Phase transitions of Cu3+xSi observed by temperature-dependent x-ray powder diffraction

Phases in the system Cu3+xSi were analyzed by temperature-dependent x-ray powder diffraction and differential scanning calorimetry on samples with nominal composition Cu74Si26 and Cu78Si22 in the temperature range between 30 °C and 700 °C. Contrary to previous works, which report three phases in the system, we identified six distinct phases, labeled, in order of increasing temperature, η‴, η″, η′, η3, η2, η1. All these phases can be indexed with a similar basic unit cell. However, each phase has a different superstructure or modulation vectors.