Journal of The European Ceramic Society, Jul 1, 2019
Structural evolution, dielectric and energy storage properties of Na(Nb 1−x Ta x)O 3 ceramics pre... more Structural evolution, dielectric and energy storage properties of Na(Nb 1−x Ta x)O 3 ceramics prepared by spark plasma sintering,
Multilayer ceramic chip capacitors (MLC) consist of consecutive layers of ceramic dielectric and ... more Multilayer ceramic chip capacitors (MLC) consist of consecutive layers of ceramic dielectric and silver/palladium based internal electrodes. After sintering, silver termination ink is applied.
Ceramics based on the BaO-Nd{sub 2}O{sub 3}-TiO{sub 2} system are widely used the electronics ind... more Ceramics based on the BaO-Nd{sub 2}O{sub 3}-TiO{sub 2} system are widely used the electronics industry due to their high permittivity and low dielectric losses. An especially interesting part of the phase diagram is the solid solubility region with the general formula Ba{sub 6-x}Nd{sub 8+2/3x}Ti{sub 18}O{sub 54} (O < X < 2.25). For microwave applications such materials are doped with Pb or Bi oxides (or titanates) to compensate the relatively high temperature coefficient of resonant frequency tf. In the present paper, a study of Bi{sub 2}O{sub 3}-doped 1:1:4-BT{sub 4} ceramics is reported with regard to the formation of solid solution and liquid phase during sintering, and the microstructural development and its influence on the microwave properties. It was found that on addition of up to 2.5 mol % Bi{sub 2}O{sub 3}, Bi{sup 3+} is incorporated on Nd{sup 3+} sites in the Ba{sub 4.5}Nd{sub 9}Ti{sub 18}O{sub 54} phase. When the solid solubility limit is exceeded, Bi{sub 2}O{sub 3} concentrates at the grain boundaries at Bi-rich phase, forming a liquid phase and causing a considerable decrease of the Q-value and an increase of tf.
Epitaxial integration of transition-metal oxides with silicon brings a variety of functional prop... more Epitaxial integration of transition-metal oxides with silicon brings a variety of functional properties to the well-established platform of electronic components. In this process, deoxidation and passivation of the silicon surface are one of the most important steps, which in our study were controlled by an ultra-thin layer of SrO and monitored by using transmission electron microscopy (TEM), electron energy-loss spectroscopy (EELS), synchrotron X-ray diffraction (XRD) and reflection high energy electron diffraction (RHEED) methods. Results revealed that an insufficient amount of SrO leads to uneven deoxidation of the silicon surface i.e. formation of pits and islands, whereas the composition of the as-formed heterostructure gradually changes from strontium silicide at the interface with silicon, to strontium silicate and SrO in the topmost layer. Epitaxial ordering of SrO, occurring simultaneously with silicon deoxidation, was observed. RHEED analysis has identified that SrO is epitaxially aligned with the (001) Si substrate both with SrO (001) and SrO (111) out-of-plane directions. This observation was discussed from the point of view of SrO desorption, SrO-induced deoxidation of the Si (001) surface and other interfacial reactions as well as structural ordering of deposited SrO. Results of the study present an important milestone in understanding subsequent epitaxial integration of functional oxides with silicon using SrO.
Journal of The European Ceramic Society, Nov 1, 2016
Please cite this article in press as: L. Li, et al., The microstructure, dielectric abnormalities... more Please cite this article in press as: L. Li, et al., The microstructure, dielectric abnormalities, polar order and microwave dielectric properties of Ag(Nb 1−x Ta x)O 3 (x = 0-0.8) ceramics,
The tunable dielectric properties of Pb 0.99 [(Zr 0.6 Sn 0.4) 0.94 Ti 0.06 ] 0.98 Nb 0.02 O 3 ant... more The tunable dielectric properties of Pb 0.99 [(Zr 0.6 Sn 0.4) 0.94 Ti 0.06 ] 0.98 Nb 0.02 O 3 antiferroelectric ceramics were investigated, and high relative tunability of 49% was obtained at 25 C under a low bias electric field of 50 kV/cm. Abrupt changes and a significant hysteresis in dielectric constant and dielectric loss against bias electric field were observed, which are very different from the previously reported antiferroelectric materials. The unique dielectric tunability is attributed to the square-shaped double hysteresis loop and indicates the possible applications in some special tunable devices, such as an electrically-controlled switch. Pb 0.99 [(Zr 0.6 Sn 0.4) 0.94 Ti 0.06 ] 0.98 Nb 0.02 O 3 ceramics also exhibit unique dielectric tunability at À5 C. Abrupt changes in dielectric constant and dielectric loss were observed when the bias electric field increased to 31 kV/cm for the fresh sample, which is similar to the antiferroelectric-like dielectric tunability at 25 C. However, the dielectric tunability was ferroelectric-like in the following measurement. This response is consistent with the hysteresis loop and can be explained by the electric field-assisted irreversible antiferroelectric-ferroelectric phase transition. Published by AIP Publishing.
In the extended x-ray absorption fine structure (EXAFS) study of the local environment of Bi3+ an... more In the extended x-ray absorption fine structure (EXAFS) study of the local environment of Bi3+ and Pb2+ ions incorporated in Ba4.5Nd9Ti18O54, actual sites of Bi- and Pb-incorporation are determined. Evidence is given that dopant ions are not distributed randomly on all theoretically possible sites; Bi3+ selectively enters one out of three possible channels, corresponding to the sites x = 0.9484, y = 0.2500, z = 0.2939, and/or x = 0.0455, y = 0.2500, z = 0.6928 previously occupied by Nd3+, while Pb2+ selectively enters site x = 0.4940, y = 0.2500, and z = 0.4993 previously shared by Ba2+ and Nd3+.
This page was generated automatically upon download from the ETH Zurich Research Collection. For ... more This page was generated automatically upon download from the ETH Zurich Research Collection. For more information, please consult the Terms of use.
Methods for the crystal structure determination from powder diffraction data are reviewed with sp... more Methods for the crystal structure determination from powder diffraction data are reviewed with special emphasis on the application to technical ceramics. Experimental techniques using other than laboratory X-ray, such as synchrotron radiation, neutron and electron beams, are also described. As an illustrative example, the crystal structure determinations of compounds LaNbTiO 6 , La 0 . 4 6 2 Nb 0 . 6 1 4 Ti 0 . 3 8 6 O 3 and La 0 . 3 7 Nb 0 . 8 8 9 Ti 0 . 1 1 1 O 3 in the ternary system of La 2 O 3 -Nb 2 O 5 -TiO 2 are reported.
Using a simple organic bifunctional bridging linker, titanium dioxide (TiO2) nanoparticles were c... more Using a simple organic bifunctional bridging linker, titanium dioxide (TiO2) nanoparticles were coupled with the Au nanoparticles to form TiO2/Au nanocomposites with a variety of Au loadings. This organic bifunctional linker, meso-2,3-dimercaptosuccinic acid, contains two types of functional groups: (i) the carboxyl group, which enables binding to the TiO2, and (ii) the thiol group, which enables binding to the Au. In addition, the organic bifunctional linker acts as a stabilizing agent to prevent the agglomeration and growth of the Au particles, resulting in the formation of highly dispersed Au nanoparticles. To form the TiO2/Au nanocomposites in a simple way, we deliberately applied a synthetic method that simultaneously ensures: (i) the capping of the Au nanoparticles and (ii) the binding of different amounts of Au to the TiO2. The TiO2/Au nanocomposites formed with this method show enhanced UV and Vis photocatalytic activities when compared to the pure TiO2 nanopowders.Graphical Abstract
Ceramics based on the BaO-Nd{sub 2}O{sub 3}-TiO{sub 2} system are widely used the electronics ind... more Ceramics based on the BaO-Nd{sub 2}O{sub 3}-TiO{sub 2} system are widely used the electronics industry due to their high permittivity and low dielectric losses. An especially interesting part of the phase diagram is the solid solubility region with the general formula Ba{sub 6-x}Nd{sub 8+2/3x}Ti{sub 18}O{sub 54} (O < X < 2.25). For microwave applications such materials are doped with Pb or Bi oxides (or titanates) to compensate the relatively high temperature coefficient of resonant frequency tf. In the present paper, a study of Bi{sub 2}O{sub 3}-doped 1:1:4-BT{sub 4} ceramics is reported with regard to the formation of solid solution and liquid phase during sintering, and the microstructural development and its influence on the microwave properties. It was found that on addition of up to 2.5 mol % Bi{sub 2}O{sub 3}, Bi{sup 3+} is incorporated on Nd{sup 3+} sites in the Ba{sub 4.5}Nd{sub 9}Ti{sub 18}O{sub 54} phase. When the solid solubility limit is exceeded, Bi{sub 2}O{sub 3} concentrates at the grain boundaries at Bi-rich phase, forming a liquid phase and causing a considerable decrease of the Q-value and an increase of tf.
ABSTRACT The formation of the columbite-structure magnesium niobate MgNb2O6 is a multistep proces... more ABSTRACT The formation of the columbite-structure magnesium niobate MgNb2O6 is a multistep process. Single-phase material can only be obtained through long-term high-temperature heat treatment. Deviations from stoichiometry have a significant effect on the microwave quality factor Q of the material: magnesium-deficient ceramics contain small amounts of Nb2O5 and have relatively low Q values, whereas an excess of magnesium leads to the formation of Mg4Nb2O9 (alpha-alumina structure) as an impurity phase, thereby drastically increasing the electrical Q.
Journal of the American Ceramic Society, Jan 10, 2013
Thin films with the composition 70 mol% Na 0.5 Bi 0.5 TiO 3 + 30 mol% NaTaO 3 were prepared by so... more Thin films with the composition 70 mol% Na 0.5 Bi 0.5 TiO 3 + 30 mol% NaTaO 3 were prepared by sol-gel synthesis and spin coating. The influence of the annealing temperature on the microstructural development and its further influence on the dielectric properties in the low-(kHz-MHz) and microwave-frequency (15 GHz) ranges were investigated. In the low-frequency range we observed that with an increasing annealing temperature from 550°C to 650°C the average grain size increased from 90 to 170 nm, which led to an increase in the dielectric permittivity from 130 to 240. The temperature-stable dielectric properties were measured for thin films annealed at 650°C in the temperature range between −25°C and 150°C. The thin films deposited on corundum substrates had a lower average grain size than those on Si/SiO 2 /TiO 2 /Pt substrates. The highest average grain size of 130 nm was obtained for a thin film annealed at 600°C, which displayed a dielectric permittivity of 130, measured at 15 GHz.
Journal of The European Ceramic Society, Jul 1, 2019
Structural evolution, dielectric and energy storage properties of Na(Nb 1−x Ta x)O 3 ceramics pre... more Structural evolution, dielectric and energy storage properties of Na(Nb 1−x Ta x)O 3 ceramics prepared by spark plasma sintering,
Multilayer ceramic chip capacitors (MLC) consist of consecutive layers of ceramic dielectric and ... more Multilayer ceramic chip capacitors (MLC) consist of consecutive layers of ceramic dielectric and silver/palladium based internal electrodes. After sintering, silver termination ink is applied.
Ceramics based on the BaO-Nd{sub 2}O{sub 3}-TiO{sub 2} system are widely used the electronics ind... more Ceramics based on the BaO-Nd{sub 2}O{sub 3}-TiO{sub 2} system are widely used the electronics industry due to their high permittivity and low dielectric losses. An especially interesting part of the phase diagram is the solid solubility region with the general formula Ba{sub 6-x}Nd{sub 8+2/3x}Ti{sub 18}O{sub 54} (O < X < 2.25). For microwave applications such materials are doped with Pb or Bi oxides (or titanates) to compensate the relatively high temperature coefficient of resonant frequency tf. In the present paper, a study of Bi{sub 2}O{sub 3}-doped 1:1:4-BT{sub 4} ceramics is reported with regard to the formation of solid solution and liquid phase during sintering, and the microstructural development and its influence on the microwave properties. It was found that on addition of up to 2.5 mol % Bi{sub 2}O{sub 3}, Bi{sup 3+} is incorporated on Nd{sup 3+} sites in the Ba{sub 4.5}Nd{sub 9}Ti{sub 18}O{sub 54} phase. When the solid solubility limit is exceeded, Bi{sub 2}O{sub 3} concentrates at the grain boundaries at Bi-rich phase, forming a liquid phase and causing a considerable decrease of the Q-value and an increase of tf.
Epitaxial integration of transition-metal oxides with silicon brings a variety of functional prop... more Epitaxial integration of transition-metal oxides with silicon brings a variety of functional properties to the well-established platform of electronic components. In this process, deoxidation and passivation of the silicon surface are one of the most important steps, which in our study were controlled by an ultra-thin layer of SrO and monitored by using transmission electron microscopy (TEM), electron energy-loss spectroscopy (EELS), synchrotron X-ray diffraction (XRD) and reflection high energy electron diffraction (RHEED) methods. Results revealed that an insufficient amount of SrO leads to uneven deoxidation of the silicon surface i.e. formation of pits and islands, whereas the composition of the as-formed heterostructure gradually changes from strontium silicide at the interface with silicon, to strontium silicate and SrO in the topmost layer. Epitaxial ordering of SrO, occurring simultaneously with silicon deoxidation, was observed. RHEED analysis has identified that SrO is epitaxially aligned with the (001) Si substrate both with SrO (001) and SrO (111) out-of-plane directions. This observation was discussed from the point of view of SrO desorption, SrO-induced deoxidation of the Si (001) surface and other interfacial reactions as well as structural ordering of deposited SrO. Results of the study present an important milestone in understanding subsequent epitaxial integration of functional oxides with silicon using SrO.
Journal of The European Ceramic Society, Nov 1, 2016
Please cite this article in press as: L. Li, et al., The microstructure, dielectric abnormalities... more Please cite this article in press as: L. Li, et al., The microstructure, dielectric abnormalities, polar order and microwave dielectric properties of Ag(Nb 1−x Ta x)O 3 (x = 0-0.8) ceramics,
The tunable dielectric properties of Pb 0.99 [(Zr 0.6 Sn 0.4) 0.94 Ti 0.06 ] 0.98 Nb 0.02 O 3 ant... more The tunable dielectric properties of Pb 0.99 [(Zr 0.6 Sn 0.4) 0.94 Ti 0.06 ] 0.98 Nb 0.02 O 3 antiferroelectric ceramics were investigated, and high relative tunability of 49% was obtained at 25 C under a low bias electric field of 50 kV/cm. Abrupt changes and a significant hysteresis in dielectric constant and dielectric loss against bias electric field were observed, which are very different from the previously reported antiferroelectric materials. The unique dielectric tunability is attributed to the square-shaped double hysteresis loop and indicates the possible applications in some special tunable devices, such as an electrically-controlled switch. Pb 0.99 [(Zr 0.6 Sn 0.4) 0.94 Ti 0.06 ] 0.98 Nb 0.02 O 3 ceramics also exhibit unique dielectric tunability at À5 C. Abrupt changes in dielectric constant and dielectric loss were observed when the bias electric field increased to 31 kV/cm for the fresh sample, which is similar to the antiferroelectric-like dielectric tunability at 25 C. However, the dielectric tunability was ferroelectric-like in the following measurement. This response is consistent with the hysteresis loop and can be explained by the electric field-assisted irreversible antiferroelectric-ferroelectric phase transition. Published by AIP Publishing.
In the extended x-ray absorption fine structure (EXAFS) study of the local environment of Bi3+ an... more In the extended x-ray absorption fine structure (EXAFS) study of the local environment of Bi3+ and Pb2+ ions incorporated in Ba4.5Nd9Ti18O54, actual sites of Bi- and Pb-incorporation are determined. Evidence is given that dopant ions are not distributed randomly on all theoretically possible sites; Bi3+ selectively enters one out of three possible channels, corresponding to the sites x = 0.9484, y = 0.2500, z = 0.2939, and/or x = 0.0455, y = 0.2500, z = 0.6928 previously occupied by Nd3+, while Pb2+ selectively enters site x = 0.4940, y = 0.2500, and z = 0.4993 previously shared by Ba2+ and Nd3+.
This page was generated automatically upon download from the ETH Zurich Research Collection. For ... more This page was generated automatically upon download from the ETH Zurich Research Collection. For more information, please consult the Terms of use.
Methods for the crystal structure determination from powder diffraction data are reviewed with sp... more Methods for the crystal structure determination from powder diffraction data are reviewed with special emphasis on the application to technical ceramics. Experimental techniques using other than laboratory X-ray, such as synchrotron radiation, neutron and electron beams, are also described. As an illustrative example, the crystal structure determinations of compounds LaNbTiO 6 , La 0 . 4 6 2 Nb 0 . 6 1 4 Ti 0 . 3 8 6 O 3 and La 0 . 3 7 Nb 0 . 8 8 9 Ti 0 . 1 1 1 O 3 in the ternary system of La 2 O 3 -Nb 2 O 5 -TiO 2 are reported.
Using a simple organic bifunctional bridging linker, titanium dioxide (TiO2) nanoparticles were c... more Using a simple organic bifunctional bridging linker, titanium dioxide (TiO2) nanoparticles were coupled with the Au nanoparticles to form TiO2/Au nanocomposites with a variety of Au loadings. This organic bifunctional linker, meso-2,3-dimercaptosuccinic acid, contains two types of functional groups: (i) the carboxyl group, which enables binding to the TiO2, and (ii) the thiol group, which enables binding to the Au. In addition, the organic bifunctional linker acts as a stabilizing agent to prevent the agglomeration and growth of the Au particles, resulting in the formation of highly dispersed Au nanoparticles. To form the TiO2/Au nanocomposites in a simple way, we deliberately applied a synthetic method that simultaneously ensures: (i) the capping of the Au nanoparticles and (ii) the binding of different amounts of Au to the TiO2. The TiO2/Au nanocomposites formed with this method show enhanced UV and Vis photocatalytic activities when compared to the pure TiO2 nanopowders.Graphical Abstract
Ceramics based on the BaO-Nd{sub 2}O{sub 3}-TiO{sub 2} system are widely used the electronics ind... more Ceramics based on the BaO-Nd{sub 2}O{sub 3}-TiO{sub 2} system are widely used the electronics industry due to their high permittivity and low dielectric losses. An especially interesting part of the phase diagram is the solid solubility region with the general formula Ba{sub 6-x}Nd{sub 8+2/3x}Ti{sub 18}O{sub 54} (O < X < 2.25). For microwave applications such materials are doped with Pb or Bi oxides (or titanates) to compensate the relatively high temperature coefficient of resonant frequency tf. In the present paper, a study of Bi{sub 2}O{sub 3}-doped 1:1:4-BT{sub 4} ceramics is reported with regard to the formation of solid solution and liquid phase during sintering, and the microstructural development and its influence on the microwave properties. It was found that on addition of up to 2.5 mol % Bi{sub 2}O{sub 3}, Bi{sup 3+} is incorporated on Nd{sup 3+} sites in the Ba{sub 4.5}Nd{sub 9}Ti{sub 18}O{sub 54} phase. When the solid solubility limit is exceeded, Bi{sub 2}O{sub 3} concentrates at the grain boundaries at Bi-rich phase, forming a liquid phase and causing a considerable decrease of the Q-value and an increase of tf.
ABSTRACT The formation of the columbite-structure magnesium niobate MgNb2O6 is a multistep proces... more ABSTRACT The formation of the columbite-structure magnesium niobate MgNb2O6 is a multistep process. Single-phase material can only be obtained through long-term high-temperature heat treatment. Deviations from stoichiometry have a significant effect on the microwave quality factor Q of the material: magnesium-deficient ceramics contain small amounts of Nb2O5 and have relatively low Q values, whereas an excess of magnesium leads to the formation of Mg4Nb2O9 (alpha-alumina structure) as an impurity phase, thereby drastically increasing the electrical Q.
Journal of the American Ceramic Society, Jan 10, 2013
Thin films with the composition 70 mol% Na 0.5 Bi 0.5 TiO 3 + 30 mol% NaTaO 3 were prepared by so... more Thin films with the composition 70 mol% Na 0.5 Bi 0.5 TiO 3 + 30 mol% NaTaO 3 were prepared by sol-gel synthesis and spin coating. The influence of the annealing temperature on the microstructural development and its further influence on the dielectric properties in the low-(kHz-MHz) and microwave-frequency (15 GHz) ranges were investigated. In the low-frequency range we observed that with an increasing annealing temperature from 550°C to 650°C the average grain size increased from 90 to 170 nm, which led to an increase in the dielectric permittivity from 130 to 240. The temperature-stable dielectric properties were measured for thin films annealed at 650°C in the temperature range between −25°C and 150°C. The thin films deposited on corundum substrates had a lower average grain size than those on Si/SiO 2 /TiO 2 /Pt substrates. The highest average grain size of 130 nm was obtained for a thin film annealed at 600°C, which displayed a dielectric permittivity of 130, measured at 15 GHz.
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