Melting and homogeneity in germanium-silicon alloys and a modified micro-manufactured assembly for stable high pressure and temperature measurements

We present a modified assembly for high pressure and temperature measurements in a MAX80 press. The designs include a T-shaped power coupler with a ring-shaped insulator, a precision made, all-in-one single-piece crucible, with mirror-image located, flat-bottomed sample and pressure marker chambers, with press-fit lids and thermocouple insert in the middle of the crucible. These features facilitate assembly stability, reproducibility of in situ measurements, avoidance of chemical contamination, portability of assembly and ease of sectioning for further analysis. These attributes are important in evaluating phase relations at high pressure, especially where melting of the charge is investigated. While the cubic-diamond structured silicon-germanium system exhibits a complete solid solution, in practice, homogeneous solid solutions are not readily accessible because of the considerable difference in temperature between the liquidus and solidus and concomitant segregation coefficients. We use our designs, for in situ X-ray diffraction measurements and melting of germanium-silicon alloys at high pressure for both a germanium-rich and a silicon-rich starting composition.