Process parameter selection for strontium ferrite sintered magnets using Taguchi L9 orthogonal design

A sintering, microstructural development and dielectric property study of BaTiO3–LiF ceramics was performed to assess the potential application of low-fired multilayer capacitors. Not only does LiF allow for sintering below 1000 °C, it also allows for the manipulation of dielectric properties and interfaces within BaTiO3–LiF ceramics. Using mixing laws, a model of the dielectric properties of the core-shell microstructures is presented that agrees well with the observed experimental data.

Structure property relationships in core-shell BaTiO3—LiF ceramics

Texture engineering using reactive-templated grain growth (RTGG) is reviewed as a key processing technique for lead free piezoelectric ceramics. Bismuth layer structured ferroelectric ABi4Ti4O15 (A=Na0·5Bi0·5, Ca, Sr) ceramics with a highly preferred {001} orientation were fabricated with enhanced piezoelectric properties using Bi4Ti3O12 platelets. Textured simple perovskite type ceramics were also prepared in Bi0·5Na0·5TiO3 (BNT), BaTiO3 and K0·5Na0·5NbO3 (KNN) based compositions with Lotgering's factor higher than 0·8. The textured BNT and KNN based ceramics exhibited enhanced electromechanical coupling coefficients and piezoelectric constants when compared with their randomly oriented counterparts. The development of microstructure and texture in the RTGG processed ceramics is dependent on the target system, starting materials and processing parameters, and optimum preparation conditions must be found by analytical investigation.

Reactive-templated grain growth processing for lead free piezoelectric ceramics

The coherent (111) twin boundary in BaTiO3 has been investigated using quantitative high-resolution transmission electron microscopy and spatially resolved electron-energy-loss spectroscopy (EELS). Lattice images under different defocusing conditions were obtained and compared with simulated images for different structural models. An excellent match between calculated and observed images was obtained only for the model where the Ba-O3 plane constitutes the twin boundary. The oxidation state of Ti at twin boundaries was interrogated by studying the near-edge structure of the L23 ionization edge of Ti using spatially resolved EELS. The difference between spectra taken from the bulk and those including the boundary indicates the presence of Ti in a reduced oxidation state at the boundary. The charge is compensated by oxygen vacancies Vo in the twin plane, which is therefore composed of Ba-O3-x[Vo]x instead of Ba-O3.

Structural and spectroscopic investigation of (111) twins in barium titanate

Ferroelectric domains in pressureless-sintered barium titanate

On the basis of the topotaxy between BaTiO{sub 3} and Ba{sub 6}Ti{sub 17}O{sub 40} found recently, a model of a nonconservative (111) twin in TiO{sub 2{minus}} rich BaTiO{sub 3} was constructed. The model consists of several (001) layers of Ba{sub 6}Ti{sub 17}O{sub 40} intergrown between (111) layers of BaTiO{sub 3}, the core of the twin being a slightly modified double layer of Ba{sub 6}Ti{sub 17}O{sub 40} containing face-sharing octahedra. Using this model, anomalous grain growth below the eutectic temperature and preferential growth of (111) twins in a reducing atmosphere are explained, as well as nucleation of butterfly twins.

Genesis of the (111) twin in barium titanate

The orientational relationship between intergrown lamellae of tetragonal (t) BaTiO3 and monoclinic (m) Ba6Ti17O40 was found to be (111)t||(001)m, (001)t||(101)m, and [110]t||[010]m. On the basis of this relationship a model of a topotactic boundary between these two phases was constructed.

Miha Drofenik

Papers

Genesis of the (111) twin in barium titanate

Topotaxy between BaTiO3 and Ba6Ti17O40

High coercivity Sr hexaferrites