Metal-to-insulator transitions in 3d-band correlated oxides containing Fe compositions

Metal-to-insulator transitions (MITs),which are achieved in 3d-band correlated transitional metal oxides,trigger abrupt variations in electrical,optical,and/or magnetic properties beyond those of conventional semiconductors.Among such material families,iron(Fe:3d^(6)4s^(2))-containing oxides pique interest owing to their widely tunable MIT properties,which are associated with the various valence states of Fe.Their potential electronic applications also show promise,given the large abundance of Fe on Earth.Representative MIT properties triggered by critical temperature (TMIT) were reported for ReFe_(2)O_(4)(Fe^(2.5+)),ReBaFe_(2)O_(5)(Fe^(2.5+)),Fe_(3)O_(4)(Fe^(2.67+)),Re_(1/3)Sr_(2/3)FeO_(3)(Fe^(3.67+)),Re Cu_(3)Fe_(4)O_(12)(Fe^(3.75+)),and Ca_(1-x)Sr_(x)FeO_(3)(Fe^(4+))(where Re represents rare-earth elements).The common feature of MITs of these Fe-containing oxides is that they are usually accompanied by charge ordering transitions or disproportionation associated with the valence states of Fe.Herein,we review the material family of Fe-containing MIT oxides,their MIT functionalities,and their respective mechanisms.From the perspective of potentially correlated electronic applications,the tunability of the TMITand its resultant resistive change in Fe-containing oxides are summarized and further compared with those of other materials exhibiting MIT functionality.In particular,we highlight the abrupt MIT and wide tunability of TMITof Fe-containing quadruple perovskites,such as Re Cu3Fe4O12.However,their effective material synthesis still needs to be further explored to cater to potential applications.

Accelerated discovery of a large family of quaternary chalcogenides with very low lattice thermal conductivity

The development of efficient thermal energy management devices such as thermoelectrics and barrier coatings often relies on compounds having low lattice thermal conductivity(κl).Here,we present the computational discovery of a large family of 628 thermodynamically stable quaternary chalcogenides,AMM′Q_(3)(A=alkali/alkaline earth/post-transition metals;M/M′=transition metals,lanthanides;Q=chalcogens)using high-throughput density functional theory(DFT)calculations.We validate the presence of lowκl in these materials by calculatingκl of several predicted stable compounds using the Peierls–Boltzmann transport equation.Our analysis reveals that the lowκl originates from the presence of either a strong lattice anharmonicity that enhances the phononscatterings or rattler cations that lead to multiple scattering channels in their crystal structures.Our thermoelectric calculations indicate that some of the predicted semiconductors may possess high energy conversion efficiency with their figure-of-merits exceeding 1 near 600 K.Our predictions suggest experimental research opportunities in the synthesis and characterization of these stable,low κ_(l) compounds.

Influence of inherent iron and oxygen concentrations on selenite sorption process using bentonite

The oxygen concentration and inherent Fe in bentonite have a significant influence on the Se(IV) sorption process.In this study,the sorption of selenite on natural bentonite was investigated using a batch experiment method,and the distribution coefficient(K_d)values were obtained in the pH range from 2.0 to 10.0 under oxic/anoxic conditions.The K_d values always reached a maximum value at a pH of 4 under oxic conditions and at a pH of 8 under anoxic conditions;meanwhile,the K_d value under anoxic conditions was larger than the value under oxic conditions,especially in regard to the maximum K_d values.The oxygen conditions have a significant influence on the ratio of redox-sensitive Fe^(2+)/Fe^(3+),which was closely related to the difference in the K_d values under both oxic/anoxic conditions.Ferric selenite and green rust could be responsible for the maximum K_d values under oxic/anoxic conditions.In the leaching experiments,we found that the Fe^(2+) in bentonite could replace Mg^(2+) and Al^(3+) in the octahedral sheet.Spectroscopy methods,such as Fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD) and X-ray absorption spectroscopy(XAS) were used to characterize the surface properties of the samples after reaction.Overall,this study shows that the addition of Fe^(2+)-containing materials into backfill/buffer materials under anoxic condition could enhance the sorption of ^(79)Se(IV).

Stability of selenium and its speciation analysis in water using automatic system separation and HR-ICP-MS measurement

A simple and convenient method has been developed for the pre-concentration and separation of inorganic selenium species from environmental water samples using anion exchange chromatographic column combined with high resolution inductively coupled plasma mass spectrometry(HR-ICP-MS)measurement.^(75)Se(Ⅳ) and ^(75)Se(Ⅵ)were prepared and used as tracers during the experiments.The volatility of selenium during solution evaporation was investigated to establish a reliable water samples pretreatment procedure.The parameters which affect the uptake of Se(Ⅳ)and Se(Ⅵ)on Dowex1×8 resin was optimized and the procedure for Se(Ⅳ)and Se(Ⅵ)separation was proposed.Both Se(Ⅳ)and Se(Ⅵ)are retained on the column in natural or alkaline solution with high distribution coefficient.The successive gradient elution of pre-concentrated species of selenium with HNO_(3)solution allows to differentiate between them.Se(Ⅳ)and Se(Ⅵ)finally were eluted with 0.05 mol/L HNO_(3) and 5.0 mol/L HNO_(3),respectively.The proposed method has been successfully verified using the certified reference materials(CRMs)of real water samples,and spiked recoveries for real samples were 98%-104%with 5%relative standard deviations(RSDs).The developed procedure is proved to be reliable and can be used for the rapid determination of selenium species in environmental water samples.