Zintl phases are promising thermoelectric materials because they are composed of both ionic and covalent bonding, which can be independently tuned. An efficient thermoelectric material would have regions of the structure composed of a high-mobility compound semiconductor that provides the "electron−crystal" electronic structure, interwoven (on the atomic scale) with a phonon transport inhibiting structure to act as the "phonon−glass". The phonon−glass region would benefit from disorder and therefore would be ideal to house dopants without disrupting the electron−crystal region. The solid solution of the Zintl phase, Yb 2−x Eu x CdSb 2 , presents such an optimal structure, and here we characterize its thermoelectric properties above room temperature. Thermoelectric property measurements from 348 to 523 K show high Seebeck values (maximum of ∼269 μV/K at 523 K) with exceptionally low thermal conductivity (minimum ∼0.26 W/m K at 473 K) measured via laser flash analysis. Speed of sound data provide additional support for the low thermal conductivity. Density functional theory (DFT) was employed to determine the electronic structure and transport properties of Yb 2 CdSb 2 and YbEuCdSb 2 . Lanthanide compounds display an f-band well below (∼2 eV) the gap. This energy separation implies that f-orbitals are a silent player in thermoelectric properties; however, we find that some hybridization extends to the bottom of the gap and somewhat renormalizes hole carrier properties. Changes in the carrier concentration related to the introduction of Eu lead to higher resistivity. A zT of ∼0.67 at 523 K is demonstrated for Yb 1.6 Eu 0.4 CdSb 2 due to its high Seebeck, moderate electrical resistivity, and very low thermal conductivity.

We report the synthesis, structure, and magnetic properties of a new Zintl phase and structure type, Eu11Zn4Sn2As12. The structure and composition of this phase have been established by single-crystal X-ray diffraction and electron microprobe analysis. Eu11Zn4Sn2As12 crystallizes in monoclinic space group C2/c (No. 15) with the following lattice parameters: a = 7.5679(4) Å, b = 13.0883(6) Å, c = 31.305(2) Å, and β = 94.8444(7)° [R 1 = 0.0398; wR 2 = 0.0633 (all data)]. The anisotropic structural features staggered ethane-like [Sn2As6]12– units and infinite ∞ 2[Zn2As3]5– sheets extended in the a–b plane. Eu cations fill the space between these anionic motifs. Temperature-dependent magnetic properties and magnetoresistance of this Zintl phase have been studied, and the electronic structure and chemical bonding were elucidated using first-principles quantum chemical calculations (TB-LMTO-ASA). Quantum chemical calculations show that the ethane-like units can be considered as consisting of covalent single bonds; however, the ∞ 2[Zn2As3]5– sheets are best described with delocalized bonding and there is evidence of Eu–As interactions. Temperature-dependent magnetization and transport properties between 2 and 300 K show a ferromagnetic transition at 15 K, a band gap of 0.04 eV, and negative colossal magnetoresistance.

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The Wadsley-Roth phase (W 0.2 V 0.8) 3 O 7 , crystallizing in a structure obtained through crystallographic shear of 3×3×∞ ReO 3 blocks, is a somewhat rare exemplar for this class of compounds in that it contains a relatively small amount of 4d and/or 5d transition elements. Here we demonstrate that it functions as a high-rate, high-capacity material for lithium ion batteries. Electrochemical insertion and de-insertion in micron sized particles made by conventional solid-state preparation and in sub-100 nm particles made by combining sol-gel precursors with freeze-drying methods, indicate good rate capabilities. The materials display high capacity-close to 300 mAh g −1 at low rates-corresponding to insertion of up to 1.3 Li per transition metal at voltages above 1 V. Li insertion is associated with multielectron redox for both V and W observed from ex-situ X-ray photoelectron spectroscopy. The replacement of 4d and 5d elements with vanadium results in a higher voltage than seen in other, usually niobium-containing shear-structured electrode materials, and points to new opportunities for tuning voltage, electrical conductivity, and capacity in compounds in this structural class.

Vacancy-ordered double perovskites are attracting significant attention due to their chemical diversity and interesting optoelectronic properties. With a view to understanding both the optical and magnetic properties of these compounds, two series of Ru IV halides are presented; A 2 RuCl 6 and A 2 RuBr 6 , where A is K, NH 4 , Rb or Cs. We show that the optical properties and spin-orbit coupling (SOC) behavior can be tuned through changing the A cation and the halide. Within a series, the energy of the ligand-to-metal charge transfer increases as the unit cell expands with the larger A cation, and the band gaps are higher for the respective chlorides than for the bromides. The magnetic moments of the systems are temperature dependent due to a non-magnetic ground state with J eff = 0 caused by SOC. Ru-X covalency, and consequently, the delocalization of metal d-electrons, result in systematic trends of the SOC constants due to variations in the A cation and the halide anion. Remarkable developments in perovskite-based photovoltaics over the last decade have driven the discovery of a wide range of new halide perovskites and related solids. [1-4] These include 3D perovskites with different divalent metals (i.e., Pb II and Sn II), [5, 6] 3D double perovskites with a combination of univalent and trivalent metals (i.e., K I /Bi III and Ag I / Bi III), [7, 8] as well as low dimensional 2D, [9] and 1D perovskites. [10] Progress in this area has also rekindled interest in K 2 Pt IV Cl 6-type vacancy-ordered double perovskites, comprising isolated metal halide octahedra interspersed with mono-valent cation. For example, the vacancy-ordered halides of Sn IV , [11] Se IV , [12] Te IV , [13, 14] and Ti IV , [15] have shown to be promising photovoltaic materials. The analogous variants of

Glass and glass-ceramic samples of metastable lithium thiophosphates with compositions of 70Li2S-30P2S5 and Li7P3S11 were controllably prepared by using a rapid assisted-microwave procedure in under 30 min. The rapid preparation times and weak coupling of the evacuated silica ampules with microwave radiation ensure minimal reactivity of the reactants and the container. The microwave-prepared samples display comparable conductivity values with more conventionally prepared (melt quenched) glass and glass-ceramic samples, on the order of 0.1 and 1 mS cm–1 at room temperature, respectively. Rietveld analysis of synchrotron X-ray diffraction data acquired with an internal standard quantitatively yields phase amounts of the glassy and amorphous components, establishing the tunable nature of the microwave preparation. X-ray photoelectron spectroscopy and Raman spectroscopy confirm the composition and the appropriate ratios of isolated and corner-sharing tetrahedra in these semicrystalline systems. Solid-state 7Li nuclear magnetic resonance (NMR) spectroscopy resolves the seven crystallographic Li sites in the crystalline compound into three main environments. The diffusion behavior of these Li environments as obtained from pulsed-field gradient NMR methods can be separated into one slow and one fast component. The rapid and tunable approach to the preparation of high quality “Li7P3S11” samples presented here coupled with detailed structural and compositional analysis opens the door to new and promising metastable solid electrolytes.

MnPtGa crystallizes in the hexagonal Ni2In structure type in space group P 63/mmc, and has been reported to display a ferromagnetic Curie temperature near 220 K. Here we find a transition near TC = 236 K to a ferromagnetic state, albeit with a reduced moment from what is expected for collinear ordering. The peak magnetocaloric entropy change was determined to be ∆SM = −1.9 J kg −1 K −1 for an applied magnetic field of H = 5 T at the ferromagnetic ordering temperature. Magnetostructural coupling manifests as a change in the slope of the thermal expansion coefficients of the c lattice parameter near TC , with a negative spontaneous volume magnetostriction; ω = −300 ppm at 190 K. Neutron powder diffraction studies of the magnetic ground state reveal an evolution in complexity as temperature decreases: from a ferromagnet, to a canted antiferromagnet, to the eventual formation of a spin-density wave state at low temperatures.

Magnetic refrigeration, as well as waste-heat recovery, can be accomplished through the magnetocaloric effect, where temperature changes the magnetic state of a material or vice versa. Promising magnetocaloric materials display large changes in magnetic entropy (∆S M) upon application of a moderate magnetic field, and often associated with magnetic materials possessing some degree of magnetostructural coupling. In such compounds, the magnetic transition is coupled to some structural transition at the ordering temperature, and indicators for these are readily calculated by the magnetic deformation proxy Σ M. MnSb, with a Curie temperature T C = 577 K is has a calculated magnetic deformation of Σ M = 5.9%, and is a promising candidate material for waste-heat recovery. The temperature-dependence of structural, magnetic, and magnetocaloric properties of Mn 1+x Sb, where x is a tunable amount of interstitial Mn, are studied here. Excess Mn is incorporated as an interstitial whose magnetic moment is anti-aligned with the stoichiometric Mn, and the excess Mn has the effect of lowering T C , such that the Curie temperature can be tuned from 577 K to nearly room temperature at 318 K for x = 0.2. For x = 0.0, 0.1, and 0.2, values of ∆S M under a maximum magnetic field H = 5 T are found to be 3.65 J K −1 kg −1 , 3.00 J K −1 kg −1 , and 2.83 J K −1 kg −1 , respectively. While the maximum ∆S M decreases with x, the high refrigerant capacity-a more holistic measure of performance-is retained in this highly tunable system.