Electrical breakdown of short multiwalled carbon nanotubes

Electrical breakdown of short (∼50nm) multiwalled carbon nanotubes(MWNTs) is studied utilizing mechanically controllable break junction technique with goldelectrodes. Measurements of the conductance-biascharacteristics near the breakdown point revealed two different types of breakdown behavior for the short MWNTs. In one type designated as type I, the conductance increases nearly linearly with the bias and, over the breakdown point, decreases stepwise. On the other hand, in the type-II breakdown, the conductance shows a transient and irreversible increase right before the breakdown and subsequently jumps to zero. We consider that the type-II breakdown in vacuum is contact related, whereas the type-I breakdown occurs through the usual MWNT heatin

元素置換されたビスマス-バナジウム複合酸化物が示す高速酸化物イオン伝導と相変態挙動

京都大学0048新制・課程博士博士(工学)甲第15377号工博第3256号新制||工||1490(附属図書館)27855京都大学大学院工学研究科材料工学専攻(主査)教授 松原 英一郎, 教授 田中 功, 准教授 宇田 哲也学位規則第4条第1項該当Doctor of Philosophy (Engineering)Kyoto UniversityDFA

Phase Relationship of CsH2PO4-CsPO3 System and Electrical Properties of CsPO3

The dehydration behavior of the paraelectric phase of CsH2PO4 was investigated by thermogravimetric and X-ray diffraction analyses, and then the phase diagrams of CsH2PO4–CsPO3 system were established. The relationship between the onset temperature of dehydration (Tdehy/K) and the partial pressure of water (pH2O/atm) is logpH2O=7.62(±1.18)−4.42(±0.56)(1000/Tdehy) below 228°C. The thermodynamically stable phase just above Tdehy is the fully dehydrated product CsPO3(s), although partially dehydrated products transiently appeared in the course of the dehydration to CsPO3. Such developments allowed us to complete the temperature-humidity phase diagram and to regard the composition-temperature phase diagram as the eutectic type. This paper also reports the phase transition and electrical properties of CsPO3 examined by differential thermal analysis, ac impedance spectroscopy, and dc polarization measurement. The just-synthesized CsPO3 showed the relatively high electrical conductivity in unhumidified Ar. Ionic conductivity as high as 5×10−4 S cm−1 was observed on heating from 150 to 450°C. Such high ionic conductivity disappeared after first heating up to 620°C and was explained by the proton diffusion through the absorbed H2O. At around 600°C, a high-temperature phase of CsPO3 showed the electrical conductivity as high as 10−3 S cm−1. However, this conductivity was not purely ionic

Phase Stability of Bi-2(V1-xMEx)O5.5+delta (ME = Li and Ag, x=0.05 and 0.1)

The phase transition of high oxide-ion conductor Bi2(V1 xMEx)O5:5þ (ME ¼ Li and Ag, x ¼ 0:05 and 0.1) and its long-term phase stability against thermal decomposition have been studied. The transition behavior was determined by differential scanning calorimetry (DSC) as well as high-temperature X-ray diffraction (HT-XRD) analysis. The observed thermal and structural changes during temperature scans reveal the temperature dependence of electrical conductivity. Li- and Ag-doping do not sufficiently suppress thermal decomposition at intermediate temperatures between 400 and 600 C. In particular, partial decomposition was detected in Bi2(V0:9Ag0:1)O5:3 during a temperature scan by HT-XRD analysis, which explains the distinct change in electrical conductivity. We have generated pseudo-binary phase diagrams for Bi2(V1 xMEx)O5:5þ based on the X-ray diffraction analysis of powders annealed for 200 h and differential thermal analysis. The thermodynamically stable region of Bi2(V1 xMEx)O5:5þ is not sufficiently expanded by Li- and Ag-doping. At around 500 C, Bi2(V1 xMEx)O5:5þ is metastable, although it shows the highest oxide-ion conductivity among solid oxides