Phase relations,microstructure,and valence transition studies on CaZr1-xCexTi2O7(0.0≤x≤1.0)system

In this study, Ce-doped zirconolite was synthesized through high-temperature solid-state reaction at 1250 ℃ in air for 96 h. The crystal phase, microstructure and valence transition were studied by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and X-ray photoelectron spectroscopy （XPS）. Phase relations of CaZrl xCexTi207 systems were determined by XRD analyses and Rietveld refinements. Four different phases are identified, namely zirconolite, perovskite, pyrochlore, and cerianite. The phase transformation （2M-zirconolite → 4M-zirconolite →Ce-pyrochlore） is caused by cations rearrangement as cerium content increases. The solubility limit of cerium ions in CaZrl .xCexTi207 system is estimated to be approximately 0.80. Under sintering air atmosphere, partial reduction of Ce^4＋ in Ce^3＋ is detected in Ce 3d XPS soectra, and the ratio of Ce^3＋ and Ce^4＋ significantly decreases as cerium content increases.

Precisely quantifying bulk transition metal valence evolution in conventional battery electrode by inverse partial fluorescence yield

Precisely quantifying transition metal(TM) redox in bulk is a key to understand the fundamental of optimizing cathode materials in secondary batteries. At present, the commonly used methods to probe TM redox are hard X-ray absorption spectroscopy(hXAS) and soft X-ray absorption spectroscopy(sXAS).However, they are both facing challenges to precisely quantify the valence states of some transition metals such as Mn. In this paper, Mn-L iPFY(inverse partial fluorescence yield) spectra extracted from Mn-L m RIXS(mapping of resonant inelastic X-ray scattering) is adopted to quantify Mn valence states. Mn-L i PFY spectra has been considered as a bulk-sensitive, non-distorted probe of TM valence states.However, the exact precision of this method is still unclear in quantifying practical battery electrodes.Herein, a series of LiMn_(2)O_(4) electrodes with different charge and discharge states are prepared. Based on their electrochemical capacity(generally considered to be very precise), the precision of Mn iPFY in quantifying bulk Mn valence state is confirmed, and the error range is unraveled. Mn-L mRIXS iPFY thus is identified as one of the best methods to quantify the bulk Mn valence state comparing with hXAS and sXAS.

Study of valence intersubband absorption in tensile strained Si/SiGe quantum wells

The hole subband structures and effective masses of tensile strained Si/Sil-yGey quantum wells are calculated by using the 6 × 6 k·p method. The results show that when the tensile strain is induced in the quantum well, the light-hole state becomes the ground state, and the light hole effective masses in the growth direction are strongly reduced while the in-plane effective masses are considerable. Quantitative calculation of the valence intersubband transition between two light hole states in a 7nm tensile strained Si/Si0.55Ge0.45 quantum well grown on a relaxed Si0.5Ge0.5 （100） substrates shows a large absorption coefficient of 8400 cm^-1.

Modulating redox transition kinetics by anion regulation in Ni-Fe-X(X=O,S,Se,N,and P)electrocatalyst for efficient water oxidation

NiFe-based electrocatalysts will experience dynamical surface reconstruction during oxygen evolution reaction(OER)process,and the derived metal(oxy)hydroxide hybrids on the surface have been considered as the actual active species for OER.Tremendous efforts have been dedicated to understanding the surface reconstruction,but there is rare research on recognizing the origin of improved performance derived from anion species of substrate.Herein,the OER electrocatalytic characteristics were tuned with different anions in NiFe-based catalyst,using NiFe-based oxides/nitride/sulfide/selenides/phosphides(NiFeX,X=O,N,S,Se,and P)as the model materials.The combination of X-ray photoelectronic spectroscopy,electrochemical tests,operando spectroscopic characterizations,and density functional theory(DFT)calculations,reveals that anion with lower electronegativity in NiFe-based catalyst leads to higher conductivity and delayed valence transition of Ni sites,as well as optimized adsorption behavior towards oxygen intermediates,contributing to enhanced OER performance.Accordingly,NiFeP electrocatalyst demonstrates an ultralow overpotential of 265 mV at 20 mA·cm−2 for OER,as well as long-term stability.This work not only offers further insights into the effect of anionic electronegativity on the intrinsic OER electrocatalytic properties of NiFe-based electrocatalyst but also provides guide to design efficient non-noble metal-based electrocatalysts for water oxidation.

Photochromism in CaS:Sm

The photochromism in CaS:Sm (from white to pink) was observed for the first time by exposing it to ultraviolet light. The experiments results show that the absorption intensity of Sm2+ in the range of 500 similar to 600nm was strongly increased after irradiation. This reveals that there is the valence changing of Sm. If the sample was excited by visible light again, the pink color turned to white, indicating that CaS:Sm has potential application in the field of storage material.

First-principle study of the structural,electronic,and optical properties of SiC nanowires

We preform first-principle calculations for the geometric, electronic structures and optical properties of SiC nanowires（NWs）. The dielectric functions dominated by electronic interband transitions are investigated in terms of the calculated optical response functions. The calculated results reveal that the SiC NW is an indirect band-gap semiconductor material except at a minimum SiC NW（n = 12） diameter, showing that the NW（n = 12） is metallic. Charge density indicates that the Si–C bond of SiC NW has mixed ionic and covalent characteristics： the covalent character is stronger than the ionic character, and shows strong s–p hybrid orbit characteristics. Moreover, the band gap increases as the SiC NW diameter increases. This shows a significant quantum size and surface effect. The optical properties indicate that the obvious dielectric absorption peaks shift towards the high energy, and that there is a blue shift phenomenon in the ultraviolet region. These results show that SiC NW is a promising optoelectronic material for the potential applications in ultraviolet photoelectron devices.

Systematic dependence of SFE＊B(E2)↑ and ROTE＊B(E2)↑on N_pN_n in the framework of shape fluctuation model

A systematic dependence of shape fluctuation energy product SFE ＊ B（E2）↑ and rotational energy product ROTE ＊ B（E2）↑ on the valence nucleon product Np Nn is carried out in the Z = 50-82,N = 82-126 major shell space.For the shape transitional nuclei,the product SFE＊B（E2）↑ drops to zero and becomes negative,indicating direct dependence on N_pN_n.A relative rise,on the other hand,is observed in the product ROTE＊B（E2） ↑plotted against N_pN_n for all the nuclei in Z = 50-82 and N = 82-126.In the N 〉 104 region,large positive values of the product SFE ＊ B（E2） ↑ are observed for the Pt nucleus,which indicates sphericity.A systematic study of the product SFE ＊ B（E2）↑ and ROTE ＊ B（E2） ↑ with atomic number Z is also discussed.The products SFE ＊ B（E2） ↑and ROTE ＊ B（E2） ↑ vary sharply with Z for the N = 88 isotones.We discuss here for the first time the correlation between SFE ＊ B（E2） ↑ and ROTE ＊ B（E2） ↑ with valence nucleon product N_pN_n.