Enhanced Thermoelectric Performance of Synthetic Tetrahedrites

Electrical and thermal transport properties of synthetic tetrahedrites Cu₁₀TM₂Sb₄S₁₃ (TM = Mn, Fe, Co, Ni, Zn) and the solid solution Cu_{12–<i>x</i>}Mn_<i>x</i>Sb₄S₁₃ (0 ≤ <i>x</i> ≤ 2) have been studied in the context of thermoelectric performance. Among these materials, the parent compound Cu₁₂Sb₄S₁₃ exhibits the highest power factor, which is primarily derived from a high electrical conductivity. All substituted derivatives display a significant and uniform reduction in thermal conductivity. Within the TM series, the Mn-substituted sample displays the highest ZT (0.8 at 575 K). Changing the Mn concentration to Cu₁₁MnSb₄S₁₃ produces the highest ZT, i.e., 1.13 at 575 K. The relatively high value derives from a favorable balance of low thermal conductivity and a relatively high power factor

Monitoring Photochemical Reaction Pathways of Tungsten Hexacarbonyl in Solution from Femtoseconds to Minutes

Metal–organic complexes are widely used across disciplines for energy and biological applications, however, their photophysical and photochemical reaction coordinates remain unclear in solution due to pertaining molecular motions on ultrafast time scales. In this study, we apply transient absorption and tunable femtosecond stimulated Raman spectroscopy (FSRS) to investigate the UV photolysis of tungsten hexacarbonyl and subsequent solvent binding events. On the macroscopic time scale with UV lamp irradiation, no equilibrated intermediate is observed from W­(CO)₆ to W­(CO)₅(solvent), corroborated by vibrational normal mode calculations. Upon 267 nm femtosecond laser irradiation, the excited-state absorption band within ∼400500 nm exhibits distinct dynamics in methanol, tetrahydrofuran, and acetonitrile on molecular time scales. In methanol, solvation of the nascent pentacarbonyl–solvent complex occurs in ∼8 ps and in tetrahydrofuran, 13 ps which potentially involves the associative oxygen-donating ligand rearrangement reaction. In contrast, a stimulated emission feature above 480 nm emerges after ∼1 ps in acetonitrile with a nitrogen-donating ligand. These structural dynamics insights demonstrate the combined resolving power of ultrafast electronic and stimulated Raman spectroscopy to elucidate photochemistry of functional organometallic complexes in solution. The delineated reaction pathways in relation to ligand nucleophilicity and solvent reorientation time provide the rational design principles for solution precursors in nanowrite applications

Reaction Pathway: Aqueous Hexatantalate Clusters to High-Density Tantalum Oxide Nanofilms

The reaction path from aqueous oxohydroxometalate [(CH₃)₄N]₆[H₂Ta₆O₁₉]·<i>x</i>H₂O to Ta₂O₅ thin film explains observed thin-film morphological characteristics–high density, uniform, pore free, and smooth. Film dehydration and tetramethylammonium thermal decomposition were observed via temperature-programmed desorption. The morphological, structural, and optical properties of the films were examined by X-ray diffraction, X-ray reflectivity, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and spectroscopic ellipsometry. Evolution of (CH₃)₄N⁺ reaction products in concert with condensation of the polyoxometalate clusters and structural relaxation led to film densities as high as 95% of single-crystal β-Ta₂O₅. The process enabled film deposition with single-digit-nanometer thickness

[Sc₂(μ-OH)₂(H₂O)₆(NO₃)₂](NO₃)₂: Aqueous Synthesis and Characterization

[Sc₂(μ-OH)₂(H₂O)₆(NO₃)₂]­(NO₃)₂ has been synthesized from an aqueous scandium nitrate solution by using zinc powder as a reducing agent for nitric acid, which drives an increase in pH and forces the condensation of aqua scandium cations. This preparative route readily produces gram-scale samples with yields near 65%. A single-crystal X-ray diffraction study reveals a structure characterized by a hydroxo-bridged Sc dimer. The FTIR spectrum of the compound has been modeled via ab initio computations, allowing the identification of signature IR peaks. Some initial observations on the thermal transformation of the compound to Sc₂O₃ are also reported

Nb₂O₅ and Ta₂O₅ Thin Films from Polyoxometalate Precursors: A Single Proton Makes a Difference

Thin film materials from water-based precursors follow the principals of green chemistry, leading to a more sustainable future in the energy intensive era in which we currently reside. While simple in practice, aqueous metal-oxide chemistry is complex at the molecular level. Here we develop the first water-based formation of Nb₂O₅ and Ta₂O₅ thin films; utilizing tetramethylammonium salts of [H₂Ta₆O₁₉]^6– and [H₃Nb₆O₁₉]^5– polyoxometalates. Although the clusters are structurally identical group V analogues and differ only by a single proton, this difference has a considerable influence on the quality of the films that are obtained. Through characterization of the solid-state precursor (single-crystal X-ray diffraction), the aqueous precursor solution (X-ray scattering), and the thin films (atomic force and scanning electron microscopies, X-ray diffraction, and reflectivity), we rationalize the important roles of cluster protonation that carry through all chemical processes from the precursor to the metal oxide coating

Chemically Amplified Dehydration of Thin Oxide Films

The hydrous material Al­(PO₄)_0.6O_0.6·<i>z</i>H₂O (AlPO) is studied in thin-film form to determine whether bulk diffusion or near-surface densification controls thermal dehydration. From X-ray reflectivity measurements, a dense surface crust is found to form on heating AlPO films. Capacitance–voltage measurements reveal the presence of mobile protons associated with trapped −OH and H₂O in the films. Deposition of a thin solution-processed HfO₂ top coat on the AlPO film lowers the dehydration temperature by 250 °C. Characterization of the AlPO/HfO₂ interface by medium energy ion scattering and transmission electron microscopy reveals little interdiffusion between the layers. The top coat affects densification of the near-surface region of the AlPO film, thereby amplifying water loss at low temperatures

Role of Combustion Chemistry in Low-Temperature Deposition of Metal Oxide Thin Films from Solution

Metal-oxide thin films find many uses in (opto)­electronic and renewable energy technologies. Their deposition by solution methods aims to reduce manufacturing costs relative to vacuum deposition while achieving comparable electronic properties. Solution deposition on temperature-sensitive substrates (e.g., plastics), however, remains difficult due to the need to produce dense films with minimal thermal input. Here, we investigate combustion thin-film deposition, which has been proposed to produce high-quality metal-oxide films with little externally applied heat, thereby enabling low-temperature fabrication. We compare chemical composition, chemical structure, and evolved species from reactions of several metal nitrate [In­(NO₃)₃, Y­(NO₃)₃, and Mg­(NO₃)₂] and fuel additive (acetylacetone and glycine) mixtures in bulk and thin-film forms. We observe combustion in bulk materials but not in films. It appears acetylacetone is removed from the films before the nitrates, whereas glycine persists in the film beyond the annealing temperatures required for ignition in the bulk system. From analysis of X-ray photoelectron spectra, the oxide and nitrate content as a function of temperature are also inconsistent with combustion reactions occurring in the films. In­(NO₃)₃ decomposes alone at low temperature (∼200–250 °C) without fuel, and Y­(NO₃)₃ and Mg­(NO₃)₂ do not decompose fully until high temperature even in the presence of fuel when used to make thin films. This study therefore distinguishes bulk and thin-film reactivity for several model oxidizer-fuel systems, and we propose ways in which fuel additives may alter the film formation reaction pathway

Amorphous In–Ga–Zn Oxide Semiconducting Thin Films with High Mobility from Electrochemically Generated Aqueous Nanocluster Inks

Solution processing is a scalable means of depositing large-area electronics for applications in displays, sensors, smart windows, and photovoltaics. However, solution routes typically yield films with electronic quality inferior to traditional vacuum deposition, as the solution precursors contain excess organic ligands, counterions, and/or solvent that leads to porosity in the final film. We show that electrolysis of aq. mixed metal nitrate salt solutions drives the formation of indium gallium zinc oxide (IGZO) precursor solutions, without purification, that consist of ∼1 nm radii metal–hydroxo clusters, minimal nitrate counterions, and no organic ligands. Films deposited from cluster precursors over a wide range of composition are smooth (roughness of 0.24 nm), homogeneous, dense (80% of crystalline phase), and crack-free. The transistor performance of IGZO films deposited from electrochemically synthesized clusters is compared to those from the starting nitrate salt solution, sol–gel precursors, and, as a control, vacuum-sputter-deposited films. The average channel mobility (μ_<i>AVE</i>) of air-annealed cluster films (In:Ga:Zn = 69:12:19) at 400 °C was ∼9 cm² V^–1 s^–1, whereas those of control nitrate salt and sol–gel precursor films were ∼5 and ∼2 cm² V^–1 s^–1, respectively. By incorporating an ultrathin indium–tin–zinc oxide interface layer prior to IGZO film deposition and air-annealing at 550 °C, a μ_<i>AVE</i> of ∼30 cm² V^–1 s^–1 was achieved, exceeding that of sputtered IGZO control films. These data show that electrochemically derived cluster precursors yield films that are structurally and electrically superior to those deposited from metal nitrate salt and related organic sol–gel precursor solutions and approach the quality of sputtered films

Minerals to Materials: Bulk Synthesis of Aqueous Aluminum Clusters and Their Use as Precursors for Metal Oxide Thin Films

We describe a process to produce aqueous precursor solutions of the <i><b>flat</b></i><b>-Al</b>_<b>13</b> hydroxo cluster (Al₁₃(μ₃-OH)₆(μ₂-OH)₁₈(H₂O)₂₄(NO₃)₁₅) via stoichiometric dissolution of bulk Al­(OH)₃(s) in HNO₃(aq). We highlight its facility by demonstrating high yields and large-scale synthesis. X-ray diffraction confirms formation of a single-phase product, and Raman spectra show characteristic O-Al-O vibrational modes, both techniques confirming the identity of the <i><b>flat</b></i><b>-Al</b>_<b>13</b> cluster in the bulk. ²⁷Al NMR spectroscopy and dynamic light scattering also confirm the presence of the cluster in aqueous solution. We show the as-prepared solution produces smooth and continuous thin films via spin-coating. In capacitors, the films exhibit low leakage currents (near 10 nA/cm²) and dielectric constants expected for amorphous Al₂O₃. Because the precursor preparation requires no postsynthesis purification, it is readily scalable to large volumes