Negative Thermal Expansion Property Of Eu_1-xSr_xMnO_3-δ （X= 0.1,0.15,0.2） And (Gd_0.5Eu_0.5)_0.8Sr_0.2MnO₃

Most of the materials with positive coefficients of thermal expansion （CTE） can cause the thermal stress and the micro cracks of the devices, thus result in a decline in the performance of the devices and even failure. The discovery of negative thermal expansion （NTE） materials make up the defects, it has received the widespread attention and research. Controlled thermal expansion materials, low thermal expansion materials and nearly zero material development and application of reduced the devices of the thermal stress, improve the performance of its thermal stability. However, the NTE materials still has great limitations in applications, this is mainly due to the NTE materials has some drawbacks to be solved:for example, the preparation process trival, high cost and energy consumption, poor material stable performance, high phase transition temperature point, after absorbing water led to the decrease of the mechanical properties lossing the NTE properties, single function and so on. Therefore, to explore and preparate a new NTE materials of excellent properties has important application value.Doped perovskite manganese oxide has been pay more attention because of its unique physical properties, but the research of its thermal expansion is not enough. This paper take Eui xSrxMnO3-δ （x= 0.1,0.15,0.1） and (Gd_0.5Eu_0.5)_0.8Sr_0.2MnO₃ as the research object, both of them show the NTE properties, and its thermal shrinkage mechanism is analyzed, the main work and results are as follows:（1） We firstly synthesized the novel negative thermal expansion material Eui xSrxMnO3-δ （x= 0.1,0.15,0.1） with superior physical properties by solid state method. With the increasing of doping concentration x, samples show more excellent NTE properties, and Eu_0.8 Sr0.2 MnO3-δ has average linear expansion coefficient of-14.0 x 10-6/K （298-873 K）（2） The phase composition and microstructure of Eu_0.8Sr_0.2MnO_3-δ were studied. X-ray diffraction （XRD） analysis shows that the sample Eu_0.8Sr_0.2MnO_3-δ is orthogonal perovskite structure;By scanning electron microscope （SEM） and EDS spectrum element analysis, we found that the sample consists of a single, closely arranged Eu_0.8Sr_0.2MnO_3-δ polyhedron particle phase composition, particle size 5～7μm, uniform particle size distribution, crystallization degree is good.（3） This paper mainly analyzes the NTE mechanism of Eu_0.8Sr_0.2MnO_3-δ. We consider that this NTE is caused by the lattice distortion and the release of Jahn-Teller effect. The dopping of Sr2+ in EuMnO3 changed its perovskite structure distortion degree, set up necessary conditions for the generation of NTE. With the increasing of the temperature and the oxygen deficiency, causing a release from MnO6 octahedral distortion by a Mn3+ ions, makes the axial shrinkage occurs, a lattice symmetry increases, volume decreases, and the overall showed NTE performance.（4） The NTE materials (Gd_0.5Eu_0.5)_0.8Sr_0.2MnO₃ was prepared by solid phase method. X-ray diffraction （XRD） analysis shows that the sample (Gd_0.5Eu_0.5)_0.8Sr_0.2MnO₃ is orthogonal perovskite structure. In 495～673 K temperature region, the samples shows good NTE properties, with an average linear expansion coefficient of α=-0.9×10-6/K. The source of the NTE may releates to the holes of sample and the change of lattice in the heating process.