Magnetism and Thermoelectric Properties of the Zintl Semiconductor: EuZnAs.

Compositional diversity and intriguing structural features have made Zintl phases excellent candidates as thermoelectric materials. Zintl phase with 21-4-18 composition has shown high thermoelectric performance in the mid- to high-temperature ranges. The complex crystal structure and favorable transport properties of these compounds indicate the potential for high thermoelectric efficiency.

Colloidal synthesis of two-dimensional nanocrystals by the polyol route.

The field of 2D nanomaterials is ever-growing with a myriad of synthetic advancements that have been used to obtain such materials. There are top-down, as well as bottom-up, fabrication methods for obtaining 2D nanomaterials; however, synthesis of 2D nanomaterials from solution offers a simple scalable way to control size, shape, and surface. This review outlines the recent advances in colloidal polyol synthesis of 2D nanomaterials and provides perspectives on the similarities and differences in various syntheses.

Into the Void: Single Nanopore in Colloidally Synthesized BiTe Nanoplates with Ultralow Lattice Thermal Conductivity.

BiTe is a well-known thermoelectric material that was first investigated in the 1960s, optimized over decades, and is now one of the highest performing room-temperature thermoelectric materials to-date. Herein, we report on the colloidal synthesis, growth mechanism, and thermoelectric properties of BiTe nanoplates with a single nanopore in the center. Analysis of the reaction products during the colloidal synthesis reveals that the reaction progresses via a two-step nucleation and epitaxial growth: first of elemental Te nanorods and then the binary BiTe nanoplate growth.

High Thermoelectric Performance in 2D SbTe and BiTe Nanoplate Composites Enabled by Energy Carrier Filtering and Low Thermal Conductivity.

Thermoelectrics are an important class of materials with great potential in alternative energy applications. In this study, two-dimensional (2D) nanoplates of the layered chalcogenides, SbTe and BiTe, are synthesized and composites of the two are investigated for their thermoelectric properties. The two materials, SbTe and BiTe, were synthesized as hexagonal, 2D nanoplates via a colloidal polyol route.

β-Phase YbSbH: Magnetic and Thermoelectric Properties Traversing from an Electride to a Semiconductor.

An electride is a compound that contains a localized electron in an empty crystallographic site. This class of materials has a wide range of applications, including superconductivity, batteries, photonics, and catalysis. Both polymorphs of YbSb (the orthorhombic CaSbF structure type (β phase) and hexagonal MnSi structure type (α phase)) are known to be electrides with electrons localized in 0D tetrahedral cavities and 1D octahedral chains, respectively.

Impact of Lu-Substitution in YbLuZnSb: Thermoelectric Properties and Oxidation Studies.

YbZnSb is one of the newest additions to the high-performance YbMSb (M = Mn, Mg, and Zn) family of p-type high-temperature thermoelectric materials and shows promise for forming passivating oxide coatings. Work on the oxidation of rare earth (RE)-substituted YbREMnSb single crystals suggested that substituting late RE elements may form more stable passivation oxide coatings. YbLuZnSb ( = 0.

Zintl Phases: From Curiosities to Impactful Materials.

The synthesis of new compounds and crystal structures remains an important research endeavor in pursuing technologically relevant materials. The Zintl concept is a guidepost for the design of new functional solid-state compounds. Zintl phases are named in recognition of Eduard Zintl, a German chemist who first studied a subgroup of intermetallics prepared with electropositive metals combined with main-group metalloids from groups 13-15 in the 1930s.

Experiment and Theory in Concert To Unravel the Remarkable Electronic Properties of Na-Doped EuZnSnAs: A Layered Zintl Phase.

Low-dimensional materials have unique optical, electronic, mechanical, and chemical properties that make them desirable for a wide range of applications. Nano-scaling materials to confine transport in at least one direction is a common method of designing materials with low-dimensional electronic structures. However, bulk materials give rise to low-dimensional electronic structures when bonding is highly anisotropic.

In Science Journals.

Highlights from the family of journals.

Atomic-scale in situ observation of electron beam and heat induced crystallization of Ge nanoparticles and transformation of Ag@Ge core-shell nanocrystals.

Crystallization of amorphous materials by thermal annealing has been investigated for numerous applications in the fields of nanotechnology, such as thin-film transistors and thermoelectric devices. The phase transition and shape evolution of amorphous germanium (Ge) and Ag@Ge core-shell nanoparticles with average diameters of 10 and 12 nm, respectively, were investigated by high-energy electron beam irradiation and in situ heating within a transmission electron microscope. The transition of a single Ge amorphous nanoparticle to the crystalline diamond cubic structure at the atomic scale was clearly demonstrated.

Thermoelectric Properties of BaEuZnSb, a Zintl Phase with One-Dimensional Covalent Chains.

The compound BaZnSb has been predicted to be a promising thermoelectric material, potentially achieving > 2 at 900 K due to its one-dimensional chains of edge-shared [ZnSb] tetrahedra and interspersed Ba cations. However, the high air sensitivity of this material makes it difficult to measure its thermoelectric properties. In this work, isovalent substitution of Eu for Ba was carried out to make BaEuZnSb in order to improve the stability of the material in air and to allow characterization of thermal and electronic properties of three different compositions ( = 0.

Single-Crystalline Germanium Nanocrystals via a Two-Step Microwave-Assisted Colloidal Synthesis from GeI.

Colloidal germanium (Ge) nanocrystals (NCs) are of great interest with possible applications for photovoltaics and near-IR detectors. In many examples of colloidal reactions, Ge(II) precursors are employed, and NCs of diameter ∼3-10 nm have been prepared. Herein, we employed a two-step microwave-assisted reduction of GeI in oleylamine (OAm) to prepare monodispersed Ge NCs with a size of 18.

Tuning the Intermediate Valence Behavior in the Zintl Compound YbZnSb by Incorporation of RE [YbREZnSb (0.2 ≤ ≤ 0.7), RE = Sc, Y, La, Lu and Gd].

The solid solutions of YbREZnSb (RE = Sc, Y, La, Lu, and Gd; 0.2 ≤ ≤ 0.7) were prepared to probe the intermediate valency of Yb in YbZnSb.

Probing High-Temperature Oxidation of Thermoelectric Phases YbSb ( = Mg, Mn, Zn).

YbSb ( = Mg, Mn, Zn) are p-type Zintl phases with high thermoelectric efficiencies at 1000 °C and melting points above 1200 °C under vacuum and/or inert atmosphere. In a thermoelectric generator, even within a vacuum jacket, small amounts of oxygen may be present, and therefore, elucidating chemical reactions in the presence of air or oxygen provides a framework for engineering design. The oxidation of YbSb was investigated from room temperature to 1000 °C in dry air with thermogravimetric/differential scanning calorimetry (TG/DSC) on small pellets and visually after heat treatment to 1000 °C under ambient conditions on large pellets.

Unlocking the thermoelectric potential of the CaAlSb structure type.

YbMnSb and YbMgSb are among the best p-type high-temperature (>1200 K) thermoelectric materials, yet other compounds of this CaAlSb structure type have not matched their stability and efficiency. First-principles computations show that the features in the electronic structures that have been identified to lead to high thermoelectric performances are present in YbZnSb, which has been presumed to be a poor thermoelectric material. We show that the previously reported low power factor of YbZnSb is not intrinsic and is due to the presence of a YbZnSb impurity uniquely present in the Zn system.

Study of the Thermoelectric Properties of BiTe/SbTe Core-Shell Heterojunction Nanostructures.

Thermoelectric materials convert heat energy into electricity, hold promising capabilities for energy waste harvesting, and may be the future of sustainable energy utilization. In this work, we successfully synthesized core-shell BiTe/SbTe (BTST) nanostructured heterojunctions via a two-step solution route. Samples with different BiTe core to SbTe shell ratios could be synthesized by controlling the reaction precursors.

Recent developments in germanium containing clusters in intermetallics and nanocrystals.

Multimetallic clusters can be described as building blocks in intermetallics, compounds prepared from all metals and/or semi-metals, and in Zintl phases, a subset of intermetallics containing metals with large differences in electronegativity. In many cases, these intermetallic and Zintl phases provide the first clue for the possibilities of bond formation between metals and semi-metals. Recent advances in multimetallic clusters found in Zintl phases and nanoparticles focusing on Ge with transition metals and semi-metals is presented.

Solid Solution YbCaCdSb: Structure, Thermoelectric Properties, and Quality Factor.

Solid solutions of YbACdSb (A = Ca, Sr, Eu; ≤ 1) are of interest for their promising thermoelectric (TE) properties. Of these solid solutions, YbCaCdSb has end members with different crystal structures. YbCdSb crystallizes in the polar space group 2, whereas CaCdSb crystallizes in the centrosymmetric space group .

Crystal structure characterization and electronic structure of a rare-earth-containing Zintl phase in the Yb-Al-Sb family: YbAlSb.

A rare-earth-containing compound, ytterbium aluminium antimonide, YbAlSb (CaAlAs-type structure), has been successfully synthesized within the Yb-Al-Sb system through flux methods. According to the Zintl formalism, this structure is nominally made up of (Yb)[(Al)(1b - Sb)(2b - Sb)], where 1b and 2b indicate 1-bonded and 2-bonded, respectively, and Al is treated as part of the covalent anionic network. The crystal structure features infinite corner-sharing AlSb tetrahedra, [AlSbSb], with Yb cations residing between the tetrahedra to provide charge balance.

Deconvoluting the Magnetic Structure of the Commensurately Modulated Quinary Zintl Phase EuSrZnSnAs.

The structure, magnetic properties, and Eu and Sn Mössbauer spectra of the solid-solution EuSrZnSnAs are presented. A new commensurately modulated structure is described for EuZnSnAs (3 space group, average structure) that closely resembles the original structural description in the monoclinic 2/ space group with layers of Eu, puckered hexagonal ZnAs sheets, and ZnAs ethane-like isolated pillars. The solid-solution EuSrZnSnAs (0 < < 10) is found to crystallize in the commensurately modulated 3 space group, related to the parent phase but lacking the mirror symmetry.

Discovery of multivalley Fermi surface responsible for the high thermoelectric performance in YbMnSb and YbMgSb.

The Zintl phases, Yb Sb ( = Mn, Mg, Al, Zn), are now some of the highest thermoelectric efficiency p-type materials with stability above 873 K. YbMnSb gained prominence as the first p-type thermoelectric material to double the efficiency of SiGe alloy, the heritage material in radioisotope thermoelectric generators used to power NASA's deep space exploration. This study investigates the solid solution of YbMg Al Sb (0 ≤ ≤ 1), which enables a full mapping of the metal-to-semiconductor transition.

Structural Insights on Microwave-Synthesized Antimony-Doped Germanium Nanocrystals.

Doped and alloyed germanium nanocrystals (Ge NCs) are potential candidates for a variety of applications such as photovoltaics and near IR detectors. Recently, bismuth (Bi) as an -type group 15 element was shown to be successfully and kinetically doped into Ge NCs through a microwave-assisted solution-based synthesis, although Bi is thermodynamically insoluble in bulk crystalline Ge. To expand the composition manipulation of Ge NCs, another more common -type group 15 element for semiconductors, antimony (Sb), is investigated.

Ambient and High Pressure CuNiSb: Metal-Ordered and Metal-Disordered NiAs-Type Derivative Pnictides.

The mineral Zlatogorite, CuNiSb, was synthesized in the laboratory for the first time by annealing elements at ambient pressure (CuNiSb-AP). Rietveld refinement of synchrotron powder X-ray diffraction data indicates that CuNiSb-AP crystallizes in the NiAs-derived structure (31, #164) with Cu and Ni ordering. The structure consists of alternate NiSb and CuSb octahedral layers via face-sharing.