As essential electrochromic(EC) materials are related to energy savings in fenestration technology,tungsten oxide(WO3) films have been intensively studied recently.In order to achieve better understanding of the mechanism of EC properties,and thus facilitate optimization of device performance,clarification of the correlation between cation storage and transfer properties and the coloration performance is needed.In this study,transparent polycrystalline and amorphous WO3 thin films were deposited on SnO2:F-coated glass substrates by the pulsed laser deposition technique.Investigation into optical transmittance in a wavelength range of 400-800 nm measured at a current density of 130 μA·cm-2 with the applied potential ranging from 3.2 to 2.2 V indicates that polycrystalline films have a larger optical modulation of ～ 30% at 600 nm and a larger coloration switch time of 95 s in the whole wavelength range compared with amorphous films(～ 24% and 50 s).Meanwhile,under the same conditions,polycrystalline films show a larger lithium storage capacity corresponding to a Li/W ratio of 0.5,a smaller lithium diffusion coefficient(2×10-12cm2·s-1 for Li/W=0.24) compared with the amorphous ones,which have a Li/W ratio of 0.29 and a coefficient of ～2.5×10-11cm2·s-1 as Li/W=0.24.These results demonstrate that the large optical modulation relates to the large lithium storage capacity,and the fast coloration transition is associated with fast lithium diffusion.
Zintl phase compounds AM2Sb2(A=Ca,Sr,Ba,Eu,Yb;M=Zn,Cd)is a new class of promising thermoelectrics owing to their intrinsic features in electronic and crystal structure,such as a small or even disappeared band-gap,large density-of-states at the Fermi level,covalently bonded network of M-Sb,as well as the layered stacking by cations A2+and anionic slabs(M2Sb2)2–.In addition,the rich solid-state chemistry of Zintl phase allows structural modification and chemical substitution to adjust the fundamental transport parameters(carrier concentration,mobility,effective mass,electronic and lattice thermal conductivity)for improving the thermoelectric performance.In the present review,the recent advances in synthesis and thermoelectric characterization of title compounds AM2Sb2were presented,and the effects of alloying or substitution for sites A,M and Sb on the electrical and thermal transport were emphasized.The structural disorder yielded by the incorporation of multiple ions significantly increased the thermoelectric figure of merit mainly resulted from the reduction of thermal conductivity without disrupting the carrier transport region in substance.Therefore,alloying or substitution has been a feasible and common route utilized to enhance thermoelectric properties in these Zintl phase compounds,especially for YbZn0.4Cd1.6Sb2(ZT700 K=1.26),EuZn1.8Cd0.2Sb2(ZT650 K=1.06),and YbCd1.85Mn0.15Sb2(ZT650 K=1.14).
