Y_2-xEr_xMo₄O₁₅与Y_2-xSm_xW₃O₁₂系列复合氧化物材料的合成、结构表征和负热膨胀性能研究

【作者】 余周香；

【导师】 陈东风； 胡中波； 肖红文；

【作者基本信息】 中国原子能科学研究院 ， 凝聚态物理， 2006， 硕士

【摘要】 为了寻找新的负热膨胀材料，深入探讨负热膨胀机理，研究其基本物理性能，本文利用固相合成法合成了Y_2-xEr_xMo₄O₁₅与Y_2-xSm_xW₃O₁₂两个系列，并利用常温X-ray粉末衍射、高温X-ray粉末衍射和热重分析等手段系统地研究了其晶体结构及热膨胀等一些物理性能，主要研究内容及结果如下：（1）合成了系列新型稀土化合物Y_2-xEr_xMO₄O₁₅（x=0.0-2.0）。通过X-ray粉末衍射实验研究发现：结构上与典型的负热膨胀材料ZrW₂O₈和ZrV₂O₇有拓扑相似性，其晶格参数a，b，c，β和晶胞体积V随着Er含量的增加线性减小。高温X-ray粉末衍射结果显示此系列的化合物有相似的正热膨胀性能。通过衍射数据的分析，得出：共有边O14-O23是阻碍负热膨胀产生的主要因素，弱键Mo2-O14是正热膨胀产生的主要原因。通过类比，探讨了ZrW₂O₈的W1-O3键随着温度的升高对晶格产生的影响，提出了ZrW₂O₈相变的可能模型。（2）合成了系列新型稀土固溶体Y_2-xSm_xW₃O₁₂（x=0.0-0.4），并利用X-ray粉末衍射研究了其结构。所有的样品以Pnca的正交空间群结晶。它们的晶胞参数和晶胞体积随着Sm含量的增加而增加。本文也通过X-ray粉末衍射研究了纯Sm₂W₃O₁₂的结构。常温Y_2-xSm_xW₃O₁₂的吸水性能通过热重分析和高温X-ray粉末衍射得到了研究。本文也讨论了水分子在晶体结构和热膨胀性能的改变方面所扮演的角色。利用高温X-ray粉末衍射实验研究了Y_2-xSm_xW₃O₁₂系列的热膨胀性能。在研究的200—600℃温区范围内，这个系列的化合物在a，b，c三个方向表现出很强的负热膨胀行为。通过调节Y₍2-x_Sm_xW₃O₁₂中的Sm的含量，成功地制备了具有可变热膨胀系数的化合物。所制备的化合物随着Sm含量的增加，其负热膨胀性能变小，室温下的晶胞吸水量变少。通过分析，探讨了Sm含量的掺杂所产生的影响。更多还原

【Abstract】 To search for more negative thermal expansion（NTE） materials, better understand mechanisms of NTE and study their physical properties, new series of rare earth compounds Y_2-xEr_xMo₄O₁₅ and Y_2-xSm_xW₃O₁₂ were prepared successfully by the conventional solid state reaction technique. Their structures, thermal expansion properties and other physical properties were studied systematically by ambient X-ray diffraction, high temperature X-ray diffraction, thermogravimetric analysis etc. The main research contents and results are as follows:（1） A new series of rare earth compounds Y_2-xEr_xMo₄O₁₅（x=0.0-2.0） were prepared successfully. Their structures have been studied using powder X-ray diffraction（XRD） and were found to have the topological similarity to the structures of typical NTE materials ZrW₂O₈ and ZrV₂O₇. The lattice parameters a, b, e,βand the unit cell volume V decrease linearly with increasing Er content. Thermal expansion properties have been investigated by high-temperature X-ray diffraction. The results indicate that the compounds of this series have similar normal positive thermal expansion behavior. According to the analysis of diffraction data, the common edge O14-O23 should be the main resistance for NTE behavior and the weak bond M02-O14 should be responsible for the positive thermal expansion in these compounds. By comparison, the effect of band W1-O3 in ZrW₂O₈ is discussed. As a result, a possible model for the phase transition of ZrW₂O₈ is put forward.（2） A new series of rare earth solid solutions Y_2-xSm_xW₃O₁₂（x=0.0-0.4） were synthesized successfully and studied by means of powder X-ray diffraction. All samples crystallize in an orthorhombic space group Pnca. The lattice parameters a, b, c and unit-cell volume V of Y_2-xSm_xW₃O₁₂ increase monotonically with increasing Sm content. The structure of pure Sm₂W₃O₁₂ was also studied by powder X-ray diffraction. The hygroscopic property of Y_2-xSm_xW₃O₁₂ at room temperature was studied by TG analysis and high temperature X-ray diffraction. The role of water molecules, in determining the change of crystal structures and thermal expansion behavior has been discussed. The thermal expansion behavior of the Y_2-xSm_xW₃O₁₂ compositions has been studied by high temperature X-ray diffraction. In the studied temperature range, 200-600℃, the compounds of this series show strong negative thermal expansion along all three axes（a, b and c）. By adjusting the Sm content in Y_2-xSm_xW₃O₁₂, compounds with variable thermal expansion coefficient can be prepared. The prepared compound becomes less pronounced in negative thermal expansion and stores less water content with increasing Sm content at room temperature. The effect of the intermingle of Sm content has been speculated in this paper.更多还原