Ju-Hyun Yoo

Piezoelectric and Dielectric Properties of (LiNaK)(NbTaSb)O3 Ceramics with Variation in Poling Temperature

In this study, lead-free (LiNaK)(NbTaSb)O3 piezoelectric ceramics were fabricated on the basis of the amount of K2CO3 addition, and their piezoelectric and dielectric properties were investigated by varying the amount of K2CO3 addition and poling temperature. First, to achieve optimum poling conditions for manufactured specimens, the poling temperature was varied to be 0, 20, 50, 80, and 110 °C. The optimum poling temperature was 20 °C. It was found that 0.1 wt % K2CO3-added (Li0.04Na0.44K0.52) (Nb0.86Ta0.1Sb0.04)O3 ceramics exhibit excellent piezoelectric properties in an experiment performed on the basis of the amount of K2CO3 addition. That is, a 0.1 wt % K2CO3-added specimen showed a large electromechanical coupling factor kp=0.494, a large piezoelectric constant d33=274 pC/N, and a high density of 4.65 g/cm3 at the poling temperature of 20 °C.

EFFECT OF Nb SUBSTITUTION ON THE PIEZOELECTRIC AND DIELECTRIC PROPERTIES OF 0.95(K0.5Na0.5) NbO3-0.05Li (Sb1 − x Nb x )O3 CERAMICS

ABSTRACT In this study, lead-free 0.95(K0.5Na0.5)NbO3-0.05Li(Sb1 − x Nb x )O3 system ceramics were fabricated according to the amount of Nb substitution for Sb site of LiSbO3 ceramics and their dielectric and piezoelectric characteristics were investigated. With increasing the amount of Nb substitution, electromechanical coupling factor (kp), density and piezoelectric constant (d33) increased up to 1mol% Nb and decreased above 1mol% Nb. With increasing the amount of Nb substitution, dielectric constant linearly decreased and Curie temperature increased. At the 1mol% Nb substitution composition ceramics sintered at 1040°C, electromechanical coupling factor (kp), density, dielectric constant (ϵr), piezoelectric constant (d33) and Curie temperature (Tc) showed the optimal value of 0.41, 4.35 g/cm3, 789, 206 pC/N and 395°C, respectively for piezoelectric device application.

Dielectric and piezoelectric properties of CeO 2 -added nonstoichiometric (Na 0.5 K 0.5 ) 0.97 (Nb 0.96 Sb 0.04 )O 3 ceramics for piezoelectric energy harvesting device applications

In this study, nonstoichiometric (Na_0.5K_0.5)_0.97(Nb_0.96Sb_0.04)O₃ ceramics were fabricated and their dielectric and piezoelectric properties were investigated according to the CeO₂ addition. In this ceramic composition, CeO₂ addition improved sinterability, electromechanical coupling factor k_p, mechanical quality factor Q_m, piezoelectric constant d₃₃, and g₃₃. At the sintering temperature of 1100°C, for the 0.2wt% CeO₂ added specimen, the optimum values of density = 4.359 g/cm³, k_p = 0.443, Q_m = 588, ε_r = 444, d₃₃ = 159 pC/N, and g₃₃ = 35 × 10^¿3 V·m/N, were obtained. A piezoelectric energy harvesting device using 0.2wt% CeO₂- added lead-free (K_0.5Na_0.5)_0.97(Nb_0.96Sb_0.04)O₃ ceramics and a rectifying circuit for energy harvesting were fabricated and their electrical characteristics were investigated. Under an external vibration acceleration of 0.7g, when the mass, the frequency of vibration generator, and matching load resistance were 2.4 g, 70 Hz, and 721 Ω, respectively, output voltage and power of piezoelectric harvesting device indicated the optimum values of 24.6 mV_rms and 0.839 μW, respectively - suitable for application as the electric power source of a ubiquitous sensor network (USN) sensor node.

Dielectric and Piezoelectric Properties of Low-Temperature-Sintering Pb(Mg1/2W1/2)O3-Pb(Ni1/3Nb2/3)O3-Pb(Zr,Ti)O3 Ceramics for Multilayer Piezoelectric Actuator

In this study, in order to develop low-temperature-sintering ceramics for a multilayer piezoelectric actuator, Pb(Mg1/2W1/2)O3-Pb(Ni1/3Nb2/3)O3-Pb(Zr,Ti)O3 (PMW-PNN-PZT) ceramics were fabricated using Li2CO3 and CaCO3 as sintering aids and their dielectric and piezoelectric properties were investigated in relation to the amount of Bi substitution. Piezoelectric actuators require both a high piezoelectric constant (d33) and a high electromechanical coupling factor (kp). Accordingly, in this study, Bi was substituted at the Pb site of basic composition PMW-PNN-PZT ceramics for the enhancement of kp and d33. With increasing Bi substitution, density gradually increased. At the sintering temperature of 900°C, the electromechanical coupling factor (kp) and piezoelectric constant (d33) of PMW-PNN-PZT composition ceramics with 1.0 mol % Bi substitution as well as 0.2 wt % Li2CO3 and 0.25 wt % CaCO3 showed the optimal value of 0.618 and 473 pC/N, respectively, for multilayer piezoelectric actuator application.

Dielectric and Piezoelectric Properties of (K0.5Na0.5)(Nb0.96Sb0.04)O3 Ceramics Doped with La2O3

In this study, lead free (K0.5Na0.5)(Nb0.94Sb0.04)O3 + 1.2 mol% K4CuNb8O23 + x mol%La2O3 ceramics were prepared by conventional solid-state sintering method. The effect of La2O3 on the crystal structure, dielectric and piezoelectric properties of the ceramics were investigated in order to improve the dielectric and piezoelectric properties of lead-free piezoelectric ceramics under the fixed 1.2 mol%K4CuNb8O23. The density and the dielectric constant increased with increasing the amount of La2O3 content. So, electromechanical coupling factor (kp) and piezoelectric constant (d33) of the ceramics were considerably improved. When La2O3 was 0.2 mol% under the fixed 1.2 mol%K4CuNb8O23, kp, d33 and g33 showed optimum values of 0.38, 160pC/N and 37.4[10−3 V·m/N], respectively. The results reflected that the material is a promising candidate for lead-free piezoelectric devices such as piezoelectric harvesters.

Characteristics of Acoustic Emission Sensor Using Lead-Free (LiNaK)(NaTaSb)O3 Ceramics for Fluid Leak Detection at Power Plant Valves

In this study, acoustic emission (AE) sensor was fabricated using lead-free (LiNaK)-(NbTaSb)O3 ceramics for preventing environmental pollution. The structure of the AE sensor was designed as a Langevin-type one with air backing. The electromechanical coupling factor kp and piezoelectric constants d33 and g33 of lead-free (LiNaK)-(NbTaSb)O3 ceramics were 0.49, 300 pC/N, 27.02 mV·m/N, respectively. The peak sensitivity and frequency of the AE sensor using this ceramic material were 66.3 dB and 29.4 kHz, respectively. The results for fluid leak detection at a power plant valve were as follows; the peak frequency of response was 25 kHz at 2 and 6 kgf/cm2 N2 gas pressures, and increased up to 50 kHz at a 10 kgf/cm2 N2 gas pressure. The magnitude of the response voltage was about 40 mV at all the pressures.

The dielectric and electric characteristics of piezoelectric ceramics for ultrasonic oscillator application

The application of the ultrasonic nozzle has been extended because it can atomize liquid material. In this study, the characteristics of the ultrasonic nozzle and ceramic oscillator were investigated. The oscillator for the ultrasonic nozzle is made of piezoelectric ceramic of Pb[(Sb1/2Nb1/2)0.035, (Mn1/3Nb2/3)0.065, (ZrxTi1-x)0.90O3 The electromechanical coupling factor (kp) and mechanical quality factor (Qm) were 0.555 and 1,214, respectively, when the Zr/Ti ratio was 49/51. Moreover, this oscillator will have temperature stability because its curie temperature is 322. The driving current of the ultrasonic nozzle was 80 mA, when the driving time was 10 min. Also, the surface temperature of the ceramic oscillator was 80 at a driving time of 10 min. We discovered that the ultrasonic nozzle will be subjected to stable driving after 10 min.

Dielectric and piezoelectric properties of Bi2O3 added (Pb,Ca,Sr)(Ti,Mn,Sb)O3 ceramics sintered at low temperature

In this study, in order to develop low temperature sintering ceramics for a thickness mode multilayer piezoelectric transformer, (Pb,Ca,Sr)(Ti,Mn,Sb)O3 ceramics were fabricated using Na2CO3, Li2CO3, MnO2, and Bi2O3 as sintering aids at 870, 900, and 930 °C. Their respective dielectric and piezoelectric properties were investigated according to the amount of Bi2O3 addition. At the sintering temperature of 900 °C, the optimum value was shown for the density of 6.94 g/cm3, thickness vibration mode electromechanical coupling factor (henceforth, kt) of 0.497, thickness vibration mode mechanical quality factor (henceforth, Qmt) of 3162, and dielectric constant (henceforth, er) of 209 for thickness mode multilayer piezoelectric transformer application.

Dielectric and Piezoelectric Properties of (K 0.5 Na 0.5 ) (Nb 0.97 Sb 0.03 )O 3 Ceramics Doped with K 4 CuNb 8 O 23

Visual displays have been widely used to gain information. However, it is evident that visual displays in handheld mobile devices can be limited in the delivery of the full feelings of people. Thus, a haptic interface with tactile feedback can play an important role in the delivery of accurate and obvious feelings between human and machine [1]. In addition, a tactile sensation is about five times faster than a visual one [2]. A vibrating motor [3], solenoid type actuator, and piezoelectric actuator have been generally used until now to generate haptic feeling in mobile devices. Piezoelectric actuators with the advantages of low power consumption and a fast response time can produce various kinds of vibration for haptic feelings [4]. Pb(Zr,Ti)O3 (PZT) composition ceramics, which have been widely utilized for piezoelectric device application, contain the toxicity of lead oxide. The use of these ceramics can cause serious environmental pollution and human health problems. In addition, it is very difficult to maintain the reproducibility of the original ceramic composition due to the fluctuation in composition of the ceramics caused by the rapid evaporation of PbO when sintered at temperatures above 1,000°C. Thus, PbO should be excessively added to prevent composition fluctuation in the manufacture of PZT system ceramics. It also can cause serious environmental problems. Therefore, it is necessary to develop new lead-free piezoelectric composition ceramics to replace PZT-based ceramics. Lead-free piezoelectric ceramics, such as tungsten bronze type, bismuth layered type, and alkaline niobate-based type ceramics, have been extensively studied for the replacement of lead-containing ceramics. However, it is difficult to obtain the dense lead-free piezoelectric ceramic using ordinary sintering methods due to the high volatility of alkaline elements at high temperatures. Therefore, the optimum sintering temperature plays an important role in obtaining excellent electrical properties. Accordingly, special manufacturReceived February 18, 2011; Revised March 16, 2011; Accepted March 17, 2011 Sang-ho Lee, Kab-Soo Lee, and Ju-Hyun Yoo Department of Electrical Engineering, Semyung University, Jecheon 390-711, Korea Dielectric and Piezoelectric Properties of (K0.5Na0.5) (Nb0.97Sb0.03)O3 Ceramics Doped with K4CuNb8O23

Improvement of field emission from printed carbon nanotubes by a critical bias field

By applying a critical bias field instead of conventional surface treatments, the electron emission properties of screen-printed nanotubes were investigated through scanning electron microscopy and emission current-voltage characteristics. After the surface treatment, at the bias field of 2.5V∕μm, the electron emission current density with good uniform emission sites reached the value of 2.13mA∕cm2, which was 400 times higher than that of the untreated sample, and the turn-on voltage decreased markedly from 700to460V. In addition, the enhancement of the alignment of carbon nanotubes to the vertical direction was observed, resulting in an increase in the field-enhancement factor.