Journal of the American Ceramic Society
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Thermodynamic Assessment of the Strontium–Copper–Oxygen System The phase diagram and thermodynamic data on the Sr–Cu–O system at a total pressure of 105 Pa (1 bar) have been reviewed and assessed. Gibbs energy functions for the ternary oxides Sr2 CuO3 , SrCuO2 , Sr14 Cu24 O41 , SrCu2 O2 , and the liquid phase have been optimized, and a consistent thermodynamic description is presented. Calculated SrOCuOx phase diagrams in air and in 1.01 ×105 Pa (1.01 bar) O2 , the oxygen potential diagram, and various thermodynamic properties are shown and compared to experimental data.
Journal of the American Ceramic Society - Tập 80 Số 3 - Trang 527-536 - 1997
Microstructure and Piezoelectric Properties of (K<sub>0.5</sub>Na<sub>0.5</sub>)NbO<sub>3</sub>–BaTiO<sub>3</sub> Lead‐Free Piezoelectric Ceramics Modified by B<sub>2</sub>O<sub>3</sub>–CuO A combined sintering aid mixture of B2 O3 and CuO for lead‐free piezoelectric ceramics having the composition 0.95K0.5 Na0.5 NbO3 –0.05BaTiO3 (KNN‐BT) is introduced. The effects of the sintering aid mixture of 0.6B2 O3 –0.4CuO on the sintering behavior, microstructure, and electrical properties of KNN‐BT are investigated. Adding 2 wt% of the sintering aid mixture can effectively broaden the narrow sintering temperature range having a size of 20°C to above 50°C and increase the grain size of samples as well as maintain the high density of samples sintered at a low temperature. The increase in grain size contributes to an improvement in electrical properties. High piezoelectric properties of d 33 =205 pC/N, k p =38.0%, Q m =119, ɛ33 T 0 =1254, and tan δ=0.0264 are obtained for a KNN‐BT‐2wt% (B2 O3 –CuO) sample sintered at 1120°C.
Journal of the American Ceramic Society - Tập 93 Số 11 - Trang 3823-3827 - 2010
Decoding the Fingerprint of Ferroelectric Loops: Comprehension of the Material Properties and Structures Due to the nature of domains, ferroics, including ferromagnetic, ferroelectric, and ferroelastic materials, exhibit hysteresis phenomena with respect to external driving fields (magnetic field, electric field, or stress). In principle, every ferroic material has its own hysteresis loop, like a fingerprint, which contains information related to its properties and structures. For ferroelectrics, many characteristic parameters, such as coercive field, spontaneous, and remnant polarizations can be directly extracted from the hysteresis loops. Furthermore, many impact factors, including the effect of materials (grain size and grain boundary, phase and phase boundary, doping, anisotropy, thickness), aging (with and without poling), and measurement conditions (applied field amplitude, fatigue, frequency, temperature, stress), can affect the hysteretic behaviors of the ferroelectrics. In this feature article, we will first give the background of the ferroic materials and multiferroics, with an emphasis on ferroelectrics. Then it is followed by an introduction of the characterizing techniques for the loops, including the polarization–electric field loops and strain–electric field curves. A caution is made to avoid misinterpretation of the loops due to the existence of conductivity. Based on their morphologic features, the hysteresis loops are categorized to four groups and the corresponding material usages are introduced. The impact factors on the hysteresis loops are discussed based on recent developments in ferroelectric and related materials. It is suggested that decoding the fingerprint of loops in ferroelectrics is feasible and the comprehension of the material properties and structures through the hysteresis loops is established.
Journal of the American Ceramic Society - Tập 97 Số 1 - Trang 1-27 - 2014
Dielectric and Piezoelectric Properties in Mn‐Modified (1−<i>x</i>)BiFeO<sub>3</sub>–<i>x</i>BaTiO<sub>3</sub> Ceramics In the current work, the bulk (1−x )BiFeO3 –x BaTiO3 system has been studied as a potential lead‐free piezoelectric material. Barium titanate (BaTiO3 ) in solid solution with bismuth ferrite (BiFeO3 ) is observed to stabilize the perovskite structure and improve switching behavior. Samples with various content of BaTiO3 were prepared via solid‐state route, and pure perovskite phase was confirmed by X‐ray diffraction. Modification of the BaTiO3 –BiFeO3 material with Mn improved DC resistivity by one to five orders of magnitude (7.6 × 1012 vs. 2.7 × 107 Ω·m for 25 mol% BaTiO3 at room temperature) and polarization hysteresis measurements indicated “hard” ferroelectric behavior with the highest strain response at 33 mol% BaTiO3 . Finally, low‐field piezoelectric d 33 coefficient of 116 pC/N and ferroelectric transition temperature above 450°C are reported for 25 mol% BaTiO3 composition.
Journal of the American Ceramic Society - Tập 92 Số 12 - Trang 2957-2961 - 2009
Large electric‐field‐induced strain and enhanced piezoelectric constant in CuO‐modified BiFeO<sub>3</sub>‐BaTiO<sub>3</sub> ceramics Abstract In this work, we fabricated the (1‐x )BiFeO3 ‐x BaTiO3 +y ‰ mol CuO ceramics by the modified thermal quenching technique. The pure perovskite phase was formed and a morphotropic phase boundary (MPB ) was observed in the ceramics with x = 0.30‐0.33. The addition of CuO can significantly enhance the density of the BiFeO3 ‐BaTiO3 material. Importantly, an enhanced piezoelectric constant (d 33 =165 pC /N), a large electric‐field‐induced strain (∆S = 0.54%: peak to peak strain) and a large piezoelectric actuator constant (d 33 *=449 pm/V) together with a high Curie temperature (T C x = 0.30 and y = 5. As a result, the enhanced piezoelectricity and large electric‐field‐induced strain could significantly stimulate further researches in BFO ‐based ceramics.
Journal of the American Ceramic Society - Tập 101 Số 8 - Trang 3383-3392 - 2018
Electronic Conductivity and Related Properties of Amorphous and Crystallized V<sub>2</sub>O<sub>5</sub>‐Based Glasses Crystallization of V2 O3 from V2 O3 P2 O3 , glasses containing 0 to 9 mol% B2 O3 , during heat treatment in the range 220° to 410°C, caused progressive micro structural changes which dramatically affected the electronic conductivity (γ), the activation energy for conduction (W ), and the resistance to chemical attack. All compositions were ≊83% crystalline after heating to 410°C. As a result, the values of γ and W were almost identical to those observed for pure polycrystalline V2 O5 .
Journal of the American Ceramic Society - Tập 62 Số 7-8 - Trang 403-410 - 1979
Lead Hafnate (PbHfO<sub>3</sub>) Perovskite Powders Synthesized by the Oxidant Peroxo Method Perovskite lead hafnate (PbHfO3 , PH) nanoparticles that were free from halides and organics were synthesized via the oxidant peroxo method. Stoichiometric amounts of hafnium nitrate (HfO(NO3 )2 ) and lead nitrate (PbHfO3 ) were dissolved in a diluted hydrogen peroxide (H2 O2 ) aqueous solution, which was slowly added to a solution of H2 O2 and ammonia (NH3 ) (pH 11). The lead–hafnium precipitate obtained was filtered and washed, to eliminate all nitrate ions. The precipitate was dried, ground, and calcined at temperatures of 400°–900°C. A tetragonal intermediate phase was identified using X‐ray diffractometry and Raman spectroscopy during the calcination process, followed by the crystallization of the orthorhombic PH phase at ∼700°C.
Journal of the American Ceramic Society - Tập 85 Số 8 - Trang 2107-2109 - 2002
Mixed 3D/2D dimensional TiO<sub>2</sub> nanoflowers/MoSe<sub>2</sub> nanosheets for enhanced photoelectrochemical hydrogen generation Abstract Recently, v arious kinds of methods have been implemented to broaden the visible light response and fasten the carrier's separation of TiO2 ‐based photoanodes. As a promising hydrogen evolution reaction catalyst, MoSe2 is rarely investigated especially combined with TiO2 photoanode. In this study, we report a composite photoanode of MoSe2 nanosheets (with 1T and 2H phase)‐modified 3D TiO2 nanoflowers (NFs).The hybrid of 3D TiO2 NFs/2D MoSe2 holds great promise in boosting the PEC water splitting performance. TiO2 NFs/MoSe2 ‐15 showed the largest photocurrent density of 1.40 mA/cm2 , which was five times higher than that of pure TiO2 NFs under AM1.5G illumination. Moreover 10 times improvement in current density was observed for the TiO2 NFs/MoSe2 ‐15 under visible light. This increase could be ascribed to synergistic effects of light absorption enhancement and more efficient carrier separation after MoSe2 modification. This study not only provides a reference to boost the photoelectrochemical performance of photoelectrodes but also renders a perspective on the potential applications of MoSe2 nanosheets.
Journal of the American Ceramic Society - Tập 103 Số 2 - Trang 1187-1196 - 2020
High carriers transmission efficiency ZnS/SnS<sub>2</sub> heterojunction channel toward excellent photoelectrochemical activity Abstract ZnS has been found superiority in photoelectrochemistry for the fast response of photo‐inducing and its high conductor band position (~0.8 eV) results in strong reduction ability for hydrogen production. However, the solar absorbance of ZnS is much low for the wide band gap (~3.2 eV) and the carriers’ migration efficiency also need to be improved. Here, nano‐ZnS were coupled with ultrathin SnS2 nanosheets as heterojunction composites. This heterojunction composite demonstrated largely increase in specific surface area (from 4 to 12‐25 m2 /g), obvious improvement of UV ‐vis absorbance and narrower band gap. Furthermore, the carriers’ migration efficiency of ZnS/SnS2 heterojunction has been confirmed to be much higher by photocurrent response and electrochemical impedance spectroscopy. Due to the improvement in structure, compared with pristine ZnS, this ZnS/SnS2 heterojunction exhibited vast enhancement in photoelectrochemical performance. The composite with best activity exhibited 12.8 times enhancement in photocurrent density. The conduction band and valence band of ZnS are both more negative than those of SnS2 , the photo‐induced electrons at the conduction band of ZnS will transfer into the conduction band of SnS2 while the photo‐induced holes at the valence band of SnS2 will transfer into the valence band of ZnS. In this way, the photo‐produced carriers will flow into different semiconductors and the carriers’ migration efficiency is enhanced. The work improves a new structure to develop the heterojunction property for photoelectrochemical application.
Journal of the American Ceramic Society - Tập 102 Số 5 - Trang 2810-2819 - 2019
Elastic/Plastic Indentation Damage in Ceramics: The Median/Radial Crack System A theory for describing the evolution of the median/radial crack system in the far field of sharp‐indenter contacts is developed. Analysis is based on a model in which the complex elastic/plastic field beneath the indenter is resolved into elastic and residual components. The elastic component, being reversible, assumes a secondary role in the fracture process: although it does enhance downward (median) extension during the loading half‐cycle, it suppresses surface (radial) extension to the extent that significant growth continues during unloading. The residual component accordingly provides the primary driving force for the crack configuration in the final stages of evolution, where the crack tends to near‐half‐penny geometry. On the hypothesis that the origin of the irreversible field lies in the accommodation of an expanding plastic hardness impression by the surrounding elastic matrix, the ensuing fracture mechanics relations for equilibrium crack growth are found to involve the ratio hardness‐to‐modulus as well as toughness. Observations of crack evolution in soda‐lime glass provide a suitable calibration of indentation coefficients in these relations. The calibrated equations are then demonstrated to be capable of predicting the widely variable median and radial growth characteristics observed in other ceramic materials. The theory is shown to have a vital bearing on important practical areas of ceramics evaluation, including toughness and strength.
Journal of the American Ceramic Society - Tập 63 Số 9-10 - Trang 574-581 - 1980
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