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The growth mechanism and synthetic controls for colloidal multinary metal chalcogenide nanocrystals (NCs) involving alkali metals and the pnictogen metals Sb and Bi are unknown. Sb and Bi are prone to form metallic nanocrystals that stay as impurities in the final product. Herein, we synthesize colloidal NaBi1–xSbxSe2–ySyNCs using amine–thiol–Se chemistry. We find that ternary NaBiSe2NCs initiate with Bi0nuclei and an amorphous intermediate nanoparticle formation that gradually transforms into NaBiSe2upon Se addition. Furthermore, we extend our methods to substitute Sb in place of Bi and S in place of Se. Our findings show the initial quasi-cubic morphology transforms into a spherical shape upon increased Sb substitution, and the S incorporation promotes elongation along the <111> direction. We further investigate the thermoelectric transport properties of the Sb-substituted material displaying very low thermal conductivity and n-type transport behavior. Notably, the NaBi0.75Sb0.25Se2material exhibits an ultralow thermal conductivity of 0.25 W·m–1·K–1at 596 K with an average thermal conductivity of 0.35 W·m–1·K–1between 358 and 596 K and a ZTmaxof 0.24.

We have developed a new method for synthesizing mono- and bimetallic two-dimensional selenophosphates by using a reactive flux technique with powder precursors dissolved in a P2Se5melt. This method allows us to bypass the difficulties commonly encountered in synthesizing these materials. M2P2Se6(M = Mn, Fe, Cr, Cd, Mg, and Zn) and bimetallic MM′P2Se6(M = Cu, Ag; M′ = Cr, In) powders were synthesized over 60 h using a P2Se5reactive flux. As a further demonstration of potential optimization, Mn2P2Se6powder with minor MnSe impurity was synthesized in 30 min. Reactions of Mn and Cr in P2Se5flux were analyzed in situ using variable-temperature powder X-ray diffraction to investigate the formation reaction pathways, suggesting single-step formation of Cr2P2Se6at 775 °C and formation of Mn2P2Se6at 575 °C through an intermediate MnSe phase. Follow-up experimental syntheses generated crystals of the monometallic family M2P2Se6(M = Mn, Fe, and Cd) and bimetallic family MM′P2Se6(M = Li, Cu, Ag; M′ = Cr, In) with area dimensions of several square millimeters using heating profiles of just over 60 h. The homogeneity of bimetallic selenophosphates MM′P2Se6was confirmed using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Rietveld refinement. The crystallinity of the selected materials was characterized by transmission electron microscopy and atomic force microscopy measurements. The work functions of flakes were determined and ranged from 5.25 to 5.72 eV.

Control of polytypism in colloidal nanocrystals allows for a shape evolution from 0D to 3D and also provides an opportunity to tailor physical properties that are crystal phase dependent. Initiating polytypism in nanostructures is a function of multiple different control parameters that dictate nucleation and growth, including reaction temperature, ligands, and precursors. This is further complicated as the number of metal ions increases in progressing from binary to ternary to quaternary compositions. Here, a synthesis method with dual injections is developed to initiate two- and three-dimensional polytypism in the nonstoichiometricαβδ CuαZnβSnγSeδsystem simply by changing a single commercially available chemical precursor. Synthesis parameters were developed to grow single-crystal wurtzite and zinc-blende forms with a further extension to linear and branched morphologies deriving from nucleation in one phase and growth termination in the other. Photoluminescence measurements were carried out on the particles at a low temperature with emission peaks ranging from ∼1.93 to ∼2.32 eV observed.

CuZnSe2(CZSe) is an important ternary semiconductor comprised of earth-abundant elements with a suitable bandgap for visible light absorption and structural/stoichiometric versatility that make it a promising candidate for photovoltaic applications. Here we report the controlled synthesis of the compound copper chalcogenide in nanocrystal form using a colloidal hot injection approach. Furthermore, we demonstrate control over the crystal phase to occur as either wurtzite (WZ) or zinc blende (ZB) as a function of the presence and absence of phosphine-based ligands. A major emission peak was observed at ∼1.7 eV using low-temperature photoluminescence (PL), ranging from 30 to 200 K. Additionally, we demonstrate the ability to extend this synthetic protocol to form a polytype structure comprised of a ZB core with a WZ shell.

Herein, we report the synthesis and complete structural characterization of curved CuIn1–xGax(S1–ySey)2(x= y= 0.5) nanocrystals, which adopt a two-dimensional (2D) nanoplate morphology and crystallize in the hexagonal wurtzite phase. A detailed transmission electron microscopy (TEM) analysis reveals that the 2D nanoplates are predominately [001]-oriented and exhibit a unique bend contour pattern, because of curvature on the (001) basal plane. The contrast behavior of bend contours in this system is further supported through specimen-tilting experiments inside TEM, in combination with dark-field imaging in both TEM and scanning TEM modes. This bending is believed to originate from the proximity effect of the top and bottom (001) surfaces.