Oxygen BaTiO

In sodium nitrite the ferroelectric polarization only occurs in one direction. In BaTiOs it is not restricted to one direction. BaTiOs has the structure of a distorted perovskite between 5 and 120 °C. Due to the size of the Ba2+ ions, which form a closest packing of spheres together with the oxygen atoms, the octahedral interstices are rather too large for... 

Oxides play many roles in modem electronic technology from insulators which can be used as capacitors, such as the perovskite BaTiOs, to the superconductors, of which the prototype was also a perovskite, Lao.sSro CutT A, where the value of x is a function of the temperature cycle and oxygen pressure which were used in the preparation of the material. Clearly the chemical difference between these two materials is that the capacitor production does not require oxygen partial pressure control as is the case in the superconductor. Intermediate between these extremes of electrical conduction are many semiconducting materials which are used as magnetic ferrites or fuel cell electrodes. The electrical properties of the semiconductors depend on the presence of transition metal ions which can be in two valence states, and the conduction mechanism involves the transfer of electrons or positive holes from one ion to another of the same species. The production problem associated with this behaviour arises from the fact that the relative concentration of each valence state depends on both the temperature and the oxygen partial pressure of the atmosphere. 

BaTiOs crystallizes in the perovskite structure. This structure may be described as a barium-oxygen face-centered cubic lattice, with barium ions occupying the corners of the unit cell, oxide ions occupying the face-centers, and titanium ions occupying the centers of the unit cells, (a) If titanium is described as occupying holes in the Ba-O lattice, what type of hole does it occupy (b) What fraction of the holes of this type does it occupy (c) Suggest a reason why it occupies those holes of this type but not the other holes of the same type ... 

The rate of formation of ozone in an oxygen plasma at atmospheric pressure increased when the ozonizer was packed with materials such as soda glass, TiOa, 2 MgO/Ti02, BaTiOs and 95 BaTi03/5 Sn02 A linear relationship was found... 

As an example, consider barium titanate, BaTiOs. Above 120 °C the paraelectric form of BaTiOa has the cubic perovskite structure, with oq = 0.4018 nm (Figure 11.22a). The large Ba " cations are surrounded by 12 oxygen ions, and the medium-sized Ti" " " ions are situated at the centre of an octahedron... 

The sigmoid variation of AHq (5) crossing 6 = 0 in Figure 10.8 may be understood from a slightly different viewpoint [19]. For simplicity s sake, consider the pure BaTiOs with no traps. Then, oxidation or oxygen incorporation reaction may take place simultaneously in two ways (i) by producing the free holes and (ii) by consuming free electrons or... 

Figure 10.11 Relative partial molar enthalpy of component oxygen versus nonstoichiometry for undoped BaTiOs. The solid curve is best fitted to Eq. (50). Data from Ref. [19].

The results of a recent study [30] showed that, compared to the usual relaxation behavior of the undoped counterpart (see Figure 10.12), the relaxation behavior of donor-doped BaTiOs appeared somewhat unusual, and depended on the oxygen activity. 

Figure 10.23 Thermodynamic factors ( A ) for O (solid line) and Ti (dotted line) versus oxygen activity, as evaluated from the equilibrium defect structure of 1 mol% La-doped BaTiOs in Figure 10.17. Data from Ref [30].

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