Perovskites thermodynamic parameters

Figure 3 Effects upon olivine phase equilibria near 410 km depth of low temperatures in subduction zones, for mineral thermodynamic parameters of Fei et al. (1991). Dark lines denote boundaries of subducting slab. Phases are (a) olivine, (P) wadsleyite, (-y) ringwoodite, (mw) magnesiowustite, and (pv) ferro-magnesian silicate perovskite. Note that the a — 3 transition near 410 km is first uplifted and then bifurcates into a strongly uplifted diffuse a — a + -y transition overlying a weakly uplifted sharp boundary (after Bina, 2002) (vertical resolution is 1 km).

Fig. 5.57 Upon heavy negative doping of the perovskite oxides SrTiOs (left) and BaCeOa (right), it is possible to recognize the regions of n-lype, p-type and ionic conductions. At this high level of doping it is expected that the thermodynamic parameters differ from those of the undoped material (see footnote 146, page 216). According to Refe. [191, 192].

It is also possible that the coupling coefficients can be temperature-dependent, in which case the apparent thermodynamic character of a phase transition might appear to vary with temperature. This effect would be detectable as an unusual evolution pattern for the order parameter, as shown, perhaps, by NaMgFs perovskite. In this perovskite, the orthorhombic structure appears to develop directly from the cubic structure according to a transition Pm3m < Pnma (Zhao et al. 1993a,b, 1994 Topor et al. 1997). The orthorhombic structure has q2t qA = and qi = q , = q = 0. Equation (32) yields... 

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