Absence of the c/a anomaly in Zn under high pressure with a helium-pressure medium

A high-pressure powder x-ray diffraction experiment on Zn has been carried out at room temperature with He pressure-transmitting medium in order to ac hieve the best hydrostatic conditions. The anomaly in the volume-dependence of the c/a axial ratio, which has been observed previously, can no longer be observed. Hence the anomaly is most probably induced by the nonhydrostat icity associated with the solidification of the methanol-ethanol-water pres sure-transmitting medium used in the previous studies. The present results suggest reconsideration of the calculated c/a anomaly based on the electron ic topological transition. [S0163-1829(99)11233-5].