Chih-Ta Chia | National Taiwan Normal University (original) (raw)
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Papers by Chih-Ta Chia
Applied Physics Letters, 2006
The structures of TaO6 and NbO6 oxygen octahedra in xBa(Mg1∕3Ta2∕3)O3+(1−x)Ba(Mg1∕3Nb2∕3)O3 perov... more The structures of TaO6 and NbO6 oxygen octahedra in xBa(Mg1∕3Ta2∕3)O3+(1−x)Ba(Mg1∕3Nb2∕3)O3 perovskite ceramics with x=0, 0.25, 0.50, 0.75, and 1.0 were investigated by the extended x-ray absorption fine structure method. The decline in the microwave dielectric constant as x increases is caused mainly by the decrease of the mean volume of the oxygen octahedra, regardless of the 1:2 ordered structure and the distortion of the oxygen octahedron. The low Qf values of the TaO6 and NbO6 mixed samples are caused by not only the degrading of the 1:2 ordered structure but also the distortion of oxygen octahedral cages.
Journal of Applied Physics, 2007
Ceramics of 0.35Ba͑Ni 1/3 Nb 2/3 ͒O 3-0.65Ba͑Zn 1/3 Nb 2/3 ͒O 3 were prepared by the mixed oxide ... more Ceramics of 0.35Ba͑Ni 1/3 Nb 2/3 ͒O 3-0.65Ba͑Zn 1/3 Nb 2/3 ͒O 3 were prepared by the mixed oxide route. The effect of the cooling rate ͑2°C-240°C/h͒ after sintering on the microwave dielectric properties of the ceramics was examined. While the extrinsic factors, such as porosity and secondary phases, markedly influence the dielectric properties in the low-frequency regime, they have minimal effect on these properties in the high-frequency regime. The mechanisms involved in modifying the high-frequency dielectric properties of the materials were investigated by Fourier transform infrared and Raman spectroscopy, in conjunction with the Rietveld analysis of x-ray diffraction ͑XRD͒ spectra. A reduction in the cooling rate after sintering results in an increase in the high-frequency Q ϫ f ͑product of dielectric Q value and measurement frequency͒ from 42 to 58 THz in the high-frequency regime ͑ϳ1.5 THz͒. Such behavior correlates very well with the increase in the B-site occupancy by Nb ͑deduced from the Rietveld analyses of XRD spectra͒ and the increase in the coherency of the lattice vibration ͑deduced from the reduction in the full-width-athalf-maximum of the A 1g ͑O͒ Raman mode͒. In contrast, the cooling rate after sintering has very limited effect on the relative permittivity ͑varying from 40.8 to 41.9 at 1.5 THz͒, which is in accord with the phenomenon that the cell volume and the Raman shift of A 1g ͑O͒ Raman mode are essentially independent of the cooling rate.
![Research paper thumbnail of Correlation of microwave dielectric properties and normal vibration modes of xBa (Mg [sub 1/3] Ta [sub 2/3]) O [sub 3](1− x) Ba (Mg [sub 1/3] Nb [sub 2/3]) …](https://attachments.academia-assets.com/68263824/thumbnails/1.jpg)
](Journal of Applied Physics, 2003
Microwave dielectric properties of Ba(Mg 1/3 Ta 2/3)O 3-series materials were investigated using ... more Microwave dielectric properties of Ba(Mg 1/3 Ta 2/3)O 3-series materials were investigated using Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The normal vibration modes of these spectra were assigned, and the origin of dielectric response of the materials was deduced. Among the prominent normal vibration modes in the FTIR spectra, those which correlated with O-layers and Ba-layers change with Sr-ratio most significantly, whereas in micro-Raman measurements, the A 1g (O) phonon of oxygen-octahedron stretch mode changes with Sr-ratio most profoundly. These results reveal clearly the close relationship between the characteristics of FTIR and Raman spectra of the BMT-series materials and their microwave dielectric properties.
Applied Physics Letters, 2006
The structures of TaO6 and NbO6 oxygen octahedra in xBa(Mg1∕3Ta2∕3)O3+(1−x)Ba(Mg1∕3Nb2∕3)O3 perov... more The structures of TaO6 and NbO6 oxygen octahedra in xBa(Mg1∕3Ta2∕3)O3+(1−x)Ba(Mg1∕3Nb2∕3)O3 perovskite ceramics with x=0, 0.25, 0.50, 0.75, and 1.0 were investigated by the extended x-ray absorption fine structure method. The decline in the microwave dielectric constant as x increases is caused mainly by the decrease of the mean volume of the oxygen octahedra, regardless of the 1:2 ordered structure and the distortion of the oxygen octahedron. The low Qf values of the TaO6 and NbO6 mixed samples are caused by not only the degrading of the 1:2 ordered structure but also the distortion of oxygen octahedral cages.
Journal of Applied Physics, 2007
Ceramics of 0.35Ba͑Ni 1/3 Nb 2/3 ͒O 3-0.65Ba͑Zn 1/3 Nb 2/3 ͒O 3 were prepared by the mixed oxide ... more Ceramics of 0.35Ba͑Ni 1/3 Nb 2/3 ͒O 3-0.65Ba͑Zn 1/3 Nb 2/3 ͒O 3 were prepared by the mixed oxide route. The effect of the cooling rate ͑2°C-240°C/h͒ after sintering on the microwave dielectric properties of the ceramics was examined. While the extrinsic factors, such as porosity and secondary phases, markedly influence the dielectric properties in the low-frequency regime, they have minimal effect on these properties in the high-frequency regime. The mechanisms involved in modifying the high-frequency dielectric properties of the materials were investigated by Fourier transform infrared and Raman spectroscopy, in conjunction with the Rietveld analysis of x-ray diffraction ͑XRD͒ spectra. A reduction in the cooling rate after sintering results in an increase in the high-frequency Q ϫ f ͑product of dielectric Q value and measurement frequency͒ from 42 to 58 THz in the high-frequency regime ͑ϳ1.5 THz͒. Such behavior correlates very well with the increase in the B-site occupancy by Nb ͑deduced from the Rietveld analyses of XRD spectra͒ and the increase in the coherency of the lattice vibration ͑deduced from the reduction in the full-width-athalf-maximum of the A 1g ͑O͒ Raman mode͒. In contrast, the cooling rate after sintering has very limited effect on the relative permittivity ͑varying from 40.8 to 41.9 at 1.5 THz͒, which is in accord with the phenomenon that the cell volume and the Raman shift of A 1g ͑O͒ Raman mode are essentially independent of the cooling rate.
Journal of Applied Physics, 2003
Microwave dielectric properties of Ba(Mg 1/3 Ta 2/3)O 3-series materials were investigated using ... more Microwave dielectric properties of Ba(Mg 1/3 Ta 2/3)O 3-series materials were investigated using Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The normal vibration modes of these spectra were assigned, and the origin of dielectric response of the materials was deduced. Among the prominent normal vibration modes in the FTIR spectra, those which correlated with O-layers and Ba-layers change with Sr-ratio most significantly, whereas in micro-Raman measurements, the A 1g (O) phonon of oxygen-octahedron stretch mode changes with Sr-ratio most profoundly. These results reveal clearly the close relationship between the characteristics of FTIR and Raman spectra of the BMT-series materials and their microwave dielectric properties.