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CaCu3-xNixTi4O12 (x?=?0, 0.05, and 0.10) powders were synthesized using a solid state reaction method. Phase structure and microstructure analyses revealed that all sintered CaCu3-xNixTi4O12 ceramics were of a pure phase. The CaCu3Ti4O12 ceramics had a dense microstructure and grain sizes were enlarged by doping with Ni2+. Interestingly, the dielectric permittivity was significantly enhanced, whereas the loss tangent was greatly suppressed to ~0.046–0.034 at 1?kHz. All sintered ceramics exhibited non-Ohmic characteristics. Clarification of the influences of DC bias showed that the dielectric permittivity and loss tangent values were increased by DC bias. The resistance of grain boundaries and the associated conduction activation energy of CaCu3-xNixTi4O12 ceramics were reduced as the DC bias voltage increased. Therefore, the observed non-Ohmic behavior and significantly enhanced dielectric properties should be closely related to variation in the Schottky barriers at the grain boundaries. 相似文献
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Tai-Shan Liao Prasit Champa 《电子设计技术》2005,12(1):92-92
近来高压驱动器颇受人们关注,因为这类驱动器在驱动压电元件和光电元件方面起着重要作用;图1示出了一种简单廉价的IkV驱动器.该电路使用了脱机电流型控制技术以及一种回扫开关电源设计,1ct(UC3844)为主要控制元件其开关频率为100kHz。该IC提供频率调制以降低轻载或无载状况下的开关频率:从误差放大器输出端取得的反馈电压用作负载状况指示信号。 相似文献
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Non‐Ohmic Properties and Electrical Responses of Grains and Grain Boundaries of Na1/2Y1/2Cu3Ti4O12 Ceramics
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Jutapol Jumpatam Weeraya Somphan Jakkree Boonlakhorn Bundit Putasaeng Pinit Kidkhunthod Prasit Thongbai Santi Maensiri 《Journal of the American Ceramic Society》2017,100(1):157-166
The dielectric and non‐Ohmic properties of Na1/2Y1/2Cu3Ti4O12 ceramics sintered under various conditions to obtain different microstructures were investigated. Microstructure analysis confirmed the presence of Na, Y, Cu, Ti, and O and these elements were well dispersed in the microstructure. Na1/2Y1/2Cu3Ti4O12 ceramics exhibited non‐Ohmic characteristics with large nonlinear coefficients of about 5.7–6.6 irrespectively of sintering conditions. The breakdown electric field of fine‐grained ceramic with the mean grain size of ≈1.7 μm (≈5600 V/cm) was much larger than those of the course‐grained ceramics with grain sizes of ≈9.5–10.4 μm (≈1850–2180 V/cm). Through optimization of sintering conditions, a low loss tangent of about 0.03 and very high dielectric permittivities of 18 000–23 000 with good temperature stability were successfully accomplished. The electrical responses of the grains and grain boundaries can, respectively, be well described using admittance and impedance spectroscopy analyses based on the brickwork layer model. A possible mechanism for the origin of semiconducting grains is discussed. The colossal dielectric response was reasonably described as closely correlated with the electrically heterogeneous microstructure by means of strong interfacial polarization at the insulating grain‐boundary layers. The non‐Ohmic properties of Na1/2Y1/2Cu3Ti4O12 ceramics were primarily related to their microstructure, i.e., grain size and volume fraction of grain boundaries. 相似文献
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Rachan Lekkla Prasit Prapinmongkolkarn 《International Journal of Satellite Communications and Networking》1998,16(5):219-236
This paper presents analytical results of the diurnal variations in Ku band rain attenuation along earth–space paths at four locations in Southeast Asia and proposes a new model that can predict rain fade in a short period of every 2 h daily. Data from four radiometers and four rain gauges over a 3 year period were analysed to obtain the characteristics of diurnal variations in rain attenuation and rainfall as well as cumulative attenuation distributions in every 2 h interval. The results of this analysis are applied to develop an intensive prediction model using the knowledge of rainfall and attenuation statistics. This model is tested with the measured data and is found to be useful for the design of a more efficient Ku band satellite system especially between 99 per cent and 99·9 per cent link availability in an area of heavy rainfall. © 1998 John Wiley & Sons, Ltd. 相似文献
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Jakkree Boonlakhorn Narong Chanlek Jedsada Manyam Sriprajak Krongsuk Prasit Thongbai Pornjuk Srepusharawoot 《Ceramics International》2021,47(16):22390-22396
CaCu3-xZnxTi4O12 ceramics (x = 0, 0.05, 0.10) were successfully prepared by a conventional solid-state reaction method. Their structural and dielectric properties, and nonlinear electrical response were systematically inspected. The X-ray diffraction results indicated that single-phase CaCu3Ti4O12 (JCPDS no. 75–2188) was obtained in all sintered ceramics. Changes in the lattice parameter are well-matched with the computational result, indicating an occupation of Zn2+ doping ions at Cu2+ sites. The overall tendency shows that the average grain size decreases when x increases. Due to a decrease in overall grain size, the dielectric permittivity of CaCu3-xZnxTi4O12 decreases expressively. Despite a decrease in the dielectric permittivity, it remains at a high level in the doped ceramics (~3,406–11,441). Besides retention in high dielectric permittivity, the dielectric loss tangent of x = 0.05 and 0.10 (~0.074–0.076) is lower than that of x = 0 (~0.227). A reduction in the dielectric loss tangent in the CaCu3-xZnxTi4O12 ceramics is closely associated with the enhanced grain boundary response. Increases in grain boundary resistance, breakdown electric field, and conduction activation energy of grain boundary as a result of Zn2+ substitution are shown to play a crucial role in improved grain boundary response. Furthermore, the XPS analysis shows the existence of Cu+/Cu2+ and Ti3+/Ti4+, indicating charge compensation due to the loss of oxygen lattice. Based on all results of this work, enhanced dielectric properties of the Zn-doped CCTO can be explained using the internal barrier layer capacitor model. 相似文献
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Tanun Jaruvitayakovit Prasit Prapinmongkolkarn 《International Journal of Communication Systems》2004,17(7):689-704
This paper proposes a novel explicit rate allocation algorithm called Fast Rate Allocation Congestion Avoidance (FRACA) algorithm supporting non‐zero minimum cell rate (MCR). The non‐zero MCR guarantee strategy for ABR service in ATM networks focused in this paper is MCR plus equal share (The ATM Forum Traffic Management Specification, version 4.0. April 1996). The main goals for designing the algorithm are the fast convergence according to the max–min fairness criteria, fairness among all sessions, maximum network utilization while the switch queue length is properly controlled. At the same time, it should work well under a wide range of network conditions without the need for adjusting the algorithm parameters. The performance of the proposed algorithm is evaluated and compared with the Generic Weighted Fairness (GWF) ERICA + (J Comput Comm 2000; 149). Simulation results show that the proposed algorithm achieves the design goals in the evaluated scenarios. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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Microstructural evolution,non‐Ohmic properties,and giant dielectric response in CaCu3Ti4−xGexO12 ceramics
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Jakkree Boonlakhorn Prasit Thongbai Bundit Putasaeng Pinit Kidkhunthod Santi Maensiri Prinya Chindaprasirt 《Journal of the American Ceramic Society》2017,100(8):3478-3487
The microstructural evolution, non‐Ohmic properties, and giant dielectric properties of CaCu3Ti4?xGexO12 ceramics (x=0‐0.10) are systematically investigated. The Rietveld refinement confirms the existence of a pure CaCu3Ti4O12 phase in all samples. Significantly enlarged grain sizes of CaCu3Ti4?xGexO12 ceramics are associated with the liquid phase sintering mechanism. Enhanced dielectric permittivity from 6.90×104 to 1.08×105 can be achieved by increasing Ge4+ dopant from x=0‐0.10, whereas the loss tangent is remarkably reduced by a factor of ≈10. Non‐Ohmic properties are enhanced by Ge4+ doping ions. Using impedance and admittance spectroscopies, the underlying mechanisms for the dielectric and nonlinear properties are well described. The improved nonlinear properties and reduced loss tangent are attributed to the enhanced resistance and conduction activation energy of the grain boundaries. The largely enhanced permittivity is closely associated with the enlarged grain sizes and the increase in the Cu+/Cu2+ and Ti3+/Ti4+ ratios, which are calculated from the X‐ray absorption near‐edge structure. 相似文献
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Prasit Thongbai Jutapol Jumpatam Teerapon Yamwong Santi Maensiri 《Journal of the European Ceramic Society》2012,32(10):2423-2430
The effects of Ta5+ substitution on the microstructure, electrical response of grain boundary, and dielectric properties of CaCu3Ti4O12 ceramics were investigated. The mean grain size decreased with increasing Ta5+ concentration, which was ascribed to the ability of Ta5+ doping to inhibit grain boundary mobility. This can decrease dielectric constant values. Grain boundary resistance and potential barrier height of CaCu3Ti4O12 ceramics were reduced by doping with Ta5+. This results in enhancement of dc conductivity and the related loss tangent. Influence of charge compensations on microstructure and intrinsic electrical properties of grain boundaries resulting from the effects of replacing Ti4+ with Ta5+ are discussed. The experimental data and variation caused by the substitution of Ta5+ can be described well by the internal barrier layer capacitor model based on space charge polarization at the grain boundaries. 相似文献