Entropies lanthanide oxides

Oxides. Decomposition pressure measurements on the TbO system by Eyring and his collaborators (64) have been supplemented by similar and related studies on the PrO system (46) and on other lanthanide-oxygen systems (43, 44). Extensive and systematic studies of vaporization processes in lanthanide-oxide systems have been undertaken by White, et al. (6, 188,196) using conventional Knudsen effusion measurements of the rates of vaporization of the oxides into high vacuum. Combination of these data with information on the entropies and Gibbs energy functions of reactants and products of the reaction yields enthalpies of reaction. In favorable instances i.e., if spectroscopic data on the gaseous species are available), the enthalpies of formation and the stabilities of previously undetermined individual species are also derived. The rates of vaporization of 17 lanthanide-oxide systems (196) and the vaporization of lanthanum, neodymium, and yttrium oxides at temperatures between 22° and 2700°K. have been reported (188). 

Brauer (88) has reported the AH values for the A, B, and C type lanthanide oxides. Reasonable linear plots have been obtained (Fig. 52), accounting for the scarcity of the data. The plots for the estimated and experimental entropy (S°9g) data (89) for the sesquioxides are also shown in Fig. 53. The estimated data were calculated from the relationship S°98 = S,.lttice + Smag. The points for La and Lu, where no contribution from Smag is present, deviate from linearity, as expected, (Fig. 53(a)), but the experimental values do reflect some linearity (Fig. 53(b)). 

Fig. 53. Variation of the estimated and observed entropy of formation of the M2C>3 type lanthanide oxides with the L-values.

Entropy evaluations from published cryothermal data on the lanthanide (III) oxides are summarized in Table II with an indication of the lowest temperature of the measurements and the estimated magnetic entropy increments below this temperature. Their original assignment of crystalline field levels from thermal data still appears to be in good accord with recent findings e.g., 17). Unfortunately, measurements on these substances were made only down to about 8°K. because the finely divided oxide samples tend to absorb the helium gas utilized to enhance thermal equilibration between sample and calorimeter. 

Table II. Experimental Entropies of Lanthanide (III) at 298.15 K. Entropies Oxides...

Enthalpies, Entropies, and Gibbs Energies of Formation of Lanthanide (III) Oxides at 298.15... 

Table VIII. High Temperature Entropies of the Lanthanide (III) Oxides ...

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