Yun-Han Chen

High Power Characterization of Piezoelectric Materials

Three techniques for measuring high voltage/power piezoelectric properties, which have been developed recently, are compared: a voltage-constant piezoelectric resonance method, a current-constant piezoelectric resonance method, and a pulse drive method. The conventional resonance method with a constant voltage circuit exhibits significant distortion (or a hysteresis) in the resonance frequency spectrum under a high vibration level due to large elastic non-linearity, which limits precise determination of the electromechanical coupling parameters. To the contrary, the resonance method with a constant current circuit (i.e., constant velocity) can determine the coupling parameters more precisely from a perfectly-symmetrical resonance spectrum. The general problem in both resonance methods is heat generation in the sample during the measurement. In order to separate the temperature characteristic from the non-linearity, it is recommended that the pulse method be used in parallel, even though the accuracy is not very high.

Eu and Yb Substituent Effects on the Properties of Pb(Zr0.52Ti0.48)O3–Pb(Mn1/3Sb2/3)O3 Ceramics: Development of a New High-Power Piezoelectric with Enhanced Vibrational Velocity

Improved piezoelectric materials with higher vibrational velocities are needed to meet the demands of advanced high power electromechanical applications. In this paper, the effects of Eu and Yb substituents on the vibrational velocity and the piezoelectric properties of Pb(Zr, Ti)O3–Pb(Mn, Sb)O3 ceramics will be reported. Both of these substituents resulted in a significant increase in the mechanical quality factor Qm, a decrease in the dielectric constant, and improvements in the electromechanical properties. Root mean square value (rms value) of vibration velocity as high as 1.0 m/s under an electric field of 10 kV/m (rms value) has been found for Yb-substituted specimens, which is 1.7 times higher than that of Pb(Zr, Ti)O3–Pb(Mn, Sb)O3 ceramics and 3 times higher than that of the commercialized hard Pb(Zr, Ti)O3 ceramics.

Loss mechanisms and high power piezoelectrics

Heat generation is one of the significant problems in piezoelectrics for high power density applications. In this paper, we review the loss mechanisms in piezoelectrics first, followed by the heat generation processes for various drive conditions. Heat generation at off-resonance is caused mainly by dielectric loss tan δ′ (i.e., P-E hysteresis loss), not by mechanical loss, while the heat generation at resonance is mainly attributed to mechanical loss tan ′. Then, practical high power materials developed at Penn State is introduced, which exhibit the vibration velocity more than 1 m/s, leading to the power density capability 10 times of the commercially available “hard” PZTs. We propose a internal bias field model to explain the low loss and high power origin of these materials. Finally, using a low temperature sinterable “hard” PZT, we demonstrated a high power multilayer piezoelectric transformers

Substituent effects on the mechanical quality factor of Pb(Mg1/3Nb2/3)O3–PbTiO3 and Pb(Sc1/2Nb1/2)O3–PbTiO3 ceramics

The mechanical quality factor of Pb(Mg1/3Nb2/3)O3–PbTiO3(PMN–PT) and Pb(Sc1/2Nb1/2)O3–PbTiO3(PSN–PT) ceramics have been investigated for compositions close to the morphotropic phase boundary. Investigations were performed for various types of lower valent substituents on the B-site cation. These investigations have shown significant differences between the modified PMN–PT and PSN–PT crystalline solutions. In PMN–PT, lower valent substitutents had little effect upon the mechanical quality factor; however in PSN–PT it was found to be significantly increased. A crystal chemical approach is then used to explain these differences.

Substituent Effects in 0.65Pb(Mg1/3Nb2/3O30.35PbTiO3 Piezoelectric Ceramics

Pb(Mg1/3Nb2/3O3–-PbTiO3 (PMN-PT) ceramics with base compositions close to the morphotropic phase boundary are potential materials for many applications such as transducers and actuators due to their high dielectric constants and electromechanical coupling factors. However, their dielectrical and mechanical losses are too high for high-power applications. In this paper, the dielectric and electromechanical properties of piezoelectric PMN-PT ceramics were investigated in specimens containing various A-site and B-site substituents with the goal of developing lower loss materials for wider applications. Emphasis was placed on various transition metal cation substituents of both lower and higher valences. Mn substituent was found to be the most promising substituent investigated for developing high power low loss piezoelectric PMN-PT ceramics.

Microwave sintering of flyash

Abstract Class F flyash has been sintered by microwave and conventional processes. The sintering was carried out in a temperature range of 800 to 1000 °C. Densities up to 2.2 g/cm 3 , and diametral tensile strength up to 26 MPa (corresponding diametral compressive strength 78 MPa) were achieved after sintering for 10–20 min. The microwave sintered samples were denser and thus stronger than the samples conventionally sintered at the same temperature for the same time. The sintered bodies are glass-ceramic material, with mullite (Al 6 Si 2 O 13 ) as the major crystalline phase.

Substituent-introduction of “hard” polarization characteristics in “soft” Pb(BIBII)O3–PbTiO3 ferroelectric ceramics

The polarization versus field (P–E) characteristics of modified Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) and Pb(Sc1/2Nb1/2)O3–PbTiO3 (PSN–PT) ceramics has been investigated for compositions close to the morphotropic phase boundary. Investigations were performed for various types of lower valent substituents on the B-site cation positions. It has been found possible to introduce “hard” P–E characteristics in “soft” PMN–PT and PSN–PT ferroelectric ceramics. In PMN–PT, only Mn was found to be effective in introducing such characteristics, however, in PSN–PT various lower valent substituents on higher valent sites were found to be effective. The results indicate that using a defect-engineering approach that it may be possible to develop materials with combinatory characteristics of hard and soft ferroelectrics.

Loss Mechanisms in Piezoelectrics

Losses in piezoelectrics are considered in general to have three different mechanisms; dielectric, mechanical and piezoelectric losses. This paper deals with the phenomenology of losses, first, then how to measure these losses separately in experiments.

Loss mechanisms in piezoelectrics and resonance/antiresonance

Losses in piezoelectrics are considered in general to have three different mechanisms: dielectric, mechanical and piezoelectric losses. This paper deals with the phenomenology of losses, first, then how to measure these losses experimentally. We will discuss two methods for measuring the electrical, mechanical, and piezoelectric coupling losses separately: (1) strain versus stress and field and displacement versus stress and field curves, and (2) a resonance/antiresonance technique. Also, one can measure heat generation at an off‐resonance frequency to obtain a total loss. By combining the above methods, we can investigate the loss mechanisms in practical piezoelectric materials and their consequences in devices. It will be shown that heat generation is caused mainly by the dielectric loss, not by the mechanical loss. Furthermore, a drastic decrease in mechanical Q with an increase of vibration level is observed in resonant piezoelectric ceramic devices, a result not observable using conventional impedanc...

Doping Effects in Pb(Mg1/3Nb2/3)O3-PbTiO3 Ceramics for High Power Transduction Applications

Piezoelectric ceramics are potential high-power electro-acoustic sources, and have been studied for many years. However, when these devices are driven under high level vibration, the electromechanical characteristics depart significantly due to the loss and nonlinear behavior in terms of elastic and dielectric properties. In this paper, we present results concerning the development of modified Pb(Mgl/ 3 Nb 2 / 3 )O 3 -PbTiO 3 (PMN-PT) ceramics for high-power application. We have focused efforts on base PMN-PT compositions close to the morphotropic phase boundary. Different mono-doping have been studied to understand the doping effects on the properties of PMN-PT ceramics and, moreover, to improve the properties for the high-power application. Of all the substitutents investigated in this study, Mn-doping was found the only one to improve the properties of PMN-PT significantly for high-power application by reducing the total loss (including mechanical loss as well as the dielectric loss), yet keeping the coupling factor constant. This work is supported by Office of Naval Research.