In this chapter, in order to understand the structural related magnetic and transport properties of B site substituted perovskites La 0.7 Sr 0.3 MnO 3 (LSMO), we have systematically investigated the effects of replacing some of the Mn with nonmagnetic elements Ti, Zr, Cu, Al, Zn and magnetic elements Co, Ni, Cr, Fe. The structural, magnetic and electrical phase transitions and transport properties of these compounds were investigated by neutron diffraction, magnetization and electric resistivity measurements. The abnormal behaviors relative to the parent manganite perovskite are explained by the competition between the double exchange and super exchange interactions, Mn-O bond distance, Mn-O-Mn bond angle, local Jahn-Teller distortion, the dilution of magnetization, the frustration of spins, and the change of valence states.
The dielectric and piezoelectric properties of Pbl-312~La~Ti03 (PLT) ceramics, with varying the composition in the range of x=O.O5-0.25, have been investigated. The substitution of La atoms into Pb-site was found to enhance the grain growth and densification of PLT ceramics. With increasing x, the lattice anisotropy (c/a) was decreased, resulting in a lowering of the Curie point. Energytrapped thickness vibration mode resonators with dimension of 6x4x0.3mm showed better characteristics in the 3rd harmonic resonance at around 25MHz than in the fundamental resonance at around 8MHz. Their piezoelectric coupling coefficients at the 3rd resonance were about lo%, and the electromechanical quality factor reached 3500 when x=O. 15.. IntroductionCeramic resonators are oscillation devices using the mechanical vibration of piezoelectric ceramic body, excited by external electric field. Compared with quartz resonators, they have advantages of relatively simple fabrication process, good thermal stability and low cost [l]. Various vibration modes are used in wide frequency ranges for high frequency electronic systems. Area expansion mode resonators, for which Pb(Zr1-~Ti,)03 (abbreviated as PZT) ceramics are generally used, are suitable for a few hundreds kHz-band applications. On the other hand, thickness vibration mode ones using PbTi03 (abbreviated as PT) ceramics show superior characteristics at a few MHzband [2,3]. Recently resonators used at few tens of MHz-bands become very important for information related systems. In this paper the dielectric and piezoelectric properties of La-modified PbTi03 (PLT) ceramics have been investigated in order to examine their applicability to resonators used in the range of few tens of MHz-band.Experimental procedure High purity powders of PbO, TiO2, La2O3, and MnO2 were used as the starting materials. The compositions investigated in this work were (Pb~.l,s,La,) (Ti0.98Mn0.02)03 with x=O.O5-0.25. The powders weighed for appropriate compositions were mixed with deionized water for 24 h using
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