of these experimental findings has been largely missing so far. Here, we present comprehensive dispersion-corrected density functional theory (DFT-D) simulations of the low-index crystal facets of GeTe and how they interact with relevant ligand molecules. These results enable a systematic understanding of experimental findings regarding GeTe nanocrystals and clarify the origin of the broad range of particle shapes observed. This study also affords semiquantitative signposts assisting future synthetic studies of nanocrystalline PCMs. [ABSTRACT FROM AUTHOR]

Germaniumtelluride (GeTe) is an iconic functional material, bothin itself and as the parent compound for a range of ternary phase-changedata-storage alloys. Long taken to be a “simple” ABcompound, crystalline GeTe is today known to contain a large numberof germanium vacancies which directly affect the material’smacroscopic properties. Here, we use atomistic simulations to elucidatelocal mechanisms behind the motion of Ge atoms (and thus, vacancydiffusion) in crystalline GeTe. Transition pathways are computed usingthe nudged elastic band (NEB) approach at the gradient-corrected levelof density-functional theory (GGA-DFT), both for the idealized rhombohedral(R3m) crystal and a number of defectiveconfigurations. Besides obvious structural arguments (i.e., beyonda simple rigid-sphere model), the diffusion barriers show a delicatedependence on the material’s electronic structure. The latteris controlled by vacancy formation, Sb adatoms, and charge injection,all of which is discussed in a unified framework. [ABSTRACT FROM AUTHOR]

Tellurium-based phase-change materials (PCMs) enable applications from optical and electronic data storage to thermoelectrics and plasmonics, which all demand precise control of electronic properties. These materials contain an unusually large number of vacancies: "stoichiometric" ones that stem from the chemical composition and "excess" vacancies that act like classical dopants. Here we show how both types of vacancies can be controlled independently in the solid solution Sn(Sb1-xBix)2Te4. We vary x in small steps over the entire compositional range and show that this has a profound effect on the material's electronic nature: remarkably, we observe a change from p- to n-type conduction at x ≈ 0.7, solely controlled by composition. Our findings lead to a new compositionally (that is, chemically) tunable materials platform that enables precise control of electrical properties. [ABSTRACT FROM AUTHOR]