| Layered compounds exhibit a series of excellent physical properties due to their quasi-two-dimensional crystal structure.The preparation/modification and the design and application of their functional devices have attracted extensive attention by the materials science and physics communities.The oxygen-containing characteristics in layered oxide materials make them excellently thermal stability,which broadens the temperature window in their applications.Therefore,the research on layered oxide materials has important scientific and practical significance.Bismuth-based layered oxides Bi2O2Se and BiCuSeO have a band gap around 0.8 e V,low thermal conductivity,high Seebeck coefficient and high carrier mobility.These properties make them have excellent thermo-electric and photo-electric energy conversion properties.Up to now,most of research was focused on doping thin films/ceramic samples to enhance the electrical conductivity through increasing the carrier concentrations.The overall properties,thermo-electric and photo-electric energy conversion properties,of these two comopounds need to be further optimized.A series of high-quality crystals were obtained by chemcial vapor transport and melt-solidification method,and their carrier concentration can be well manipulated through adjusting the growth conditions（halogen doping and changing the growth temperature）.The electrical and magnetoelectric transport properties were systematically studied.Finally,we summarized the effect of carrier concentration to Seebeck coefficient,as well as electrical properties（scattering mechanism and mobility）.Main research contents are as follows:（1）High-quality Bi2O2Se single crystals were grown by chemical vapor transport method.Electrical transport studies show that Bi2O2Se crystals show ultra-high mobility,obvious quantum oscillation and extremely large magnetoresistance.Parameters of the Fermiology of Bi2O2Se were obtained through analysis of quantum osicllation.And the ultrahigh mobility of Bi2O2Se may come from sole electron-electron scattering.（2）The thermoelectric properties of Bi2O2Se crystals are optimized by adjusting the carrier concentration.A series of Bi2O2Se crystals（doped and undoped）were obtained by melt-solidification method.The transport and theoretical calculation show that the scattering mechanism of doped crystals has evolved from electron-electron scattering to electron-phonon scattering.The dependence of the power factor PF on the carrier concentration was studied,and the PF was about four times higher than that of undoped sample,reaching 2.02μW cm-1 K-2.（3）BiCuSeO single crystals with different hole concentrations(1017–1020 cm-3)were grown by chemical vapor transport at different temperatures.We realize the electric transport evolution from variable range hopping to degenerate semiconductor.Finally,the electronic phase diagram of BiCuSeO with hole concentration and temperature is obtained.Through above research,we have realized the accurate control of the carrier concentration of Bi2O2Se and BiCuSeO crystals.On the one hand,we have a deeper understanding of the electrical transport mechanism of bismuth-based layered oxides.On the other hand,we have provided an experimental basis for the application of these materials in thermoelectric and optoelectronic fields. |
