Key-words : Piezoelectric ceramics, Lead-free, Microstructure, Electrical properties [Received November 15, 2007; Accepted February 21, 2008] 1. Introduction The most successful piezoelectric ceramics are based on lead zirconate and lead titanate. Environmental concerns over their lead content could disappear with the advent of a new ceramic that is lead-free.1) Potassium-sodium niobium (KNN)-based lead-free piezoelectric ceramics, the promising candidates for PZT counterparts, has been paid much attention by many specialists in the world especially since 2004.2) However, pure KNN (K0.5Na0.5NbO3) ceramics show relatively lower electrical properties (the piezoelectric constant d33 ~ 80 pC/N, and the planar electromechanical coupling factor kp ~ 36%) due to difficulty in the processing of dense ceramics by ordinary sintering.3),4) For the sake of obtaining better electrical performance of the ceramics, lots of routine and unfamiliar approaches have been attempted. 5)-8) However, the electrical properties of ceramics were not significantly improved by routine approaches, and that unfamiliar ones suffered from the high cost of equipment and from low yield.Recently with the development of processing techniques, preferable properties, for instance 9),10) d33 ~ 314-328 pC/N, and kp 4 8%, of KNN-based piezoelectric ceramics have been prepared by conventional methods in the labs. It was noticeable that most researchers 2),5),11)-15) focused their attention on preparing KNNbased ceramics with 0.5/0.5 K/Na ratio and Na rich compositions. Nevertheless, there were few studies on the preparation of lithium and antimony modified KNN lead-free piezoelectric ceramics with K rich compositions. It is well known that the loss of potassium were much higher than sodium's at high temperature, K rich compositions could compensate this kind of loss. It was also intrigued by the phase diagram 16) of NaNbO3-KNbO3 system. Therefore, in this work the K/Na ratio was changed from

The conductivity and conductivity‐temperature characteristics of the Sr(Fe1−xTixO3−δ system fired in air are studied by means of Mössbauer spectroscopy at room temperature and at 78 K. On the basis of quantitative analysis of the Fe4+ content in the solid solution, the concentrations of oxygen vacancies are calculated and the relationship between Fe4+ content and conductivity is found. It is also found that the turning points of conductivity and material constant B, as well as Fe4+ and the percentage of oxygen vacancies, occur at x=0.7 on the curve. When x=0.7, Fe3+ (II), which has never been reported before, disappears and the lattice parameters no longer vary with x. Besides Fe4+, Fe3+(II) is also a factor affecting the conductivity of this system.

No abstract

No abstract

No abstract