Hydrostatic Pressure Derivatives of the Single-Crystal Elastic Moduli of Zirconium

The adiabatic elastic moduli of single‐crystal Zr vary linearly with hydrostatic pressures up to 4.7 kbar. The pressure derivatives are dC₁₁/dP=3.93, dC₃₃/dP=5.49, dC₄₄/dP=−0.22, dC₆₆/dP=0.26, dC₁₂/dP=3.42, and dC₁₃/dP=4.25. The average high‐temperature Gruneisen mode $\mathrm{\gamma ̄H}$ calculated from this data is in wide disagreement with that calculated from the volume thermal expansion coefficient. It is proposed that this disagreement arises because the negative dC₄₄/dP is caused by the change with pressure in the c/a ratio, rather than the volume change.