Thermodynamic quantities and oxygen nonstoichiometry of undoped BaTiO3− by thermogravimetric analysis

Kim

et al. 2018

J. Electrochem. Soc.

In this work, the defect structure analysis of La 0.8 Sr 0.2 FeO 3-δ (LSF82) was presented. Thermogravimetric measurements were performed to determine change in oxygen nonstoichiometry ( δ) with oxygen partial pressure (P O 2 ) in 10 −19 ≤(P O 2 /atm) ≤0.21 and 750≤(T/ • C)≤900 range. LSF82 showed a clear electronic stoichiometric point around δ≈0.1. The negative sign of partial molar enthalpy ( H 0 ) and entropy ( S 0 ) indicated that the incorporation of oxygen was an exothermic process and showed that the experimentally observed variations in H 0 and S 0 with δ fitted well with the statistical thermodynamic analysis. The defect diagram analysis showed that in n-type regime Fe / Fe concentration varied with (P O 2 ) −1/4 whereas in p-type regime Fe • Fe concentration varied with (P O 2 ) +1/4 . The electrical conductivity relaxation (ECR) experiments were performed to extract partial ionic conductivity and oxygen self diffusivity. The oxygen self-diffusivity (D O ) increased from 1.20 × 10 −8 cm 2 •s −1 at 800 • C to 3.54 × 10 −8 cm 2 •s −1 at 900 • C with an activation energy of 1.17 ± 0.23 eV. Dilatometry was performed for expansion measurements as function of P O 2 and temperature. The chemical expansion model based on the relative change in mean ionic radius vs. δ showed that Fe 3+ existed as a mixture of high-spin and low-spin states and made a transition from low-spin to high-spin state with increasing δ.

“…The change in oxygen nonstoichiometry ( δ) was measured by home-made TGA with Cahn 200 microbalance using Eq. 9 36 δ = w…”

Section: Resultsmentioning

confidence: 99%

Section: Synthesis Of Lsf82 Powder and Sample Preparation-lsf82mentioning

confidence: 99%

Thermodynamic Quantities and Defect Chemical Properties of La_0.8Sr_0.2FeO_3-δ

Bae

Kim

et al. 2018

J. Electrochem. Soc.

“…The details of the TGA measurement set-up and its control are reported elsewhere. 36 Under the same thermodynamic conditions as the TGA experiment, DC 4-probe conductivity measurement was performed to measure total electrical conductivity of LSF55. For this purpose, the size of the specimen was 16.0 × 2.5 × 2.5 mm 3 and a digital multimeter (Keithley 2700) combined with a programmable current source (Keithley 220) was used.…”

Section: Methodsmentioning

confidence: 99%

Investigations on Defect Equilibrium, Thermodynamic Quantities, and Transport Properties of La_0.5Sr_0.5FeO_3-δ

Bae

Hong

et al. 2019

J. Electrochem. Soc.

In this work, relationship between defect equilibrium and thermodynamic quantities is investigated to elucidate mass and charge transport properties of La 0.5 Sr 0.5 FeO 3-δ (LSF55). The oxygen nonstoichiometry (δ) was measured as a function of oxygen partial pressure in 10 −19 ≤ (P O 2 /at m)≤ 0.21 and 750 ≤ (T/°C) ≤ 900 range. The δ − P O 2 − T relationships indicated an electronic n-p transition point at δ = 0.25 which moved to a higher P O 2 value with increasing temperature. The relative partial molar enthalpy ( H O ) and entropy ( S O ) of oxygen indicated that across the electronic stoichiometric point H O stabilized around −86.9 ± 3.6 kJ/mol in p-type and −402.2 ± 12.6 kJ/mol in n-type regimes, whereas S O values were kept changing because of the contribution from configuration entropy (S O(Con f ) ). From the DC 4-probe conductivity and electrical conductivity relaxation (ECR) measurement, the oxygen-ion conductivity at 900°C was 0.29 S.cm −1 with activation energy of 0.72 ± 0.04 eV and the oxygen self-diffusivity (D O ) for LSF55 with δ = 0.114 during oxidation increased from (8.27 ± 0.05) × 10 −8 cm 2 s −1 at 800°C to (2.55 ± 0.01) × 10 −7 cm 2 s −1 at 900°C with an activation energy of 1.22 ± 0.14 eV. Dilatometry measurements indicated an isothermal chemical expansion as function of P O 2 , which was explained on the basis of the relative change in mean ionic radius of transition metal cation Fe against δ. This model showed that transition metal cation existed as a mixture of high-spin and low-spin states and made a transition from low-spin to high-spin state with increasing δ.

“…The absolute value for the nonstoichiometry was determined by TGA of the overall mass loss upon decomposition via the reaction 10 19 The change in oxygen nonstoichiometry of La 2 Ni 0.95 Al 0.05 O 4.025 + d was measured from room temperature to 1000°C in air gas at a flow rate of 200 cm 3 /min. The relationship between the oxygen nonstoichiometric variation and the measured weight change can be described as…”

Section: Resultsmentioning

confidence: 99%

Oxygen Nonstoichiometry and Thermodynamic Quantities of La₂Ni_0.95Al_0.05O_4.025 + δ

Jeon

Yoo³

et al. 2014

J. Am. Ceram. Soc.

The oxygen nonstoichiometry of La2Ni0.95Al0.05O4.025 + δ (LNAO) is measured as a function of oxygen partial pressure (pO2) and temperature by coulometric titration method and thermogravimetric analysis (TGA) in 800°C–1000°C temperature range and 10−16‐1 atm pO2 range. The partial molar quantities for mixing of oxygen were calculated and results were compared with the literature results on La2NiO4 + δ (LNO). The variation in activity coefficient of holes versus oxygen nonstoichiometry illustrated an early positive deviation of the activity coefficient of holes from unity, leading to γh∙ ≈ 7 at δ ≈ 0.08, which was lower than the literature value of γh∙ ≈ 14 for La2NiO4 + δ at δ ≈ 0.08, indicating lesser deviation of LNAO from ideal solution behavior. The effective mass of holes (mh∗) was 1.02–1.21 times the rest mass (mo), which indicated the band‐like conduction and allowed the effect of the small degree of polaron hopping to be ignored. The comparison of oxygen nonstoichiometry and partial molar quantities showed that incorporation of interstitial oxygen is less favorable in LNAO in comparison to LNO.