We have searched ∼40 000 fully ordered, main-group containing solids in the Inorganic Crystal Structural Database and ∼13 000 structures of the American Mineralogist Crystal Structure Database to identify compounds containing a transition metal or a rare-earth kagome sublattice, a geometrically magnetically frustrated lattice, ultimately identifying ∼500 materials. A broad analysis of the chemical and structural trends of these materials shows three types of kagome sheet stacking and several classes of magnetic complexity. Following the search and classification, we rapidly screen the magnetic properties of a subset of the materials using density functional theory to eliminate those that are unlikely to exhibit magnetic frustration. From the results of our computational screening, we rediscover six materials that have previously been explored for their low-temperature magnetic behavior, albeit showing symmetry breaking distortions, spin glass behavior, or magnetic ordering. However, all are materials with antiferromagnetic behavior, which we correctly predict. Finally, we also report three materials that appear to be unexplored for their magnetic properties.
Ternary chalcogenide semiconductors (e.g., CuInTe2, AgInTe2, AgGaTe2, Hg2GeTe4) have significant potential for excellent thermoelectric performance if appropriately doped. However, the efficacy of extrinsic dopants in these materials varies widely based...
We use a random forest (RF) model to predict the critical cooling rate (R C) for glass formation of various alloys from features of their constituent elements. The RF model was trained on a database that integrates multiple sources of direct and indirect R C data for metallic glasses to expand the directly measured R C database of less than 100 values to a training set of over 2000 values. The model error on 5-fold cross-validation (CV) is 0.66 orders of magnitude in K/s. The error on leave-out-one-group CV on alloy system groups is 0.59 log units in K/s when the target alloy constituents appear more than 500 times in training data. Using this model, we make predictions for the set of compositions with melt-spun glasses in the database and for the full set of quaternary alloys that have constituents which appear more than 500 times in training data. These predictions identify a number of potential new bulk metallic glass systems for future study, but the model is most useful for the identification of alloy systems likely to contain good glass formers rather than detailed discovery of bulk glass composition regions within known glassy systems.
AMX compounds with the ZrBeSi structure tolerate a vacancy concentration of up to 50 % on the M‐site in the planar MX‐layers. Here, we investigate the impact of vacancies on the thermal and electronic properties across the full EuCu1−xZn0.5xSb solid solution. The transition from a fully‐occupied honeycomb layer (EuCuSb) to one with a quarter of the atoms missing (EuZn0.5Sb) leads to non‐linear bond expansion in the honeycomb layer, increasing atomic displacement parameters on the M and Sb‐sites, and significant lattice softening. This, combined with a rapid increase in point defect scattering, causes the lattice thermal conductivity to decrease from 3 to 0.5 W mK−1 at 300 K. The effect of vacancies on the electronic properties is more nuanced; we see a small increase in effective mass, large increase in band gap, and decrease in carrier concentration. Ultimately, the maximum zT increases from 0.09 to 0.7 as we go from EuCuSb to EuZn0.5Sb.
Recent discoveries of materials with ultralow thermal conductivity open a pathway to significant developments in the field of thermoelectricity. Here, we conduct a comparative study of three chemically similar antimonides to establish the root causes of their extraordinarily low thermal conductivity (0.4–0.6 W m–1 K–1 at 525 K). The materials of interest are the unconventional type-XI clathrate K58Zn122Sb207, the tunnel compound K6.9Zn21Sb16, and the type-I clathrate K8Zn15.5Cu2.5Sb28 discovered herein. Calculations of the phonon dispersions show that the type-XI compound exhibits localized (i.e., rattling) phonon modes with unusually low frequencies that span the entire acoustic regime. In contrast, rattling in type I clathrate is observed only at higher frequencies, and no rattling modes are present in the tunnel structure. Modeling reveals that low-frequency rattling modes profoundly limit the acoustic scattering time; the scattering time of the type-XI clathrate is half that of the type-I clathrate and a quarter of that of the tunnel compound. For all three materials, the thermal conductivities are additionally suppressed by soft framework bonding that lowers the acoustic group velocities and structural complexity that leads to diffusonic character of the optical modes. Understanding the details of thermal transport in structurally complex materials will be crucial for developing the next generation of thermoelectrics.
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