Lattice dynamics of disordered perovskite Pb(Zn1/3Nb2/3)O-3

Inelastic-neutron-scattering experiments were performed to investigate the phonon-dispersion relations in the cubic relaxer Pb(Zn1/3Nb2/3)O-3. The tra nsverse acoustic (TA) phonon branches have hat and isotropic dispersion cur ves. The zone-boundary [zeta zeta0]-TA(2) phonon energy is approximately 6 meV, considerably lower than the values reported for simple perovskites. Th e low-lying transverse optical (TO) branches drop sharply with decreasing: C, similar to the behavior observed for the complicated system Pb(Zn1/3Nb2/ 3)(0.92)Ti0.08O3 The constant-Q scans reveal the absence of the well-define d TO phonon spectra ill the range 0 less than or equal to zeta less than or equal to 0.1, in contrast with the sharp TA spectra. The TA, TA(2) and TO phonon energies at zeta = 0.1 and 0.2 decrease with increasing temperature up, to 673 K. The phonon hardening toward the transition temperature contra dicts the usual soft mode behavior in simple perovskites.