INVESTIGADORES
TINTE silvia Noemi
congresos y reuniones científicas
Título:
Origin of the relaxor state in perovskite Pb(BxB'1-x)O3
Autor/es:
S. TINTE
Lugar:
Univ. Nac. de la Plata, La Plata, Buenos Aires
Reunión:
Workshop; Workshop on novel methods for electronic structure calculations & 6th FPLO Workshop; 2007
Resumen:
Perovskite-based A(B_xB´_1-x)O_3 relaxor ferroelectrics, as Pb(Sc_0.5 Nb_0.5)O_3 (PSN) and Pb(Mn_1/3 Nb_2/3)O_3 (PMN), are technologically inportant transducer/actuator materials with extraordinary dielectric and electromechanical properties. Relaxors exhibit phenomena on different length nad time scales that highlight their fundamental importance as disordered systems. Experiments suggest that the formation of polar nanoregions is the key, but until know, no first-principles based connection has been demostrated between atomic-level interactions and the formation of polar nanorefions. In this talk I will present simulation results of first-principles-based effective Hamiltonians for PSN under hydrostatic pressure and for PMN at ambient pressure taht show clear evidence of a relaxor state in these systems.[1] The simulated systems contain chemically ordered nanodomains in a chemically disordered matrix. Their phase transitions are controlled by the polarization of the chemically ordered regions. At sufficiently high temperature, these regions are unpolarized. Below a temperature corresponding to the experimental Burns temperature, these regions become polars (i.e . form polar nanoregions), but without long-range order, and the disordered matrix remains unpolarized. For PSN under intermediate pressure, a first-order transition to a ferroelectric phase is observed at lower temperatures. The effect of pressure in PSN demostrates that the stability of the relaxor state depends on a delicate balance between the energetics that stabilize normal ferroelectricity, and the average strngth of the ´random´ local fields, that promote thte relaxor state.[1] S. Tinte, B. Burton, E. Cockayne, U. Waghmare, Phys. Rev. Lett. 97, 137601 (2007).