Oxygen nonstoichiometry

Equations (15), (20) and (25) indicate that, whether the system is undoped or doped, its oxygen nonstoichiometry is a measure of the concentrations of the electronic charge carriers, n and p  

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Electrical Conductivity and Oxygen Nonstoichiometry of La0.2Sr0 8Fe0.55Ti0 4503 8... 

The dc four-probe method was used to determine the conductivity at 25 =S T =S 900°C and 5 X 10 5 =S pQ =S 1 atm. Gold wire contacts were made to a rectangular bar with dimensions 9.02 X 2.54 X 1.91 mm. The electrical conductivity and oxygen nonstoichiometry (8) as a function of p0 were determined by using gas-tight electrochemical cells. The details of the method can be found elsewhere but are briefly summarized here.12,13... 

Figure 8. The p0, dependence of average oxygen nonstoichiometry (8) measured on increasing and decreasing pQ for Lao 2Sr0 8Fe0. 55T 0.45O3-S.

The p0 dependence of oxygen nonstoichiometry (8) was determined by using coulometric titration. The data were analyzed using a simple point defect model and thermodynamic quantities were calculated. From this model, the standard enthalpy for oxidation (AH0f) and disproportionation (A77D) were determined to be -140.7 and 228.7 kJ/mol, respectively. The mobilities of the electron holes, electrons, and oxygen ions were calculated from the conductivity data using the defect concentrations determined from the stoichiometry and point defect model. 

E. Kaldis, Oxygen nonstoichiometry and lattice effects in YBa2Cu30x. Phase transitions, structural distortions and phase separation 1... 

Martin et al. [126] have made single-phase TlBaSrCa2Cu309 8 with a Tc value of 103 K. On annealing in a reducing atmosphere, the Tc value has been shown to increase up to 116 K. It has also been proven that the irreversibility line does not depend on Tc (i.e., oxygen nonstoichiometry does not influence the nature of the irreversibility line in this phase). The TlSrCa2Cu309 phase has not been made in a pure phase yet since the Tl-1223 structure needs all Cu to be 2.33 +. But it is possible to stabilize this... 

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