【作者】 许杰；

【导师】 王万录； 雒建林；

【作者基本信息】 重庆大学 ， 凝聚态物理， 2003， 硕士

【摘要】 比热是凝聚态物质最重要的宏观参量之一。在很低的温度下，由于晶格振动变得很弱，电子和低能激发贡献越来越突出，这对我们通过低温比热研究很多现象的微观机制十分有利。系统、子系统的熵或微观状态数与微观粒子间的相互作用及能级分布密切相关，因此研究比热与温度的依赖关系能够提供被测量系统许多极其有用的微观信息，对理解固体的电子结构、电子态密度、声子谱等起着十分重要的作用。低温比热的测量和研究对热力学第三定律、固体量子理论和超导BCS等理论的建立起到了积极的推动作用。比热研究还有助于认识各类相变〔如结构相变, 磁性相变, 超导相变等〕及临界点附近的标度规律。为了研究毫克量级的小样品的比热随组分或其它因素的变化，从总的热容或晶格贡献中分离出附加的热容。我们研制和开发了绝热连续升温差分比热测量装置。和普通的差分比热设备相比,我们的绝热连续升温差分比热测量装置主要有以下几个方面创新:a.在测量原理上有改进,我们在测量中保证待测样品和标准样品的温度一致,代替了加热功率一致,同时用42对热电偶作为测温元件来控制两个样品温度的一致性,这样一方面提高了测量的灵敏度,同时使得样品的连续升温容易实现,提高了测量效率;b.采用惠斯通电桥来控制两个样品间加热功率的比例, 这样能够更准确控制和测量两个样品加热的功率差异，从而提高了测量的灵敏度。和普通差分比热设备相比，本装置的分辨率由1：1000提高到1：10000，甚至更高。目前是国际上同类装置中分辨率最高之一。 c.为了保证与环境绝热，在样品架与铜块之间安装了20对热电偶，同时还在铜块和内辐射屏之间装了5对热电偶来监视样品与环境的温差，以便于自动加热控温。 d.所有加热控温、数据采集和分析处理都是按照我们自已设计的算法开发出来的软件通过电脑自动控制，以代替手工操作的不准确性。同时，我们研究了用自组装法制备的纳米结构的聚苯胺在低温下的比热性质。我们测量了聚苯胺及其掺杂盐酸后在1.8K至45K的热容，利用声子－分形子模型来处理非晶态对比热的贡献，对获得的数据进行处理，发现EB和ES的比热数据均不符合德拜理论，超出德拜模型的比热来源于非晶态的贡献。我们引进声子-分形子模型，并用晶态贡献和非晶态贡献叠加的方法成功地拟合了实验数据，解释了聚苯胺掺杂盐酸后比热升高的原因。在测量温区内，没有观察到电子对比热的贡献。更多还原

【Abstract】 Specific heat is one of the most important parameters in condensed matter physics. Because the lattice vibration is weak at very low temperature, the contributions of electrics and other low energy excitations become dominant parts of specific heat. Therefore, we can study the micromechanism of many physical phenomena from specific heat measurement. The entropy or number of states of system or subsystem are closely related to interaction of particles and energy level distribution, therefore , to study the temperature dependence of the specific heat may supply some important and useful microscopic information which may play an important role in understanding electronic structure, density of state, phonon spectrum etc. The specific heat measurements at low temperatures also play important roles in the finding of the third law of thermodynamics, the quantum theory of solid and BCS theory for superconducting etc. Moreover, specific heat measurements help us to understand the different kinds of phase transitions (such as: structural phase transition, magnetic phase transition, superconducting phase transition etc.) and the scaling behavior near the critical point. In order to study the change of specific heat of milligram samples with the changing components or other factors, we hope to separate addition part from the total specific heat or lattice contribution. So, we developed the adiabatic, continuous heating, differential specific heat measurement system. This system has several innovations shown as follows:a. We improved the measuring method. We keep the measured sample to have same temperature instead of heating power with the reference sample. At the same time, we use 42 pairs of thermopiles as the temperature sensor to keep the two samples to be at same temperature. It increases not only measurement sensitivity, also is easy to perform continuous heating the samples and improves measurement efficiency.b. We made use of Wheatstone bridge to control ratio of heating power between the samples, Thus , it enable to control and measure the differential heating power accurately. Consequently, it improves sensitivity of the system. The resolution of the measurement can reach from 1:1000 to 1:10000 or better in comparison with the traditional differential technique. At present, this system is one of the similar systems with the highest resolution.c. We installed 20 pairs of thermopiles between the sample holder and the copper<WP=5>heat sink, and 5 pairs of thermopiles between the copper heat sink and inner radiation shield respectively for sample adiabatic. They can monitor temperature difference very well and auto heat the samples.d. The soft ware of temperature control system, data acquisition and data analysis system are designed and written by ourself .Apart from setting up the Specific heat measured system, we investigated the specific heat of self-assembled PANI nanostructures at low temperatures. The specific heat of the emeraldine base form of polyaniline and the emeradine salt of polyaniline has been measured at temperatures between 1.8 and 45K. The experimental results have been interpreted in terms of the contributions from both the crystalline and the amorphous phases characterizing the polymer. Anomaly of the specific heat which is much larger than that would be expected from the Debye theory has been successfully explained by phonon-fracton model at low temperatures. The electronic specific heat has not been observed from the present data.更多还原