Browsing by Author "Chen, Haydn"

Now showing 1 - 7 of 7

Correlation of Microstructures and Conductivities of Ferroelectric Ceramics Using Complex Impedance Spectroscopy
(2010-06-01)
Chen, Pin-Yi
;
Chou, Chen-Chia
;
Tseng, Tseung-Yuen
;
Chen, Haydn
;
電子工程學系及電子研究所
The microstructures and conductivities of lead-free ceramics [Bi(0.5)(Na(1-x)K(x))(0.5)]TiO(3) with x = 0.18 (BNKT) and lead-based ceramics of x(0.94PbZn(1/3)Nb(2/3)O(3) + 0.06BaTiO(3)) + (1 - x)PbZr(y)Ti(1-y)O(3) with x = 0.5, y = 0.52 (PBZNZT) were investigated. Experimental results show that the activation energy of grain boundary conductivity is higher than that of grain conductivity for the BNKT system, indicating that the Bi(2)O(3) evaporation of grains induces an easy conduction path through grains. However, the activation energy of grain boundary conductivity is lower than that of grain conductivity for the PBZNZT system, which might be attributed to the charged particles in the amorphous phase at grain boundaries, participating in the conduction process. A conduction model of both grain and grain boundary conductivities was proposed, and the microstructural characteristics and AC impedance data of ferroelectric ceramics correlate fairly well, suggesting that impedance spectroscopy is an efficient characterization technique for the grain boundary engineering of ferroelectric ceramics. (C) 2010 The Japan Society of Applied Physics DOI: 10.1143/JJAP.49.061505
Effects of Second Phase and Defect on Electrical Properties in Bi0.5Na0.5-xKxTiO3 Lead-Free Piezoelectric Ceramics
(2011)
Chen, Pin Yi
;
Chen, Cheng Sao
;
Chou, Chen-Chia
;
Tseng, Tseung-Yuen
;
Chen, Haydn
Second phase and defect formation mechanism of (Bi-0.5(Na1-xKx)(0.5))TiO3 (BNKT100x) ceramics were investigated using electron microscopy, x-ray photoelectron spectroscope (XPS) and electrical properties measurements. Experimental results indicated that second phase formation induces Bi-rich regions and compositional inhomogeneity within matrix due to thermodynamic stability of potassium titanate. Ti valence transition for BNKT ceramics sintered in air might be ascribed to formation of the secondary phase, rather than simply attributed to volatilization of bismuth. Li substitution at A-site in BNKT ceramics suppresses formation of the second phase and Ti valence transition. Appropriate Li doped BNKT ceramics suppress oxygen vacancies and titanium valence transition, and therefore decrease the leakage current.
Evolution of dielectric properties in the (1-x) PbFe0.5Nb0.5O3-xBaFe(0.5)Nb(0.5)O(3) solid solution system
(2019-08-01)
Raevski, I. P.
;
Titov, V. V.
;
Chen, Haydn
;
Zakharchenko, I. N.
;
Raevskaya, S. I.
Temperature dependences of the dielectric permittivity epsilon of (1-x)PbFe0.5Nb0.5O3-x BaFe0.5Nb0.5O3 solid solution ceramics at 100Hz-1MHz have been studied in the 12-500K temperature range. To lower the conductivity values and exclude the corresponding relaxations, 1wt% of Li2CO3 was added to the starting mixture of oxides. It was found that Li-doping is effective in lowering the conductivity only for compositions with x0.5. T he permittivity-temperature dependences of the (1-x)PbFe0.5Nb0.5O3-xBaFe(0.5)Nb(0.5)O(3) compositions were found to change, as x grows, from relatively sharp frequency-independent maxima typical of usual ferroelectrics to the diffused and frequency-dependent maxima typical of relaxors and then to the saturated at low temperatures and frequency-independent epsilon(T) curves typical of incipient ferroelectrics and at last, to the step-like frequency-dependent epsilon(T) curves known for the dielectrics with Maxwell-Wagner-type polarization. The epsilon value of BaFe0.5Nb0.5O3 at 20K measured at 1MHz does not exceed 30. The character of the evolution of dielectric properties in the (1-x)PbFe0.5Nb0.5O3-x BaFe0.5Nb0.5O3 system and low epsilon value of BaFe0.5Nb0.5O3 implies that BaFe0.5Nb0.5O3 is a paraelectric rather than ferroelectric relaxor.
Interfacial Coupling Effect in Organic/Inorganic Nanocomposites with High Energy Density
(2018-04-25)
Pan, Zhongbin
;
Yao, Lingmin
;
Zhai, Jiwei
;
Yao, Xi
;
Chen, Haydn
Organic/inorganic nanocomposites (OINs) can be potentially used as high-performance capacitors due to their rapid charge-discharge capability along with respectable power density. The coupling effect of the filler/matrix interface plays a prominent role in the dielectric and electric properties of OINs. Along with a review of contemporary theoretical models, recent advances in interfacial optimization to improve energy density through careful interface control and design are also presented. Possible mechanisms that may improve energy density and potential applications for high-energy-density capacitors are also highlighted.
Progress in high-strain perovskite piezoelectric ceramics
(2019-01-01)
Hao, Jigong
;
Li, Wei
;
Zhai, Jiwei
;
Chen, Haydn
;
國際半導體學院
High strain piezoelectric ceramics are the state-of-the-art materials for high precision, positioning devices. A comprehensive review of the latest developments of the various types of perovskite piezoelectric ceramic systems is presented herein, with special attention given to three promising families of lead-free perovskite ferroelectrics: the barium titanate, alkaline niobate and bismuth perovskites. Included in this review are details of phase transition behavior, strain enhancement approaches, material reliabilities as well as the status of some promising applications. This current review describes both compositional and structural engineering approaches that are intended to achieve enhanced strain properties in perovskite piezoelectric ceramics. The factors that affect the strain behavior of high-strain perovskite piezoelectric ceramics are addressed. The reliability characteristics of these high-strain ferroelectrics as well as the recent approaches to the long-term electrical, thermal and time-stability enhancement are summarized. Several promising applications of high-strain perovskite materials are introduced, which take advantages of their characteristics; examples include high-energy storage, pyroelectric and electro-caloric effect and luminescent properties.
Second Phase and Defect Formation in Bi(0.5)Na(0.5-x)K(x)TiO(3) Ceramics
(2010-06-01)
Chen, Pin-Yi
;
Chou, Chen-Chia
;
Tseng, Tseung-Yuen
;
Chen, Haydn
;
電子工程學系及電子研究所
The second phase and defect formation mechanisms of [Bi(0.5)(Na(1-x)K(x))(0.5)]TiO(3) (BNKT100x) ceramics were investigated using electron microscopy, X-ray photoelectron spectroscopy (XPS), and electrical properties measurement. Experimental results indicated that second phase formation induces Bi-rich regions and compositional inhomogeneity within the matrix owing to the thermodynamic stability of potassium titanate. The Ti valence transition for BNKT ceramics sintered in air might be ascribed to the formation of secondary phase and low oxygen atmosphere, rather than simply attributed to the volatilization of bismuth. Li substitution at the A-site in BNKT ceramics suppresses formation of the second phase and Ti valence transition. Appropriate atmosphere control during material processing, such as sintering at higher oxygen pressure, and post oxidization annealing suppress oxygen vacancies and titanium valence transition, and therefore decrease the leakage current as well as improve electrical properties. (C) 2010 The Japan Society of Applied Physics DOI: 10.1143/JJAP.49.061506
Second Phase and Defect Formation in Bi0.5Na0.5-xKxTiO3 Ceramics
(2010-06-01)
Chen, Pin-Yi
;
Chou, Chen-Chia
;
Tseng, Tseung-Yuen
;
Chen, Haydn
;
電子工程學系及電子研究所
The second phase and defect formation mechanisms of [Bi-0.5(Na1-xKx)(0.5)]TiO3 (BNKT100x) ceramics were investigated using electron microscopy, X-ray photoelectron spectroscopy (XPS), and electrical properties measurement. Experimental results indicated that second phase formation induces Bi-rich regions and compositional inhomogeneity within the matrix owing to the thermodynamic stability of potassium titanate. The Ti valence transition for BNKT ceramics sintered in air might be ascribed to the formation of secondary phase and low oxygen atmosphere, rather than simply attributed to the volatilization of bismuth. Li substitution at the A-site in BNKT ceramics suppresses formation of the second phase and Ti valence transition. Appropriate atmosphere control during material processing, such as sintering at higher oxygen pressure, and post oxidization annealing suppress oxygen vacancies and titanium valence transition, and therefore decrease the leakage current as well as improve electrical properties. (C) 2010 The Japan Society of Applied Physics DOI: 10.1143/JJAP.49.061506