BEGIN:VCALENDAR VERSION:2.0 PRODID:Data::ICal 0.22 BEGIN:VEVENT DESCRIPTION:Sergey Vakhrushev\, Ioffe Institute\, St. Petersburg\, Russia\n \n
(PbZrO3)1-x-(PbTiO3)x (PZT) solid solutions probably represent the most studied group of functional dielectrics materi als. For many years the main efforts were devote to the study of the PZT c ompounds at the morphotropic boundary region (x&asymp\;0.5). However recen tly Zr-rich (x<\;0.06) compounds attracted new attention due to their po tential for the electric energy storage and electricaloric application. Be side possible application related interest these crystals demonstrate extr emely reach phase diagram including antiferroelectric\, ferroelectric and incommensurate phases.
\n\nIn my presentation I would like to concentrate on the dynamical features rela ted to the phase transitions in the Zr-rich PZT (including PbZrO3 itself) and in the PbHfO3. In the papers [1\,2] we demonstrated that the antiferroelectric phase transi tion In PbZrO3 with order parameter described by the wavevector qAFE< /sub>=(¼\; ¼\; 0) can be considered as a missed incommensurate transition with some arbitrary wavevector\, corresponding to the flat par t of the dispersion curve of the TA mode. Later in PbHfO3 and P bZrO3 at high pressure the minima at the TA dispersion curves w ere found [3\,4]\, resulting in the realization of the incommensurate phas es.
\n\nExtremely complicated diffraction pattern is obse rved in the PZr1-xTixO3 crystals with x&l t\;0.06. In the intermediate phase between the paraelectric and antiferroe lectric phases incommensurate phase is sometime observed similar to that i n the PbZrO3 under high presuure. And in addition complicated s ystem of the satellite peaks in the vicinity of the qM=(½ \; ½\; 0) including first order and second order satellites exists. In addition to the satellite peaks near the M-points we found second order satellites near the main Bragg peaks.
\n\nObserved diffra ction pattern can be fully described by the incommensurate structure deter mined by 2 wavevectors from the same star: q1=(0.5+&delta\; 0.5-&delta\; -&delta\;) \; and q2 =(0.5-&delta\; &delta\; 0.5+ &delta\;). Combination of the q1 and q2 describes all observed superstructure p eaks.
\n\nCreation of the true incommensurate phase can be attributed to the mode softening not at qM\, but at a position shifted from the zone boundary. Such unusual soft mode can be described i n terms of the coupling of 2 modes in the vicinity of M-point\, namely TA mode and oxygen tilt mode. Such coupling is forbidden at qM but became allowed aside of it. Proposed model provides qualitative agreement with the results of the inelastic and diffuse X-ray scattering measuremen ts \;
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