scholarly journals Effect of Oxygen Partial Pressure on the Phase Stability of Copper–Iron Delafossites at Elevated Temperatures

Materials ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 1888 ◽  
Author(s):  
Thomas Stöcker ◽  
Ralf Moos
Keyword(s):  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
High Temperatures ◽  
Phase Stability ◽  
Elevated Temperatures ◽  
Process Window ◽  
Thermoelectric Generators ◽  
X Ray Diffraction ◽  
Characterization Methods ◽  
X Ray

Oxide-based materials are promising candidates for use in high temperature thermoelectric generators. While their thermoelectric performance is inferior to commonly used thermoelectrics, oxides are environmentally friendly and cost-effective. In this study, Cu-based delafossites (CuFeO2), a material class with promising thermoelectric properties at high temperatures, were investigated. This work focuses on the phase stability of CuFeO2 with respect to the temperature and the oxygen partial pressure. For this reason, classical material characterization methods, such as scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction, were combined in order to elucidate the phase composition of delafossites at 900 °C at various oxygen partial pressures. The experimentally obtained results are supported by the theoretical calculation of the Ellingham diagram of the copper–oxygen system. In addition, hot-stage X-ray diffraction and long-term annealing tests of CuFeO2 were performed in order to obtain a holistic review of the phase stability of delafossites at high temperatures and varying oxygen partial pressure. The results support the thermoelectric measurements in previous publications and provide a process window for the use of CuFeO2 in thermoelectric generators.

Tensile Properties and Creep Behavior of SiC-Based Fibers under Various Oxygen Partial Pressures

2005 ◽  
Vol 475-479 ◽  
pp. 1333-1336 ◽  
Author(s):  
Jan Ji Sha ◽  
J.S. Park ◽  
Tatsuya Hinoki ◽  
Akira Kohyama ◽  
J. Yu
Keyword(s):  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Tensile Properties ◽  
Creep Behavior ◽  
Elevated Temperatures ◽  
Low Oxygen ◽  
X Ray Diffraction ◽  
Sic Fibers ◽  
Partial Pressures ◽  
Ar Gas

Three kinds of atmospheres (air, highly-pure Ar and ultra highly-pure Ar gas) with different oxygen partial pressures were applied to investigate the tensile properties and creep behavior of SiC fibers such as Hi-NicalonTM and TyrannoTM-SA. These fibers were annealed and crept at elevated temperatures ranging from1273-1773 K in such environments. After annealing at 1773 K, the room temperature tensile strengths of SiC-based fibers decreased with decreasing the oxygen partial pressure and the near stoichiometric fiber TyrannoTM-SA shows excellent strength retention. At temperatures above the 1573 K, the creep resistance of SiC fibers evaluated by bending stress relaxation (BSR) method under high oxygen partial pressure was lower than that of in low oxygen partial pressure. The microstructural features on these fibers were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD).

Effect of Oxygen Partial Pressure on Stability of High-Tc Phase in Sintered Bi-Pb-Sr-Ca-Cu-O Superconductos

1989 ◽  
Vol 169 ◽  
Author(s):  
H.K. Lee ◽  
K.W. Lee ◽  
D.H. Ha ◽  
J.C. Park
Keyword(s):  
Phase Transformation ◽  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Superconducting Phase ◽  
Low Oxygen ◽  
X Ray Diffraction ◽  
High Tc ◽  
X Ray ◽  
High Tc Phase ◽  
Effect Of Oxygen

AbstractThe effect of oxygen partial pressure on stability of high-Tc phase in Bi-Pb-Sr-Ca-Cu-O system has been investigated using x-ray diffraction, resistivity and a.c. susceptibility measurements. It was found that part of the high-Tc phase in Bi-Pb-Sr-Ca-Cu-O system was transformed into the low-Tc phase (80 K) and insulating phases by heating in the temperature range 600 C to 880°C in O2 of one atmosphere. The original high-Tc phase was restored upon retreatment in a low oxygen partial pressure of 0.1 atmosphere. The reversible superconducting phase transformation is discussed in conjunction with the formation mechanism of the high-Tc phase in Bi-Pb-Sr-Ca-Cu-O system.

High temperature X-ray diffraction studies of the decomposition mechanism of YBa2Cu3O7−δ at an oxygen partial pressure less than 10 Pa

1995 ◽  
Vol 10 (3) ◽  
pp. 165-169 ◽  
Author(s):  
W. Pitschke ◽  
W. Bieger ◽  
G. Krabbes ◽  
U. Wiesner
Keyword(s):  
High Temperature ◽  
Solid State ◽  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Solid State Reaction ◽  
Peritectic Reaction ◽  
Decomposition Reaction ◽  
Primary Decomposition ◽  
X Ray Diffraction ◽  
X Ray

The crystallographic data of YBa2Cu3O7−δ, Y2BaCuO5, BaCu2O2, and YBa4Cu3O9 at high temperatures and p(O2)<10 Pa have been derived on the basis of HT-XRD measurements. Whereas Y2BaCuO5 expands nearly isotropically, YBa2Cu3O7−δ and BaCu2O2 show anisotropic expansions. Furthermore, the first decomposition step of the considered compounds at p(O2)<10 Pa was observed. BaCu2O2 melts congruently at T ≍ 1273 K and Y2BaCuO5 decomposes via a peritectic reaction into Y2O3, Y2BaO4 and melts at T ≍ 1323 K. A solid-state reaction into Y2BaCuO5 and BaCu2O2 was indicated for YBa2Cu3O7−δ at T ≍ 1123 K. Because YBa4Cu3O9 becomes unstable at T ≍ 1123 K, this compound cannot be formed by the primary decomposition reaction of YBa2Cu3O7−δ

scholarly journals Effect of V and Ti on the Oxidation Resistance of WMoTaNb Refractory High-Entropy Alloy at High Temperatures

Metals ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 41
Author(s):  
Shuaidan Lu ◽  
Xiaoxiao Li ◽  
Xiaoyu Liang ◽  
Wei Yang ◽  
Jian Chen
Keyword(s):  
Oxidation Resistance ◽  
High Temperatures ◽  
Elevated Temperatures ◽  
Early Stage ◽  
Mass Gain ◽  
High Entropy Alloy ◽  
High Entropy Alloys ◽  
X Ray Diffraction ◽  
X Ray ◽  
High Entropy

Alloying with V and Ti elements effectively improves the strength of WMoTaNb refractory high entropy alloys (RHEAs) at elevated temperatures. However, their effects on the oxidation resistance of WMoTaNb RHEAs are unknown, which is vitally important to their application at high temperatures. In this work, the effect of V and Ti on the oxidation behavior of WMoTaNb RHEA at 1000 °C was investigated using a thermogravimetric system, X-ray diffraction and scanning electron microscopy. The oxidation of all alloys was found to obey a power law passivating oxidation at the early stage. The addition of V aggravates the volatility of V2O5, MoO3 and WO3, and leads to disastrous internal oxidation. The addition of Ti reduces the mass gain in forming the full coverage of passivating scale and prolongs the passivation duration of alloys.

Electrical Conductivity Prediction in Langasite for Optimized Microbalance Performance at Elevated Temperatures

2002 ◽  
Vol 756 ◽  
Author(s):  
Huankiat Seh ◽  
Harry Tuller ◽  
Holger Fritze
Keyword(s):  
Electrical Conductivity ◽  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
High Temperatures ◽  
Gas Sensors ◽  
Elevated Temperatures ◽  
Operating Conditions ◽  
Total Conductivity ◽  
Defect Model ◽  
Partial Pressures

ABSTRACTThe performance of the langasite-based crystal microbalance is limited due to reductions in its resistivity at high temperatures and reduced oxygen partial pressures. In this work, we utilize a recently developed defect model to predict the dependence of the ionic and electronic contributions to the total conductivity of langasite on temperature, oxygen partial pressure and acceptor and donor dopants. These results are used to select the type and concentrations of dopants expected to provide extended operating conditions for langasite-based gas sensors and crystal microbalances.

In-situ analysis of chemical expansion and stability of SOFC cathodes

2014 ◽  
Vol 1655 ◽  
Author(s):  
Mirela Dragan ◽  
Scott Misture
Keyword(s):  
High Temperature ◽  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Lattice Parameter ◽  
Low Oxygen ◽  
X Ray Diffraction ◽  
Chemical Expansion ◽  
X Ray ◽  
Reducing Conditions ◽  
The Stability

ABSTRACTIn this work high-temperature X-ray diffraction has been used to investigate thermal and chemical expansion as well as overall phase stability for various cathode materials: Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF), La0.3Sr0.7CoO3 (LSC37), La0.6Sr0.4CoO3 (LSC64) and La0.6Sr0.4Fe0.8Co0.2O3 (LSCF), as a function of temperature in reducing conditions. When perovskites materials are under a low oxygen partial-pressure condition, the lattice parameter and overall dimension increase. Their chemical expansion has comparable values. From the viewpoint of the stability of these phases, the high-temperature X-ray diffraction results indicate no phase decomposition can be one of the reasons for material failure at the current experimental oxygen partial pressure. LSF is most stable, while LSC and LSCF form oxygen vacancy-ordered phases and then decompose when heated to 1000°C under atmospheres with pO2 as low as 10-5 atm.

scholarly journals The changes of Ba0.5Sr0.5Co0.8Fe0.2O3-δ perovskite oxide on heating in oxygen and carbon dioxide atmospheres

2014 ◽  
Vol 79 (9) ◽  
pp. 1141-1154 ◽  
Author(s):  
Sasa Zeljkovic ◽  
Toni Ivas ◽  
Sebastien Vaucher ◽  
Dijana Jelic ◽  
Ludwig Gauckler
Keyword(s):  
Carbon Dioxide ◽  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Elevated Temperatures ◽  
Oxygen Deficiency ◽  
Perovskite Oxide ◽  
X Ray ◽  
Equilibrium Reaction ◽  
Increasing Temperature

In the first part of this study, the oxygen deficiency, ?, in Ba0.5Sr0.5Co0.8Fe0.2O3 - ? (BSCF) was measured by means of thermogravimetry as a function of oxygen partial pressure, p(O2), in the range of 1.1?10?6 < p(O2)/% < 41.67 at elevated temperatures ranging 873 ? T/K ? 1073. It was shown that ? becomes more pronounced with increasing T and with decreasing p(O2). The isotherms ? vs. p(O2) were determined. The second part of this study relates to the reaction of CO2 with Ba0.5Sr0.5Co0.8Fe0.8O3-? perovskite oxide in the absence and presence of O2 at temperatures ranging from 673 to 973 K also by thermogravimetry. The reactivity of CO2 with BSCF increased with increasing temperature and increasing exposure to CO2. Reaction of CO2 with BSCF was described by a equilibrium reaction isotherms. The results of X-ray diffractometry evidenced that the exposure to CO2 leads to the formation of carbonates.

scholarly journals Self-Organized V - Mo Oxide Fibers by the Micro-Pulling Down Method

2009 ◽  
Vol 1223 ◽  
Author(s):  
Detlef Klimm ◽  
Krzysztof Orlinski ◽  
Dorota A. Pawlak
Keyword(s):  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Eutectic Composition ◽  
Intermediate Phase ◽  
X Ray Diffraction ◽  
Simple Modification ◽  
X Ray ◽  
On Demand ◽  
Self Organized ◽  
Experimental Parameters

ABSTRACTThe V2O5-MoO3 mixtures offer a whole range of materials where properties can be adjusted by simple modification of experimental parameters, which may be utilized for manufacturing metamaterials with on-demand properties. The V2O5-MoO3 system contains an intermediate phase V9Mo6O40, with a small fraction of V4+ instead of V5+. Consequently, this system should rather be considered as pseudobinary. The V4+ content depends on the oxygen partial pressure in the atmosphere. Thus, by changing the oxygen partial pressure one can tailor the electric properties of the system, and by changing the supercooling, the morphologic structure of crystallized bodies as well. For better understanding of this system differential thermal analysis and thermodynamic modeling was performed. Fibers of eutectic composition between V9Mo6O40 and MoO3 were grown by the micro-pulling-down technique. X-ray diffraction confirmed the existence of the V9Mo6O40 intermediate phase.

Structure refinements of seven natural olivine crystals and the influence of the oxygen partial pressure on the cation distribution

1981 ◽  
Vol 155 (1-2) ◽  
Author(s):  
G. Nover ◽  
G. Will
Keyword(s):  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Extinction Coefficient ◽  
Diffraction Data ◽  
X Ray Diffraction ◽  
Volcanic Origin ◽  
X Ray ◽  
Anisotropic Temperature ◽  
Natural Olivine ◽  
Temperature Factors

AbstractMg/Fe order in olivine has been determined by X-ray diffraction data, for example by Wenk and Raymond (1973). We have now studied the dependence of the Mg/Fe order vs. oxygen partial pressure. Two natural olivine samples of volcanic origin containing respectively 10 and 12 % fayalite were selected. The atomic positions, anisotropic temperature factors, extinction coefficient and site occupancies have been refined toThese experiments seem to indicate that the prevailing oxygen partial pressure determines the different Mg/Fe order found in natural olivine crystals.

Growth and Characterization of PbTiO3 and Pb(Zr,Ti)O3 Thin Films by MOCVD

1994 ◽  
Vol 361 ◽  
Author(s):  
Y. Gao ◽  
W. Dong ◽  
B.A. Turtle
Keyword(s):  
Thin Films ◽  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Depth Profiling ◽  
X Ray Diffraction ◽  
X Ray ◽  
Si Substrates ◽  
Pzt Films ◽  
Uniform Composition

ABSTRACTFerroelectric PbTiO3 and Pb(Zr,Ti)O3 thin films with a perovskite structure were grown on MgO and Pt/Ti/SiO2/Si by MOCV.D. The microstructure and composition of the films were characterized by x-ray diffraction, SEM, and AES. Preferred orientation of either (111) or (100)/(001) was obtained on the Pt/Ti/SiO2/Si substrates at temperatures from 600 °C to 650 °C The preferred (111) orientation was attributed to the formation of the Pt3Ti phase in the Pt layer of the substrates, whereas the (100)/(001) orientations were inferred as the growth rate effect. AES depth profiling indicated a uniform composition through the thickness of the PZT films. However, SEM showed different topography and microstructure of the PZT films deposited in different oxygen partial pressure. Electrical properties of the PZT films appear varied as a function of the oxygen partial pressure in the reactor.

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