Defect-chemical analysis of the nonstoichiometry, conductivity and thermopower of La2NiO4+δ

Abstract

La(2)NiO(4+delta) is an oxygen excess compound (delta > 0) with oxygen interstitials (O(i) and holes (h*) in majority, which deviates positively from the ideal-dilute-solution behavior of defects. It was earlier attempted to interpret this positive deviation by taking into account the activity coefficients of both O(i) and h*. In this work, we examined the nonstoichiometry, electrical conductivity, and thermopower against oxygen activity in the entire stability range of the oxide at 800 degrees , 900 degrees and 1000 degrees C, respectively. It has been found that the positive deviation is ascribed essentially to the hole degeneracy and quantitatively described by using the Joyce-Dixon approximation of the Fermi-Dirac integral. Consequently evaluated are the effective density of states of the valence band (20.3 <or= log(N(v)/cm(-3)) <or= 20.5), the Fermi energy relative to the valence band edge (-5 <or= (E(F)-E(V))/kT<or= 1.5), and the effective mass (1.2<or=m(h)*/m(0)<or=1.3)), mobility (0.14-0.17 cm(2) V(-1) s(-1)), and reduced heat-of-transport (ca. 0.02 eV) of holes. The stability limit of the oxide is also evaluated and compiled together with the reported values.

Synthesis, Sintering, Transport Properties, and Surface Exchange of La2Ni0.9Cu0.1O4+δ

“…The slope of log (δ) and log (σ) vs log ( p O 2 ) is around 1/20 at high temperatures, and decreases slightly as temperature decreases. Similar slope was also observed in undoped La 2 NiO 4+δ at high p O 2 , which was ascribed to hole degeneracy …”

Oxygen Nonstoichiometry and Thermodynamic Quantities of La2Ni0.95Al0.05O4.025 + δ

“…17 Considering the fact that Al 3+ would act as a donor at Ni site in LNAO, the value of d is supposed to be higher in LNAO than that in LNO. The molar Gibbs free energies for the mixing of oxygen relative to gaseous oxygen at the standard state (D G M O ) can be represented as 14,17,20 Figure 5 shows pO 2 dependence of oxygen nonstoichiometry at different temperature.…”

“…It is clear from the above observation that the oxygen exponent decreases with increasing oxygen activity, suggesting a positive deviation of the LNAO system from the ideal solution behavior. 11,20 The temperature dependence of oxygen nonstoichiometry can be used to calculate partial thermodynamic quantities of LNAO by solving the Gibbs-Helmholtz equation. The molar Gibbs free energies for the mixing of oxygen relative to gaseous oxygen at the standard state (D G M O ) can be represented as 14,17,20…”

Investigation of Effect of Al3+-Doping on Mass/Charge Transport Properties of La2NiO4+δby Blocking Cell Method

“…1 The LNO systems are unique in a way that they accommodate hyper-stoichiometric oxygen in the crystal, with the interstitial oxygen ions residing in R-layer, though there are evidence that oxygen vacancies can exist in P-layer. [5][6][7][8] However, they also have oxide-ion conductivity which is an order of magnitude higher than conventional perovskite-type oxides and comparable to that of yttria-stabilized zirconia 3,[9][10][11] and which is attributed to a complex mechanism involving interstitial migration in the rock salt layers and vacancy migration in the perovskite planes. [5][6][7][8] However, they also have oxide-ion conductivity which is an order of magnitude higher than conventional perovskite-type oxides and comparable to that of yttria-stabilized zirconia 3,[9][10][11] and which is attributed to a complex mechanism involving interstitial migration in the rock salt layers and vacancy migration in the perovskite planes.…”