Heat capacities and entropies of La2O2CO3fromT= (12 to 300) K and of Nd2O2CO3fromT= (12 to 930) K, and their interpretation

On the Crystal Structure of Ln2O2CO3 II (Ln=La and Nd)

“…The¸n sites are similar but subject to somewhat di!erent electric "elds, which may indicate di!erent modes of packing of CO\ ions from one layer to the next (9). For some samples, the electron di!raction patterns indicate an enlarged hexagonal unit cell, a 2#+ "a 60" ) (3 (8 (11). According to Reeder (12), the geometry of the CO\ group is remarkably uniform in most solids despite the wide variety of crystal structures of minerals and synthetic carbonates.…”

Synthesis of rare earth oxide carbonates and thermal stability of Nd2O2CO3 II

“…The enthalpy of decomposition of Nd 2 O 2 CO 3 determined by Patil et al16 and Sastry et al17 are 50¡8 kJ mol21 and 167 kJ mol21 , respectively, are both Watanabe et al12 for the decomposition of La 2 O 2 CO 3 II. Furthermore, D d S m o ~206¡26 J K 21 mol 21 at 298 K is 16% higher than the reported decomposition entropy of neodymium oxide carbonate at 300 K (177.0¡0.9 J K 21 mol 21 ) 15. The determination of reaction enthalpies for the decomposition of Ln 2 O 2 CO 3 into Ln 2 O 3 , by means of thermal analysis studies on the decomposition of compounds like Ln 2 (C 2 O 4 ) 2 ?xH 2 O and Ln 2 (CO 3 ) 3 ?8H 2 O, the method used by Patil et al16 and Sastry et al, 17 frequently gives values burdened by large errors.…”

“…In a recent study based on adiabatic calorimetry, Olafsen et al 15 calculated, from integrated heat capacity values, the standard molar entropy of decomposition for La 2 O 2 CO 3 II at 300 K and for Nd 2 O 2 CO 3 II at 300 and 900 K to be 170.2¡0.6, 177.0¡0.6 and 166.9¡0.9 J K 21 mol 21 , respectively. The entropy of formation was calculated on the assumption that there is no zero point entropy either for the oxide components or for the oxide carbonate.…”

The Constituent Additivity Method to Estimate Heat Capacities of Complex Inorganic Solids

“…A case would be carbonates, for example MCO 3 , in which the experimental heat capacity of MO might be known, but CO 2 would not be a suitable constituent for this method. However, in this case, data for M′CO 3 and M′O (where M′ ≠ M) could be used to calculate the heat capacity of MCO 3 as follows: (32) and La 2 O 2 CO 3 (32) were treated in this way (with data for Nd 2 O 3 [33], SrCO 3 [34] and SrO [12], and La 2 O 3 [23]); the results are shown in Figure 4.…”