Displacement parameter, soft-mode frequency, and fluctuations in quartz below its α-β Phase transition

The displacement parameter in α-quartz consists of a rotation of the SiO4 tetrahedra around their two-fold symmetry axis. Its magnitude is given by x0(ω,T)-x0(ω,Tc)=A(ω)×(Tc-T)β, with β=0.34±0.02 as determined independently by x rays, ultrasound, and Raman scattering. © 1971 The American Physical Society.