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Molecular Dynamics Study of Complex Dopant Electrolyte Nd 2– x Ho x Zr 2 O 7 : Structure, Conductivity, and Thermal Expansion
Author(s) -
Razmkhah M.,
Hamed Mosavian M. T.,
Moosavi F.
Publication year - 2013
Publication title -
fuel cells
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.485
H-Index - 69
eISSN - 1615-6854
pISSN - 1615-6846
DOI - 10.1002/fuce.201300097
Subject(s) - ionic conductivity , electrolyte , arrhenius equation , conductivity , ionic bonding , dopant , analytical chemistry (journal) , materials science , oxide , fast ion conductor , atmospheric temperature range , ion , inorganic chemistry , chemistry , activation energy , thermodynamics , doping , electrode , metallurgy , physics , optoelectronics , organic chemistry , chromatography
Nd 2– x Ho x Zr 2 O 7 is an ionic conductor for solid oxide fuel cell electrolytes. Temperature and dopant composition are two main factors that affect ionic conductivity of these groups of materials. Accordingly, Nd 2– x Ho x Zr 2 O 7 was studied in a wide range of temperature, 1,173–1,873 K, and dopant composition, x = 0.0–2.0, by molecular dynamics simulation. Arrhenius plots of ionic conductivity in region of low temperature declared that the maximum occurred at composition x = 0.6 (H6). Surprisingly, it was observed that complexity of dopant improved ionic conductivity of the electrolyte. Moreover, radial distribution function confirmed this result. Two types of anions were observed in the electrolyte, which were dynamic oxygen ions (DOIs) and static oxygen ions (SOIs). Mean square displacement (MSD) of DOIs was higher than SOIs and enhanced oxygen ionic conductivity. Migration barrier of Nd 2– x Ho x Zr 2 O 7 varied from 0.68 to 1.22 eV that was in the range of a good solid oxide electrolyte. Nd 1.2 Gd 0.8 Zr 2 O 7 (G8) and Y 0.2 Zr 0.9 O 2.1 (Y2) were simulated and their results of simulations were compared with H6. Order of ionic conductivity at low temperatures was H6 > Y2 > G8. Another important factor of electrolyte is thermal expansion. Thermal expansion of Nd 2– x Ho x Zr 2 O 7 was around a constant value in the studied temperature range.