Manipulating metal–insulator transitions in strongly correlated materials is of great importance in condensed matter physics, with implications for both fundamental science and technology. Vanadium dioxide (VO2), as an ideal model system, is metallic at high temperatures and shown a typical metal–insulator structural phase transition at341 K from rutile structure to monoclinic structure. This behavior has been absorbed tons of attention for years. However, how to control this phase transition is still challenging and little studied. Here we demonstrated that to control the Ag nanonet arrays (NAs) in monoclinic VO2(M) could be effective to adjust this metal–insulator transition. With the increase of Ag NAs volume fraction by reducing the template spheres size, the transition temperature (T
c) decreased from 68 ° C to 51 °C. The mechanism of T
c decrease was revealed as: the carrier density increases through the increase of Ag NAs volume fraction, and more free electrons injected into the VO2 films induced greater absorption energy at the internal nanometal–semiconductor junction. These results supply a new strategy to control the metal–insulator transitions in VO2, which must be instructive for the other strongly correlated materials and important for applications.
Building gypsum has the disadvantage of short setting time and fast hardening characteristics. Based on the systematic experiments, a combined retarding system of phosphoric acid modified steel slag (3%, gypsum-based) and protein-based material (Sika 200P 0.005%, gypsum-based) is proposed. The initial setting time of gypsum is prolonged to 206 min and the final setting time is 221 min. The retarding effect for desulfurization building gypsum is significantly better than Sika 200P, and the cost is greatly reduced.
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