Thin Film Superlattices of Lead Based Relaxors
- PDF / 363,823 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 11 Downloads / 182 Views
Thin Film Superlattices of Lead Based Relaxors M. H. Corbett, J. M. Gregg, R. M. Bowman Condensed Matter Physics and Material Science Division, Department of Pure and Applied Physics, Queen’s University Belfast, University Road, Belfast, BT7 1NN, UNITED KINGDOM. ABSTRACT Thin film capacitor structures in which the dielectric is composed of superlattices of the relaxors [0.2Pb(Zn1/3Nb2/3)O3 – 0.8BaTiO3] and Pb(Mg1/3Nb2/3)O3 have been fabricated on MgO {100} substrates by Pulsed Laser Deposition. Structural studies show dielectrics to be 100% perovskite, with strong chemical distinction between individual relaxor layers. The dielectric properties of the superlattices were investigated as a function of periodicity. Significant enhancement of the dielectric constant was observed in relatively fine-scale superlattices, consistent with previous studies. However, unlike previous work, in these relaxor superlattices dielectric enhancement is not associated with increased loss. Rather tan δ is low across the entire superlattice series. Polarisation measurements as a function of temperature suggest that the observed enhancement in dielectric constant is associated with the onset of coupled behaviour. The thickness of the individual layers in the superlattice at which coupled functional behaviour becomes apparent is ~10nm and is comparable to that found in literature for coupled structural behaviour.
INTRODUCTION An enhancement of the dielectric constant of thin film ferroelectrics is believed to be obtainable if two or more materials are multi-layered together in a fine superlattice structure [1,2]. Experimental work has shown this to be the case [3-6]. However the degree of observed enhancement and the scales of superlattice periodicity at which enhancement occurs are inconsistent across the literature. Recent work has noted that such increased dielectric constants can be correlated to the onset of significant Maxwell-Wagner effects rather than any co-operative dielectric interaction [7], and modelling has shown that all the novel features displayed by ferroelectric superlattices can be generated by Maxwell-Wagner considerations [11]. The implication is that increased defect-related transport, rather than dielectric interactions between nanolayers, is responsible for the enhancements experimentally observed. In spite of this, work on the structural phase transformation behaviour in KTaO3/KNbO3 superlattices [8] indicates that genuine coupled behaviour can occur at fine layer thicknesses. To date though, such inter-layer coupling has not been clearly manifested in functional properties. In an attempt to observe coupled functional behaviour in superlattices without interference from Maxwell-Wagner effects, the authors have studied thin film capacitor structures in which the dielectric is composed of superlattices of two relaxor electroceramics [0.2Pb(Zn1/3Nb2/3)O3 – 0.8BaTiO3 (0.2PZN-0.8BT) and Pb(Mg1/3Nb2/3)O3 (PMN)]. This paper presents results from the study and their interpretation.
CC13.2.1
EXPERIMENTAL DETAILS Superl
Data Loading...
