BaTiO based materials

In order to establish the model of intergranular impedance for doped barium titanate, it is important to notice that miorostructure properties of BaTiOj based materials, expressed in their grain boundary contacts, are of basic importance for electric properties of these materials. The barrier character of the grain boundaries is especially pronounced for doped BaTiOs materials which are used as PTC resistors. Basically two types of dopants can be introduced into BaTiOs large ions of valence 3+ and higher, can be incorporated into Ba positions, while the small ions of valence 5+ and higher, can be incorporated into the Ti sublattice [9-11], Usually, the extent of the solid solution of a dopant ion in a host structure depends on the site where the dopant ion is incorporated into the host structure, the compensation mechanism and the solid solubility limit [12], For the rare-earth-ion incorporation into the BaTiOs lattice, the BaTiOs defect chemistry mainly depends on the lattice site where the ion is incorporated [13], It has been shown that the three-valent ions incorporated at the Ba -sites act as donors, which extra donor charge is compensated by ionized Ti vacancies (V -), the three-valent ions... 

Figure 8.38 shows the characteristics of a typical dielectric resonator made from a BaTiOs-based ceramic materials with e = 38, coupled via air lines and operating in the SHF band. The small bandwidth (<50MHz) and insertion losses (<0.8dB) guarantee excellent frequency separation. 

A wide array of ferroelectric, piezoelectric and pyroelectric materials have titanium, zirconium and zinc metal cations as part of their elemental composition Many electrical materials based on titanium oxide (titanates) and zirconium oxide (zirconates) are known to have structures based on perovskite-type oxide lattices Barium titanate, BaTiOs and a diverse compositional range of PZT materials (lead zirconate titanates, Pb Zr Tij-yOs) and PLZT materials (lead lanthanum zirconate titanates, PbxLai-xZryTii-yOs) are among these perovskite-type electrical materials. 

Materials of particular interest are the perovskite oxides BaTiOs-SrTiOs (BST) and PbZrOs-PbTiOs (PZT) solid solutions as well as the layered perovskites based upon SrBi2Ta209 (SBT). Since the ferroelectric effect requires... 

Ultraviolet Raman spectroscopy has emerged as a powerful technique for characterization of nanoscale materials, in particular, wide-bandgap semiconductors and dielectrics. The advantages of ultraviolet excitation for Raman measurements of ferroelectric thin films and heterostructures, such as reduced penetration depth and enhanced scattering intensity, are discussed. Recent results of application of ultraviolet Raman spectroscopy for studies of the lattice dynamics and phase transitions in nanoscale ferroelectric structures, such as superlattices based on BaTiOs, SrTiOs, and CaTiOs, as well as ultrathin films of BaTiOs and SrTi03 are reviewed. 

Ceramic capacitors are prepared with their chemical compositions placing them close to a ferroelectric-paraelectric phase boundary, where the dielectric permittivity is anomalously high. These materials are commonly based on BaTiOs which is similar in structure and properties to the piezoelectric ceramics. 

The main uses of piezoceramics are in the generation of charge at high voltages, detection of mechanical vibrations, control of frequency, and generation of acoustic and ultrasonic vibrations. Most, if not all, commercial piezoelectric materials are based on ferroelectric crystals. The first commercially developed piezoelectric material was BaTiO. One of the most widely exploited piezoelectric materials today, however, is based on the Pb(Ti,Zr)03 or PZT solid solution system. 

The ceramic of PTCs is based on BaTiOs with certain additions. Normal grains of ceramic are surrounded by barrier layers of strongly oxidized material. The barrier potential is inversely proportional to the dielectric constant of the crystals. Therefore,... 

In the so-called piezo-mode of atomic force microscopy an ac voltage is applied to a conductive AFM cantilever while scanning the surface of a piezoelectric material. The tip of the cantilever senses the local deformation of the surface caused by the electric field between the tip and a counter electrode (Fig. 5b, see also Fig. 10). Usually the ac frequency is far below the free resonance frequency of the AFM cantilever [16,17,19,20]. In BaTiOs, an image series based on vertical and torsional cantilever vibration signals of the same surface area allowed the reconstruction of the domain orientation using this mode [20]. 

Barium titanate (BaTiOs) is historically one of the most important ferroelectric ceramic materials its main use in modern applications is as a base composition for capacitors, due to its high dielectric constant [98]. 

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