锆钛酸铅在高压下的拉曼光谱

THE RAMAN SPECTROSCOPY OF PZT UNDER HIGH PRESSURE

赵振征

11649048

硕士

物理学

赵予生

2018-05-30

2018-07-03

哈尔滨工业大学

深圳

锆钛酸铅是一种非常优异的压电、铁电和介电材料，已经广泛应用于铁电存储器、微器件和红外探测器等多方面。最近在锆钛酸铅准同相界附近发现了两个低温单斜相，对其具有优良性质的起源有了更进一步的解释。本文选择了在准同相界附近的PbZr0.52Ti0.48O3（PZT）及反铁电相PbZrO3（PZO）作为研究对象，利用金刚石对顶砧及变温拉曼光谱作为研究手段，对固相煅烧法制成的样品进行了结构和相变的研究。研究发现 PZT 由三方相和四方相组成，而且分别在4.70 GPa 和5.98 GPa 时发生了相变，对应于三方相完全转化四方相和四方相转化为立方相。随着压力上升，A1(1TO)和A1(2TO)模逐渐消失，到了相变压力以上时并没有完全消失，还可以观察得到两个很小的峰，说明在立方相中还存在极化小区域。利用变温拉曼进行测试，在低温下发现了两个单斜相（Cm 和Cc），其中单斜相Cm 是三方相R3m 和四方相P4mm 之间的过渡相。在高温下，PZT 首先在623K 以下某个温度时由三方相完全转变为四方相，再由四方相转变为立方相，其居里温度为648K，在居里温度点以上，立方相同样能观察到拉曼峰，说明在立方相中存在一些极化小区域。对 PZO 进行高压下的拉曼光谱测量，在升压过程中，除了发现2.85 GPa 和21.76 GPa 发生相变之外，还在30.50 GPa、36.81 GPa 和39.57 GPa 发生了相变，其中可以观察到在36.81 GPa 时低频波段出现两个明显的拉曼峰。在43GPa 以上时因背景太强而观察不到任何信息了。降压过程中又与升压过程有所不同，相变分别发生在40.72 GPa、36.02 GPa、28.25 GPa 和20.72 GPa；从20.72 GPa 到1.18 GPa都没有观察到相变的发生，说明相变发生了延迟，可能直到常压PZO 才完全变成具有Pbam 空间群的相。对高温下PZO 进行拉曼光谱测量发现在529K 时发生了相变，转变为立方相，但在立方相中还可以观察得到PZO 的拉曼峰，说明在样品在相变时伴随着有序无序的发生和Pb2+离子产生了位移。

Lead zirconate titanate (PZT) is a very excellent piezoelectric, ferroelectric and dielectric material that has been widely used many aspects such as ferroelectric randomaccess memory, micro devices and infrared detectors. Recently, two monoclinic phases were discovered at lower temperature near the morphotropic phase boundary of PZT which could further reveal origin of excellent properties of PZT. In this thesis, PbZr0.52Ti0.48O3 near the morphotropic phase boundary and PbZrO3(PZO) are selected as the research objects. The diamond anvil cell and Raman spectrometer are used as research tools to study phase transition of samples which are from the solid phase sintering method.It is found that PZT is comprised of rhombohedral phase (Space group: R3m) and tetragonal phase (Space group: P4mm) at room temperature and undergoes phase transitions at 4.70 GPa and 5.98 GPa, respectively, which correspond to from rhombohedral phase changed to tetragonal phase and from tetragonal phase changed to cubic phase. The intensity of A1 (1TO) and A1 (2TO) modes gradually decreases but not completely disappear above the phase transition pressure. It shows that there are some small polarized areas in the cubic phase, which is caused by cation disorder. By using Raman spectrometer which the temperature can change, two monoclinic phases (Cm and Cc) were found at low temperatures. And the group Cm is the subgroup of group R3m and group P4mm, so the monoclinic phase Cm phase is regard as the transitional phase between the rhombohedral and tetragonal phase. At high temperatures, PZT firstly transforms from trigonal phase into tetragonal phase at the temperature below 623K, and then into cubic phase above the Curie temperature of 648 K. Above the Curie temperature, some Raman peaks can also be observed, indicating that there are still some small polarized regions in the cubic phase.In the Raman spectroscopy measurement of PZO under high pressure, in addition to phase transition occurred at 2.85 GPa and 21.76 GPa during the pressure increasing, phase transitions also take place at 30.50 GPa, 36.81 GPa and 39.57 GPa. It can be observed that there are two distinct Raman peaks in the low frequency band at 36.81GPa. Above 43 GPa, no information is observed due to the strong background. The process of pressure decreasing was different from the process of the pressure boosting. When the pressure decreases, the phase transitions occurs at 40.72 GPa, 36.02 GPa, 28.25 GPa, and 20.72 GPa, respectively. No phase transitions are observed from 20.72 GPa to 1.18 GPa, indicating that phase transitions retard when the pressure reduces. The PZO with the Pbam space group does not appear until at the atmospheric pressure. Raman spectroscopy measurement of PZO at high temperature reveals a phase transition which transforms a cubic phase at 529 K. However, the Raman peak of PZO can also be observed in the cubic phase, indicating that the phase transition of the sample is accompanied by order-disorder and some ions have shifted.

锆钛酸铅 锆酸铅 拉曼光谱 金刚石对顶砧 准同相界 相变

PbZr0.52Ti0.48O3 PbZrO3 Raman diamond anvil cell morphotropic phase boundary phase transition

中文

联合培养

哈尔滨工业大学

赵振征. 锆钛酸铅在高压下的拉曼光谱[D]. 深圳. 哈尔滨工业大学,2018.