铁弹性磷酸铅的结构相变：高温光散射研究

发布时间：2018-05-24 03:32

本文选题：磷酸铅 + 拉曼光谱　；参考：《新疆大学》2017年硕士论文

【摘要】：随着社会的发展和能源的消耗,环境污染问题越来越严重。多铁性材料的研究在解决该问题上能够提供一个很有效的解决方法。多铁性材料是多性能的材料,具有铁电、铁磁、铁弹的特性,同时具有两种或者两种以上铁性的新型材料。多铁性材料在现代科学研究领域与实际应用当中吸引了越来越多的关注,引发了大量的研究,发表了许多科研论文。目前为止依然是研究的热门话题之一。尽管如此,由于多铁性材料的铁弹性能很难满足实际应用的需要,因此发展铁弹性材料的弹性性能是非常重要的,并在该材料的研究中具有主导作用。磷酸铅Pb_3(PO_4)_2是一种典型的铁弹性材料。在材料和地球科学领域中,其在高压和室温下的相变行为采用各种方法已被广泛研究。本文采用高温拉曼光谱和高温布里渊光谱方法来研究铁弹性磷酸铅单晶体,发现该单晶体具有很强的铁弹性能力,晶体分别在光路平行极化、垂直极化、无偏振的情况下的内外振动模式、居里温度、生成的模数都不同而已。论文的主要工作,内容布局、得到的结果如下:(1)本论文的前三章主要是解释多铁性材料的研究背景、描述了国内和国外的研究现状和研究目的及其研究意义、分类、性能、自由能、热熔、应力与应变等理论基础,光的散射、晶体的相变以及相变的分类这为我们的科学研究打下一定的基础。(2)铁弹性磷酸铅单晶体在高温拉曼光谱研究。拉曼光谱中显示出,单晶体的温度高达182℃的显着变化,然后没有显示出明显的温度依赖性。在VH几何环境温度下41cm~(-1)处的模式显示轻度软化至182℃,并且在该温度以上消失,而在VV几何形状中,该最低模式在182℃以上没有完全消失。在温度大概达到180℃时,140 cm~(-1),159 cm~(-1)和184 cm~(-1)处的三个模随着温度的升高逐渐变宽。在386 cm~(-1)和413 cm~(-1)处的拉曼模式也合并成185℃以上的拉曼模式。表明当T_c=182℃时,在三角相中L点的失稳引起Pb_3(PO_4)_2的一阶铁弹相变,即从高温(HT)三角形铁弹相,空间晶体结构R(?)m-D_(3d)~5,向低温(LT)单斜相,空间晶体结构C2/C_(2h)~6,转变,从而使晶胞体积加倍。我们的结果也表明,高温相变过程非常复杂。VV几何振动模式中41 cm~(-1)处,最低拉曼模式的高温行为表明,尽管相转变发生在182℃,但是一些单斜晶体微畴仍然存在于T_c以上。在高于T_c的高温下的中间范围内的拉曼模式的广泛性质表明在三角相中存在无序的局部结构。(3)铁弹性磷酸铅单晶体在高温布里渊光谱研究。使用布里渊光谱学研究了高温下弹性Pb_3(PO_4)_2在后向散射几何中的弹性特性和相变机理。在室温下观察到一个纵向声学(LA)和两个横向声学(TA)模式,与反向散射几何中单斜对称的选择规则一致。在20℃至300℃的温度范围内测量三个声学声子。随着温度的升高,声子频率,线宽和强度显示明显的变化。在181℃时,两个TA模式减少到一个了。然后我们观察到只有两个声学声子直到300℃,表明从单斜晶系结构到较高对称相的相变。在180℃以上观察到的LA和TA声子与该测量几何中的三角对称性的选择规则一致。
[Abstract]:With the development of society and the consumption of energy, the problem of environmental pollution is becoming more and more serious. The study of multi iron materials can provide a very effective solution to this problem. The multi iron material is a multi performance material with the characteristics of ferroelectric, ferromagnetic and iron, with two or more than two kinds of iron. Sexual materials have attracted more and more attention in the field of modern scientific research and practical applications, which have caused a lot of research and published many scientific research papers. So far, it is still one of the hot topics of research. Nevertheless, the development of ferroelastic material is due to the difficulty of the ferroelastic properties of the multi iron material to be full of practical application. The elastic properties of the material are very important and play a leading role in the study of the material. Lead phosphate Pb_3 (PO_4) _2 is a typical kind of iron elastic material. In the field of material and earth science, the phase transition behavior at high pressure and room temperature has been widely studied. The spectral method is used to study the iron elastic lead phosphate single crystal. It is found that the single crystal has a strong iron elastic ability. The internal and external vibration modes of the crystal are in parallel polarization, vertical polarization and no polarization respectively. The Curie temperature and the generated modulus are different. The main work of the paper and the content layout are as follows: (1) this paper (1) this paper The first three chapters mainly explain the background of the research on the multiferroic materials, and describe the status and purpose of research at home and abroad and the significance of research, classification, performance, free energy, thermal melting, stress and strain and other theoretical bases, light scattering, crystal phase transition and phase transition. (2) iron Raman spectra of elastic lead phosphate single crystals show that the temperature of the single crystal is significantly higher than 182 degrees C, and there is no apparent temperature dependence. The mode of 41cm~ (-1) at the temperature of VH shows a mild softening to 182 C, and it disappears above the temperature, but in the geometry of the VV, The minimum mode is not completely disappearing at 182 degrees centigrade. At the temperature of 180 C, the three modes at 140 cm~ (-1), 159 cm~ (-1) and 184 cm~ (-1) gradually widen with the increase of temperature. The Raman modes at 386 cm~ (-1) and 413 cm~ (-1) are also merged into the Raman modes above 185 degrees C. Instability causes the first order iron elastic phase transition of Pb_3 (PO_4) _2, that is, from high temperature (HT) triangular iron projectile phase, space crystal structure R (?) m-D_ (3D) ~5, low temperature (LT) monoclinic phase, and C2/C_ (2H) ~6 of space crystal structure, so that the cell volume doubles. The high temperature behavior in the low Raman mode shows that although the phase transition occurs at 182 C, some monoclonal crystal microdomains still exist above T_c. The extensive properties of Raman modes in the intermediate range above the high temperature of T_c indicate that there is a disordered local structure in the triangle phase. (3) the high temperature Brillouin spectrum of the iron elastic lead phosphate single crystal. Study. The Brillouin spectroscopy was used to study the elastic properties and phase transition mechanism of elastic Pb_3 (PO_4) _2 at high temperature in backscattering geometry. A longitudinal acoustic (LA) and two transverse acoustic (TA) modes were observed at room temperature, consistent with the selection rules of monoclinic symmetry in the backscatter geometry. The measurement of three in the temperature range of 20 to 300 C Acoustic phonons. With the increase of temperature, the phonon frequency, line width and strength show obvious changes. At 181 C, two TA modes are reduced to one. Then we observe only two acoustic phonons until 300 degrees, indicating the phase transition from the monoclinic system to the higher symmetric phase. The LA and TA phonons observed above 180 degrees C and the measurement are also observed. The selection rules of trigonometric symmetry in geometry are consistent.
【学位授予单位】：新疆大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ134.33

【参考文献】