Résumé
Ferroelectric materials with the perovskite structure have drawn considerable attention for many years. Among them, PbZr1−xTixO3 (PZT) materials are particularly interesting due to their high piezoelectric response in the so-called "morphotropic phase boundary" (MPB) region. Recently, synchrotron X-ray powder diffraction experiments done by Noheda et al. showed the existence of a monoclinic (M) phase (near x ~ 0.5) between the tetragonal and rhombohedral phases1,2. The effect of high pressure on the physical properties of PZT has been studied recently3. Experiments based on electron diffraction4 and neutron diffraction studies5, Raman scattering results6, as well as theoretical calculations7 have indicated the existence of an intrinsic short range dynamical disorder over nearly the entire PZT solid solution. Rouquette et al. observed the presence of diffuse X-ray/neutron scattering in PbZr0.52Ti0.48O3 diffraction patterns which is an evidence of local lattice deformations with respect to the average structure. Additional high-pressure high-temperature investigations showed the disappearance of the polar phonons A1(TO) (which is the origin of the ferroelectric instability) upon compression around 5 GPa in agreement with neutron diffraction data. High-pressure high-temperature EXAFS experiments were carried out on BM29 at the ESRF to follow the corresponding changes in short-range order around Zr at the ferro-to-paraelectric phase transition. The EXAFS results at 300 K isotherm show a change in the fine structure that starts at 5.3 GPa and this is in consistent with the value of the curie pressure Pc obtained by neutron diffraction3 and Resonance Raman Spectroscopy3 experiments. By fitting the first coordination shell (Zr,Ti)O6 octahedra using a cubic model, the values of the Debye-Waller (DW) factor at different pressure points were obtained. A noticeable drop in the DW factor above 6 GPa was observed, and these values agree with the value of the DW for BaZrO38 that has a centro-symmetric structure with no shift in the position of the Zr atom. This drop at an isotherm can be considered as a representative of the polar displacement and therefore of the ferro-to-paraelectric phase transition. Below 6 GPa, the obtained values of DW are in good agreement with what was obtained for PZT9. 1B. Noheda, D. E. Cox, G. Shirane, J. A. Gonzalo, L. E. Cross, and S.-E. Park, Appl. Phys. Lett. 74, 2059 (1999). 2B. Noheda, J. A. Gonzalo, L. E. Cross, R. Guo, S.-E. Park, D. E. Cox, and G. Shirane, Phys. Rev. B 61, 8687 (2000). 3J. Rouquette, J. Haines, V. Bornand, M. Pintard, Ph. Papet, R. Astier, J. M. Léger, and F. Gorelli, Phys. Rev. B 65, 2141021 (2002); J. Rouquette, J. Haines, V. Bornand, M. Pintard, Ph. Papet, W. G. Marshall, and S. Hull, Phys. Rev. B 71, 024112 (2005). 4 A.M. Glazer, P.A. Thomas, K. Z. Baba-Kishi, G. K. H. Pang, and C. W. Tai, Phys. Rev. B 70, 184123 (2004). 5 D. L. Corker, A. M. Glazer, R. W. Whatmore, A. Stallard, and F. J. Fauth, J. Phys.: Condens. Matter 10, 6251 (1998). 6 J. Frantti, S. Ivanov, J. Lappalainen, S. Eriksson, V. Lantto, S. Nishio, K. Kakihana, and H. Rudlöf, Ferroelectrics 266, 73 (2002). 7 I. Grinberg, V. R. Cooper, and A. M. Rappe, Nature 419, 909 (2002). 8 C.Laulhe, F.Hippert, J.Kreisel, M.Maglione, A.Simon, J.L.Hazemann, and V.Nassif, Phys. Rev. B 74, 014106, (2006). 9 D.Cao, I.-K.Jeong, R.H.heffner, T.Darling, J.-K.Lee, F.Bridges, J.-S.Park, and K.-S.Hong , Phys. Rev. B 70, 224102, (2004).