NMR Studies of Structural Phase Transitions of Quasi one-dimensional Jahn-Teller Crystals

ABX_3型Jahn-Teller晶体CsCuCl3和RbCuCl3发生了结构相变，并用核磁共振和核磁共振研究了结构相变。由于共振的频率、线宽和弛豫时间揭示了由相变引起的物理性质的变化，因此需要对这些量进行精确的测量。由于铜原子在室温下是复磁的，每个原子的共振信号的线宽和弛豫时间都比非磁性物质宽10个数量级。此外，由于需要在高温下进行测量，迫切需要提高S/N比，这必然导致核磁共振和核磁共振装置的建设和改进。该仪器的建设和改进有两个特点：1)研制宽线自动测量的边际振荡器。2)脉冲法核磁共振和核磁共振成像装置的研制。用这些装置测量了高温超导体YBa2Cu3O7-H&lt；0.2&gt；的~1H核磁共振。磁场穿透深度可由核磁共振谱线宽与温度的关系确定，从而获得了自旋-晶格驰豫时间T_1的知识。此外，在三氯乙醛异丁基半缩醛中使用C1NQR装置，提供了许多关于晶格缺陷的知识。对Jahn-Teller晶体CsCuCl3和RbCuCl3的研究以及对其结构相变起源的澄清将继续进行。

The ABX_3 type of Jahn-Teller crystal such as CsCuCl_3 and RbCuCl_3 undergo structural phase transition which has been studied microscopically by NMR and NQR. Since the change of physical properties induced by the phase transition is revealed by the frequency, line width and relaxation time of resonance, accurate measurement of these quantities is necessary. Since the Cu atom is par-amagnetic in room temperatures, line width and relaxation time of resonance signal of each atom are broader than those of non-magnetic substances by the order of 10. Moreover, since measurement at high temperatures are required, it was urgent to improve S/N ratio, necessarily resulting in construction and improvement of NMR and NQR apparatus. Following are two features in constructing and improving the apparatus 1) Development of a marginal oscillator capable of wide-line and automatic measurement. 2) Construction of apparatus for NMR and NQR for pulse method. These apparatus were employed in NMR measurements of ^1H nucleus of high temperature superconductor YBa_2Cu_3O_7- H_<0.2>. The magnetic field penetration depth can be de-termined from the temperature dependence of NMR line width and the knowledge of spin-lattice relaxation time T_1 has been acquired. Moreover, use of the apparatus for Cl NQR in Chloral Iso-Butylhemiacetal has given much knowledge about lattice defect. The study of Jahn-Teller crystals CsCuCl_3 and RbCuCl_3 and clarification of the origin of their structural phase transitions will be extensively continued.