Polyol-Made Spinel Ferrite Nanoparticles—Local Structure and Operating Conditions: NiFe2O4 as a Case Study

We report the effect of a polyol-mediated annealing on nickel ferrite nanoparticles. By combining X-ray fluorescence spectroscopy, X-ray diffraction, and 57Fe Mössbauer spectrometry, we showed that whereas the as-prepared nanoparticles (NFO) are stoichiometric, the annealed ones (a-NFO) are not, since Ni0-based crystals precipitate. Nickel depletion from the spinel lattice and reduction in the polyol solvent are accompanied with an important cation migration. Indeed, thanks to Mössbauer hyperfine structure analysis, we evidenced that the cation distribution in NFO departs from the thermodynamically stable inverse spinel structure with a concentration of tetrahedrally coordinated Ni2+ of 20 wt-% (A sites). After annealing, and nickel demixing, originated very probably from the A sites of NFO lattice, the spinel phase accommodates with cation and anion vacancies, leading to the (Fe3+0.84□0.16)A[Ni2+0.80Fe3+1.16□0.04]BO4-0.20 formula, meaning that the applied polyol-mediated treatment is not so trivial.

Challenges in Improving Performance of Oxide Thermoelectrics Using Defect Engineering

Oxide thermoelectric materials are considered promising for high-temperature thermoelectric applications in terms of low cost, temperature stability, reversible reaction, and so on. Oxide materials have been intensively studied to suppress the defects and electronic charge carriers for many electronic device applications, but the studies with a high concentration of defects are limited. It desires to improve thermoelectric performance by enhancing its charge transport and lowering its lattice thermal conductivity. For this purpose, here, we modified the stoichiometry of cation and anion vacancies in two different systems to regulate the carrier concentration and explored their thermoelectric properties. Both cation and anion vacancies act as a donor of charge carriers and act as phonon scattering centers, decoupling the electrical conductivity and thermal conductivity.

A Comprehensive Density-of-States Model for Oxide Semiconductor Thin Film Transistors

In this paper, a comprehensive Density of States model was proposed to understand the origin of conductivity and the performance of p-type and n-type oxide semiconductor thin film transistors (TFTs). To validate the model, the simulated I-V characteristics are compared with measured results of p-type Cu2O & SnO and n-type SnO2 TFTs. It was found that cation vacancies were responsible for hole conduction in p-type TFTs, while anion vacancies and/or metal interstitial were responsible for electron conduction in n-type TFTs. This was observed by assigning the cation vacancies to acceptor-like Gaussian states and anion vacancies and/or metal interstitial to Donor-like Gaussian states respectively. The characteristic slopes in conduction/valence band-tail states are due to disorders present in the oxide semiconductors. The model is successfully delivering the physical insight and path way to circuit simulation of large scale integration of pixel circuits AMLCD/AMOLED displays.

Construction of Atomically Dispersed Cu Sites and S Vacancies on CdS for Enhanced Photocatalytic CO2 Reduction

The controllable introduction of anion vacancies (such as O vacancies，S vacancies) or atomic-dispersion metal sites in semiconductors is a promising strategy to improve photocatalytic performance. However, the facile construction of...