Synthesis And Properties Of Tellurium Compound Nanomaterials

Tellurium compound nanomaterials are important semiconducting optoelectronic materials, and have attracted much attention due to their unique physical, chemical properties and the wide applications in optoelectronic devices and biological medicines. Nevertheless, the research and application on the tellurium compound nanomaterials lag far behind the sulfur and selenium compounds. So, it is greatly significant to develop systematically different synthetic approaches of telluride nanomaterials, adjust their structure, morphology, dimension, or composition and investigate their optical, electrical, thermal and other properties. In this dissertation, the work is maily focused on tellurium compound nanomaterials, the goal is exploring novel synthetic methods and routes to synthesize telluride micro- and nano-scal materials with controlled structures and morphologies. We have developed a novel synthetic route of tellurium compound nanomaterials based on the composite alkali melts as medium, improved on several reaction systems on the above result, and gotten some high quality telluride nanomaterials. And, their optical, electronic and thermal properties have been studied. The main contents can be summarized as follows:Firstly, a novel synthetic route to telluride nanomaterials base on Composite- Hydroxide-Mediated Approach (CHM method) is developed. The composite alkali melts is used as reaction media, elemental tellurium as tellurium source, the PbTe microcubes and nanorods have been successfully synthesized in the same reaction system through a different reducing agent (NaBH₄, ascorbic acid, and N₂H₄). Though adjusting the reaction temperature and time, the dimensionm, size and morphology of PbTe can be easily controlled. And, thermoelectric properties of PbTe crystals are studied and the Seebeck coefficient of PbTe nanorods is greatly increased. Adding an appropriate amount of complexing agent (ethylenediamine), the above method was successfully applied to the synthesis Ag₂Te crystal, and the clean, uniform Ag₂Te one-dimensional nanowires are obtained. The phase transformation of the nanowires betweenβ-Ag₂Te andα-Ag₂Te is prone to take place at about 140 oC. The synthetic mechanisms of telluride and the function of hudrazine as reduction, complexation and growth control in the molten alkali system are explored and discussed in detail.Secondly, based on the above result, a simple, rapid, high yield, room-temperature synthetic method of lead chalcogenide nanomaterials is developed. By adjusting the ratio of the hydroxide and hydrazine to form a saturated hydrazine alkaline solution system, regulate successfully the kinetics, the uniform PbS, PbSe, PbTe nanocubes are obtained. And, the alkalinity of the reaction system is reduced furtherly. Under magnetic stirring, the ZnTe-N₂H₄ compounds are prepared in only hydrazine solution at low temperature. After thermal decomposition, the pure ZnTe nanorods are gained, which can not exist in strong alkaline solution. The mechanism of the N₂H₄ molecules and tellurium compound embedding in ZnTe networks is discussed.Finally, based on the CHM ideas,the neutral complex molten salt (LiNO₃/KNO₃) substitutes for complex hydroxide (NaOH/KOH), with the aid of magnetic stirring, the tellurite nanomaterials——lead tellurite nanobelts are first synthesized in atmospheric ambient. The nanobelts are amorphous and glassy, have lower thermal stability and Blu-ray fluorescent property at room temperature. In the melts, the exploring synthetic research of telluride has opened up a new way for semiconducting nanomaterials.