DF oxides

In this chapter, we present some latest analysis results of lanthanides (Lns Eu and Gd)-M6ssbauer structure and powder X-ray diffraction (XRD) lattice parameter (oq) data of defect-fluorite (DF) oxides with the new defect crystal chemistry (DCC) Oq model [ 1,2] as an upgrade of the former random oxygen coordination number (CN) Oq model [3,4]. This is, thus, the first report of our ongoing efforts to further elaborate the model and extend its applicability to more various systems, especially to pyrochlore (P)-type stabilized zirconias (SZs) and stabilized hafnias (SHs). 

Our systematic XRD and Lns ( Eu and Gd) Mossbauer studies of DF oxides [18,19] also stand as one such. Their detailed summary up to 2006 [4] clarified several novel P-based local structure features of SZ(SH)s. These are basically (a) the presence of a broad Oq hump over the extended middle-y range, (b) Eu Mossbauer isomer-shift (IS) data of Zr-Eu and Hf-Eu exhibiting V-shaped minima at y 0.50, and (c) rich Gd Mossbauer data of Zr-Gd (IS, quadrupole-splitting (QS), and relative absorption area (RAA)) revealing its unique P/DF phase and structure relationships. 

Such significant success of the DCC model signifies that these parent F-type DF oxides such as M = Ce, Th, and Ans are indeed F-type M02-C-type LnO 5 (i.e., F-C) binary systems, their coupled oo-nonrandomness behavior being fully describable as distortional-dilation phenomenon of the latter fc > /f in Fig. 4.2a. Of course the model should be further validated with more various systems and with their more various structure and basic property data. This is what we initiate here with these (Ce, Th, U, Zr, and Hf)-Eus and Zr-Gd and with their Lns Mossbauer and XRD Oq As mentioned in (4.1), our prime interest here is in how to attain such successful F-C binary F-P-C ternary or other type model extension for P-type Zr-Eu, Hf-Eu, and Zr-Gd exhibiting more complex sigmoid Oq behavior (as is obvious in Figs. 4.4a and 4.6a). 

Lns-MOSSB AUER AND LATHCE PARAMETER DATA OF DF OXIDES... 

Eu Mossbauer isomer-shift (IS(Eu )) data of the five M-Eus (where = Ce, Th, U, Zr, and Hf) and the rich Gd Mossbauer IS, QS, recoil-free (f), and Debye temperature ( d). data of Zr-Gd are very useful and even indispensable for establishing the P-based local structure nature of these three P-type Hf-Eu, Zr-Eu, and Zr-Gd entirely different from that of parent F-type DF oxides. Its most clear-cut evidence is the deep V-shaped IS(Eu ) minima, that is, the inverse V-shaped sharp BL(Eu +—) maxima, at the ideal-P composition of y=0.50, found for both Zr-Eu and Hf-Eu. From the careful coupled IS(Eu +)-Oo analysis of these five M-Eus with the DCC model, we have successfully derived the key quantitative BL(Eu +—) y data for these two Zr-Eu and Hf-Eu that exhibit strongly sigmoid variation with y closely... 

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