The paper will trace the evolution of understanding related to the modification of sharp ferroelectric phase transition behavior that occurs in composition systems which exhibit diffuse and relaxor ferroelectric properties. The focus will be primarily upon the perovskite structure families where cations of different valence occupying similar crystallographic sites in the structure appear to play an important role. Limited ordering in the Pb(B1B2)O3 systems will be discussed and possible mechanisms for self limiting to nanometer scales in some systems explored. New studies of the break up of the simple ferroelectric behavior in lanthanum modified lead zirconate titanate (PLZT) and in lead titanate (PLT) systems will be discussed and the relevance to the general problem of relaxor behavior examined. Evidence for enhanced polarization fluctuations and super paraelectric behavior at high temperatures will be discussed and random field and spin glass models for the lower temperature state considered. ...

Relaxorferroelectrics: An overview

B-cation arrangements in double perovskites

A2B′B″O6 perovskites: A review

The use of nanocomposites in materials processing can lead to monophasic or multiphasic ceramics, glasses or porous materials, with tailored and improved properties. This review deals with a variety of nanocomposites such as sol–gel, intercalation, entrapment, electroceramic and structural ceramic types, which exhibit superior properties when compared to the monophasic or microcomposite alternatives. The utilization of nanocomposites in materials processing is forecasted to have a major impact in catalytic, sensor, optical, electroceramic and structural ceramic materials.

Feature article. Nanocomposites

From a number of studies on ferroelectric and related materials based on complex lead perovskites [Pb(Bx′B1−x″)O3], it is apparent that the B-site cation order influences the crystallography, phase transitions, and other physical properties. A classification of complex lead perovskites is presented based on the relative scale of long-range cation order. In particular, we discuss the implications of cation order in relation to relaxor and normal ferroelectric behavior.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S088429140000933X

Classification and consequences of complex lead perovskite ferroelectrics with regard to B-site cation order

Ordering behaviour and the factors which influence the ordering have been studied in both single crystals and hot-pressed ceramics of Pb(Sc1/2Ta1/2)O3 using TEM techniques, including low-temperature microscopy. The characteristics of the structurally-ordered domains are described and also the observation by electron diffraction of new superlattice reflections and diffuse scattering in both the paraelectric and ferroelectric phases. The superlattice reflections are interpreted in terms of Pb2+ cation displacements. The non-interaction of ordered domains and ferroelectric domains is explained within this model.

A TEM study of ordering in the perovskite, Pb(Sc1/2Ta1/2)O3

A transmission electron microscopy study of the order-disorder perovskite Pb(In1/2Nb1/2)O3 (PIN) has shown that its microstructures are dependent on the In: Nb B-site cation distribution. In disordered PIN the dielectric properties are those of a relaxor ferroelectric. Lowering the temperature of disordered PIN by means of a liquid nitrogen-cooled stage has been found to stabilize polar ferroelectric micro-domains, ∼ 20 to 30 nm in size. On increasing the long range order of the B-site cations to give ordered domains > 80 nm in size, an antiferroelectric phase is shown to develop that is isostructural with the antiferroelectric perovskite, PbZrO3. Coexisting antiferroelectric and non-antiferroelectric regions have been observed in partially ordered PIN.

TEM study of the disorder-order perovskite, Pb(In1/2Nb1/2)O3

The electron diffraction patterns of many monocrystalline and polycrystalline lead-based perovskites have common superstructure features consisting of weak {h+1/2,k+1/2,O} spots, together with rods of diffuse scattering in 〈110〉 reciprocal lattice directions. These superstructure phenomena are thought to be associated with the short-range ordering of lead-site vacancies to form microregions with an I-centred 2ao x 2ao x 2ao superlattice.

Short-range order phenomena in lead-based perovskites

Fabrication techniques are investigated with a view to producing single phase perovskite lead indium niobate (PbIn1/2Nb1/2O3). The physical properties of ceramics produced using the various techniques are investigated. The dielectric relaxation of lead indium niobate is also characterised.

Fabrication and characterisation of ferroelectric perovskite lead indium niobate

The phase transition behaviour of lead scandium tantalate is discussed and the variation of this behaviour with the degree of long-range order is considered. Using the model of Diamond (1960),1 curves for dielectric constant and spontaneous polarisation are calculated, and a comparison with experimental results made. Good agreement is found. Expressions are given which allow these curves to be calculated for any given degree of long-range order.

Paul Groves

Papers

A TEM study of ordering in the perovskite, Pb(Sc1/2Ta1/2)O3

TEM study of the disorder-order perovskite, Pb(In1/2Nb1/2)O3

Short-range order phenomena in lead-based perovskites

Fabrication and characterisation of ferroelectric perovskite lead indium niobate

Phase transition behaviour in lead scandium tantalate