【作者】 李志远；

【导师】 晁明举； 梁二军；

【作者基本信息】 郑州大学 ， 光学， 2011， 硕士

【摘要】 在种类繁多的负膨胀材料中,A2M3012系列材料是负膨胀材料中的一个重要的分支。其中‘A’是三价的金属原子,它的原子半径介于三价金属原子A1(0.675A)和Gd(1.075A)之间(这样的金属原子有数十个之多),M是W或Mo。由于金属原子(A)的半径大小不同,A2M3012系列材料分别以单斜相和正交相的结构存在。只有正交相的晶体结构,才有明显的负膨胀性质。在A2M3012系列材料中,A3+离子半径越小它的负膨胀系数也就越小,有些材料在室温时以单斜相的晶体结构存在,它们只有在高温转变为正交相之后,才有负膨胀的性质。A3+离子半径越大,它的负膨胀系数就越大,呈现负膨胀的温度范围也就越宽。另外随着A3+离子半径变大,开放式晶体结构之间的空隙也就越大,水分子也就很容易进入到晶体结构内部。这些水分子的会影响多面体和引起负膨胀效应的分子振动,使材料失去负膨胀性质。本文选取Fe2-xYxMo3O12系列材料,分别对不同x值(x=0.2,0.4,0.5,0.6,0.8,1.0,1.2,1.4,1.6和1.8)的材料进行烧结合成。对它们的结构、相变和吸水性等性质分别进行了研究。研究发现,这些材料室温时都是单斜相(x≤0.4)或正交相(x≥0.5)的晶体结构。随着Fe2MoO12(?)中掺入Y3+含量的增加,Fe2-xYxMo3O12的相变温度也逐渐下降,当x的值达到0.5时Fe1.5Y0.5Mo3O12在室温范围内晶体结构就变成了正交相,而且这种结构一直保持到103K。当x>0.8时Fe1-xYxMo3O12系列材料都有很强的吸水性,材料中的水分子存在两种状态,一种状态的水分子对晶体结构中多面体的振动没有什么影响,另一种状态的水分子对晶体中的多面体振动有很大抑制作用,正是这种对多面体分子振动的抑制,才导致了材料负膨胀性质的消失。研究发现,当0.4<x≤0.8时,Fe2-xYxMo3O12系列材料中吸附的水分子只存在一种状态,这种状态的水分子对晶体结构中多面体的振动没有什么影响。许多过渡金属原子、镧系金属原子以及具有很高传导性的金属原子等三价离子,都适合存在于A2M3012系列材料之中。包含这些具有不同性能元素的化合物,也着有多种不同的用处,比如燃电池、荧光粉、发光材料、超导材料、光导纤维、气敏原件和激光材料等等。本文采用高温固相烧结的方法,制备出了Y2MO3012:Eu3+和Y2MO3012:Er3+(?)等负膨胀材料的荧光粉,同时也对它们的发光性质进行了研究。研究发现Y2MO3O12:Eu3+荧光粉在594 nm,613 nm,655nm和701 nm处有比较强的发光峰；Y2MO3O12:Er3+荧光粉在655-675 nm的波长范围内有强的荧光出现。更多还原

【Abstract】 Of the NTE materials, compounds with general formula A2M3O12, where’A’is one of the trivalent cations ranging in size from Al (radius of 0.675 A) to Gd (radius of 1.075 A) and M is W or Mo, are an important class of materials exhibiting NTE. A2M3O12 may crystallize either in monoclinic or orthorhombic structure depending on the A cation size. Only the orthorhombic corner shows significant negative thermal expansion behavior.The materials of the A2M3O12 family with smaller A3+ cation size give rise to smaller NTE or even crystallize in a monoclinic structure at room temperature whose NTE is only possible after monoclinic-to-orthorhombic phase transition at higher temperatures. On the other hand, those with larger A3+cation size exhibit larger NTE over a wide temperature range, and the openings in the network become large enough to admit water molecules which inhibit the flexibility as well as the internal vibrations of the polyhedra which are essential for negative thermal expansion.Materials with the formula Fe2-xYxMo3O12 (x=0.2,0.4,0.5,0.6,0.8,1.0,1.2, 1.4,1.6 and 1.8) have been synthesized and their structures, phase transitions and hygroscopicity have been studied. It is found that Fe2-xYxMo3O12 crystallized in a single monoclinic for x≤0.4 and a single orthorhombic structure for x≥0.5. The monoclinic to orthorhombic phase-transition temperature can be effectively decreased with increasing the contents of Y3+so that of Fe1.5Y0.5Mo3O12 crystallizes already in orthorhombic at room temperature and keeps this structure till to very low temperature (lower than 103 K).There are two kinds of water species presenting in Fe2-xYxMo3O12 for x> 0.8, one having little influence on the motions of the polyhedra and another interacting strongly with the polyhedra and hence deteriorating the negative thermal expansion properties of the materials. However, only one kind of water species which does not affect the motions of the polyhedra is found in Fe2-xYxMo3O12 for 0.4<x≤0.8.The materials of the A2M3O12 family are found to be suitable hosts for transition metal and lanthanide ions and have unusually high trivalent ion conduction as well. These features of the compounds are useful for many applications such as fuel cell, phosphor, luminescent materials, superconducting material, optical fiber, gas sensors and laser materials, etc. In this paper, the phosphor of Y2Mo3O12:Eu3+ and Y2Mo3O12:Er3+ are synthesized by high temperature solid-state reaction and their luminescence properties are investigated. It shows that the phosphor Y2Mo3O12:Eu3+ has four major emission peaks locating at 594 nm,613 nm,655 nm and 701 nm and the phosphor Y2Mo3O12:Er3+ has major emission around 655-675 nm.更多还原