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

✍ Scribed by A. Olafsen; H. Fjellvåg; S. Sølen; T. Atake; H. Kawaji; K. Matsuo

Publisher
Elsevier Science
Year
1999
Tongue
English
Weight
213 KB
Volume
31
Category
Article
ISSN
0021-9614

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✦ Synopsis

The heat capacities of La 2 O 2 CO 3 and Nd 2 O 2 CO 3 were determined by adiabatic shield calorimetry from T = (12 to 300) K and T = (12 to 930) K, respectively. For the dineodymium dioxide carbonate a Schottky-type heat capacity with maximum near T = 60 K was observed. The transition is due to splitting of the 4 I 9/2 ground term in the crystal field of the Nd 3+ . The vibrational contributions to the heat capacities of La 2 O 2 CO 3 and Nd 2 O 2 CO 3 are discussed in terms of a modified Kieffer model. Although the heat capacity can be modelled reasonably well, deviations, especially at low temperatures, give rise to significant errors in entropy. Thermodynamic properties at selected temperatures have been evaluated, and the values of the molar heat capacities C p,m , enthalpy increments T 0 H m , and entropies T 0 S m for La 2 O 2 CO 3 at T = 298.15 K and for Nd 2 O 2 CO 3 at T = (298.15 and 900) K are (R = 8.3145 J•K -1 •mol -1

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