金刚石压腔结合拉曼光谱技术进行Pb掺杂对二氧化锡高压结构性能的影响研究

因稳定的分子结构和物理化学性质,近年来SnO2在光、电、磁等方面应用日益广泛。为拓宽SnO2应用范围,对高压条件下纯SnO2和Pb掺杂SnO2结构的相变行为和拉曼光谱活性振动模的变化进行了探究。实验采用水热法制备了纯SnO2和Pb掺杂量为10%的SnO2样品。扫描电子显微镜(SEM)图表明,上述制备样品由多个纳米棒从中心发散排列而成,整体成类花状。X射线衍射图谱表明,样品在常温常压下晶体结构为四方金红石型SnO2(空间群P 42)。采用Mao-Bell型金刚石压腔结合原位拉曼光谱探究了金红石型SnO2和Pb掺杂SnO2两种材料的高压相变过程。研究结果显示,两种材料加压至26 GPa过程中,纯SnO2和Pb掺杂的SnO2的活性拉曼振动模(B 1g,E g,A2g,B2g)均向高频移动。在14 GPa时,纯SnO2的E g峰分裂,563 cm-1处出现新峰,表明SnO2从常压四方金红石型结构向CaCl2型结构相变。Pb掺杂SnO2在常压拉曼谱图中出现了577 cm-1的拉曼峰。当加压至13 GPa时,B1g振动模向A g模转变,材料发生一级相变。上述对比表明Pb掺杂的SnO2具有更低的一级相变压力点13 GPa,结果归因于SnO2晶胞中Pb离子代替Sn离子,原子之间间距变小,离子大小不同造成掺杂后价态差异表面缺陷,导致SnO2结构稳定性降低,进而降低了相变压力。此外Pb掺杂SnO2在压力12 GPa时,晶体的对称性降低,577cm-1和639cm-1处特征峰宽化开始合并成包状峰,表明有部分晶体表面原子无序性程度增加,出现晶体向非晶的转变过程。继续加压至26 GPa,两种材料特征峰渐渐消失,并未观测到其他特征峰的出现。非静水压对相变压力也存在一定程度影响。非静水压条件下部分晶体更易趋向于非晶,晶界处存在较大的应力使纳米晶体在晶界处极易形成高压相成核点,导致相变发生,进而降低相变压力。本文研究不同条件下SnO2的相变行为,丰富了极端条件下SnO2的物理化学性质的多样性研究。

Study on the Influence of Pb Doping on High Pressure Structural Properties of Tin Dioxide Using Diamond Anvil Cell and Raman Spectra

Based on the stable molecular structure and physicochemical property,SnO 2 has been more and more useful in the field of optical,electrical and magnetic materials in recent years.In order to broaden the application of SnO 2,the research focused on the phase transition behavior of pure SnO 2 and SnO 2 doped by lead ions under high pressure,and the changes of Raman spectrum active vibration modes were investigated at the same time.The pure SnO 2 and SnO 2 doped by lead ions with 10%content were prepared by hydrothermal method.And the Scanning Electron Microscopy(SEM)images and X-ray diffraction(XRD)patterns of samples were measured.SEM images showed that samples were arranged as divergent nanorods which from the center to form a whole flower-like shape.XRD patterns showed that the crystal structure of samples was rutile tin dioxide(space group is P 42)at room temperature and pressure.In this paper,the high pressure phase transition processes of materials rutile tin dioxide and SnO 2 doped by lead ions with 10%content were investigated by using Mao-Bell Diamond anvil cell and in situ Raman spectroscopy.The results showed the active Raman modes(B 1g,E g,A 2g,B 2g)of pure SnO 2 and SnO 2 doped by lead ions all moved to high frequencies when the pressure was added to 26 GPa.The E g peak of pure SnO 2 split and a new peak appeared in 563 cm-1 when the pressure was added to 14GPa,which indicated that SnO 2 transformed from tetragonal rutile structure to CaCl 2 structure.The Raman peak of 577 cm-1 happened in the sample SnO 2 doped by lead ions in room pressure,and the vibration mode of B 1g changed to Ag mode when the pressure was addeda to 13 GPa which indicated the first-order phase transition of SnO 2 doped by lead ions.Compared to pure SnO 2,SnO 2 doped by lead ions had a lower first-order phase transition pressure,which were attributed to the fact that lead ions replace tin ions in SnO 2 cells.The spacing between atoms decreased and surface defects of valence difference happened after doping,which caused the decrease of structural stability of SnO 2 and the decrease of phase transition pressure.In addition,the characteristic peaks at 577 and 639 cm-1 of SnO 2 doped by lead ions began to coalesce into cladding peaks and its symmetry decreased when the pressure was added to 12 GPa,which indicated that the disorder degree of atoms on the surface of crystals increased and transition process from crystals to amorphous crystals occurred.The characteristic peaks of the two materials disappeared when the pressure reached to 26 GPa,and no other characteristic peaks were observed.Non-hydrostatic pressure in this research had a certain effect on the phase transformation pressure.The large stress at the grain boundary made nanocrystals form to nucleation point of high-pressure phases more easily,which might reduce the phase transformation pressure and cause some crystals tend to be amorphous more easily.In summary,the phase transition behavior of pure SnO 2 and SnO 2 doped by lead ions on different pressure conditions were studied,which enriched the diversity of physical and chemical properties of SnO 2 under extreme conditions.