Negative Thermal Expansion Materials Of Er_0.7Sr_0.3NiO_3-δ Synthesis And Properties

Most of materials have the properties of heat bilges cold shrink, which can bringthe phenomenon of deformation and thermal stress, then causing the sensitivity andperformance of the equipment be lower, and even failure. The negative thermalexpansion (NTE) materials can be used to obtain the near-zero expansion orcontrollable expansion materials by reviewing with general materials due to itsunusual thermal expansion properties, which can ensure the equipment not affectedby temperature change in a certain range, thus, the near-zero expansion orcontrollable expansion materials can greatly improve the stability and precision of theinstrument or equipment, at the same time, extend their service life.Over the past20years, the NTE materials received extensive attention byresearchers. Many types of NTE materials have been found by researchers, but littlematerials could be used in large-scale production and practical applications in currentdue to their performance disadvantages more or less. Therefore, discovered orpreparation of a new type of negative thermal expansion materials is a hot spot inmaterial science research. This work has been prepared a new NTE materialEr0.7Sr0.3NiO3-, in addition, analysis and studied its performance. This thesis ismainly divided into three parts, the specific content are as follows:The first part of this paper detailed introduce the definition, classification, anddevelopment status of the NTE materials, and give a detailed description of severalkinds of heat expansion mechanism, common preparation methods and the respectiveadvantages and disadvantages of some ceramic materials which have been reported.The second part introduce the performance characterization methods of NTEmaterials and the experimental instruments. Furthermore, it also giving a brieflydescription about the research purpose, main contents and significances.The third part is the specific contents and main conclusions of this experiment.This experiment adopts traditional solid phase method to obtain the material ofEr0.7Sr0.3NiO3-, the method is simple and has a good repeatability. The experimentalresults show that:(1) The sample of Er0.7Sr0.3NiO3-is a single phase of perovskite structure, without other impurity phase;(2) Er0.7Sr0.3NiO3-sample has a large NTE property from655K to780K, andthe linear NTE coefficient is calculated to be–39.0×10–6K–1.(3) The reason why the Er0.7Sr0.3NiO3-sample shows a large NTE propertyfrom655K to780K is that: Er0.7Sr0.3NiO3-crystal has a phase transition fromorthorhombic to rhombohedral phase near655K. The NiO6octahedra inEr0.7Sr0.3NiO3-shows serious distortion in orthorhombic, but the distortion degreechanges to be smaller and becomes well-regular in rhombohedral phase. In theprocess of this phase transition, the N i-O distance becomes short, the Er-O distance isstretched, and the contraction degree is larger than the stretched, so the materialshows great volume shrinkage on the whole.