Propriétés d'un point-mémoire en boracite Fe3B7O 13I ferro-électrique-ferro-élastique orthorhombique

Abstract

For a crystal (thickness 96 μm) of iodo iron boracite (Fe3B7O13I) entirely free of external and internal stresses (absence of self-blocking by differently oriented ferroelec. domains), the propagation velocity (v) of a 180°-domain wall at ambient temp. as a function of the elec. field (E) was given by v = v∞ exp[-δ/E], where v∞ is the limiting velocity at E = ∞, δ is the activation field, and v ≈2.2 × 10-3 cm/sec and 4.3 m/sec for E = 0.7 and 28 kV/cm, resp.; no intrinsic threshold field for ferroelec.-polarization reversal (switching) was obsd. for E ≥0.7 kV/cm. An elec.-switched domain, totally or partially surrounded by a domain of opposite polarization, spontaneously resumed its initial polarization at E = O via elastic backswitching; the stable configurations of domains having antiparallel polarization involved bands of domains that were parallel to 1 of the principal crystallog. axes and that extended over the whole width (or length) of the crystal. For a given E at -100 to +40°, v decreased with decreasing temp. For a crystal totally free of stress, no intrinsic ferroelec. fatigue was obsd. after >108 complete switching cycles. When the shearing angle (J. Kobayashi, et al., 1970) was decreased, the mechanism of switching via propagation of 1 or 2 domain walls changed to a mechanism involving nucleation of many approx. rectangular domains. Owing to domain interactions arising from the mech. and elec. proximity effects of neighboring domains, the individual memory elements of a monolithic unit cannot be arranged in a checkboard pattern and operated via cross-bar access.