Non Ergodic Aging in an Orientational Glass

Abstract

: In K1-xLi,Ta03, small Li+ ions are randomly substituted to large K+ ions. They take off-centre positions creating therefore electric dipoles and elastic quadnrpoles at random sites. This disordered system presents frozen random interactions and frustration. For x > 2.5 %. thermal hysteresis signals a structural transition with a first order character towards a ferroelectric low temperature phase. For x c 2.5 %, at low temperatures the system is frozen in a disordered phase called orientational glass. Measurements of the dielectric constant E and of the elastic constant c provide a lot of information about the nature of the transition and the relaxation of the Li+ ions which has been studied in detaik and analyzed in the form of Argand diagrams exhibiting a very particular (strophoidal) shape. After zero field cooling from 100 K to 4.2 K the time evolution of E and c during 80,000 s has been followed. The behaviour of the system (amplitude and asymptot) strongly depends on the cooling rate. The fact that the asymptotic limit depends on the initial conditions shows that ergodicity is broken in this system.

Aging of the asymmetry induced by the biasing electric field in a disordered ferroelectric

“…Discussion. -Aging experiments in disordered ferroelectrics are well interpreted in the framework of a model [13][14][15] which attributes the time-dependent part of the dielectric constant to the evolution of the polarization domain walls [16]. The isothermal evolution is very slow because it is hindered by the Nb 5+ invited impurities which are frozen below T tr .…”