Kinetics and mechanism of the beta- to alpha-CuAlCl(4) phase transition: a time-resolved (63)Cu MAS NMR and powder X-ray diffraction study.
Kinetics and mechanism of the beta- to alpha-CuAlCl(4) phase transition: a time-resolved (63)Cu MAS NMR and powder X-ray diffraction study.
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DOI：
10.1021/ja010688v
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发表时间：
2001-07
影响因子：
15
通讯作者：
H. Liu;R. Sullivan;J. Hanson;C. Grey;J. Martín
中科院分区：
文献类型：
--
作者：
H. Liu;R. Sullivan;J. Hanson;C. Grey;J. Martín
用（27）Al和（63）Cu魔角自旋核磁共振谱对CuAlCl（4）的β和α相进行了表征。铜自旋的非常短的自旋-晶格弛豫时间，以及I = 3/2（63）Cu核对两相中Cu局部结构的微小差异的敏感性，允许在非常短的时间段（1分钟）内获得（63）Cu光谱，其中β和α相被清楚地分辨。利用这种时间分辨率来跟踪从伪六方密排β-CuAlCl（4）到伪立方密排α-CuAlCl（4）的相变，该相变发生在100摄氏度以上。原位时间分辨（63）Cu MAS NMR和同步加速器X射线衍射实验被用来测量作为温度的函数的相变动力学。该转变被证明是一个一级相变，不涉及中间相，活化能为138 kJ/mol。动力学数据服从一阶Avrami-Erofe'ev速率定律。提出了一种一维生长机制，该机制涉及Cu（+）离子自扩散和[AlCl（4）]（-）四面体周期性旋转所施加的密集阴离子层的平移重组的组合。这种从β到α的相变可以在环境温度下由低分压的乙烯诱导。
The beta and alpha phases of CuAlCl(4) have been characterized by solid-state (27)Al and (63)Cu magic angle spinning nuclear magnetic resonance. The very short spin--lattice relaxation times of the copper spins, and the sensitivity of the I = 3/2 (63)Cu nucleus to the small differences in the local structure of Cu in the two phases, allowed (63)Cu spectra to be acquired in very short time periods (1 min), in which the beta and alpha phases were clearly resolved. This time resolution was exploited to follow the phase transition from the pseudohexagonal close-packed beta-CuAlCl(4) into the pseudocubic close-packed alpha-CuAlCl(4), which occurs above 100 degrees C. In situ time-resolved (63)Cu MAS NMR and synchrotron X-ray diffraction experiments were used to measure the kinetics of this phase transition as a function of temperature. The transformation was shown to be a first-order phase transition involving no intermediate phases with an activation energy of 138 kJ/mol. The kinetic data obey a first-order Avrami--Erofe'ev rate law. A one-dimensional growth mechanism is proposed that involves a combination of Cu(+) ion self-diffusion and a translational reorganization of the close-packed anion layers imposed by the periodic rotations of [AlCl(4)](-) tetrahedra. This beta to alpha phase transformation can be induced at ambient temperatures by low partial pressures of ethylene.