The characteristics of the diffuse phase transition of Pb(Fe2/3W1/3)O3 relaxor ceramics doped with different amounts of Mn are investigated. The freezing temperature Tf, obtained by fitting the ω,Tmax to the Vogel–Fulcher relationship, clearly changes with the Mn content. It increases as the Mn content increases, approaching the Tmax(1 MHz) value of the relaxor curve. A concomitant decrease in the frequency dispersion of Tmax is also observed. The freezing temperature also increases as the 1:1 order of Fe3+ and W6+on B sites increases by air annealing but decreases by oxygen annealing. It is suggested that the Mn ions, which are predominantly compensated by oxygen vacancies, form with them defect pairs and that these pairs can couple to the spontaneous polarization vectors, increasing the correlation between the dipole moments and originating the increase of the freezing temperature. It is further suggested that filling up the oxygen vacancies by oxygen annealing will decrease the defect pairs and cause the opposite effect.

No abstract

No abstract

Outburst floods can have disastrous impacts on people, and are an important driving force in landscape change and have been studied widely on Earth. In China, although outburst floods have occurred frequently, they have been relatively little systematic studied. Here, we review outburst floods in China in terms of the characteristics, distribution, causes of dams and outburst floods. In terms of natural dams, landslides accounted for the majority (287 cases), followed by moraine dams (33 cases), which are mainly found on and around the Tibetan Plateau, and although other types (such as glacier and volcanic dams) were historically rare, many examples may be preserved in the geologic record. In addition, there have been thousands of outburst floods from artificial-constructed dams, the majority of which were from small earth dams. The largest reliably recorded peak discharge for an outburst flood was 1.24×10 5 m 3 /s, which occurred in Yigong, Tibet. The peak discharge of the 1975 Banqiao collapse was 7.9×10 4 m 3 /s, was the largest outburst flood of man-made dam. Our recent investigations on the Yarlung Tsangpo in Southeast Tibet have identified gravel deposits that probably record megafloods and offer great potential for paleoflood analysis.