Study of relaxation process in the incommensurate phase by means of specific-heat spectroscopy.

最近我们发现铁电亚硝酸钠的热容在无公度相内温度突变时表现出时间依赖性。在玻璃化转变附近的有限情况下，也曾报道过热容量的这种动态变化，而在无公度相中发现了“时间依赖性热容量”，这还是第一次。在开始测量之前，对量热计的精度进行了改进。在新的装置中，热浴的温度测量使用交流驱动的惠斯通电桥，这是比直流驱动的电桥灵敏得多。利用该基金购买了一个锁相放大器、一个数字放大器等，用弛豫法对亚硝酸钠进行了测量。结果发现，在无公度相的弛豫过程超过几百秒，并且弛豫表现出明显的偏离简单的指数行为。我们还同时测量了热容和介电常数，发现它们的弛豫过程是一致的，并发现在DPPC、DMPC和DSPC等磷脂酰胆碱基水悬浮液的主相变过程中也观察到类似的弛豫过程。从多频交流模式测量，弛豫时间和表征弛豫时间分布的参数β已被估计。应注意的是，再结晶时间强烈地取决于侧链长度。

Recently we found that the heat capacity of ferroelectric sodium nitrite shows time-dependence when the temperature is changed suddenly within the incommensurate phase. Such a dynamic behavior of the heat capacity has been reported before for only limited cases including in the vicinity of the glass transition, and this is the first case that the "time-dependent heat capacity" is found in the incommensurate phase.Before starting the measurement, the precision of the calorimeter was improved. In the new apparatus, the temperature of the thermal bath is measured using an ac-driven wheatstone bridge, which is much more sensitive than the dc-driven bridge. An lock-in amplifier, a digital multimeter, etc, were purchased by the grant.Using the new apparatus, measurements were done on sodium nitrite by the relaxation method. It was found that the relaxation in the incommensurate phase proceeds over more than a few hundreds seconds, and that the relaxation shows a distinct deviation from the simple exponential behavior. We also done a simultaneous measurement of heat capacity and dielectric constant, and found that their relaxation processes agree quite well with each other.We also found that similar relaxation processes are seen during the main transition in aqueous suspensions of phosphatidylcholinesky such as DPPC, DMPC, and DSPC. From multi-Frequency ac-mode measurements, the relaxation time and the parameter beta which characterizes the distribution of relaxation time have been estimated. It is to be noted that the rexlaxation time strongly depends on the side-chain length.