Evidence for another low-temperature phase transition in tetragonal Pb(ZrxTi1-x)O-3 (x=0.515,0.520) - art. no. 054101

Results of dielectric and resonance frequency (f(r)) measurements below roo m temperature are presented for Pb(ZrxTi1-x)O-3, x = 0.515 and 0.520. It is shown that the temperature coefficient of f(r) changes sign from negative to positive around 210 and 265 K for x = 0.520 and 200 and 260 K for x = 0. 515. Anomalies in the real part of the dielectric constant (epsilon') are o bserved around the same temperatures at which the temperature coefficient o f f(r) changes sign because of the electrostrictive coupling between the el astic and dielectric responses. Low-temperature powder x-ray-diffraction (X RD) data, however, reveal only one transition from the tetragonal to monocl inic phase similar to that reported by Noheda et al. [Phys. Rev. B, 61, 868 7 (2000)]. Electron-diffraction data, on the other hand, reveal yet another structural transition at lower temperatures corresponding to the second an omaly in the epsilon' vs T and f(r) vs T curves. This second transition is shown to be a cell-doubling transition not observed by Noheda et al. in the ir XRD studies. The observation of superlattice reflections raises doubts a bout the correctness of the Cm space group proposed by Noheda et al. for th e monoclinic phase of Pb(ZrxTi(1-x))O-3 below the second transition tempera ture.