Structure and electrical properties in the K1/2Bi1/2TiO3-K1/2Bi1/2ZrO3 solid solution (KBT-KBZ)

International audienceThe present work is devoted to the study of the Zr 4þ /Ti 4 substitution in the K1/2Bi1/2Ti(1-x)ZrxO3 solid solution (x ¼ 0.0 to x ¼ 1.0), based upon the K1/2Bi1/2TiO3 (KBT) ferroelectric compound. The tetragonal distortion of KBT is suppressed by this substitution and leads to the cubic compound K1/2Bi1/2ZrO3 (KBZ). These results agree with the values of the ionic radii of the Zr 4þ and Ti 4 ions (rTi 4þ ¼ 0.605 A˚ and rZr 4þ ¼ 0.72 A˚ ). Close to KBT (x 0.05), the symmetry remains tetragonal. For higher values of x, the ''a'' lattice parameter (cubic indexing) follows Vegard's law, thus confirming the formation of a solid solution. The transformation from tetragonal to cubic proceeds via an intermediate pseudocubic symmetry (0.1 x < 0.5), for which the X-ray diffraction peaks present small broadening and asymmetry. For x 0.5 and up to the KBZ compound (a 4.158 A˚ ), the samples are cubic but some extra peaks are also observed, indicating the occurrence of a secondary phase. The microstructure shows fine-grained ceramic samples for the first range, while for the KBZ-rich range the grains are micrometer-sized and associated to very small grains of the secondary phase. Piezoelectricity is observed for the tetragonal and pseudocubic range, the substitution quickly reducing the piezoelectric properties. The measurement of the dielectric properties revealed close to KBT a dielectric anomaly probably associated to the tetragonal-cubic phase transition. For thepseudocubic and cubic range, a broad dielectric anomaly is observed around 300 8C, corresponding to a relaxor behavior

Review: Defect chemistry and electrical properties of sodium bismuth titanate perovskite

The ferroelectric perovskite Na0.5Bi0.5TiO3, NBT, can exhibit three types of electrical behaviour, i.e. oxide-ion conduction (Type I), mixed ionic-electronic conduction (Type II) and insulating/dielectric (Type III) based on various defect mechanisms. Here we review how to tune the electrical properties of NBT via several mechanisms, including A-site Na or Bi non-stoichiometry, isovalent substitution, acceptor- and donor-doping. The diversity of electrical behaviour in the NBT lattice is attributed to the high level of oxide-ion conductivity originating from highly mobile oxygen ions which can be fine-tuned to optimise or suppress the ionic conduction. High oxide-ion conductivity can be obtained by manipulating the starting Na/Bi ≥ 1 and by acceptor-doping to make NBT a potential electrolyte material for intermediate temperature solid oxide fuel cells (IT-SOFCs). In contrast, the oxide-ion conduction can be partially or fully suppressed by having a starting (nominal) composition with Na/Bi < 1, donor-doping, or utilising the trapping between oxygen vacancies and some B-site acceptor dopants. This significantly reduces the dielectric loss and makes NBT-based materials excellent candidates as high-temperature dielectrics for capacitor applications

Propriétés diélectriques et transitions de phases de composés ferroélectriques exempts de plomb (Na(0,5)Bi(0,5)TiO(3) (M = Ba, Sr, Ca))

Ce travail a été entrepris dans le cadre général des études sur les matériaux céramiques ferroélectriques exempts de plomb. A la suite de travaux antérieurs réalisés au SPCTS, le choix s'est porté sur les solutions solides des systèmes Na0,5Bi0,5TiO3- BaTiO3(NBT-BT), Na0,5Bi0,5TiO3 - SrTiO3 (NBT-ST) et Na0,5Bi0,5TiO3 - CaTiO3 (NBT-CT). Les échantillons céramiques étudiés ont été préparés par voie solide. L'étude radiocristallographique a permis de délimiter les domaines d'existence à la température ambiante des diverses variétés cristallines dont la symétrie peut être rhomboédrique (domaines riches en NBT), quadrique, cubique ou orthorhombique selon que les compositions sont riches en BT, ST ou CT. L'étude des propriétés diélectriques en fonction de la température et de la fréquence a conduit à distinguer divers comportements dépendant de la composition et de la symétrie cristalline. La caractéristique la plus marquante est la présence pour tous les systèmes d'un domaine de composition assez large pour lequel les matériaux correspondant ont un comportement similaire à celui des relaxeurs, certainement dû au désordre cationique provoqué par les substitutions. Pour les systèmes NBT-BT et NBT-ST, un diagramme des états diélectriques a été proposé. Les coefficients piézoélectriques mesurés pour certaines compositions voisines des limites structurales peuvent laisser envisager une utilisation prochaine de ce type de matériaux dans des dispositifs électromécaniques.LIMOGES-BU Sciences (870852109) / SudocLIMOGES-ENSCI (870852305) / SudocSudocFranceF

Valorization of clay materials from Central African Republic (RCA) and plant skins waste as silicate ceramics

International audienc

Dielectric properties of Na0.5TiO3-BaTiO3 ceramics

At the present time, the most widely-used piezoelectric materials belongs mainly to the PZT solid solution system (1 - x)PbTixO3-xZrTiO3..