Temperature dependence of the soft acoustic shear modes in h.c.p. zirconium

Neutron measurements of the dispersion curve v(q) for 10·0] phonons polarized in 11·0] are presented for hexagonal close-packed Zr at 300°, 773°, and 1073°K. Given that the crystal transforms to b.c.c. at 1135°K and demonstrates a pronounced softening in the C₆₆ elastic constant, v(q) shows only a uniform lowering of the entire branch, consistent with the behavior of C₆₆(T) but fractionally smaller for large wave vectors. No anomalous phonon linewidths are observed.