Phase transition and near-zero thermal expansion of Zr_(0.5)Hf_(0.5)VPO_7

The Zr_(0.5)Hf_(0.5)VPO_7 is successfully synthesized by the solid-state method with near-zero thermal expansion. Powder x-ray diffraction(XRD), Raman spectroscopy, thermal dilatometry, and scanning electron microscopy(SEM) are used to investigate the structure, the phase transition, and the coefficient of thermal expansion(CTE) of Zr_(0.5)Hf_(0.5)VPO_7. The investigation results show that the samples are of the single cubic type with a space group of Pa3ˉ at room temperature(RT).It can be inferred that the superstructure is transformed from the 3 × 3 × 3 superstructure to the 1 × 1 × 1 ideal crystal in a temperature range between 310 K and 323 K. The CTE is measured by a dilatometer to be 0.59 × 10~(-6) K~(-1)(310 K–673 K). The values of intrinsic(XRD) and extrinsic(dilatometric) thermal expansion are both near zero. The results show that Zr_(0.5)Hf_(0.5)VPO_7 has near-zero thermal expansion behavior over a wide temperature range.     

快速烧结合成Zr1-xMxW2O8(M=Hf,Sn,Y)固溶体的Raman光谱研究

首次采用快速烧结合成技术制备了Zr1-xMxW2O8 (M=Hf,Sn,Y)系列固溶体.制备的合适条件为:温度1523～1553 K,时间30 min～1 h,同传统固相反应烧结相比,该方法合成时间和能耗显著降低.XRD和Raman光谱分析表明,Zr1-xMxW2O8 (M=Hf,Sn,Y)固溶体具有α-ZrW2O8的...     

A2( MoO4)3(A=Al,Cr,Fe)结构与相变的Raman光谱研究

用XRD、Raman光谱和DSC研究了Al2 (MoO4)3、Cr2( MoO4)3和Fe2 (MoO4)3的结构与相变.Al2(MoO4)3、Cr2 (MoO4)3和Fe2 (MoO4)3在室温下为单斜相,分别在483 K、673 K和783 K附近转变为正交相.发现MO4四面体的对称和反对称伸缩振动模的频率和相对强...     

ZrV2-xPxO7固溶体的相变与热膨胀性质的研究

本文采用固相烧结法制备了ZrV2-xPxO7@=0,0．2,0．4,0．6,0．8,1）系列材料．粉末X射线衍射（XRD）分析表明,所制备材料的结构为单一立方相．应用变温拉曼光谱研究该材料相变,变温拉曼光谱研究结果表明,材料起始相变温度随着P5＋替代V5＋量的增加逐渐降低,x=0,0．4,0．8,1对应的相变温度分别为383K,363K,273K,213K．热膨胀测试结果表明：随着P替代量的增加正一负膨胀转变温度先降低后增加,x=0,0．2,0．4,0．6,0．8,1对应的正一负膨胀转变温度分别为429K,403K,372K,390K,398K和435K．本文指出了该系列材料存在两个相变过程,为设计和制备ZrV2O7基室温附近的负热膨胀材料奠定了良好的基础．     

Phase transition and thermal expansion property of Cr_(2-x)Zr_(0.5x)Mg_(0.5x)Mo_3O_(12) solid solution

Compounds with the formula Cr2-xZr0.5xMg0.5xMo3O12（x = 0.0, 0.3, 0.5, 0.9, 1.3, 1.5, 1.7, 1.9） are synthesized, and the effects of Zr4＋ and Mg2＋ co-incorporation on the phase transition, thermal expansion, and Raman mode are investigated. It is found that Cr2-xZr0.5xMg0.5xMo3O12 crystallize into monoclinic structures for x 〈 1.3 and orthorhombic structures for x _〉 1.5 at room temperature. The phase transition temperature from a monoclinic to an orthorhombic structure of Cr2Mo3O12 can be reduced by the partial substitution of （ZrMg）6＋ for Cr3＋. The overall linear thermal expansion coefficient decreases with the increase of the （ZrMg）6＋ content in an orthorhombic structure sample. The co-incorporation of Zr4＋ and Mg2＋ in the lattice results in the occurrence of new Raman modes and the hardening of the symmetric vibrational modes, which are attributed to the MoO4 tetrahedra sharing comers with ZrO6/MgO6 octahedra and to the strengthening of Mo-O bonds due to less electronegativities of Zr4＋ and Mg2＋ than Cr3＋, respectively.     

High Solubility of Hetero-Valence Ion （Cu^2＋） for Reducing Phase Transition and Thermal Expansion of ZrV1.6P0.4O7

Large thermal expansion at room temperature and high phase transition temperature of ZrV2O7 limit its practical applications and are reduced by the high solubility of hetero-valence ion （Cu^2＋） on the basis of an equal-valence substitution of P^5＋ for V^5＋. The temperature-dependent Raman spectra show that Zr0.9CU0.1V1.6P0.4O6.9 maintains a normal parent cubic structure till 173 K and transforms to a 3 × 3 × 3 cubic superstructure below 173K. Temperature dependent x-ray diffraction patterns of Zr0.9CU0.1V1.6P0.4O6.9 show near zero and negative thermal expansion. High solubility of lower valence Cu^2＋ relates to an equal-valence substitution of smaller pH for P^5＋, which extends the bond angle of V（P）-O-V in ZrV1.6P0.4O7 close to 180°. The change of microstructure is considered to be responsible for reduced phase transition temperature and thermal expansion.     

CO_2激光烧结合成负热膨胀材料Sc_2(MO_4)_3(M=W,Mo)及其拉曼光谱

用CO2激光烧结合成了负热膨胀材料Sc2(WO4)3和Sc2(MoO4)3.实验表明,激光合成负热膨胀材料Sc2(WO4)3和Sc2(MoO4)3属于快速合成技术,合成一个样品的时间仅需几秒到十几秒,具有快速凝固的特征;X射线衍射和拉曼光谱分析表明,所合成的材料为正交相结构,且具有较高的纯度;变温拉曼光谱分析表明,所合成的材料在室温以上没有相变,但可能有微弱的吸水性;在对Sc2O3,Mo O3,WO3,Sc2(MoO4)3和Sc2(WO4)3拉曼光谱分析的基础上,给出了激光光子能量及原料和合成产物的声子能级图,分析了激光烧结合成的机理.激光光子能量转化为激发声子的能量是光热转化的主要通道,原料在熔池中反应并快速凝固形成最终产物.     

Near-zero thermal expansion in β-CuZnV2O7 in a large temperature range

We report a new type of near-zero thermal expansion material β-CuZnV₂O₇ in a large temperature range from 173 K to 673 K. It belongs to a monoclinic structure (C2/c space group) in the whole temperature range. No structural phase transition is observed at atmospheric pressure based on the x-ray diffraction and Raman experiment. The high-pressure Raman experiment demonstrates that two structural phase transitions exist at 0.94 GPa and 6.53 GPa, respectively. The mechanism of negative thermal expansion in β-CuZnV₂O₇ is interpreted by the variations of the angles between atoms intuitively and the phonon anharmonicity intrinsically resorting to the negative Grüneisen parameter.     

不同氮源制备CNx纳米管薄膜及其低场致电子发射性能

采用高温热解法,分别以氯化铵(NH4Cl)和乙二胺(C2H8N2)为氮源在洁净的硅片上沉积生长CNx纳米管薄膜.利用扫描电子显微镜、高分辨率透射电子显微镜和拉曼光谱对CNx纳米管进行形貌观察和表征.结果显示不同氮源制备出的CNx纳米管薄膜的洁净度、有序度以及纳米管的结构明显不同.热解乙二胺(C2H8N2)/二茂铁(C10H10Fe)制备出的结晶度较低的"竹节状"结构CNx纳米管平行基底表面有序生长,而且低场致电子发射性能优越,开启电场1.0V/μm,外加电场达到2.89V/μm时发射电流密度为860μA/cm2.     

硼碳氮纳米管的热解法制备及生长机理研究

以乙二胺、二茂铁和硼氢化钠为原料,以N2和H2为辅气,用钴作催化剂,在不同温度下制备出了具有竹节状结构的硼碳氮(BCN)纳米管.根据透射电子显微镜观察,分析了BCN纳米管的生长机理.B和N的同时掺杂,所形成的五边形结构比单独N掺杂时具有更低的形成能,是竹节状结构形成的主要原因.用Raman光谱可以用来表征BCN纳米管中B和N的掺杂程度及纳米管的质量.分析表明,在860℃下制备的BCN纳米管竹节状结构最密集,质量最好,产率最高.扫描俄歇微探针分析表明,在860℃下制备的BCN纳米管的元素组成比为B∶N∶C= 关键词： BCN纳米管 热解 透射电子显微镜 Raman光谱