| dc.description.abstract | Thermal property plays an important role in the characteristic of bulk materials, the measurement is necessary to understand the underlying physics that leads to certain phenomena. However, the accurate measurement and characterization of thermal property of bulk materials can pose many challenges. In order to improve and modify the measurement of thermal property, two investigations of different region have been reported in this thesis.
A thermal rectifier is the heat transfer analog to the familiar electrical diode. And thermal rectification is very interest because of its potential to open up new ground for the control of heat transport. In the first study, the thermal rectification in a two–terminal bulk material has been measured. We have prepared pure metal, Au, and polycrystalline insulator, Al2O3, as the two-terminal bulk material which glued with Ag paste and ductile indium wire. Hereby, we made an experimental system (steady state method) which is essentially a measurement of the heat flow through the sample to detect the thermal rectification. The observed thermal conductance of Au-X-Al2O3 (X=Ag, In) in the forward and reverse direction is no rectifying effect with the temperature difference of 10 K between heat baths. We have calculated thermal rectification using thermal conductivity data and found that the calculation is in discordancy with experimental data.
In the second study, thermoelectric materials have great potential for use in solid-state power generation and cooling devices. These devices have numerous advantages over conventional methods, but they are not widely used today is because of the poor efficiency. Much of the effort in the thermoelectric field has been directed at improving the efficiency of thermoelectric devices. In order to improve the efficiency of these devices, solid understanding on the properties of the materials from which they are made is required. This usually involves extensive measurement of the thermal and electrical properties of the material. In many cases, the measurement of characteristics of bulk materials is necessary to understand the underlying physics the leads to certain phenomena. Measurement of the properties of bulk material often involves working with specific samples because of synthesis of bulks materials. The measurement of the thermal conductivity of the specific size samples has been a little bit formidable challenge for many years due to the low thermal conductance and the low mechanical strength of the sample. One of the methods developed to address this problem is the steady state method.
The steady state method was modified and the results and description of the modified technique are presented in this thesis. Improvements were made to the sample stage and measurement system. The system was evaluated with standards to confirm the validity of the measurements. Investigation of thermoelectric material, the thermal conductivity of CuxBi0.5Sb1.5Te3 (x=0.01) at room temperature is 1.25 W/m-K by steady state method. In addition, the Seebeck coefficient measurement was already established, and the sample stage and measurement are similar to the steady state method. However, our research included an investigation of all properties of thermoelectric materials of CuxBi0.5Sb1.5Te3, and the figure of merit (ZT) has been reported.
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