水热法合成FeS2粉晶及其生长热动力学的研究

采用溶胶-凝胶水热法合成了单相黄铁矿结构的FeS2粉晶.用x射线衍射、傅氏变换红外光谱等分析手段对FeS2粉晶进行了表征,以简化的数学模型及相变理论讨论了晶体生长过程.结果表明:FeS2晶粒的生长过程属于相变与扩散的混合机制,符合经时间指数修正的二次方动力学方程,是一个生长速率随时间变化的过程;水热晶化温度高于453 K、反应时间超过18 h且有适量的硫参与反应时,可得到单相的黄铁矿型的FeS2.该过程可分为三个阶段:前期为白铁矿和黄铁矿的成核孕育阶段,中期为FeS2晶核以黄铁矿吞并白铁矿的相变方式逐渐长大的阶段,后期为小晶粒融合而大晶粒继续长大的扩散生长过程.     

水热法合成FeS2粉晶及其生长热动力学的研究

采用溶胶_凝胶水热法合成了单相黄铁矿结构的FeS2₂粉晶. 用x射线衍射、傅 氏变换红外光谱等分析手段对FeS2₂粉晶进行了表征，以简化的数学模型及相 变理论讨论了晶体 生长过程. 结果表明：FeS2₂晶粒的生长过程属于相变与扩散的混合机制，符 合经时间 指数修正的二次方动力学方程，是一个生长速率随时间变化的过程；水热晶化温度高于453 K、反应时间超过18 h且有适量的硫参与反应时，可得到单相的黄铁矿型的FeS2₂关键词： 溶胶_凝胶水热法 2粉晶')" href="#">FeS2₂粉晶 晶粒生长 热动力学     

受限钠盐水溶液孔外结晶现象

多孔材料内含盐水溶液中离子的析出结晶是造成多孔结构破坏的重要因素, 因此在建筑保护和地貌学研究中受到了极大关注. 现有研究主要集中于微孔介质中盐的孔内结晶行为. 本文对比研究了限制于纳孔硅胶颗粒孔隙内的NaCl, NaNO₃, Na₂SO₄三种盐溶液在蒸发过程中盐的孔外结晶行为. 利用扫描电子显微镜对所形成晶体的形貌进行了表征. 实验结果表明: 1) 随孔径从2 nm增加至15 nm, NaCl和NaNO₃在硅胶颗粒表面的结晶由晶粒转变为晶须形态, 而Na₂SO₄则由晶须转变为晶粒形态; 2) NaCl和NaNO₃晶须的生长主要沿垂直于颗粒表面的方向, 而Na₂SO₄晶须则在硅胶颗粒表面斜向生长, 后一种生长方式对硅胶颗粒产生横向的应力, 从而对孔结构具有更强的破坏作用; 3) NaNO₃的细长晶须所具有的分支和珠链结构表明其在结晶过程中发生了Plateau-Rayleigh失稳.     

对硅片上自组装生长的Pentacene薄膜生长机制及其结晶相态的研究

采用热蒸发的方法在硅片衬底上自组装生长的Pentacene薄膜,薄膜在80℃温度下经2 h恒温真空热处理,通过原子力显微镜(AFM)对Pentacene薄膜表面形貌及其生长机制进行研究.结果得到,在硅片上生长的Pentacene薄膜足以台阶岛状结构生长,其岛状直径约为100 nm.且Pentacene分子以垂直于衬底的方向生长,台阶岛状结构中每个台阶的平均高度约为1.54 nnl·s-1,与Pentacene分子的沿长轴方向的长度相近.从Pentacene薄膜的XRD图谱中可以看出,薄膜在形成的过程中会因条件的不同而形成不同的结晶相,分别为薄膜相和三斜体相,且薄膜的结晶相将随着薄膜厚度的增加向三斜体相转变,其临界厚度为80和150 nm,当薄膜大于150 nm时,薄膜的三斜体相占主导地位,而当Pentacene薄膜的厚度小于80 nm时,Pentacene薄膜呈薄膜相存在.     

SnO纳米晶须的制备及其性能表征

以SnCl2·2H2O为主要原料, Na2CO3 为矿化剂,十六烷基三甲基溴化铵为表面活性剂,采用压力热晶法,在160~200℃成功地制备出分散性好、晶型完整、结构稳定的氧化亚锡纳米晶须,并用透射电子显微镜、电子衍射、X射线衍射等技术手段对氧化亚锡纳米晶须的结构和形貌进行表征.表征结果显示,制得的SnO晶须具有棒状外观结构,其直径和长度分别为10~40、100~400nm. 实验还考察了反应时间、体系压力等条件对产物结构和形貌的影响,实验结果表明,增加压力和延长反应时间都有利于四方晶型氧化亚锡晶须的形成. 同时探论了四方晶型氧化亚锡纳米晶的须形成机理,初步认为其形成过程是一个成核并沿晶格延伸生长的过程.     

粤西眼球状花岗岩FeS_2拉曼光谱特征及意义(英文)

选取粤西官山嶂岩体眼球状花岗岩研究其内不同形态和期次FeS2的拉曼光谱特征。结果显示各组样品拉曼位移(Δν)、散射强度(Ι)及其半高宽(FHWM)明显不同。分析表明条带状样品拉曼位移Δν1,Δν2,Δν3分别位于318,381和440cm-1附近;而骸晶样品对应值分布于344,379和430cm-1附近;且与后者相比变形、自形样品对应Δν分别较向低频偏移。条带状样品ΙEgΙAgΙTg而其余样品ΙEg≈ΙAgΙTg;且自骸晶样品向自形、变形样品Ι及FHWM值均依次增大。上述光谱证据指示条带状样品Δν及Ι与白铁矿相似而其余样品均展现出黄铁矿的特征。与骸晶样品相比变形、自形样品Δν向低频偏移表明后二者形成温度依次增高;骸晶、自形、变形样品Ι及FHWM递增表明三者形成压力依次明显增大。据此研究认为官山嶂岩体内黄铁矿形成先后经历了:白铁矿期→高压黄铁矿期→高温黄铁矿期→常温常压蚀变期。     

粤西眼球状花岗岩FeS2拉曼光谱特征及意义（英文）

选取粤西官山嶂岩体眼球状花岗岩研究其内不同形态和期次FeS2的拉曼光谱特征。结果显示各组样品拉曼位移(Δν)、散射强度(Ι)及其半高宽(FHWM)明显不同。分析表明条带状样品拉曼位移Δν1,Δν2,Δν3分别位于318,381和440cm-1附近;而骸晶样品对应值分布于344,379和430cm-1附近;且与后者相比变形、自形样品对应Δν分别较向低频偏移。条带状样品ΙEgΙAgΙTg而其余样品ΙEg≈ΙAgΙTg;且自骸晶样品向自形、变形样品Ι及FHWM值均依次增大。上述光谱证据指示条带状样品Δν及Ι与白铁矿相似而其余样品均展现出黄铁矿的特征。与骸晶样品相比变形、自形样品Δν向低频偏移表明后二者形成温度依次增高;骸晶、自形、变形样品Ι及FHWM递增表明三者形成压力依次明显增大。据此研究认为官山嶂岩体内黄铁矿形成先后经历了:白铁矿期→高压黄铁矿期→高温黄铁矿期→常温常压蚀变期。     

Sm123 在Sm211晶须上取向生长研究

通过热力学参数的控制,我们在Sm-Ba-Cu-O的高温熔体中获得了长度可达4.2mm的Sm211晶须.通过SEM、HRTEM及SCXD等表征手段,对晶须的表面形貌和微观结构进行了分析,并确定其生长方向为晶须的<001>方向.通过高温金相显微镜,我们原位观察到Sm123 晶体在Sm211晶须上按照特定取向生长.本文对Sm123 与Sm211的取向关系进行了探讨.     

水热条件下生长FeS_2-Fe_(1-x)S异质结构的光吸收特征研究

铁硫系列矿物是重要的金属硫化物,FeS2和Fe1-xS分别是铁硫系列矿物的重要成员。其中黄铁矿(FeS2)具有较大的吸收系数及合适的禁带宽度,适用于做太阳能电池材料,具有较好的应用前景。前人对不同条件下的铁硫系列矿物光伏特性进行了一定的研究,但对于FeS2和Fe1-xS共存情况下光吸收性能研究较少。FeS2和Fe1-xS分别是铁硫系列矿物的重要成员,由于形成条件较为接近,常共生出现。因此,对FeS2和Fe1-xS光吸收性能的研究具有重要意义。以水热条件下合成微米粒状FeS2-Fe1-xS为样本,分别使用SSX-550扫描电子显微镜、多晶X射线衍射仪(XRD)观测表征粉末晶体的形态、成分和结构。结果表明:所测样品主要为FeS2中立方晶系黄铁矿,含有一定量的斜方晶系磁黄铁矿(Fe1-xS),样品平均粒度在5~10μm左右。用Cary500型紫外-可见近红外分光光度计在200~2 000nm范围内测出了样品的吸收谱介于1 860~1 889nm之间,吸收峰值为1 879nm。根据带隙(eV)公式计算样品的禁带宽度为0.657 8eV,对应的"极限转换效率"可达到15%左右,利用第一性原理分析样品禁带宽度变化的原因,并与前人研究结果进行对比。分析认为:矿物内部结构是影响光电转化的重要原因,所合成具有FeS2-Fe1-xS异质结构材料的光吸收特性,较天然地质体中含Co和Ni缺陷的黄铁矿光吸收特性好,光电转换效率有所提高,为深入研究Fe-S系列材料的光伏性能提供了科学依据。     

Sm123在Sm211晶须上取向生长研究

通过热力学参数的控制，我们在Sm-Ba-Cu-O的高温熔体中获得了长度可达4．2mm的Sm211晶须．通过SEM、HRTEM及SCXD等表征手段，对晶须的表面形貌和微观结构进行了分析，并确定其生长方向为晶须的〈001〉方向．通过高温金相显微镜，我们原位观察到Sm123晶体在Sm211晶须上按照特定取向生长．本文对Sm123与Sm211的取向关系进行了探讨．     

Sulphur L2,3 and L1 XANES investigations of pyrite and marcasite

S L_2,3 and L₁ XANES of the polymorph minerals pyrite (FeS₂) and marcasite (two different cleavage planes) were measured in total electron yield mode using synchrotron radiation. Small but distinct differences were found in the fine structure of these spectra. Calculations with the FEFF-8 code were performed to reproduce the experimental data. Ex situ UV–ozone oxidation of the samples reveals different reactivity. Sulphate was identified on the pyrite and one marcasite cleavage planes whereas the second plane normal to the first one oxidises with changing quanta of sulphate and sulphite.     

Hydrothermal synthesis of FeS2 for lithium batteries

Nanocrystalline FeS₂ cathode material of lithium cell was synthesized from cheap materials of FeSO₄, Na₂S₂O₃, and sulfur by a hydrothermal process. The scanning electron microscopy analysis showed the obtained material was nano-sized, about 500 nm. The X-ray powder diffraction analysis showed that the synthetic FeS₂ material had two phases of the crystalline structure, pyrite and marcasite. The phase of marcasite seems to have no negative effect on the electrochemical performance of the material. The synthetic FeS₂ showed a significant improvement of electrochemical performance for Li/FeS₂ cells.     

The quantitative determination of FeS2 phases in coal by means of57Fe Mössbauer spectroscopy

A knowledge of the concentration of pyrite and marcasite in coals can provide important insight into the genesis of coal deposits. Determinations of the relative amounts of pyrite and marcasite by traditional methods of coal analysis are, however, beset with many difficulties. Using⁵⁷Fe Mössbauer spectroscopy and a mild chemical treatment with hydrofluoric acid, a technique has been devised for the quantitative determination of the relative concentrations of pyrite and marcasite in samples of whole coals or their low-temperature ashes. The sample preparation procedure is comparable to less accurate methods. Good qualitative agreement has been obtained between ore microscopic and Mössbauer spectroscopic techniques for a series of extensively investigated whole coal samples.     

An ab initio study of 5d noble metal nitrides: OsN2, IrN2, PtN2 and AuN2

The crystal structure, phonon stability, elasticity and electronic properties of four noble metal nitrides (PtN₂, IrN₂, OsN₂ and AuN₂) with three structural types (pyrite, marcasite and CoSb₂ structure) were studied by first principles calculations. In agreement with experiments and previous theoretical predictions, it is found that the most stable structure for OsN₂ is marcasite, for PtN₂ is pyrite, and for IrN₂ is the CoSb₂ structure. It is found that these three compounds are thermodynamically metastable with respect to solid N₂ and the metal at zero pressure. The structures are mechanically and dynamically stable. The lowest energy structure of AuN₂ is the CoSb₂ structure. The formation energy of AuN₂ is found to be very high compared to the other three nitrides studied here. This underlies the experimental difficulty in the synthesis of this compound. OsN₂ is found to be metallic, while IrN₂ and PtN₂ are both semiconductors.     

Transformations of Pyrite and Pyrrhotite in Supercritical Water

The interaction of pyrite (FeS₂) with water at the uniform heating (1.5 K/min) of the reaction mixture to 923 K and its subsequent cooling (about 3 K/min) to 423 K is studied. The reaction products are analyzed using the methods of mass-spectrometry, elemental and X-ray diffraction analyses, and scanning electron microscopy. It is established that H₂S, SO₂, and rhombic and hexagonal pyrrhotite (FeS) are formed while heating, and the subsequent cooling of the reaction system gives rise to the formation of H₂S, H₂, cubic pyrite, and monoclinic pyrrhotite exhibiting ferromagnetic properties. It is shown that the transformations FeS₂ → FeS → FeS _x (1 < x ≤ 2) are accompanied by changes in the morphology and size of particles.     

FeS2能隙的外压微扰调制

 采用基于密度泛函理论的自洽赝势方法，计算了FeS₂在外压调制下的电子结构性质。计算结果表明：随着压缩度的增加，外压调制下的Fe—S键长缩短，FeS₂小的能隙变宽，Fe的d电子与S的p电子杂化增强，原子间相互作用增大。这一能隙随压力增大而增大的结果，与非导体在高压下金属化的特征相反。     

FeS2(pyrite)电子结构与光学性质的密度泛函计算

采用局域密度近似的自洽密度泛函理论计算了FeS2的电子结构与光学性质。费米能级附近区域的能带与态密度计算表明价带极大值在X（100）点和导带极小值在G（000）点，直接带隙和音接带隙分别为0.74eV、0.6eV。并用电子结构信息精确计算了介质极化矩阵元，从而给出了FeS2的介电函数虚部及相关光学参量，理论结果与实验符合甚佳。     

Electrical resistivity and band gap of marcasite (FeS2)

For a natural crystal of marcasite, an energy gap of 0.34 eV and an acceptor level at 0.052 eV are determined from temperature-dependent (53–370 K) electrical resistivity measurements. Magnetic susceptibilities and dielectric constants of marcasite and pyrite are compared in view of the large difference in their energy gaps.     

Pressure induced phase transition in MnTe2

Energy dispersive high-pressure powder X-ray experiments have been performed for MnTe₂ up to a pressure of 20 GPa. MnTe₂ undergoes a discontinuous transformation from the cubic pyrite type structure to the orthorhombic marcasite type structure at 7.0±0.5 GPa upon increasing pressure. The transformation is accompanied by a large reduction in the specific volume (ΔV/V=0.18) which probably reflects different magnetic properties of the two modifications of MnTe₂.