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1.
Defect engineering on phase structure and temperature stability of KNN‐based ceramics sintered in different atmospheres
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Zhenyong Cen Xiaohui Wang Yu Huan Yichao Zhen Wei Feng Longtu Li 《Journal of the American Ceramic Society》2018,101(7):3032-3043
Lead‐free MnO‐doped 0.955K0.5Na0.5NbO3‐0.045Bi0.5Na0.5ZrO3 (Abbreviated as KNN‐0.045BNZ) ceramics have been prepared by the conventional solid‐state sintering method in reducing atmosphere ( = 1 × 10?10 atm) and air. For ceramics sintered in reducing atmosphere, only Mn2+ ions exist in ceramics who preferentially occupy the cation vacancies in A‐site at x = 0.2‐0.4, whereas Mn2+ ions substitute for Zr4+ ions in B‐site to form defects () at x > 0.4. For ceramics sintered in air, mixed Mn2+, Mn3+, and Mn4+ ions coexist here. The Mn2+ ions preferentially occupy the cation vacancies in A‐site at x = 0.2‐0.4 and then Mn2+ ions substitute for Zr4+ ions in B‐site at x > 0.4. Meanwhile, the Mn3+ ions and Mn4+ ions substitute for Nb5+ ions in B‐site to form defects () at x = 0.2‐0.8. The (, , and ) dipolar defects show a positive dipolar defect contribution (DDC) to the , whereas the dipolar defects () show a negative DDC to the . The dipolar defects ( ‐ and ) can help improve the temperature stability of . The 0.4% MnO‐doped KNN‐0.045BNZ ceramics sintered in reducing atmosphere show excellent piezoelectric constant d33 = 300 pC/N and 0.2% MnO‐doped KNN‐0.045BNZ ceramics sintered in air possess optimal piezoelectric constant d33 = 290 pC/N. 相似文献
2.
First‐Principles Study of Sc1−xTixF3 (x ≤ 0.375): Negative Thermal Expansion,Phase Transition,and Compressibility
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Lei Wang Cong Wang Ying Sun Sihao Deng Kewen Shi Huiqing Lu Pengwei Hu Xiaoyun Zhang 《Journal of the American Ceramic Society》2015,98(9):2852-2857
We present the first‐principles investigation of (x ≤ 0.375). Controllable thermal expansion of is achieved by different Ti contents. The negative thermal expansion (NTE) behavior is weakened gradually with increasing Ti content, which is consistent with experimental measurements. The Jahn–Teller effect plays an important role in the cubic‐to‐rhombohedral phase transition, which stems from the enhanced energy stability when the 3d orbitals of cation split into triply degenerate and sets. The unusual thermal stiffening of is found, which is similar to that of and but contrary to other NTE materials. 相似文献
3.
Joon Sung Choi Youngjoo Park Sunghee Lee Dong Joon Min 《Journal of the American Ceramic Society》2018,101(7):2856-2867
The effect of CaO on the sulfide capacity of CaO‐Al2O3‐SiO2 slags was studied from the viewpoint of the ionic structure of alumina in slag. The aluminum coordination number was analyzed using 27Al 500‐MHz solid nuclear magnetic resonance spectroscopy and the results were compared with those of the sulfide capacity analysis. The sulfide capacity of slag, in the peralkaline region (), exhibited a linear relationship with respect to basicity () as excess free Ca2+ formed a 4‐coordinated aluminum unit structure ([IV]Al; ) and stabilized the sulfide ions (). However, sulfide capacity in the peraluminous region () exhibited a nonlinear relationship with respect to basicity () owing to the structure of higher‐coordinated aluminum units ([V]Al, [VI]Al; Al3+) and the relative lack of Ca2+. Therefore, the sulfide capacity of high Al2O3‐bearing slags strongly depended on the basicity () and stability of sulfide ions (), which depended on the competitive behavior of Ca2+ owing to the structural changes in Al2O3. The effect of the aluminum coordination number on the sulfide capacity was discussed in detail using an analysis of the slag structure and thermodynamics model. 相似文献
4.
First‐principles investigation of the thermodynamic stability of MB2 materials surfaces (M = Ti/Zr/Hf)
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Some of the renewed interest in transition metal diborides (MB2, M = Ti/Zr/Hf) arises from their potential use as matrices in ultrahigh‐temperature ceramic matrix composites (UHTCMCs). Crucial to the understanding of such composites is the study of the fiber/matrix interfaces, which in turn requires a deep knowledge of the surface structures and the thermodynamics of the matrix material. Here we investigate the surface stability of MB2 compounds by first‐principles calculations. Five surfaces are stabilized when going from a M‐rich to a B‐rich environment, respectively (0001)M, (100)M, (101)B(M), (113)M and (0001)B, with the highly stable (100)M, (101)B(M) and (113)M surfaces being discussed here for the first time. The mechanism behind the surface stability is analyzed in terms of cleavage energy, surface strain and surface bonding states. Our results provide important information for a better understanding of the most likely surfaces exposed to the fibers in UHTCMCs, thereby for the construction of reliable interfaces and ultimately UHTCMCs models. 相似文献
5.
Yu Shi Bao‐Wei Li Ming Zhao Ming‐Xing Zhang 《Journal of the American Ceramic Society》2018,101(9):3968-3978
CaO–Al2O3–MgO–SiO2 (CAMS)‐based glass‐ceramics were prepared using body crystallization method. Adding Cr2O3 into the ceramics not only effectively lowered the crystallization temperature, but also led to significant grain refinement of diopside that crystallized in the CAMS glass‐ceramic after crystallization treatment at 900°C for 2 hours. Experimental work verified that the epitaxial growth of the diopside on the spinel particles, which formed during nucleation treatment when fabricating the glass‐ceramics, facilitated the heterogeneous nucleation of diopside on the spinel and refined the diopside. In addition, two energetically favored crystallographic orientation relationships between the epitaxial growth diopside and spinel were experimentally observed. They are //[001]diopside,////(200)diopside and //[101]diopside, (311)spinel//. These two novel results can be potentially used to develop new glass‐ceramic materials with improved performance. 相似文献
6.
Grain Boundary Curvatures Measurements in Annealed Yttria‐Stabilized Zirconia (3Y‐TZP) and Their Relation to Mean Grain Size
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It was determined that the mean grain boundary radius of curvature in 3 mol% yttria‐stabilized zirconia isothermally annealed without and with a DC electric field = 18 V/cm was uniquely proportional to the mean linear intercept grain size , the proportionality constant α = 3/2 being in accord with the Rios‐Fonseca stereological model. 相似文献
7.
A piezomicrobalance system for high‐temperature mass relaxation characterization of metal oxides: A case study of Pr‐doped ceria
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Philipp Simons Ho‐Il Ji Timothy C. Davenport Sossina M. Haile 《Journal of the American Ceramic Society》2017,100(3):1161-1171
A system for mass relaxation studies based on a gallium phosphate piezocrystal microbalance has been developed, built, and successfully used to characterize a representative mixed ionic and electronic conducting material. The apparatus is constructed to achieve reactor gas exchange times as short as 2 seconds and temporal resolution in mass measurement of 0.1 seconds. These characteristics enabled evaluation of mass relaxations that occurred on the 6 seconds time scale. Proof of concept for materials characterization capabilities of the system was carried out using 10% praseodymium‐doped cerium oxide (PCO), a material that undergoes, at selected temperatures and oxygen partial pressures, changes in mass but not in conductivity. Thin films were deposited on the piezocrystals via pulsed laser deposition (PLD). Mass relaxation curves were collected at 700°C upon application of a small step change in oxygen partial pressure, . Using two different films, the surface reaction constant, kS, was obtained over the range from 10?4 to 0.1 atm. Its value is found to vary between 9.7 × 10?6 and 1.7 × 10?4 cm/s, displaying a power law dependence on , with a law exponent of 0.67 ± 0.02, as averaged over the two sets of results. This steep dependence of kS on is surprisingly independent of a change in dominant defect type within the range of measurement. 相似文献
8.
Belay Brehane Tesfamariam Byoungjin So Jong Heo 《Journal of the American Ceramic Society》2018,101(10):4447-4451
The influence of electric field on the precipitation and optical properties of PbSe quantum dots (QDs) in borosilicate glasses was investigated. Diameters of the PbSe QDs increased as was increased from 0.0 to 0.6 kV/mm even at the same subsequent heat treatment at 510°C for 2 hours. Increase in to 0.9 kV/mm caused red‐shift of the absorption and photoluminescence (PL) bands of QDs. Application of also led to decreases in viscosities that accelerated diffusion of ions; this phenomenon led to the formation of large QDs and resulted in the red‐shifts of the absorption and PL bands. Increase in the temperature due to Joule heating was ~38°C that led to an observed decrease in viscosities. 相似文献
9.
Jongseong Park Dae‐Hyeon Kim Su‐Jin Park Tae‐gon Lee Mir Im Jeong‐Seog Kim Sahn Nahm 《Journal of the American Ceramic Society》2016,99(7):2229-2232
A specimen having a stoichiometric composition of KSbO3·(KSb) calcined at 800°C has an R rhombohedral structure (RS), and changes to a Pn cubic structure (CS) when calcined at 1100°C. Finally, a <111>‐oriented rhombohedral phase is formed in the specimen calcined at 1230°C. K/Sb ratio decreases from 1.0 in RS, 0.93 in CS, and finally to 0.85 in <111>‐oriented rhombohedral phases. On the other hand, a specimen having a K‐excess composition of K1.1SbO3 calcined at 800°C shows a RS that is maintained in the K‐excess specimen calcined at 1230°C. The composition of these specimens is very close to KSb. Therefore, the RS with a space group of R is a stable form of KSbO3. The formation of Pn cubic and <111>‐oriented R phases can be explained by the evaporation of K2O during the calcination process at temperatures above 1100°C. 相似文献
10.
Confirmation of the Dominant Defect Mechanism in Amorphous In–Zn–O Through the Application of In Situ Brouwer Analysis
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Stephanie L. Moffitt Alexander U. Adler Thomas Gennett David S. Ginley John D. Perkins Thomas O. Mason 《Journal of the American Ceramic Society》2015,98(7):2099-2103
The dominant point defect mechanism of amorphous (a‐) indium zinc oxide (IZO) was probed through in situ electrical characterization of sputtered a‐IZO thin films in response to changes in oxygen partial pressure (pO) at 300C. The results yielded a power law dependence of conductivity (σ) versus pO of ~?1/6. This experimental method, known as Brouwer analysis, confirms doubly‐charged oxygen vacancies as the dominant defect species in a‐IZO. The success of this study suggests that Brouwer analysis is a viable method for studying the defect mechanisms of amorphous oxides. 相似文献
11.
Effect of Oxygen Vacancy on Electrical Property of Acceptor Doped BaTiO3–Na0.5Bi0.5TiO3–Nb2O5 X8R Systems
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Yue Sun Hanxing Liu Hua Hao Shujun Zhang 《Journal of the American Ceramic Society》2016,99(9):3067-3073
In this study, we reported a new BaTiO3–Na0.5Bi0.5TiO3–Nb2O5–Mn2O3/Fe2O3/Co3O4/In2O3 X8R system with high dielectric constant (>2100) at room temperature. The impacts of oxygen vacancy ( ) on dielectric, electrical conductivity, and ferroelectric properties were systematically studied. The Curie point is largely depended on the concentration, which can be confirmed by the dielectric behavior and A1g octahedral breathing modes in Raman spectrum. In addition, the activation energy of diffusion is greatly reduced with the increase in concentration. It was found that the remnant polarization and coercive field were both decreased with increasing concentration, due to the facilitated defect dipoles reorientation and domain switching. 相似文献
12.
Tatsuo Kumagai 《Journal of the American Ceramic Society》2013,96(3):852-858
The rapid densification behavior of 8 mol% Y2O3‐stabilized ZrO2 polycrystalline (8Y‐SZP) powder compacts at the initial stage of pressure sintering (relative density () below 0.92) has been investigated using an electric current‐activated/assisted sintering (ECAS) system. Data points corresponding to a fixed heating rate were extracted from the densification rate () versus ρ and versus temperature (T) curves. These curves were obtained experimentally by consolidation at a fixed current. Under fixed current ECAS, the heating rate () decreases continuously over sintering time. Using a quasi‐ constant heating rate (CHR) method, data points were extracted to plot vs. ρ, vs. T, and ρ vs. T curves at a fixed . The stress exponent (n), estimated from a log‐log plot of grain size (d)‐corrected /ρ and effective stress (σeff) at 1300–1400 K, shows an almost constant value of 1. In addition, the activation energy (Q) for rapid densification, estimated from an Arrhenius plot of d‐corrected /ρ also shows an almost constant value of 350 kJ/mol, which is considerably lower than the previously reported value of the activation energy for Zr4+ lattice diffusion of about 440 kJ/mol. These results suggest that rapid densification of 8Y‐SZP by ECAS seems to proceed by diffusional creep controlled by grain‐boundary diffusion of Zr4+ ions. 相似文献
13.
Thermodynamic properties of Si(OH)4(g) based on combined experimental and quantum chemistry data
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Andrey V. Plyasunov Alexander S. Zyubin Tatiana S. Zyubina 《Journal of the American Ceramic Society》2018,101(11):4921-4926
The volatility of silicon‐based ceramics in combustion environments is primarily controlled by the formation of gaseous Si(OH)4. The heat capacities and entropies of this species at 298.15‐2100 K and P = 0.1 MPa have been studied with the B3LYP density functional theory for the 6‐311+G(d,p) basis set in different approximations: a harmonic oscillator, an anharmonic oscillator, and with corrections for hindered rotors. Experimentally based Gibbs energies of Si(OH)4(g) at 424‐1661 K have been employed to evaluate the Gibbs energy of formation, , and the entropy, , of Si(OH)4(g) at = 298.15 K and P = 0.1 MPa. We found that the QC and “experimental” values are very close for the harmonic and anharmonic oscillator approximations, but not for the “hindered rotor” approximation. This conclusion is also supported by calculations of the OH rotational energy for Si(OH)4 molecule, where the potential barrier was found to exceed 12 kJ/mol. Finally, we recommend the thermodynamic properties of Si(OH)4 in the ideal gas state at P = 0.1 MPa over the temperature range of 298‐2100 K. 相似文献
14.
Masashi Wada Tsuneaki Matsudaira Takeharu Kato Satoshi Kitaoka 《Journal of the American Ceramic Society》2013,96(7):2322-2329
The effect of Lu surface concentration on oxygen permeation in polycrystalline α‐alumina wafers was determined at 1773 K under limited oxygen potential gradients (Δ), where the two surfaces of the wafer were deliberately subjected to different oxygen partial pressures [ (I) ? (II)]. When oxygen permeation occurred mainly by oxygen GB diffusion under a Δ generated by a combination of low values, the Lu‐coating on the (I) [ (II)] surface decreased [increased] the oxygen permeability constants. When Δ was the result of a combination of high values, where oxygen permeation proceeded mainly by aluminum GB diffusion, the oxygen permeability constants were decreased only by the Lu‐coating on the (I) surface. The analysis of mass transfer parameters, such as the chemical potentials, GB diffusion coefficients, and fluxes of aluminum and oxygen in the wafers, suggested that ambient oxygen molecules were effectively attracted toward Lu‐coated surfaces exposed to low‐ environments, leading to a change in oxygen permeability. 相似文献
15.
Bin Liu Benjamin Petersen Yanwen Zhang Jingyang Wang William J. Weber 《Journal of the American Ceramic Society》2016,99(8):2693-2698
Low‐energy recoil events in Ti3SiC2 are studied using ab initio molecular dynamics simulations. We find that the threshold displacement energies are orientation dependent because of anisotropic structural and/or bonding characteristic. For Ti and Si in the Ti–Si layer with weak bonds that have mixed covalent, ionic, and metallic characteristic, the threshold displacement energies for recoils perpendicular to the basal planes are larger than those parallel to the basal planes, which is an obvious layered‐structure‐related behavior. The calculated minimum threshold displacement energies are 7 eV for the C recoil along the direction, 26 eV for the Si recoil along the direction, 24 eV for the Ti in the Ti–C layer along the direction and 23 eV for the Ti in the Ti–Si layer along the direction. These results will advance the understanding of the cascade processes of Ti3SiC2 under irradiation and are expected to yield new perspective on the MAX phase family that includes more than 100 compounds. 相似文献
16.
Calcium‐substituted lanthanum ferrites (La1?xCaxFeO3?δ x = 0, 0.1, 0.2, 0.3, 0.4) were synthesized in air and subsequently decomposed in reducing atmospheres. The partial pressure of oxygen () was controlled by varying the H2/H2O ratio by bubbling hydrogen/argon mixtures through water baths at controlled temperatures. Three regions of mass loss were identified as the was reduced, two of which were determined to be associated with decomposition reactions. Calcium was shown to decrease the thermal stability of the perovskite compound, but rather than incrementally increasing the required for decomposition proportional to calcium concentration, all samples partially decomposed at a single . The extent of the partial decomposition was dependent on the amount of calcium substitution and temperature. The perovskite phase remaining after the partial decomposition was found to fully decompose at the same oxygen partial pressure as pure lanthanum ferrite. 相似文献
17.
Rong Tu Qingyun Sun Song Zhang Mingxu Han Qizhong Li Hidenori Hirayama Lianmeng Zhang Takashi Goto 《Journal of the American Ceramic Society》2015,98(1):214-222
ZrB2‐60 mol%SiC composite with a eutectic microstructure was oxidized at 1573 to 1873 K with reduced total pressures (Ptot) and low oxygen partial pressures (). The mass change was continuously measured by a thermobalance, and then fit with a multiple paralinear model. Oxidation scale of SiO2/ZrO2+SiO2/ZrO2/ZrB2 was formed at > 0.13 kPa, whereas only porous ZrO2 remained at < 0.13 kPa, Ptot < 1.33 kPa and higher than 1773 K. With increasing , the parabolic oxidation constant decreased, whereas the linear oxidation constant increased. 相似文献
18.
Effect of the (Ba + Sr)/Ti ratio on the microwave‐tunable properties of Ba0.6Sr0.4TiO3 ceramics
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Takashi Teranishi Riku Kanemoto Hidetaka Hayashi Akira Kishimoto 《Journal of the American Ceramic Society》2017,100(3):1037-1043
The impact of the (Ba + Sr)/Ti (A/B) ratio on the microwave‐tunable characteristics of diffuse phase transition (DPT) ferroelectric Ba0.6Sr0.4TiO3 (0.6‐BST) ceramics was investigated. The reduction in the lattice constant with increasing nonstoichiometry was attributed to introduced partial Schottky defects, i.e., and . The magnitude of the dielectric constant, ε′, at room temperature in the absence of an applied electric field was governed by the shift in the dielectric maximum temperature, Tm, because Tm was close to room temperature for the 0.6‐BST. The dielectric loss, tanδ, diminished as the ε′ decreased for 0.98≤A/B≤1.05, while the tanδ was much higher for A/B=0.95 having the greatest A‐site vacancy loading. The negatively charged and were mainly compensated by oxygen vacancies and likely partly compensated by holes, h?, which contributed to the electrical conduction. The tunability, T, at 100 MHz was almost constant at 20%–25% for A/B≥1.00 despite the reduction of the ε′, whereas T decreased for A/B<1.00 to ca. 10% for A/B=0.95 having the greatest A‐site vacancy loading. The results implied that the for larger A/B values was more efficient in generating nucleation sites in the polar nanoregions (PNRs) than the for smaller A/B values, thereby providing greater dipole polarization. Consequently, the figure of merit, FOM, reached its maximum of 250 at A/B=0.9875, which was ca. 155% higher than that of the stoichiometric BST. 相似文献
19.
Hydroxyl Defect Effect on Reoxidation of Sc‐Doped (Ba,Ca)(Ti,Zr)O3 Fired in Reducing Atmospheres
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Yu‐Ju Kao Che‐Yi Su Christian Pithan Detlev F. Hennings Chi‐Yuen Huang Rainer Waser 《Journal of the American Ceramic Society》2016,99(4):1311-1317
The behavior of grain and grain‐boundary conductivity of acceptor (Sc)‐doped (Ba,Ca)(Ti,Zr)O3 ceramics sintered in moist reducing atmosphere and subsequently reoxidized in dry and moist atmosphere was investigated by means of impedance spectroscopy (IS). In moist firing atmosphere, water vapor was found to react with oxygen vacancies, forming positively charged hydroxyl defects on regular oxygen sites in the crystal lattice. Proton hopping is considered to raise the ionic conductivity significantly. Therefore, hydroxyl defects in turn influence the grain conduction. Hydroxyl defects are also considered to be responsible for alternations of the dielectric maximum at the Curie point. 相似文献
20.
Wen Xing Liv‐Elisif Kalland Zuoan Li Reidar Haugsrud 《Journal of the American Ceramic Society》2013,96(12):3775-3781
The electrical conductivity of TiNb2O7 was characterized as a function of temperature, and . The total conductivity was independent of in the low oxygen partial pressure regime, while a dependency of was observed at higher oxygen partial pressures. The conductivity increased with increasing under oxidizing conditions below 700°C. Mixed electronic and protonic conduction was indicated by H/D isotope exchange and transport number measurements. A defect model based on interstitial type of hydration was established and fitted to the conductivity data allowing for determination of physicochemical parameters of hydration and electron migration. 相似文献