Consecutive hybrid mechanism boosting Na+storage performance of dual-confined SnSe2 in N,Se-doping double-walled hollow carbon spheres

Rationally designed hierarchical structures and heteroatomic doping of carbon are effective strategies to enhance the stability and electrical conductivity of materials.Herein,SnSe_(2)flakes were generated in the double-walled hollow carbon spheres(DWHCSs),in which N and Se atoms were doped in the carbon walls,to construct SnSe_(2)@N,Se-DWHCSs by confined growth and in-situ derivatization.The N and Sedoped DWHCSs can effectively limit the size increase of SnSe_(2),promote ion diffusion kinetics,and buffer volume expansion,which can be proved by electron microscope observation and density functional theory calculation.Consequently,the SnSe_(2)@N,Se-DWHCSs as an anode material for sodium ion batteries(SIBs)demonstrated a distinguished reversible capacity of 322.8 mAh g^(-1)at 5 A g^(-1)after 1000 cycles and a superior rate ability of 235.3 m Ah g^(-1)at an ultrahigh rate of 15 A g^(-1).Furthermore,the structure evolution and electrochemical reaction processes of SnSe2@N,Se-DWHCSs in SIBs were analyzed by exsitu methods,which confirmed the consecutive hybrid mechanism and the phase transition process.

Integration of cobalt selenide nanocrystals with interlayer expanded 3D Se/N Co-doped carbon networks for superior sodium-ion storage

Rational electrode structure design is of great significance for realizing superior Na^(+)storage performance.Herein,a metal salt-induced polymer blowing-bubble approach followed by selenization procedure is developed to in-situ generate abundant sub-10 nm CoSe_(2) nanocrystals on 3D Se/N co-doped carbon networks(CoSe_(2)@3DSNC).The phase transition from Co to CoSe_(2) and the incorporation of Se into the carbon layer are realized simultaneously to establish above configuration,in which the CoSe_(2) nanocrystals are anchored on interlayer expanded carbon networks.Such unique configuration endows electrode with lower Na+diffusion energy barrier,higher Na+storage capability and better structural durability.Reflected in SIBs,the optimized CoSe_(2)@3 DSNC delivers superior rate capability(310 m Ah g^(-1) at 10 A g^(-1))and excellent longterm cycling stability(409 m Ah g^(-1) after 1200 cycles at 5 A g^(-1)).Moreover,this configuration can also be obtained in other metal selenides-carbon composite through a similar approach.

High thermoelectric performance at room temperature of n-type Mg_(3)Bi_(2)-based materials by Se doping

Bi_(2)Te_(3) based alloys have been the most widely used thermoelectric material at low temperature for many decades.Here we report Se doped n-type Mg_(3)Bi_(2) based materials with a thermoelectric figure-of-merit ZT of 0.82 at 300 K and a peak ZT of 1.24 at 498 K,which is comparable to the n-type Bi_(2)Te_(3) and Te doped Mg_(3)Bi_(1.4)Sb_(0.6).The improved thermoelectric performance is benefited from the high carrier concentration and mobility as well as the thermal conductivity reduction.The reduced resistivity increased the power factor at all measured temperatures,leading to a higher engineering ZT(ZTeng)and engineering power factor(PFeng)for n-type Mg_(3)Bi_(2).The n-type Mg_(3)Bi_(1.4)Sb_(0.6) materials are promising for thermoelectric power generation and cooling applications near room temperature.

Raman Study of Defects in SI－GaAs and Se－doped Epitaxial Layer Irradiated by 10 MeV Electrons

Raman scattering measurements on Se-doped GaAs epitaxial layers and semi-insulating (SI) GaAs irradi-ated by 10 Mev electrons have been investigated. Several defect-related features were observed. We suggestthat the 220 cm ￣-1mode is attribute to As_1 which is associated, at least in part, with EL2 and EL12 defects.For Sedoped samples, the Raman peaks at 205 and 258 cm￣-1 may be due to vibrational modes in small clus-ters of arsenic, and the 77 and 185 ￣-1modes are probably associated with disorder-activated first order Ra-man scattering.Irradiated results show that the small clusters of arsenic and disorder state are increased with in-creasing irradiation fluences. Other Raman peaks will also be discussed in this paper.