Thursday, 19.10. 2017, 14.00,
Lecture room F2 (1st floor), MFF UK, Ke Karlovu 5
Cinthia Antunes Corrêa
Institute of Physics of the Czech Academy of Sciences
Phase transitions of Cu3+xSi and crystal structures of
η’’-Cu3+xSi and η’’’-Cu3+xSi
The binary phase diagram of Cu-Si was extensively studied and is considered well estab-lished. Three phases are reported in the Cu3+xSi phase-field: η’’ below 470°C, η’ between 470°C and 560°C, and η up to 859°C, where it melts congruently. However, our investigation of samples of Cu3+x Si with nominal composition 74%, 76% and 78% copper suggests a more complex phase diagram than what have been assumed. In this talk I will present our analysis of Cu3+x Si by temperature dependent powder x-ray diffraction (PXRD), in-situ high-temperature single crystal x-ray diffraction (SCXRD), and differential scanning calorimetry (DSC), within the temperature range of 30°C to 750°C. The temperature dependent powder x-ray diffraction revealed a complex phase diagram, where six distinct phases could be identi-fied within the Cu3+xSi phase-field: in order of increasing temperature, η’’’, η’’, η’, η3, η2 and η1. Single crystal x-ray diffraction data enabled us to elucidate the crystal structures of η’’’ and η’’. The structures are incommensurately modulated, whose diffraction patterns could be indexed in a trigonal unit cell and two modulation vectors q1=(α,β,1/3) and q2=(-α-β, α,1/3). Powder diffraction patterns were indexed using the models obtained by SCXRD and the in-dexed patterns were used to characterize the phase transitions. Differential scanning calorime-try confirmed four of the five transitions by PXRD.