Preparation And Study Of The Negative Thermal Expansion Materials HfScWV₃O₁₄ And Sc_1.45W_3.23O_12-?

The majority of natural materials have positive properties of thermal expansion that they expand on heating and contract on cooling.The device generates thermal stress when heated.When devices are heated unevenly,or possess different capacities of heat conduction of different parts,the uneven distribution of heat will lead to cracks in the internal or on the surface of the device.Even more,part of the devices' performances drop or even lose its effectiveness,which brings great inconvenience for the productions and our lives.Some materials have opposite properties,i.e.expanding when cooled and contracting when heated,are named as negative thermal expansion materials?NTE?.The materials with such abnormal thermal properties bring to the attention of scientists.The emergence of negative thermal expansion materials provides a possibility for the preparation of controllable thermal expansion materials and near-zero thermal expansion materials.Preparation for the devices of appropriate expansion coefficient material effectively reduces the change in length and volume when the device is heated,improving the thermal stability of the device performance.However,negative thermal expansion materials is not widely effectively applied so far.The main reason is that there are some drawbacks of the negative thermal expansion materials in the preparation and the control of performances.Such as tedious process of preparation,high costs of preparation,high energy consumption,uneven material,the temperature of the phase transition points is higher than the room temperature,the changing in mechanical properties after absorbing water,single functional,etc.In this thesis,by controlling the reaction process,material with the formula Hf Sc WV₃O₁₄ which with well-distributed was prepared.By changing the proportion and replacing some elements and doping?Fe3+,Cr3+?,the coefficient of thermal expansion?CTE?,the phase transition temperature,the difference of CTEs before and after the material phase transition are tuned and the thermal shock resistance of the is improved.A new type of negative thermal expansion luminescent material Sc_1.45W_3.23O_12-? was prepared.The optical properties and electrical properties of the material are investigated.The content of Sc element of negative thermal expansion material with excellent characteristics was successfully reduced compared to Sc₂W₃O₁₂.We use experiment instruments such as XRD?X-ray diffraction?,Raman spectrometer,scanning electron microscopy?SEM?,X-ray Photoelectron spectroscopy?XPS?,Thermo gravimetric Analysis and Differential Scanning Calorimetry?TG-DSC?,Ultraviolet spectrophotometer?UV?,impedance analyzers,X-ray fluorescence,Fluorescence Photoluminescence?PL?,and dilatometer to analyze the structures,phase transformation and characteristics of negative expansion and optical and electrical properties.