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1.
Etching of a natural diamond octahedron was carried out at temperatures of 800 to 1400° C and at pressures of 15 and 40 kbar
under controlled oxygen partial pressure in the range 10−17 to 104 atm by use of oxygen buffers. Well-defined etch pits of equiangular triangule outline were formed. When the results were
plotted based on logP
O
2 versus 1/T, reversal of the pit orientation clearly occurred on a boundary curve expressed by an equation, logP
O
2=−9.0×104/T+63, whereP
O
2 (atm) andT (K) are oxygen partial pressure and temperature, respectively. Etch pits with the same orientation as an octahedral face
were produced in a low temperature and highP
O
2 region, and those with the opposite orientation, i.e. the same as for natural “trigon”, were produced in the other region. 相似文献
2.
Lingwen Zhao Juanjuan Feng Adeel Abbas Chunlei Wang Hongchao Wang 《Small (Weinheim an der Bergstrasse, Germany)》2023,19(41):2302953
Designing efficient and cost-effective electrocatalysts is the primary imperative for addressing the pivotal concerns confronting lithium–oxygen batteries (LOBs). The microstructure of the catalyst is one of the key factors that influence the catalytic performance. This study proceeds to the advantage of metal-organic frameworks (MOFs) derivatives by annealing manganese 1,2,3-triazolate (MET-2) at different temperatures to optimize Mn2O3 crystals for special microstructures. It is found that at 350 °C annealing temperature, the derived Mn2O3 nanocage maintains the structure of MOF, the inherited high porosity and large specific surface area provide more channels for Li+ and O2 diffusion, beside the oxygen vacancies on the surface of Mn2O3 nanocages enhance the electrocatalytic activity. With the synergy of unique structure and rich oxygen vacancies, the Mn2O3 nanocage exhibits ultrahigh discharge capacity (21 070.6 mAh g−1 at 500 mA g−1) and excellent cycling stability (180 cycles at the limited capacity of 600 mAh g−1 with a current of 500 mA g−1). This study demonstrates that the Mn2O3 nanocage structure containing oxygen vacancies can significantly enhance catalytic performance for LOBs, which provide a simple method for structurally designed transition metal oxide electrocatalysts. 相似文献
3.
We have performed a parametric analysis of the influence of the percentage fraction of atomic oxygen in the O2:O2(1Δ):O flow on the formation of population inversion for a laser transition in iodine atoms and the temperature regime at an
elevated pressure of P = 5 Torr in a system with axisymmetric injection of a I2: He mixture to the flow of oxygen excited by an electric-discharge singlet oxygen generator. 相似文献
4.
E. P. Pakhomov 《High Temperature》2005,43(4):554-567
The mass action law is used to describe the reversible exchange between the crystal lattice of ZrO2 and the ambient medium, and the special features of positioning of interstitial particles in the lattice are taken into account. The ways of equilibrium interaction between the ZrO2−x
lattice with the ambient medium (types of defects that arise) at different partial pressures of oxygen p(O2) and temperatures T are determined, along with the form of the correlation x = f[p(O2)], the variation of its composition, the number of charge carriers, mass, volume, and density. The obtained results are compared with the available experimental data. It is demonstrated that, at low temperatures, the lattice defects in pure ZrO2 are as follows: at high values of p(O2) - oxygen vacancies in the anion sublattice and singly charged anions of oxygen in the interstice, and at low values of p(O2) - vacancies in the anion sublattice and electrons localized on the adjacent cations. At high temperatures, the lattice defects are as follows: at high values of p(O2) - singly charged anions of oxygen and quadruply charged cations of zirconium at the interstice, and at low values of p(O2) - only neutral zirconium atoms at the interstice.__________Translated from Teplofizika Vysokikh Temperatur, Vol. 43, No. 4, 2005, pp. 556–567.Original Russian Text Copyright © 2005 by E. P. Pakhomov. 相似文献
5.
S. Jayanthi T. R. N. Kutty 《Journal of Materials Science: Materials in Electronics》2008,19(7):615-626
The role of transition metals of the 3d series from V (Z = 23) to Zn (Z = 30) is investigated in modifying the crystallographic phase contents, microstructure and the dielectric properties of BaTiO3 ceramics containing
≤10 at% substituents. All the transition metals brought about the phase conversion to hexagonal BaTiO3 and the hexagonality is found to depend on Ba/Ti ratio as well as the processing conditions including the sintering temperature
and the post sinter annealing. The εr-T characteristics are modified with increasing hexagonality by way of the tremendous decrease in dielectric constant with
broad and diminished εmax for the mixed phase ceramics giving way to flat εr-T curves for totally hexagonal specimens. Doping with >1% Zn2+ or ≥5% Mg2+ also render the ceramics completely hexagonal indicating that the crystal field effects of the 3d orbital electrons are not
the cause for the conversion to hexagonal phase. Electron paramagnetic resonance (EPR) spectra of Mn-doped ceramics reveal
the prevalence of defect complexes involving oxygen vacancies and different valence states of Mn occupying the Ti-sites within
the corner-sharing as well as face-sharing octahedra present in hexagonal BaTiO3. EPR results also indicate defect complexes involving electron localization at Ti-sites and oxygen vacancies around the face-sharing
octahedra. On annealing the ceramics in lower oxygen partial pressures at elevated temperatures leads to the reversion to
corner shared (Ti3+–VO) defect complex accompanied by the conversion to cubic/tetragonal phase. The alterations in the oxygen vacancy-metal impurity
defect complexes and the modifications in the oxygen close packing are the cause for the prevalence of hexagonal BaTiO3 at room temperature. 相似文献
6.
Effects of Ho2O3 addition on defects of BaTiO3 ceramic have been studied in terms of electrical conductivity at 1200 °C as a function of oxygen partial pressure (PO2°) and oxygen vacancy concentration. The substitution of Ho3+ for the Ti site in Ba(Ti1−xHox)O3−0.5x resulted in a significant shift of conductivity minimum toward lower oxygen pressures and showed an acceptor-doped behavior. The solubility limit of Ho on Ti sites was confirmed less than 3.0 mol% by measuring the electrical conductivity and the lattice constant. Oxygen vacancy concentrations were calculated from the positions of PO2° in the conductivity minima and were in good agreement with theoretically estimated values within the solubility limit. The Curie point moved to lower temperatures with increasing the oxygen vacancy concentration and Ho contents. 相似文献
7.
M. K. Miller C. L. Fu M. Krcmar D. T. Hoelzer C. T. Liu 《Frontiers of Materials Science in China》2009,3(1):9-14
The existence of nanoclusters that are thermodynamically stable at elevated temperatures is truly intriguing because of its
scientific implications and potential applications. Highly stable nanoclusters have been observed by atom probe tomography
in iron-based alloys at temperatures close to 1400°C (0.92T
m) that appear to defy the stability constraints of artificially created nanostructured materials. The ∼4-nm-diameter Ti-,
Y- and Oenrichednanoclusters are identified in the new form of a highly defective material state with vacancies as the critical
alloying component and with (Ti + Y):O ratio different from the stable TiO2 and Y2Ti2O7 oxides. Vacancies play an indispensable role in enhancing the oxygen solubility and increasing the oxygen binding energy
in the presence of Ti and Y, resulting in the stabilization of coherent nanoclusters. Atom probe tomography characterizations
and theoretical predictions indicate that vacancies can be exploited for the first time as a nanoscale constituent to design
materials with far superior high temperature properties. 相似文献
8.
Titanium dioxide (TiO2) is widely considered to be a strongly n-type semiconductor due to its tendency for oxygen deficiency. In this work, however, room temperature p-type semiconductivity has been observed in rutile TiO2, as determined using surface photovoltage spectroscopy and cyclic voltammetry subsequent to controlled processing at elevated temperatures. In particular, room temperature p-type semiconductivity has been imposed via strong oxidation [p(O2) = 75 kPa] at elevated temperatures (1273 K), followed by rapid cooling in the same gas phase. It is reasoned that under such conditions, the observed p-type behaviour is due to the formation of titanium vacancies (acceptor-type ionic defects) at the TiO2 surface. It is also concluded that the extremely slow diffusion kinetics of these defects towards the bulk is what limits the p-type behaviour to the surface and near surface regions. Nevertheless, this could be overcome by applying appropriately lengthy annealing times. The reported observation of p-type semiconductivity in TiO2 is expected to have far reaching consequences for this intensely researched material. 相似文献
9.
Electrical conductivity of fluorite phases in the system Y2O3-Ta2O5-MgO has been studied. Y0.8Ta0.2O1.7 fluorite phase, having 15 mol% oxygen ion vacancies, showed the maximum electrical conductivity. Electrical conductivity of Y0.8Ta0.2O1.7 fluorite phase increased linearly with P1/2
HO due to the contribution of protonic conduction in water vapour. The electrical conductivity of the fluorite phase increased more remarkably at lower temperature, 700°C, than at higher temperatures, 800°C and 900°C. The obtained results imply that the protonic conduction greatly contributes to the electrical conductivity of the fluorite phases in the system Y2O3-Ta2O5-MgO in water vapour. 相似文献
10.
The d.c. conductivity, σ, and the oxygen gas-sensing behaviour of V2O5–SnO–TeO2 glass prepared by press-quenching were studied in argon and oxygen gas atmospheres at temperatures ranging from 303–473 K.
The glass of 50V2O5·20SnO·30TeO2 (mol %) was n-type semiconducting. The high-temperature conductivity was lower in oxygen and higher in argon than that in
air. This was explained by the V4+ ions in the glass being oxidized by oxygen which had diffused into the glass, resulting in an increase in V5+ with time. The experimental relationship between σ and oxygen partial pressure, P
O2, agreed quantitatively with the theoretical relation σ ∝ P
O2
-1/4
. Changes in conductivity by switching the atmospheres between oxygen and argon gases were found to be reproducible. From
the data of these dynamic changes, the oxygen gas sensitivity, S, at 473 K was obtained to be 1.3 in oxygen atmosphere. The dynamic changes could be quantitatively explained by an oxygen
diffusion model. Throughout these discussions, the present tellurite glass was found to possess a potential applicability
as an oxygen gas sensor.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
11.
W. E. Alnaser M. M. Zein M. N. Khan S. S. Al-Dallal A. M. Memon M. J. Al-Othman 《Journal of Materials Science》1994,29(2):482-485
Mechanical losses spectroscopy of two superconducting Y1Ba2Cu3O7–x
samples (T
c=93 K) measured at 5, 10, 20 and 30 MHz revealed four peaks. As the frequency of measurement was increased, the peaks shifted to higher temperatures. The relaxation process was found to have an activation enthalpy of 0.188, 0.092, 0.209 and 0.314 eV with an attempt frequency,f
o, equal to 2.46 × 1015, 5.95 × 1010, 1.64 × 1014, and 7.82 × 1013 Hz for P1, P2, P3 and P4 peaks, respectively. The mechanism responsible for these relaxation peaks is discussed. The infrared spectra of some of these compounds provide evidence for oxygen rearrangement on going from tetragonal to orthorhombic phase. X-ray diffraction analysis shows that these compounds correspond to a single phase which is an orthorhombic perovskite structure. 相似文献
12.
The (La, Sr) (Cr, Mn)O3 system was investigated in an effort to develop an interconnect and cathode materials for solid oxide fuel cells. Sintering studies were done in air at temperatures below 1500°C. Significant improvements in densification were observed with substitution of 50 mol% Mn for chromium and a density of 95% theoretical was achieved with the substitution of 70 mol% Mn for chromium in the La(Cr, Mn)O3 system. Electrical conductivity (d.c.) measurements were made as a function of temperature and oxygen activity. At 1000°C and 1 atm oxygen, the electrical conductivity ranged from 2.2–20 S cm–1 for LaCr0.8Mn0.4O3 and La0.9Sr0.1Cr0.2Mn0.8O3, respectively. All of the compositions showed similar dependence of electrical conductivity on the oxygen activity. Dependence was small at high oxygen activities; as the oxygen activity decreased, a break in electrical conductivity at 10–12 atm and 1000°C was observed, and then the electrical conductivity decreased asP
O2
1/4
. Sintering and electrical conductivity studies indicate that La0.9Sr0.1Cr0.2Mn0.8O3 appears to be a candidate for solid oxide fuel cell applications. 相似文献
13.
The defect structure of undoped polycrystalline Ta2O5 was investigated by determining the temperature [850–1050°C] and oxygen partial pressure [100–10?19 atm.] dependence of the electrical conductivity. The data were found to be proportional to the power of the oxygen partial pressure for the oxygen pressure range <10?8 atm. and independent of the oxygen partial pressure for PO2 > 10?6 atm. The enthalpy of formation of doubly ionized oxygen vacancies plus two electrons is estimated to be 118.31 Kcal/mole [5.13 eV]. The observed conductivity data are explained on the basis of the presence of unknown acceptor impurities in the undoped samples. 相似文献
14.
Qi Hu Xiaowan Huang Ziyu Wang Guomin Li Zhen Han Hengpan Yang Peng Liao XiangZhong Ren Qianling Zhang Jianhong Liu Chuanxin He 《Small (Weinheim an der Bergstrasse, Germany)》2020,16(25)
The widely used route of high‐temperature pyrolysis for transformation of Prussian blue analogs (PBAs) to functional nanomaterials leads to the fast removal of CN? ligands, and thus the formation of large metal aggregates and the loss of porous structures inside PBAs. Here, a controllable pyrolysis route at low temperature is reported for retaining the confined effect of CN? ligands to metal cations during the whole pyrolysis process, thereby preparing high‐surface‐area cubes comprising disordered bimetallic oxides (i.e., Co3O4 and Fe2O3) nanoparticles. The disordered structure of Co3O4 enables the exposure of abundant oxygen vacancies. Notably, for the first time, it is found that the in situ generated CoOOH during the oxygen evolution reaction (OER) can inherit the oxygen vacancies of pristine Co3O4 (i.e., before OER), and such CoOOH with abundant oxygen vacancies adsorbs two ?OH in the following Co3+ to Co4+ for markedly promoting OER. However, during the similar step, the ordered Co3O4 with less oxygen vacancies only involves one ?OH, resulting in the additional overpotentials for adsorbing ?OH. Consequently, with high surface area and disordered Co3O4, the as‐synthesized electrocatalysts have a low potential of 237 mV at 10 mA cm?2, surpassing most of reported electrocatalysts. 相似文献
15.
Boguslaw Kusz Leon Murawski Ryszard Barczynski Ivan Davoli Olgierd Gzowski Sergio Stizza 《Journal of Materials Science》1990,25(4):2125-2128
The internal friction (Q
–1) spectrum of YBa2Cu3Ox superconducting ceramic exhibits several peaks. It has been confirmed that the high-temperature peak (around 240 K) depends on structural changes and varies during subsequent cycles of cooling and heating.Q
–1 conductivity, X-ray spectra and the shielding effect have been measured on several samples having different superconducting properties obtained by various thermal treatments. Splitting is a characteristic feature of the high-temperature internal friction peak of the sample which exhibits good superconducting properties. In the case of the specimen exhibiting the worst properties the peaks decrease and overlap. In both cases an increase can be observed of this peak with the number of thermal cycles. After ageing at 470 K, the high-temperature peak disappears. Subsequent thermal cycles slightly recover it. Hysteresis of the Young modulus is also observed. The results are interpreted as transition of the 04 oxygen atom between two energy minima in the O4-Cu-O4 chain. 相似文献
16.
Kyong-Gue LeeKyoung-Ho Park Byung-Yong YuChong-Hong Pyun Chang-Hong KimHong Lee Park Sun-il Mho 《Materials Research Bulletin》2002,37(6):1071-1083
Photoluminescence and low-voltage cathodoluminescence characteristics of ZnGa2O4 phosphor doped with monovalent ions has been studied. Monovalent ions such as Na+ and Ag+ are incorporated into ZnGa2O4 lattices in order to increase the concentration of oxygen vacancies in the spinel lattice. By doping low concentrations of monovalent ions (Na+, Ag+) into ZnGa2O4, the self-activated blue luminescence originated from oxygen vacancies is enhanced. Also, the blue luminescence intensity is enhanced more along with a good color purity by annealing ZnGa2O4:Na+ in a reducing atmosphere, which is due to increasing the concentration of oxygen vacancies even more. The luminescence band at the UV region (λmax=360 nm) does not become the major luminescence band by introducing Na+ ion into the ZnGa2O4 lattice, while the UV luminescence band becomes the major one by annealing the undoped ZnGa2O4 in a reducing atmosphere. 相似文献
17.
Preparation of YVO4 powder from the Y2O3 + V2O5 + H2O system by a hydrolysed colloid reaction (HCR) technique 总被引:1,自引:0,他引:1
Sandor Erdei 《Journal of Materials Science》1995,30(19):4950-4959
Prior to the formation of YVO4 in the Y2O3 + V2O5 + H2O system, two intermediate, partially hydrophobic, complex colloidal mixtures with metastable characteristics can be produced at room temperature and atmospheric pressure. The ball-milled system, having both hydrophobic and hydrophilic species, transforms into the stable yttrium orthovanadate phase due to intensive hydrolysis. At room temperature an orange mixture (possessing dispersed Y2O3 and 4Y2O3–P
(OH)
p
p+
·2VO
3
–
, Y2O3–p
(OH)
p
p+
·6VO
3
–
·xH2O-like heteroaggregations) formed by 20 h mixing at pH ca. 4.0 transforms slowly, another red-brown heavily flocculated colloidal mixture (with dispersed Y2O3 and Y2O3–p
(OH)
p
p+
·V10O
28
6–
·yH2O-like aggregation) formed by 70 h mixing at pH ca. 4.5 transforms rapidly into YVO4 in water. During additional mixing of highly diluted red-brown mixtures this transformation can be completed at room temperature. At elevated temperatures (50–95 °C) the orange mixture precipitates into a red-brown decavanadate-type precipitatium which subsequently can also rapidly hydrolyse into an orthovanadate phase in the diluted aqueous systems. Both vanadium excess meta-and decavanadate-type aggregations exhibit amorphous character by X-ray diffraction.The semi-hydrophobic colloidal structure can modify the dissociation mechanism, which prevents the system from returning to the starting oxides, and gives a new HCR technique for YVO4 preparation with a simple hydrolysis process at low temperatures and atmospheric pressure. 相似文献
18.
M. Lei 《Materials Letters》2009,63(22):1928-1930
Zinc gallate (ZnGa2O4) nanowires were directly grown on the amorphous carbon-coated silicon substrates using a facile chemical vapor deposition method without any metal catalysts. The growth mechanism can be attributed to a self-organization vapor-liquid-solid (VLS) process. The amorphous carbon layer plays an important role in the nucleation and growth process of the ZnGa2O4 nanowires. The photoluminescence (PL) of the nanowires shows a broad, strong green emission band centered at 532 nm and a weak UV emission band at 381 nm, which can be attributed to a large amount of ionized oxygen vacancies and the combination of Ga3+ ions with free electrons in coordinated oxygen vacancies, respectively. 相似文献
19.
A monolithic type of toughened silicon nitride ceramics has been developed from Si3N4-Y2O3 systems. However, because of the existence of a second phase, the fracture strength decreases at elevated temperatures. To
improve the high-temperature strength of silicon nitride, some additional components were investigated. It was found that
the addition of hafnia to the Si3N4-Y2O3-AIN system gave a greater high-temperature strength based on the promotion of grain-boundary phase crystallization: namely,
126 kg mm−2 in 3-point bend strength at 1300 °C for the hot-pressed specimen, and 90 kg mm−2 at 1300 °C for the pressureless sintered specimen. The role of the hafnia in crystallization is not yet clear, and is being
characterized by electron microscopy and microanalysis. 相似文献
20.
The effect of metastable tetragonal HfO2 on the elastic properties of partially stabilized HfO2 doped with Er2O3, Y2O3 or Eu2O3 was studied using a sonic resonance technique. The elastic moduli were monitored at elevated temperatures to follow the effect
of the tetragonal-monoclinic phase transformation. Elastic moduli were also determined as a function of porosity and found
to follow linear relations. The non-linear modulus versus temperature relations from room temperature to 500° C are explained
in terms of the oxygen vacancies present in the fluorite type phase. 相似文献