Oxygen Partial Pressure Conditions Research Articles

Characteristics of hydrogen plasma treatment on Al2O3/CrxOy/AlmOn composite film via Al-ion-implantation and ultra-low partial pressure oxidation

In this paper, the preparation of Al2O3/CrxOy/AlmOn composite film and the stability of the composite film in a hydrogen plasma environment are studied. Al ions were implanted into the surface of pure chromium substrate, which was expected to induce the transformation of alumina into α-Al2O3 by using Cr2O3 formed under ultra-low oxygen partial pressure conditions as a template for crystal nucleation. This was to improve the hydrogen barrier properties of the film. The surface morphology evolution and phase composition of three different implanted doses (2 × 1017 ion/cm2, 3.5 × 1017 ion/cm2, and 5 × 1017 ion/cm2) were studied by scanning electron microscopy (SEM), atomic force microscopy (AFM), and the cross-sectional structure of the film was analyzed by transmission electron microscopy (TEM). The stability of the film in a hydrogen plasma environment was evaluated by electrochemical methods. The experimental results show that the composite coating is composed of a three-layer structure of Al2O3/CrxOy/AlmOn. The Al2O3 layer is mainly composed of γ-Al2O3 and a small amount of α-Al2O3. The CrxOy and AlmOn layers are partial metallic Cr or Al, and they contain a small amount of corresponding oxides. The composite coating shows high stability after hydrogen treatment. Electrochemical tests show that the composite film has good hydrogen permeation resistance. This research provides a new coating for potential hydrogen permeation barrier application.

Oxygen nonstoichiometry and electrical properties of La2–xSrxNiO4+δ (0 ≤ x ≤ 0.5)

The amount of interstitial oxygen (δ) in Sr-doped lanthanum nickel oxide (La2–xSrxNiO4+δ) as a function of Sr content has been investigated by the thermogravimetry analysis (TGA) and X-ray photoelectron spectroscopy (XPS). La2–xSrxNiO4+δ (0 ≤ x ≤ 0.5) ceramics were prepared by the general solid-state reaction process and sintered in different ambient of argon, air or oxygen, respectively. An increase in the amount of Sr decreased δ in La2–xSrxNiO4+δ, while the Ni2+/Ni3+ ratio analyzed by Ni3p XPS decreased indicating that the oxidation state of Ni increased. Particularly when the sample was sintered in a low oxygen partial pressure condition such as in Ar ambient, the hole concentration strongly depended on the Sr content, suggesting that the hole generation seems mostly originated from Sr2+ substitution into the La3+ site.

Investigation of the reduction roasting of saprolite ores in the Caron Process: microstructure and thermodynamic analysis

ABSTRACT Studies have been undertaken to investigate the thermodynamic aspects of the reduction roasting of saprolite ores in the Caron Process. Reduction experiments have been conducted in controlled oxygen partial pressure conditions at selected temperatures. Detailed microstructure characterisation and thermodynamic analysis of reduced ore samples, focusing on the phase transformations, nickel recoveries and Ni-Fe alloy compositions produced, were carried out. Comparison has been made between the experimental results and FactSage thermodynamic predictions for these conditions. The differences between between the experimental and predicted results are discussed. It has been shown that the system below 700°C is approximated thermodynamically by considering the nickel–iron alloy product to be in chemical equilibrium with a metastable amorphous oxide phase.

Self-healing by design: universal kinetic model of strength recovery in self-healing ceramics

ABSTRACT We propose a new theoretical kinetic model of strength recovery by oxidation-induced self-healing of surface cracks in composites containing a healing agent (HA). The kinetics is a key parameter in the design of structural components that can self-heal the damage done in service. Based on three-dimensional (3D) observations of crack-gap filling, two crack-gap filling models, i.e., a bridging model and a tip-to-mouth filling model, are incorporated in the proposed kinetic model. These crack-gap filling models account for the microstructural features of the fracture surfaces, crack geometry, and oxidation kinetics of the healing-agent. Hence, the minimum and maximum remaining flaw sizes in the healed crack gaps are estimated for various healing temperatures, times, and oxygen partial pressure conditions. Further, the nonlinear elastic fracture mechanics suitable for small-sized remaining flaws, together with a statistical analysis of the original Weibull-type strength distribution, enables the prediction of upper and lower strength limits of the healed composites. Three sintered alumina matrix composites containing silicon carbide (SiC)-type HAs with various volume fractions and shapes, together with monolithic SiC ceramics, are considered. The strength of the healed-composite predicted by our model agrees well with the experimental values. This theoretical approach can be applied to HAs other than SiC and enables the design of self-healing ceramic components for various applications.

Finite element analysis of the fracture statistics of self-healing ceramics

ABSTRACT Self-healing materials have been recognized as a promising type of next-generation materials. Among them, self-healing ceramics play a particularly important role, and understanding them better is necessary. Therefore, in this study, we applied the oxidation kinetics-based constitutive model to finite element analysis of a series of damage-healing processes in self-healing ceramics (alumina/SiC composites). In the finite element analysis, the data on the microstructure distribution, such as relative density, size and aspect ratio of pores, and grain size, were taken as input values and reflected onto the parameters of a continuum damage model using a fracture mechanical model. We then performed a 3-point bending analysis, to consider both the self-healing effect under certain temperature and oxygen partial pressure conditions and scatter of the strength of the ceramics. Our results confirmed that the proposed methodology can reasonably reproduce both strength recovery and damage propagation behavior in self-healing ceramics.

Synergetic donor–donor codoping strategy for enhanced photoelectrochemical activity of hematite

Hematite is a promising semiconductor for photoelectrochemical water splitting owing to its ideal band gap, nontoxicity, abundance, and chemical stability. However, the conversion efficiency remains less than its theoretical limit, which is in part due to a low carrier density. Although efforts have been made to increase the carrier density by incorporating appropriate donor dopants, structural instability caused by high donor doping has restricted the enhancement achieved and the resulting photocatalytic performance. Herein, we used density functional theory calculations to show that an enhanced carrier density and photocatalytic performance can be achieved without causing structural instability by using a donor–donor codoping strategy to introduce a 3d transition metal (Ti/V) and Si into hematite. Despite the Coulombic repulsion among the electrons from donors, the Coulombic attraction between donors with an oxidation number of +4 (Ti4+/V4+) and negatively charged small polarons contribute to a strong binding energy. The compensatory binding energy stabilizes the crystal structure and thus increases the density of carriers, most of which are small polarons. We also suggest that the carrier density can be further enhanced by increasing the ratio of Si interstitial doping, which produces four times more polarons than Si substitutional doping under experimental conditions of high temperature and low oxygen partial pressure. Our findings pave a way for an environment-friendly and efficient photocatalysis toward improvement of hydrogen fuel generation.

A DFT+U study of the oxidation of cobalt nanoparticles: Implications for biomedical applications

Nanomaterials – magnetic nanoparticles in particular have been shown to have significant potential in cancer theranostics, where iron oxides are commonly the materials of choice. While biocompatibility presents an advantage, the low magnetisation is a barrier to their widespread use. As a result, highly magnetic cobalt nanoparticles are attracting increasing attention as a promising alternative. Precise control of the physiochemical properties of such magnetic systems used in biomedicine is crucial, however, it is difficult to test their behaviour in vivo. In the present work, density functional theory calculations with the Dudarev approach (DFT+U) have been used to model the adsorption of oxygen on low Miller index surfaces of the hexagonal phase of cobalt. In vivo conditions of temperature and oxygen partial pressure in the blood have been considered, and the effects of oxidation on the overall properties of cobalt nanoparticles are described. It is shown that oxygen adsorbs spontaneously on all surfaces with the formation of non-magnetic cobalt tetroxide, Co3O4, at body temperature, confirming that, despite their promising magnetic properties, bare cobalt nanoparticles would not be suitable for biomedical applications. Surface modifications could be designed to preserve their favourable characteristics for future utilisation.

A Dft+U Study of the Oxidation of Cobalt Nanoparticles: Implications for Biomedical Applications

Nanomaterials - magnetic nanoparticles in particular - have been shown to have significant potential in cancer theranostics, where iron oxides are commonly the materials of choice. While biocompatibility presents an advantage, the low magnetisation is a barrier to their widespread use. As a result, highly magnetic cobalt nanoparticles are attracting increasing attention as a promising alternative. Precise control of the physiochemical properties of such magnetic systems used in biomedicine is crucial, however, it is difficult to test their behaviour in vivo. In the present work, density functional theory calculations with the Dudarev approach (DFT+U) have been used to model the adsorption of oxygen on low Miller index surfaces of the hexagonal phase of cobalt. In vivo conditions of temperature and oxygen partial pressure in the blood have been considered, and the effects of oxidation on the overall properties of cobalt nanoparticles are described. It is shown that oxygen adsorbs spontaneously on all surfaces with the formation of non-magnetic cobalt tetroxide, Co3O4, at body temperature, confirming that, despite their promising magnetic properties, bare cobalt nanoparticles would not be suitable for biomedical applications. Surface modifications could be designed to preserve their favourable characteristics for future utilisation.

Constriction of a lattice constant in an epitaxial magnesium oxide film deposited on a silicon substrate

We demonstrated epitaxial growth of magnesium oxide (MgO) on a silicon (Si) substrate with cubic on cubic structure [MgO(001)//Si(001) and MgO(100)//Si(100)]. Epitaxial films were prepared using the pulsed laser deposition method, and with dependent on deposition conditions of oxygen partial pressure and substrate temperature, the lattice constants of MgO decreased along both the surface normal and in-plane directions. To support the facts of (1) constriction of lattice constants and (2) cubic on cubic growth, we show (1) optimal lattice constants with defects in the crystal structure, (2) domain mismatch between MgO and Si instead of lattice mismatch, and (3) stability of MgO crystals on the surface of the Si substrate.

Oxygen vacancy revived phonon-glass electron-crystal in SrTiO3

Controlling oxygen vacancy in undoped SrTiO3 was used to realize the phonon-glass electron-crystal (PGEC) concept. The undoped SrTiO3 samples were synthesized through solid-state-reaction method in air and then reduced through annealing under low oxygen partial pressure conditions. We show that decreasing the oxygen partial pressure (Po2) results in increase of the electrical conductivity, and the oxygen vacancies act as phonon scattering centers, which lead to decrease in the lattice thermal conductivity. Both the enhanced electrical conductivity (σ) and reduced thermal conductivity (κ) were achieved simultaneously through oxygen vacancy in undoped SrTiO3. This significantly increases the ratio of σ/κ that results in an enormously enhanced ZT value of about 13 times larger as compared with the samples reduced under relatively high Po2. Density-functional theory calculations also reveal that oxygen vacancies in SrTiO3 reduce the band-gap, and consequently increase the electrical conductivity.

Density functional theory study of the point defect energetics in γ-LiAlO2, Li2ZrO3 and Li2TiO3 materials

The defect energetics in γ-LiAlO2, Li2TiO3, and Li2ZrO3 materials used in tritium-producing burnable absorber rods and fusion solid breeder applications was investigated using density functional theory calculations. A comprehensive analysis of the charged defects was performed for cation and anion vacancies, interstitials, antisite defects, and 3H interstitial and substitutional defects to understand the defect structures at different charge states and their stability as a function of the electron chemical potential across the electronic band gap of crystals at operating temperature and oxygen partial pressure conditions. Through investigation of the local bonding configurations and projected electronic density of states of the 3H related charged defects, including 3H interstitial (3Hint), 3Hint bound with an oxygen interstitial, and substitutional 3H defects on the Li, O, and M (M = Al, Ti, and Zr) sites (3HLi, 3HO, and 3HM), the 3H states of these defects were distinguished, i.e. triton (3H+), neutral 3H (3H0), and tritide (3H−). The two stable 3H related defects under the Li2O-LiOH rich condition at T = 1000 K, between P(O2) = 10−5 and 10−25 atm were found to be 3H interstitial (3Hint) with charge of +1 and neutral 3HLi (substitutional 3H on the Li site) in γ-LiAlO2, Li2ZrO3, and Li2TiO3 materials. For Li2TiO3, the stability of the 3HO with charge of +1 and 3HM with charge of −3 becomes comparable to that of 3Hint atm at P(O2) = 10−25 atm. Overall, our results indicate the energy cost to form the stable 3H defect species (3Hint with charge of +1 and neutral 3HLi) in γ-LiAlO2 material are higher than those of Li2TiO3 and Li2ZrO3 materials at T = 1000 K, between P(O2) = 10−5 and 10−25 atm. Interactions between the point defects and the 3H species as a function of the electron chemical potential across the band gap of the materials were also examined. All the three materials exhibit strong interactions between the 3Hint and the O vacancy, Li vacancy, and O interstitial defects with the strongest interactions found in the case of γ-LiAlO2 phase, indicating a higher tendency to trap 3H at such point defects in γ-LiAlO2.

Development of Highly Durable Thermal Barrier Coating by Suppression of Thermally Grown Oxide

Durability of thermal barrier coating (TBC) systems is important because of recent rising of turbine inlet temperature (TIT) for improved efficiency of industrial gas turbine engines. However, high-temperature environment accelerates the degradation of the TBC as well as causes spalling of the top coat. Spalling of the top coat may be attributed to several factors, but evidently the growth of thermally grown oxide (TGO) should be considered as an important factor. One method for reducing the growth rate of TGO is to provide a dense α-Al2O3 layer at the boundary of the bond coat and top coat. This α-Al2O3 layer will suppress the diffusion of oxygen to the bond coat and consumption of aluminum of the bond coat is suppressed. In this study, we focused on thermal pre-oxidation of the bond coat as a means for forming an α-Al2O3 barrier layer that would be effective at reducing the growth rate of TGO, and we studied the suitable pre-oxidation conditions. In the primary stage, we analyzed the oxidation behavior of the bond coat surface during pre-oxidation heat treatment by means of in situ synchrotron X-ray diffraction (XRD) analysis. As a result, we learned that during oxidation in ambient air environment, in the initial stage of oxidation metastable alumina is produced in addition to α-Al2O3, but if the thermal treatment is conducted under some specific low oxygen partial pressure condition, unlike in the ambient air environment, only α-Al2O3 is formed with suppressing formation of metastable alumina. We also conducted transmission electron microscope (TEM) and XRD analysis of oxide scale formed after pre-oxidation heat treatment of the bond coat. As a result, we learned that if pre-oxidation is performed under specific oxygen partial pressure conditions, a monolithic α-Al2O3 layer is formed on the bond coat. We performed a durability evaluation test of TBC with the monolithic α-Al2O3 layer formed by pre-oxidation of the bond coat. An isothermal oxidation test confirmed that the growth of TGO in the TBC that had undergone pre-oxidation was suppressed more thoroughly than that in the TBC that had not undergone pre-oxidation. Cyclic thermal shock test by hydrogen burner rig was also carried out. TBC with the monolithic α-Al2O3 layer has resistance to >2000 cycle thermal shock at a load equivalent to that of actual gas turbine.

Effects of Atmospheric Conditions on Slag Corrosion Resistance of Lightweight Al<sub>2</sub>O<sub>3</sub>-MgO Castables

By adopting dynamic induction furnace corrosion test, the corrosion mechanism of lightweight Al2O3-MgO castable with different environmental oxygen partial pressure was investigated through macro- and micro-analysis, XRD and thermodynamic simulation. The atmospheric condition was set to P(O2) = 0.21 atm or P(Ar) = 1.0 atm. The attained results showed that a reduced slag corrosion but intensified slag penetration happened at low environmental oxygen partial pressure condition. With P(O2) = 0.21atm, Mn and Fe in slag were present in the form of divalent and/or trivalent cations and were incorporated into spinel to form MnFe2O4 solutions and MgAl2O4 solutions during corrosion process. Since Fe, Mn ions are largely consumed, liquid with high viscosity formed and the continuing infiltration was suppressed. Under P(Ar) =1.0 atm, corrosion on castable aggregates was significantly weakened, and the reaction products under this condition are mainly MgAl2O4 and CA6.

Nanocrystalline CeO2−δ coated β-MnO2 nanorods with enhanced oxygen transfer property

In this research, β-MnO2 nanorods were synthesized by a hydrothermal method, followed by a facile precipitation method to obtain nanocrystalline CeO2−δ coated β-MnO2 nanorods. The as-prepared samples were characterized by XRD, HRTEM, FESEM, XPS and in-situ high-temperature XRD. The HRTEM results show that well dispersed CeO2−δ nanocrystals sized about 5 nm were coated on the surface of β-MnO2 nanorods. The oxygen storage and transfer property of as-synthesized materials were evaluated using TGA under various atmospheres (air, pure N2, and 5%H2/95%Ar). The TGA results indicate that CeO2−δ modification could favour the reduction of Mn4+ to Mn3+ and/or Mn2+ at lower temperature as compared with pure β-MnO2 nanorods and the physically mixed CeO2−δ-β-MnO2 under low oxygen partial pressure conditions (i.e., pure N2, 5%H2/95%Ar). Specifically, CeO2−δ@β-MnO2 sample can exhibit 7.5 wt% weight loss between 100 and 400 °C under flowing N2 and 11.4 wt% weight loss between 100 and 350 °C under flowing 5%H2/95%Ar. During the reduction process under pure N2 or 5%H2/95%Ar condition, the oxygen ions in β-MnO2 nanorods are expected to be released to the surroundings in the form of O2 or H2O with the coated CeO2−δ nanocrystals acting as mediator as inferred from the synergistic effect between the well-interacted CeO2−δ nanocrystals and β-MnO2 nanorods.

Slag corrosion mechanism of lightweight Al2O3–MgO castable in different atmospheric conditions

AbstractThe slag resistance of ladle lining refractory in different atmospheric conditions is of utmost importance due to the strong variation of atmospheric environment in ladle during the process cycle. In this study, by adopting dynamic induction furnace corrosion test, the corrosion mechanism of lightweight Al2O3–MgO castable with different environmental oxygen partial pressure was investigated through macro and microanalysis, XRD, and thermodynamic simulation. The atmospheric condition was set to P (O2) = 0.21 atm or P(Ar) = 1.0 atm. The attained results showed that a reduced slag corrosion but intensified slag penetration happened at low environmental oxygen partial pressure condition. With P(O2) = 0.21 atm, Mn and Fe in slag were present in the form of divalent and/or trivalent cations and were incorporated into spinel to form MnFe2O4 solutions and MgAl2O4 solutions during the corrosion process. Since Fe, Mn ions were largely consumed, liquid with high viscosity formed and the continuing infiltration was suppressed. Under P(Ar) = 1.0 atm, Fe ions in the slag were totally reduced into elemental iron while Mn existed mainly in the state of MnO, and the amount of liquid slag was therefore reduced, leading to significantly weakened corrosion on castable aggregates. Corrosion reaction products under this condition were mainly MgAl2O4 and CA6.

Work function and surface stability of tungsten-based thermionic electron emission cathodes

Materials that exhibit a low work function and therefore easily emit electrons into vacuum form the basis of electronic devices used in applications ranging from satellite communications to thermionic energy conversion. W–Ba–O is the canonical materials system that functions as the thermionic electron emitter commercially used in a range of high-power electron devices. However, the work functions, surface stability, and kinetic characteristics of a polycrystalline W emitter surface are still not well understood or characterized. In this study, we examined the work function and surface stability of the eight lowest index surfaces of the W–Ba–O system using density functional theory methods. We found that under the typical thermionic cathode operating conditions of high temperature and low oxygen partial pressure, the most stable surface adsorbates are Ba–O species with compositions in the range of Ba0.125O–Ba0.25O per surface W atom, with O passivating all dangling W bonds and Ba creating work function-lowering surface dipoles. Wulff construction analysis reveals that the presence of O and Ba significantly alters the surface energetics and changes the proportions of surface facets present under equilibrium conditions. Analysis of previously published data on W sintering kinetics suggests that fine W particles in the size range of 100-500 nm may be at or near equilibrium during cathode synthesis and thus may exhibit surface orientation fractions well described by the calculated Wulff construction.

Modeling the liquid phase autoxidation of cyclohexylbenzene to hydroperoxide

The liquid phase autoxidation of cyclohexylbenzene (CHB) to CHB hydroperoxide (CHBHP) is the key step of green production of phenol. The CHB oxidation kinetics was originally investigated by semibatch experiments under various oxygen partial pressures. Kinetic models to deal with oxygen-rich and oxygen-poor conditions were developed on the basis of free radical chain mechanism. It was found that the activation energy of the rupture of the bond OO of molecule CHBHP was close to that of cumene hydroperoxide, while the activation energy of hydrogen abstraction from the tert-butyl carbon of CHB was reasonably larger than that of cumene due to the steric effect. The kinetic model involving the oxygen addition to R (Model II) can be used to deal with various oxygen partial pressure conditions. Based on the developed kinetic model, the simulation of well-mixed reactor operated under continuous conditions was performed, and the results were in good agreement with continuous experiments.

Influence of the Oxygen Partial Pressure on the Oxygen Reduction Reaction Kinetics for the Low Platinum Loading Catalysts

The performance of fuel cells is first and foremost defined by the kinetics of the oxygen reduction reaction (ORR). The electrocatalysts have to conform among the others with the following requirements set by the Department of Energy (DOE) like: reduced precious metal loading, increased activity, improved durability/stability, and increased tolerance to air, fuel and system-derived impurities [1]. One possibility to ensure the excellent performance of the electrode is using the electrocatalyst with the small size platinum nanoparticles deposited onto the hierarchically porous carbon support. In this way, the reactant gas (oxygen or air) can be uniformly distributed over the catalyst surface. Many authors reported the influence of the oxygen/air pressure on the kinetics of ORR and demonstrated that the effect of pressure on the oxygen solubility is more significant in dilute electrolyte solutions compared to the concentrated ones [2-4]. Therefore, in this work the electrocatalytic activity toward ORR for 8.3wt%Pt-C, 12.4wt% Pt-C and 20wt%Pt-Vulcan was analysed in pure oxygen and synthetic air saturated 0.1M KOH electrolyte solutions at atmospheric pressure. Platinum nanoparticles were deposited (8.3 and 12.4wt%) onto the molybdenium carbide derived carbon support [5] using the sodium borohydride method. The commercially available 20wt%Pt-Vulcan catalyst was used as a reference system for comparison [6]. The several physical and electrochemical characterization techniques like the low temperature nitrogen sorption, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, inductively coupled plasma mass spectrometry, x-ray diffraction analysis, cyclic voltammetry and rotating disc electrode methods were applied. The results clearly indicate that increasing partial pressure of the oxygen significantly influences the ORR kinetics, due to improved solubility of the oxygen in alkaline electrolyte solution. As expected, the limiting diffusion current density values for various Pt catalysts in oxygen saturated solution found to be approximately 5 times higher than that determined for the same catalysts in the syntethic air conditions. This result is in good agreement with literature data [3]. For detailed electrochemical analysis the Tafel-like plots were constructed. The results established indicate that the ORR mechanism remains unchanged and four electron reduction mechanism is valid for both catalysts, e.q. for the synthesised and commercial one. It should be emphasized that electrochemical activity toward ORR for 8.3wt% Pt-C catalyst was higher than that for 20wt%Pt-Vulcan in 0.1M KOH solution at fixed oxygen partial pressure conditions.

Mineral chemistry and phase equilibrium constraints on the origin of accretions formed during copper flash smelting

This paper delves into the constraints on the nature, origin and thermal evolution of the accretions formed in the uptake shaft of the flash smelting furnace operated by Atlantic Copper in Huelva, Spain, outlining recommended practices for preventing accretion buildup. The accretions were investigated using quantitative electron probe microanalysis, X-ray diffraction and digital imaging techniques, and the experimental data on mineral composition, crystal chemistry and textural relationships were interpreted in terms of thermodynamic phase equilibrium in the SiO2-Fe-O-S system. The results suggest that two distinct types of accretions were formed by the fractional crystallization of two coexisting immiscible melts, under changing conditions of oxygen partial pressure (pO2). The type I accretion of magnetite + delafossite ± cuprite ± tridymite ± metallic copper crystallized from a fractionating copper-rich melt at pO2 above about 10−5 atm, while the type II accretion of magnetite + fayalite + metallic copper + chalcocite derived from a melt with lower copper concentration when pO2 levels dropped below that critical level. Phase compositions and textures were consistent with a cooling history of both compositionally contrasting liquids from about 1,250 °C, the liquidus temperature of magnetite, to eutectic or near-eutectic temperatures of around 1,100 °C. The maintenance of appropriate temperatures — above the liquidus temperature of magnetite — and oxygen partial pressure levels may be critical for the prevention of accretion buildup.

The Synthesis and Thermoelectric Properties of p-Type Li1−x NbO2-Based Compounds

We investigated the thermoelectric (TE) properties of a p-type oxide material (Li1−xNbO2, with x = 0–0.6). The composition was synthesized via a solid-state reaction method under a reducing atmosphere. The charge transport properties were determined through the electrical conductivity and Seebeck coefficient measurements. The electrical conductivity was non-monotonically varied with x value and showed metallic behavior with increased temperature and above 650 K temperature independent behavior dominated by extrinsic conduction. On the other hand, the Seebeck coefficient was increased with an increase in the temperature, and decreased gradually with an increase in the Li vacancy concentration by both synthesis and gradual phase transition to a Li-rich Li3NbO4 phase with temperature and appeared as an n-type TE at x = 0.6 under high temperatures, which was attributed to an Nb substitution into the Li site. The thermal conductivity was monotonically reduced with the increase in temperature due to the cation disorder defects and second phases. The Li vacancy induced Li1−xNbO2-based compounds under low oxygen partial pressure show promise as a candidate p-type material for thermoelectric applications, particularly for co-processing with n-type oxide thermoelectric materials fabricated under conditions of low oxygen partial pressure.