Oxygen nonstoichiometry, defect structure and oxygen diffusion in the double perovskite GdBaCo₂O_6−δ

Abstract

Oxygen nonstoichiometry of GdBaCo2O6-δ was studied by means of the thermogravimetric technique in the temperature range 600-1000 °C. The defect structure model based on the simple cubic perovskite GdCoO3-δ was shown to be valid for GdBaCo2O6-δ up to temperatures as low as 600 °C. Two independent methods, namely dc-polarization with the YSZ microelectrode and (18)O-isotope exchange with gas phase analysis, were used to determine the oxygen self-diffusion coefficient in the double perovskite GdBaCo2O6-δ. All measurements were carried out using ceramic samples identically prepared from the same single phase powder of GdBaCo2O6-δ. The experimental data on oxygen nonstoichiometry of GdBaCo2O6-δ allowed a precise calculation of the oxygen interphase exchange rate and the oxygen tracer diffusion coefficient on the basis of the isotope exchange measurements. The values of the oxygen self-diffusion coefficient measured by the dc-polarization technique were found to be in very good agreement with the ones of the oxygen tracer diffusion coefficient.

Relating defect chemistry and electronic transport in the double perovskite Ba1−xGd0.8La0.2+xCo2O6−δ (BGLC)

“…represents an average cobalt valence state of Co to 45 kJ mol -1 , close to values for cobalt double perovskites in the literature. 13,14,[16][17][18] For cobalt disproportionation (Eq. 5), the entropy change is expectedly small (-10 to -30 J mol -1 K -1) , as no gas molecules are formed or consumed in the reaction.…”

“…Several approaches have been undertaken to describe the defect chemistry of BaLnCo2O6-δ double perovskites, using a simple LnCoO3 perovskite as the reference structure with the introduction of 50% Ba on lanthanide site as an acceptor dopant. [12][13][14][15][16][17][18] The ordered oxygen vacancies are then further described by an association reaction between the lanthanide cation and the vacancy. This approach has been shown to accurately predict the oxygen nonstoichiometry in PrBaCo2O6-δ (PBCO) and GdBaCo2O6-δ (GBCO) at high temperatures.…”

“…This approach has been shown to accurately predict the oxygen nonstoichiometry in PrBaCo2O6-δ (PBCO) and GdBaCo2O6-δ (GBCO) at high temperatures. [15][16][17][18] However, the model assumes a fully disordered A-site sublattice and does not account for the two distinctly different A-site positions of the structure, and thus incorrectly accounts for the configurational entropy of the cation lattices. For many applications it may also prove beneficial to alter the A-site cation stoichiometry by aliovalent doping to tune properties such as oxygen stoichiometry, oxide basicity and degree of oxygen disorder.…”

Synthesis and conductivity properties of Gd0.8Ca0.2BaCo2O5+δ double perovskite by sol–gel combustion

“…Among various types of TMOs, GaBaCo 2 O 5?d (GBCO) has attracted a lot of attention due to its certain interesting properties, such as insulator-metal transition (IMT) [12], total conductivity [13], charge ordering [14], magnetic transition [15] and non-stoichiometry in thermogravimetric analysis [16]. GBCO 2 ] stacked sequentially along the c axis [17].…”

Proof-of-concept thermoelectric oxygen sensor exploiting oxygen mobility of GdBaCo2O5+δ

“…Further, the oxygen ions incorporated play a vital role in the properties of layered cobaltates 11,12,16 . The weak bonding of oxygen in ReO δ layer enhances the oxygen diffusivity and hence increases the mobility of oxygen through the surface 17,18 . This in-turn shows a large change in transport properties of this systems as it is proposed that the equilibrium δ value at a given temperature linearly varies with the logarithm of the oxygen partial pressure (except for δ = 0) 11 .…”